the synthesis of -amino acids has been a subject of great 
 interest and importance for quite some time but especially because it was discovered that -peptides derived from -amino acids have many 
 of the properties of -peptides but are much more proteolytically 
 stable .
there has been a decided uptick in the efforts to develop 
 catalytic asymmetric methods for the synthesis of -amino acids 
 in the past decade .
our interest in this 
 area follows from our experiences in the development of the catalytic 
 asymmetric synthesis of aziridines .
we 
 have found that aziridines can be prepared with a high degree of enantio- 
 and diastereoselection by a three - component coupling of an aldehyde , 
 an amine , and ethyl diazoacetate under the aegis of a borox catalyst 
 ( scheme 1 ) .
high yields 
 of aziridine-2-carboxylates can be realized starting with aryl , alkyl , 
 or alkynyl aldehydes with a typical selectivity for the cis isomer 
 of 50:1 .
the enantioselection 
 can depend on the nature of the amine substitutent or on the nature of the ligand ; with the right combination , 
 a minimum of 96% ee can be obtained with aryl , alkynyl , and first , 
 second , and third degree aliphatic aldehydes .
the 
 diastereoselection for the aziridine can be switched to trans with 
 the use of a diazoacetamide .
the purpose 
 of the present work is to explore the reductive opening of cis - aziridine-2-carboxylates , with the goal of directing 
 opening at the c-2 position to provide for an efficient and highly 
 stereoselective catalytic asymmetric route to -amino esters .
a number of methods are known for the reductive opening 
 of aziridine-2-carboxylates 
 to give -amino esters .
the nature of the reducing 
 agent can be quite critical when it comes to aziridines with an aryl 
 group in the 3-position . as illustrated in scheme 2 ,
such aziridines are prone to reductive opening , resulting 
 in -amino esters by hydrogenolysis or lewis or brnsted 
 acid - mediated reduction .
however , this proclivity 
 for reduction can be reversed by using electron - transfer reduction 
 methods ; because the electron preferentially adds to the carbonyl 
 function , it directs ring opening to the 2-position , resulting in 
 -amino esters .
interestingly , the use of manganese(0 ) to reduce 3-arylaziridine-2-carboxamides 
 occurs with opening at the 3-position to give -amino amides , whereas the same substrates are reduced to -amino 
 amides by samarium diiodide . in a non - electron - transfer 
 process , tributyltin hydride
is known to open aziridinyl ketones to 
 give -amino ketones in a radical process . in a distinct and mechanistically different reaction
, the 
 addition of silyl anions to 2-aziridinyl ketones leads to -amino 
 ketones via an addition , brook rearrangement , and anionic induced - ring 
 opening .
whereas 3-arylaziridine-2-carboxylates can 
 be reductively opened 
 to -amino esters with either samarium diiodide or magnesium(0 ) , 
 all examples in the literature are with trans isomers of the aziridine .
because the borox catalyst produces very high selectivities for cis - aziridines , it became imperative to determine if the 
 same regioselectivities observed in the reductive opening of trans - aziridines would translate to cis - aziridines .
we also began our studies with fmoc aziridines because 
 this would be the most desirable n - substituent for the purposes of 
 solid - state synthesis of -peptides .
fmoc aziridine cis-11a has a phenyl group in the 3-position cis to the ethyl carboxylate , and its reductive ring opening 
 was examined with both magnesium in methanol and samarium diiodide 
 in the presence of n , n - dimethylethanol 
 amine ( dmea ) .
the purpose of dmea is to sequester the samarium(iii ) 
 that formed and prevent it from opening the aziridine as a lewis acid 
 giving -amino ester product 14a .
the reduction with magnesium did not occur under the reported conditions 
 ( 23 c , fmoc aziridines were not included in the literature 
 study ) , and high conversion was realized 
 only after prolonged heating at 55 c .
however , no -cleavage 
 product 12a , -cleavage product 14a , or c  c cleavage product 13a was observed in 
 the crude reaction mixture .
the reduction of cis-11a with samarium diiodide was performed under the 
 reported conditions indicated in scheme 3 , and the result was that both -cleavage 
 product 12a and c  c cleavage product 13a were formed in substantial amounts .
the reductive ring 
 opening of cis-11a could be brought 
 to completion with 4 equiv of smi2 and 
 8 equiv of dmea in thf in 1 h at 0 c ( table 1 , entry 1 ) .
this reaction resulted in the isolation of -cleavage 
 product 12a in 45% yield and c  c cleavage product 13a in 46% yield . upon examining 
 the reductive ring opening of the corresponding trans - aziridine trans-11a under the optimized 
 conditions , it became clear that the product distribution greatly 
 depends on the stereochemistry of the aziridine .
the cis - aziridine 11a gives a 1:1 mixture of 12 and 13 , whereas the trans - aziridine 11a gives a 16.7:1 mixture of 12 and 13 ( table 1 , entries 1 and 3 , respectively ) . 

this was not the case with aziridines bearing an alkyl group in the 
 3-position .
both the cis and trans isomers of 3-cyclohexyl aziridine 11b gave exclusive opening at the -position and a highly 
 selective formation of -amino ester 12b ( table 1 , entries 2 and 4 , respectively ) . unless otherwise specified , all 
 reactions were run with 0.2 mmol of aziridine in thf ( 0.07 m ) with 
 4 equiv of smi2 and 8 equiv of dmea at 0 c for 1 
 h and went to completion .
yield from 
 the h nmr 
 spectrum of the crude reaction mixture with an internal standard .
data previously reported in 
 ref ( 18 ) . reaction with 5.5 equiv of smi2 and 11 equiv of dmea .
reaction with 6 equiv of smi2 and 12 equiv of dmea . in the search for a more general 
 reductive ring - opening method 
 for converting aziridines to -amino esters , a number of different 
 n - protecting groups were examined .
, it was 
 not surprising to find that the profile for the smi2-mediated 
 reductive ring opening of the boc - protected aziridines closely matched 
 that for the fmoc aziridines , with just slightly lower selectivities . 

the ring opening of phenyl - substituted cis - aziridine 
 was not selective ( 1.4:1 , table 2 , entry 1 ) . 

phenyl - substituted trans - aziridine 15a was more selective at 6.7:1 ( entry 3 ) , and both isomers of cyclohexyl - substituted aziridine 15b were highly selective ( table 2 , entries 2 
 and 4 ) .
clearly , the most felicitous n - protecting group , with regard 
 to the selectivity of reductive ring opening by samarium diiodide , 
 is the tosyl group .
the profile observed is flat , with > 99:1 selectivity 
 for the -amino ester ; cis- and trans - aziridines and phenyl- and cyclohexyl - substituted aziridines were 
 all in very high yields ( table 2 , entries 58 ) . 

the ses ( trimethylsilyl ethyl sulfonyl ) group is an attractive activating group for an amino function because 
 it is easier to remove than tosyl and has excellent selectivity for 
 the -amino ester 21a , as seen with cis - aziridine 17a ( 23:1 , table 2 , entry 9 ) . the slightly lower selectivity of the ses group , as compared 
 to that of the tosyl group ( table 2 , entries 
 5 and 9 , respectively ) , could be expected for an alkyl sulfonate compared 
 to an aryl sulfonate ( vide infra ) .
it was also found that the n - acetyl 
 group is capable of delivering high selectivity for -amino 
 ester 22a over the c  c cleavage product in the 
 ring opening of cis - phenyl aziridine cis-18a .
however , the isolated yield of -amino ester 22a was only moderate ; the reaction occurs with the formation 
 of 13% of the -amino ester corresponding to 14 in scheme 3 ( table 2 , entry 10 ) .
the latter may result from initial electron transfer 
 to the amide carbonyl followed by the ring opening to a benzyl radical 
 ( or anion , vide infra ) .
unless otherwise 
 specified , all 
 reactions were run with 0.2 mmol of aziridine in thf ( 0.07 m ) with 
 6 equiv of smi2 and 12 equiv of dmea at 0 c for 1 
 h and were allowed to go to completion . determined from the h nmr spectrum of the 
 crude reaction mixture .
yield from 
 the h nmr 
 spectrum of the crude reaction mixture with an internal standard .
reaction with 5 equiv of smi2 and 10 
 equiv of dmea . a small amount 
 ( 6% ) of ses - protected 
 benzylamine was also observed . reaction with 4 equiv of smi2 and 8 equiv of dmea . the 
 ring - opening product from n 
c3 
 cleavage to give an -amino ester was obtained in 13% isolated 
 yield . because this is the 
 class of aziridines that the borox catalysts 
 are most efficient at producing
, the reductive ring opening of unactivated 
 aziridines by samarium diiodide would be a very useful reaction ( scheme 1 ) .
kumamoto and coworkers examined the samarium 
 diiodide - mediated ring opening of trans - aziridine-2-carboxylates 
 with an aryl group in the 3-position and a benzyl group on the aziridine 
 nitrogen and found that -amino esters could be obtained only 
 in very low yields .
the present work finds 
 that if samarium diiodide is generated from samarium metal and iodine 
 instead of methylene iodide , it results in the isomerization of trans - aziridine to a mixture of cis- and trans - aziridines .
there are no other examples of the reductive 
 ring opening of aziridines bearing an alkyl group on the nitrogen 
 with samarium diiodide in which the aziridines have a carbonyl group 
 in the 2-position and either an aryl or alkyl substituent in the 3-position . 
 on the basis of this
, we decided to probe the first examples of the 
 reductive ring opening of unactivated cis - aziridine-2-carboxylates 
 with samarium diiodide ( table 3 ) .
the samarium 
 diiodide used in these studies was prepared from samarium metal and 
 methylene iodide , and no isomerization of the aziridine was observed . 

if the substituent in the 3-position is a phenyl group , then the only 
 product that is observed is the c  c cleavage product .
 h 
 aziridines , as well as with benzhydryl substituents on the aziridine 
 nitrogen ( table 3 , entries 1 and 2 ) .
a complete 
 switch in the product distribution is seen with cis - aziridines bearing a cyclohexyl group in the 3-position . here
c 
 cleavage product ; the yields , however , are quite low ( table 3 , entries 3 and 4 ) .
these reactions produce a complex 
 mixture from which only -amino ester 30b , starting cis - aziridine 29b , and benzhydryl amine 34 could be isolated and characterized .
the isolation of 34 suggests that -cyclohexyl ethyl acrylate should 
 also be formed , but it could not be detected in the h 
 nmr spectrum of the crude reaction mixture . unless otherwise specified , all 
 reactions used 0.2 mmol of aziridine in thf ( 0.07 m ) with 5 equiv 
 of smi2 and 10 equiv of dmea at 0 c for 40 min and were allowed 
 to go to completion . determined 
 from the h nmr spectrum of the crude reaction mixture .
isolated 
 as a 1:1.4 mixture of 30b and cis-29b ( 22% + 31% ) . 

amine 34 was isolated in 52% yield , and aziridine cis-29b was isolated in 20% yield .
the reductive ring opening of stereoisomerically 
 pure trisubstituted 
 aziridine 35(20 ) occurs with 
 loss of stereochemical information and the formation of two diastereomers 
 in a ratio of 4.8:1 ( scheme 4 ) .
the major diastereomer 
 was identified as the anti isomer of 36 by chemical correlation 
 to a known compound ( supporting information ) .
this loss of stereochemistry is to be expected on the basis of 
 the likely mechanism for this reaction ( scheme 5 ) .
the ring opening of 35 also occurs with the formation 
 of c  c cleavage product 37 in 30% yield .
note 
 that the distribution between c  n and c  c cleavage products 
 is essentially the same as for cis disubstituted n - boc aziridine cis-15a ( table 2 , entry 1 ) .
the generally accepted mechanism 
 for the reductive ring opening 
 of aziridines by samarium diiodide is illustrated in scheme 5 .
after initial reduction 
 to form ketyl 39 and in the absence of a proton source , 
 this species then undergoes a ring opening to give nitrogen - based 
 radical 40 that , upon further reduction , gives the species 41 , containing both a samarium enolate and a samarium amide . 

the intermediacy of this enolate has been demonstrated , and its utility 
 has been displayed in its alkylation with alkyl halides and aldol reactions with aldehydes . under conditions where a proton source is present , 

ketyl 39 is thought to be protonated to give neutral 
 radical 43 that , depending on the nature of the aziridine , 
 then undergoes a c 
subsequent 
 reduction of the resulting nitrogen- or carbon - based radicals 44 and 47 and final protonation would provide 
 -amino ester 46 and/or glycine derivative 49 .
this mechanistic interpretation accounts for the observations 
 made in the present work . of all of the examples in tables 1 and 2 ,
the aziridines with 
 a cyclohexyl group in the 3-position give a much higher selectivity 
 for the -amino ester over the glycine derivative than do aziridines 
 with a phenyl group in the 3-position .
n cleavage for the phenyl aziridines 
 than for the cyclohexyl aziridines , which can be attributed to the 
 greater stability of a benzyl radical compared to an alkyl radical 
 in intermediate 47 .
conversely , the presence of a radical 
 stabilizing group on the nitrogen facilitates the ring opening with 
 c  n bond scission over c  c bond scission .
this can be 
 seen in the ring - opening reactions of activated aziridines ( tables 1 and 2 ) versus unactivated 
 aziridines ( table 3 ) .
this is illustrated by 
 the comparison of n - tosyl aziridine cis-16a ( table 2 , entry 5 ) to n - benzhydryl aziridine cis-29a ( table 3 , entry 3 ) and by the comparison 
 of n - tosyl aziridine cis-16a ( table 2 , entry 5 ) to n - boc 
 aziridine cis-15a ( table 2 , entry 1 ) .
the ratio of c  n versus c  c cleavage 
 is a function 
 not only of the radical stabilizing ability of the substituent on 
 the nitrogen and the substituent on the c-3 position of the aziridine 
 but also of the stereochemistry of the aziridine .
the cis - aziridines exhibit a much greater preference for c  c bond 
 cleavage than do the trans - aziridines .
n - boc aziridine trans-15a gives a 6.7:1 
 mixture of c  n to c  c cleavage products , whereas the 
 corresponding cis-15a gives a much greater 
 propensity for the c  c cleavage product ( 1.4:1 , table 2 , entries 1 and 3 , respectively ) .
the same is also 
 true for n - fmoc aziridines cis-11a and trans-11a ( table 1 , entries 1 and 3 , respectively ) .
the greater preference 
 for c  c cleavage products with cis - aziridines 
 may be due to a relief in steric interactions between the two cis - substituents in the transition state , allowing the c  c 
 bond to begin to lengthen ( scheme 6 ) .
it is 
 intersting that this relief in steric interaction would not be realized 
 in the trans - aziridine .
c cleavage products 
 have been rarely seen in the reductive ring opening of aziridines 
 involving single electron - transfer processes ; this may be due to the 
 fact that cis - aziridines have not been previously 
 evaluated in this reaction .
the only example that we are aware of 
 involves an unactivated ( n  h ) aziridine-2-carboxylate with 
 a trans - phenyl group in the 3-position , which gives 
 a 28:16 split between c 
n and c  c cleavage products , as compared to aziridine cis-27a , which gives exclusively the c  c cleavage 
 product in 75% yield ( table 3 , entry 1 ) . from 
 the synthesis point of view , the n - tosyl group is the protecting group 
 of choice for samarium diiodide - mediated reductive ring opening of 
 aziridines if removal of the tosyl group does not cause problems in 
 a later stage .
n - tosyl aziridines are completely 
 selective for the c  n cleavage product ( > 99:1 ) for both 
 the cis- and trans - aziridines , with 
 both aryl 
 and alkyl substituents in the 3-position ( table 2 , entries 58 ) .
the ses protecting group can be considered 
 to be an alternative to a tosyl sulfonamide , which is notorious for 
 its potential to be troublesome during deprotection .
ses - protected 
 aziridine cis-17a gave 
 excellent selectivity ( 23:1 , table 2 ) for the 
 -amino ester , and the deprotection of ses is known to proceed 
 under much milder reaction conditions .
the utility of aziridine-2-carboxylates 
 in the preparation of both 
 - and -amino acids is illustrated in scheme 7 , which shows how the same aziridine provides access 
 to both l - dopa and ( r)--dopa .
l - dopa is the biological precursor to the catecholamine 
 neurotransmitters , a treatment of parkinson s disease , and a key compound in the formation of marine - adhesive 
 proteins.l - dopa became the 
 first commercial pharmaceutical agent to be manufactured by a nonproteinaceous 
 asymmetric catalyst , which was acknowledged in the 2001 nobel prize 
 in chemistry to william s. knowles .
the 
 isomeric ( r)--dopa has been isolated 
 as an iron(iii ) complex from a dark - blue - violet mushroom of the species cortinarius violaceus .
both natural 
 products could potentially be obtained from the reductive opening 
 of the same aziridine via controlled reductive ring opening at the 
 c-2 and c-3 positions . of the many synthesis methods of l - dopa and ( r)--dopa
, no other 
 method can provide access to both isomers from the same asymmetric 
 strategy .
our first approach 
 to the synthesis of l - dopa and ( r)--dopa began with bis - acetoxy aziridine 54 , which 
 was prepared in one step in 98% yield and > 98.5% 
 ee from aldehyde 50 , amine 52 , and ethyl 
 diazoacetate 53 by a catalytic , asymmetric , multicomponent 
 aziridination with 5 mol % vapol borox catalyst ( scheme 8) . to set the stage for the regiocomplementary 
 reductive ring opening of aziridine 54 ,
the resulting 
 n  h aziridine was not purified but rather directly protected 
 by tscl or sescl to give n - protected aziridines 57 and 58 in 70 and 78% yield , respectively , for the two steps .
the 
 samarium diiodide - mediated ring opening of both tosyl aziridine 57 and ses - aziridine 58 gave complex mixtures 
 because of the cleavage of zero , one , or two of the acetoxy groups 
 on the benzene ring . by treating the crude mixtures with acetic anhydride 
 in the presence of triethylamine , -amino esters
61a and 62a were isolated in good yields , although an increase 
 in the yield of the c  c cleavage product was observed in both 
 cases compared to the corresponding phenyl - substituted aziridines cis-16a and cis-17a ( table 2 ) .
this may be due to the electronic 
 effect of the two acetate groups on the benzene ring . despite the 
 effort that was expended to investigate the removal of the tosyl group 
 following many of the standard procedures , 61a
could 
 not be deprotected without decomposition . before exploring of 
 ses - deprotection of 62a , we turned 
 our attention to the acetate cleavage problem in the samarium diiodide 
 ring - opening process .
this was solved by replacing the acetate groups 
 with the bulky tert - butyl acyloxy ( pivaloyl ) groups . 

the catalytic asymmetric multicomponent aziridination worked smoothly 
 with aldehyde 51 and afforded aziridine 55 in 97% yield and 98% ee .
interestingly , the medam group could be 
 removed with trifluoroacetic acid in anisole without the cleavage 
 of the pivaloyl groups and then directly reacting the n 
the formation 
 of -amino ester 63a was smoothly achieved ( 74% 
 yield ) from the reductive ring - opening reaction with no detection 
 of cleavage of the pivolyl groups .
the first attempt to remove the 
 ses group from the amine function in 63a following a 
 literature procedure involving heating 
 with csf in dmf at 95 c resulted in the formation of only ethyl 
 3,4-dihydroxycinnamate 65 in 65% yield ( nmr yield ) .
this 
 is probably due to fluoride - mediated deprotonation at the -position 
 of the carbonyl , causing an elimination of the ses - amino group .
alternatively , 65 could result from a fluoride - mediated cleavage of the pivaloyl 
 group , followed by a phenoxide - assisted elimination of the ses - amino 
 group and a final rearomatization .
it has been 
 previously reported that the elimination of the ses group from ses - protected 
 -amino carbonyl compounds can be a problem during the ses deprotection 
 step .
however , there is no example reported 
 for the elimination of the ses - nh2 group from a -amino 
 ester during ses deprotection .
it is known that n - acyl - substituted 
 ses groups are much more readily deprotected than simple ses groups . on the basis of the latter
, we carried out the 
 acylation of 63a by treating it with ( boc)2o and subsequently treating the crude mixture with tbaf in thf at 
 25 c for 1.5 h to afford the desired -amino ester 64 , the protected form of ( r)--dopa , in 88% isolated yield .
there was some cleavage of the 
 pivaloyl groups by tbaf , and thus a workup with pivaloyl chloride 
 gives 64 as a pure compound .
no purification was performed 
 during any of the steps in the conversion of 63a to 64 . finally , the reductive ring opening of aziridine 55 with palladium hydroxide - catalyzed hydrogenation in the 
 presence of ( boc)2o resulted in the formation of -amino 
 ester 56 , the protected form of l - dopa , in 86% 
 isolated yield .
the 
 reductive ring opening of 3-substituted aziridine-2-carboxylates 
 with samarium diiodide can be controlled to proceed via c 
it is 
 necessary to have an activating group on the aziridine nitrogen to 
 achieve selective c 
aziridines with nonactivating 
 nitrogen substituents ( hydrogen or benzhydryl ) exclusively form glycine 
 derivatives when there is a phenyl group in the 3-position and , when 
 there is a cyclohexyl group in the 3-position , low yields of -amino 
 esters and other decomposition products .
n 
 and c  c bond cleavage directly correlates with the electron - withdrawing 
 power of the activating group on the nitrogen .
sulfonyl groups give 
 higher selectivity than carbamate groups , and this is especially noticeable 
 with cis - aziridines that have a phenyl group in the 
 3-position . the lower selectivity with cis - aziridines 

is thought to be due to a steric release during the c  c bond 
 cleavage , leading to glycine products .
the utility of this methodology 
 is illustrated in the synthesis of a protected form of ( r)--dopa by the reductive opening of aziridine 59 with samarium diiodide to give -amino ester 63a .
furthermore , this synthesis features the targeting of 
 ( r)--dopa and its regioisomer l - dopa by ring opening of the same aziridine , 55 , the former by reductive opening at the c-2 position and the latter 
 by reductive opening at the c-3 position .
vapol was prepared according 
 to literature procedures and was determined to be at least 99% optically 
 pure .
the preparation of aziridine esters cis-11a , b , cis-15a , b , cis-16a , b , cis-27a , trans-27a , cis-29a , b , and 35(20 ) has been previously reported .
melting points were determined on a capillary melting - point apparatus 
 and were uncorrected .
h nmr and c nmr spectra were recorded on a 300 , 
 500 , or 600 mhz spectrometer in cdcl3 , unless otherwise 
 noted .
chcl3 was used as the internal standard for both h nmr (  = 7.24 ) and c nmr (  = 77.0 ) . 

analytical thin - layer 
 chromatography ( tlc ) was performed on silica - gel plates with an f-254 
 indicator .
visualization was by short wave ( 254 nm ) and long wave 
 ( 365 nm ) ultraviolet light , by staining with phosphomolybdic acid 
 in ethanol , or with the aid of iodine vapor .
optical rotations 
 were obtained on a polarimeter at a wavelength of 589 nm ( sodium d 
 line ) using a 1.0 decimeter cell with a total volume of 1.0 ml .
specific 
 rotations are reported in degrees per decimeter at 20 c . to a 100 ml round - bottomed flask
were 
 added racemic trans-2-carboxyethyl-3-phenylaziridine 27a ( 0.296 g , 1.5 mmol , 1.0 equiv ) , nahco3 ( 0.252 
 g , 3.0 mmol , 2.0 equiv ) , 30 ml of a mixture of acetone , and h2o ( 3:1 ) .
the mixture was stirred at room temperature for 5 
 min , and then 9-fluorenylmethylchloroformate ( 0.388 g , 1.5 mmol , 1.0 
 equiv ) was added .
the reaction mixture was then stirred at room temperature 
 for 48 h. the acetone was removed by rotary evaporation , and the aqueous 
 residue was extracted with ethyl acetate ( 10 ml  3 ) .
the combined 
 organic layer was washed with sat aq nacl , dried over mgso4 , and concentrated by rotary evaporation to afford a yellow oil . 

purification by silica - gel chromatography ( column 1 : 18 mm  
 250 mm , 4:1:1 hexanes / diethyl
ether / ch2cl2 as 
 eluent ; column 2 : 18 mm  250 mm , ch2cl2 as eluent ) afforded trans-11a as a 
 colorless oil in 72% isolated yield that solidified upon standing 
 ( white solid , mp 9395 c ) .
spectral data for trans-11a : h nmr ( 500 mhz , cdcl3 )  1.25 ( t , 3h , j = 7.2 hz ) , 3.20 
 ( d , 1h , j = 2.4 hz ) , 3.90 ( d , 1h , j = 2.4 hz ) , 4.18 ( q , 2h , j = 7.2 hz ) , 4.24 ( t , 1h , j = 7.2 hz ) , 4.33 ( dd , 1h , j = 10.5 , 7.8 
 hz ) , 4.48 ( dd , 1h , j = 10.5 , 7.2 hz ) , 7.257.31 
 ( m , 2h ) , 7.327.42 ( m , 7h ) , 7.557.61 ( m , 2h ) , 7.74 
 ( d , 2h , j = 7.5 hz ) ; c nmr ( 150 mhz , 
 cdcl3 )  14.0 , 44.2 , 45.1 , 46.8 , 62.2 , 68.8 , 119.96 , 
 119.97 , 125.2 , 125.3 , 126.4 , 127.05 , 127.06 , 127.7 , 127.8 , 128.6 , 
 128.7 , 134.9 , 141.25 , 141.26 , 143.6 , 143.7 , 159.7 , 167.3 ; ir ( thin 
 film ) 1744 ( vs ) , 1179 ( s ) cm ; hrms ( esi - tof ) m / z : [ m + h ] calcd for c26h24no4 , 414.1705 ; found , 
 414.1731 . the aridizine was prepared according to the procedure 
 described above for trans-11a starting 
 with racemic trans-2-carboxyethyl-3-cyclohexylaziridine ( 296 mg , 1.50 mmol ) .
purification by silica - gel 
 chromatography ( 15 mm  250 mm , 8:1 hexanes / etoac as eluent ) 
 afforded trans-11b as a colorless oil 
 in 91% isolated yield ( 572 mg , 1.36 mmol ) .
spectral data for trans-11b : rf = 
 0.28 ( 5:1 hexanes / etoac ) ; h nmr ( 600 mhz , cdcl3 )  1.161.28 ( m , 6h ) , 1.22 ( t , 3h , j = 7.2 hz ) , 1.621.68 ( m , 1h ) , 1.691.78 ( m , 3h ) , 1.81 
 ( d , 1h , j = 12 hz ) , 2.66 ( dd , 1h , j = 7.2 , 2.7 hz ) , 2.96 ( d , 1h , j = 2.7 hz ) , 4.084.16 
 ( m , 2h ) , 4.22 ( t , 1h , j = 6.9 hz ) , 4.32 ( dd , 1h , j = 10.5 , 7.5 hz ) , 4.46 ( dd , 1h , j = 10.2 , 
 7.2 hz ) , 7.277.31 ( m , 2h ) , 7.38 ( t , 2h , j = 7.5 hz ) , 7.60 ( t , 2h , 1h , j = 7.8 hz ) , 7.74 ( d , 
 2h , 1h , j = 7.8 hz ) ; c nmr ( 150 mhz , 
 cdcl3 )  14.0 , 25.5 , 25.6 , 26.0 , 29.7 , 29.9 , 39.2 , 
 39.4 , 46.9 , 49.0 , 61.8 , 68.3 , 119.90 , 119.91 , 125.1 , 125.2 , 127.01 , 
 127.03 , 127.66 , 127.70 , 141.27 , 141.29 , 143.7 , 143.8 , 160.2 , 168.3 ; 
 ir ( thin film ) 2928 ( s ) , 2853 ( w ) , 1743 ( vs ) , 1451 ( m ) , 1310 ( m ) , 
 1177 ( s ) cm ; mass spectrum , m / z ( % rel intensity ) 419 m ( 0.07 ) , 346 
 ( 0.15 ) , 178 ( 100 ) , 165 ( 62 ) , 84 ( 34 ) , 49 ( 56 ) ; hrms ( esi - tof ) m / z : [ m + h ] calcd for c26h30no4 , 420.217 ; found , 
 420.216 . to a flame - dried 25 ml round - bottomed 
 flask filled with argon were added trans-2-carboxyethyl-3-phenylaziridine 27a(28 ) ( 150 mg , 0.784 mmol ) and 
 5 ml of meoh followed by the addition of nahco3 ( 197 mg , 
 0.450 mmol , 3.00 equiv ) .
the flask was put in an ultrasonic bath for 
 5 min , and then ( boc)2o ( 428 mg , 1.96 mmol , 2.50 equiv ) 
 was added .
the mixture was left in the ultrasonic bath for 4 h with 
 a needle in the rubber septum to release the generated co2 gas .
after 4 h , additional portions of both nahco3 and 
 ( boc)2o in equal amounts were added .
the reaction mixture was filtered through 
 celite , and the solid residue was washed with et2o .
the 
 cloudy filtrate was filtered again through celite , and then concentrated 
 by rotary evaporation to afford the crude product as a colorless liquid . 

purification by silica - gel chromatography ( 15 mm  250 mm , hexanes 
 and then 1:9 ethyl acetate / hexanes as eluent ) afforded trans-15a as a colorless oil in 71% isolated yield ( 163 mg , 
 0.56 mmol ) .
spectral data for trans-15a : rf = 0.36 ( hexanes / etoac = 4:1 ) ; h nmr ( 300 mhz , cdcl3 )  1.30 ( t , 3h , j = 7.0 hz ) , 1.44 ( s , 9h ) , 3.07 ( d , 1h , j = 2.6 hz ) , 3.79 ( d , 1h , j = 2.6 hz ) , 4.144.36 
 ( m , 2h ) , 7.247.36 ( m , 5h ) ; c
nmr ( 150 mhz , cdcl3 )  14.16 , 27.88 , 44.02 , 44.92 , 61.82 , 82.04 , 126.43 , 
 128.27 , 128.48 , 135.33 , 158.29 , 167.40 .
to a flame - dried 25 ml round - bottomed 
 flask filled with argon were added racemic trans-2-carboxyethyl-3-cyclohexylaziridine ( 198 mg , 1.0 mmol , 1.0 equiv ) , meoh ( 6.5 ml ) , 
 and nahco3 ( 0.84 g , 10 mmol , 10 equiv ) .
the flask was put 
 in an ultrasonic bath for 5 min , and then ( boc)2o ( 1.09 
 g , 5.00 mmol , 5.00 equiv ) was added .
the mixture was left in the ultrasonic 
 bath for 4 h with a needle in the rubber septum to release the generated 
 co2 gas , and then it was stirred at room temperature for 
 another 18 h. the reaction mixture was filtered through celite , and 
 the filter cake was washed with diethyl ether .
the cloudy filtrate 
 was filtered again through celite and then concentrated by rotary 
 evaporation to afford the crude product as a light - yellow liquid . 

purification by silica - gel chromatography ( 15 mm  250 mm , 45:1 
 hexanes / etoac as eluent until the first fraction came out and then 
 15:1 hexanes / etoac as eluent ) afforded trans-15b as a colorless oil in 89% isolated yield ( 265 mg , 0.89 
 mmol ) .
spectral data for trans-15b : rf = 0.42 ( 5:1 hexanes / etoac ) ; h 
 nmr ( 500 mhz , cdcl3 )  1.041.25 ( m , 6h ) , 
 1.28 ( t , 3h , j = 7.2 hz ) , 1.43 ( s , 9h ) , 1.601.65 
 ( m , 1h ) , 1.661.76 ( m , 3h ) , 1.801.86 ( m , 1h ) , 2.60 
 ( dd , 1h , j = 6.8 , 3.0 hz ) , 2.83 ( d , 1h , j = 3.0 hz ) , 4.114.28 ( m , 2h ) ; c nmr ( 150 mhz , 
 cdcl3 )  14.2 , 25.5 , 25.6 , 26.1 , 28.0 , 29.7 , 30.0 , 
 39.3 , 39.4 , 48.7 , 61.5 , 81.5 , 159.0 , 168.4 ; ir ( thin film ) 2980 ( w ) , 
 2930 ( s ) , 2855 ( w ) , 1744 ( vs ) ,
1728 ( s ) , 1154 ( s ) cm ; mass spectrum , m / z ( % rel intensity ) 
 224 ( m  73 ) ( 5.6 ) , 196 ( 21 ) , 124 ( 85 ) , 95 ( 73 ) , 
 57 ( 100 ) ; anal .
calcd for c16h27no4 : c , 64.62 ; h , 9.15 ; n , 4.71 . found : c , 64.88 ; h , 9.27 ; n , 4.72 . to a flame - dried 
 50 ml round - bottomed flask filled with argon were added racemic trans-2-carboxyethyl-3-phenylaziridine 27a(28 ) ( 0.335 g , 1.75 mmol , 1.0 equiv ) and ch2cl2 ( 14 ml , freshly distilled ) .
the solution was cooled 
 to 0 c in an ice bath followed by the addition of et3n ( 0.7 ml , 5.03 mmol , 2.9 equiv , freshly distilled ) . after the reaction 
 mixture
was stirred for 5 min at 0 c , tscl ( 0.534 g , 2.8 mmol , 
 1.6 equiv ) was added to the mixture at 0 c .
thereafter , the 
 ice bath was removed and the mixture was stirred at room temperature 
 for 94 h. the reaction was quenched by the addition of 26 ml of sat 
 aq nh4cl and 5 ml of h2o .
the organic layer 
 was separated , and the aqueous layer was extracted with ch2cl2 ( 30 ml  3 ) .
the combined organic layer was washed 
 with the following reagents in the indicated sequence : 5 ml of h2o , 10 ml of aq citric acid , 5 ml of h2o , 10 ml 
 of sat aq nahco3 , and 20 ml of sat aq nacl .
the combined 
 organic layer was dried over mgso4 and concentrated by 
 rotary evaporation to afford the crude product as an orange oil . purification 
 by silica - gel chromatography ( column 1 : 15 mm  250 mm , 40:9 
 hexanes / etoac as eluent ; column 2 : 15 mm  250 mm ,
16:4:1 hexanes / ch2cl2/etoac as eluent ) afforded trans-16a as a light - yellowish oil in 54% yield ( 0.326 g , 
 0.94 mmol ) .
spectral data for trans-16a : rf = 0.24 ( 4:1 hexanes / etoac ) ; h nmr ( 300 mhz , cdcl3 )  1.32 ( t , 3h , j = 7.0 hz ) , 2.39 ( s , 3h ) , 3.49 ( d , 1h , j = 3.9 hz ) , 4.204.39 ( m , 2h ) , 4.41 ( d , 1h , j = 3.9 hz ) , 7.197.31 ( m , 7h ) , 7.717.80 ( m , 2h ) ; c nmr ( 150 mhz , cdcl3 )  14.0 , 21.6 , 47.1 , 
 47.7 , 62.4 , 127.3 , 127.5 , 128.6 , 128.9 , 129.5 , 132.7 , 137.2 , 144.2 , 
 165.7 .
the h and c nmr data match those previously 
 reported for this compound . according to the same procedure used for trans-16a , racemic trans-2-carboxyethyl-3-cyclohexylaziridine
( 197 mg , 1.0 mmol , 1.0 equiv ) was reacted with 
 tosyl chloride ( 0.305 g , 1.6 mmol , 1.6 equiv ) and et3n 
 ( freshly distilled , 0.42 ml , 3.0 mmol , 3.0 equiv ) in 1:1(v / v ) ch2cl2/chcl3 ( 8 ml ) for 72 h. purification 
 by silica - gel chromatography ( column 1 : 15 mm  250 mm , 10:1 
 hexanes / etoac ; column 2 : 15 mm  250 mm , 6:1:16 ch2cl2/diethyl ether / hexanes as eluent ) and recrystallization 
 from hexanes afforded trans-16b as white 
 crystals ( mp 7173 c ) in 70% isolated yield ( 246 mg , 
 0.70 mmol ) .
spectral data for trans-16b : rf = 0.26 ( 5:1 hexanes / etoac ) ; h nmr ( 300 mhz , cdcl3 ) 
1.001.35 
 ( m , 8h ) , 1.581.79 ( m , 5h ) , 1.95 ( d , 1h , j = 10.5 hz ) , 2.41 ( s , 3h ) , 3.02 ( dd , 1h , j = 9.0 , 
 4.2 hz ) , 3.18 ( d , 1h , j = 4.2 hz ) , 4.15 ( q , 2h , j = 6.9 hz ) , 7.247.32 ( m , 2h ) , 7.797.83 
 ( m , 2h ) ; c nmr ( 150 mhz , cdcl3 )  13.9 , 
 21.6 , 25.2 , 25.4 , 25.9 , 30.6 , 31.1 , 37.5 , 43.7 , 53.7 , 61.9 , 127.5 , 
 129.5 , 137.1 , 144.2 , 166.7 ; ir ( thin film ) 2930 ( s ) , 2855 ( m ) , 1745 
 ( s ) , 1331 ( s ) , 1101 ( s ) cm ; mass spectrum , m / z ( % rel intensity ) 306 ( m  45 ) ( 2.3 ) , 278 ( 3.2 ) , 197 ( 34 ) , 196 ( 100 ) , 168 ( 29 ) , 122 
 ( 88 ) , 67 ( 83 ) ; anal .
calcd for c18h25no4s : c , 61.51 ; h , 7.17 ; n , 3.99 . found : c , 61.60 ; h , 7.22 ; n , 
 3.96 . to a flame - dried 10 ml round - bottomed 
 flask were added 2-(trimethylsilyl)ethanesulfonyl chloride ( 82.5 l , 
 0.639 mmol , 1.28 equiv ) , et3n ( 0.7 ml , 5 mmol , 10 equiv ) , 
 and ch2cl2 ( 2 ml , freshly distilled ) .
cis-(2r,3r)-2-carboxyethyl-3-phenylaziridine 27a(18 ) ( 95.6 mg , 0.5 mmol , 1 equiv , 
 98% ee ) was dissolved in 0.5 ml of ch2cl2 , and 
 the solution was added dropwise to the 10 ml round - bottomed flask 
 containing 2-(trimethylsilyl)ethanesulfonyl chloride .
the ice bath 
 was removed , and the reaction mixture was stirred at room temperature 
 for 45 h. subsequently , additional portions of 2-(trimethylsilyl)ethanesulfonyl 
 chloride ( 160 l , 1.26 mmol , 2.5 equiv ) and et3n 
 ( 0.7 ml , 5 mmol , 10 equiv ) were added to the reaction mixture .
after 
 the mixture was stirred for 24 h at room temperature , the reaction 
 was quenched with 2 ml of sat aq nh4cl and 1 ml of h2o .
the organic layer was separated , and the aqueous layer 
 was extracted with ch2cl2 ( 4 ml  3 ) .
the 
 combined organic layer was dried with na2so4 , filtered , and concentrated to give a dark - brown oil .
purification 
 by silica - gel chromatography ( 15 mm  180 mm , 9:1 hexanes / etoac 
 as eluent ) afforded cis-17a as a light - yellow 
 oil in 83% yield ( 0.147 g , 0.413 mmol ) .
spectral data for cis-17a : rf = 0.19 
 ( 9:1 hexanes / etoac ) ; h nmr ( 500 mhz , cdcl3 ) 
  0.04 ( s , 9h ) , 1.00 ( t , 3h , j = 7.0 hz ) , 1.131.24 
 ( m , 2h ) , 3.163.26 ( m , 2h ) , 3.67 ( d , 1h , j = 7.5 hz ) , 3.934.05 ( m , 2h ) , 4.07 ( d , 1h , j = 7.5 hz ) , 7.267.34 ( m , 3h ) , 7.377.41 ( m , 2h ) ; c nmr ( 125 mhz , cdcl3 )  2.0 , 9.7 , 
 13.9 , 43.7 , 44.3 , 49.5 , 61.6 , 127.5 , 128.3 , 128.7 , 131.4 , 164.5 ; ir 
 ( thin film ) 2955 ( s ) , 1755 ( vs ) cm ; hrms ( esi - tof ) m / z : [ m + h ] calcd for c16h26no4ssi , 356.1352 ; found , 
 356.1351 ; [ ]d20 = 38.0 ( c 1.0 , ch2cl2 ) on 98% ee material ( the optical purity was assumed 
 to be unchanged from 27a ) . to a 25 ml flame - dried round - bottomed 
 flask 
 filled with argon
were added cis-(2r,3r)-2-carboxyethyl-3-phenylaziridine 27a(18 ) ( 38 mg , 0.20 mmol ) , 1 ml chcl3 , et3n ( 90 l , 0.65 mmol ) , and acetic anhydride 
 ( 29 l , 0.31 mmol ) at room temperature .
the mixture was stirred 
 at room temperature for 4 h , and then the solvent was removed under 
 reduced pressure to give the crude cis-(2r,3r)-18a product as a white 
 solid .
purification by silica - gel chromatography ( 9 mm  250 
 mm , 1:5 etoac / hexanes as eluent ) gave 18a as a white 
 solid in 100% yield ( 47 mg , 0.20 mmol ) .
spectral data for cis-(2r,3r)-18a : rf = 0.35 ( 1:5 , etoac / hexane ) ; h nmr ( cdcl3 , 300 mhz )  0.92 ( t , 3h , j = 7.1 hz ) , 2.20 ( s , 3h ) , 3.47 ( d , 1h , j = 6.6 hz ) , 3.81 ( d , 1h , j = 6.6 hz ) , 3.853.97 
 ( m , 2h ) , 7.247.31 ( m , 3h ) , 7.357.39 ( m , 2h ) ; c nmr ( cdcl3 , 75 mhz )  13.7 , 23.1 , 42.0 , 
 43.5 , 61.1 , 127.3 , 128.0 , 128.2 , 132.5 , 165.6 , 181.13 ; ir ( thin film ) 
 1747 ( s ) , 1713 ( s ) cm ; mass spectrum , m / z ( % rel intensity ) 233 m ( 0.09 ) , 191 ( 14 ) , 146 ( 11 ) , 117 ( 100 ) , 91 ( 18 ) , 79 ( 10 ) , 55 ( 12 ) , 
 43 ( 44 ) . anal .
calcd for c13h15no3 : c , 66.94 ; h , 6.48 ; n , 6.00 . found : c , 66.87 ; h , 6.85 ; n , 5.94 . to a flame - dried 
 10 ml round - bottomed flask filled with argon
were added sm ( 180 mg , 
 1.20 mmol , 6.00 equiv ) and dry thf ( 1.8 ml , freshly distilled ) . the 
 vacuum adapter on the flask
was changed to a rubber septum , and the 
 suspension was purged with nitrogen under the surface of the solution 
 for 5 min by a needle through the septum .
another needle in the septum 
 was used as an outlet for the nitrogen gas .
ch2i2 ( 92.5 l , 1.15 mmol , 5.7 equiv ) was then added to the reaction 
 flask , and the reaction mixture was purged with nitrogen for another 
 1 min .
the outlet needle was removed , and the needle used for nitrogen 
 flow was lifted above the surface of the solution .
the reaction mixture 
 was stirred at room temperature for 2 h , resulting in a dark - blue 
 slurry .
subsequently , to a flame - dried 5 ml round - bottomed flask filled with 
 nitrogen were added cis-(2r,3r)-15a ( 78% ee , 
 60 mg , 0.2 mmol , 1.0 equiv ) , dry thf ( 1.5 ml , freshly distilled ) , 
 and n , n - dimethylethanolamine ( 0.24 
 ml , 2.4 mmol , 12.0 equiv ) . the solution was purged with nitrogen under 
 the surface of the solution for 2 min and transferred to the flask 
 containing the smi2 slurry dropwise via cannula . vigorous 
 stirring was maintained during the addition of the aziridine to the 
 smi2 slurry .
the 5 ml flask was washed with 0.3 ml of degassed 
 thf , and the rinse was also transferred to the reaction flask containing 
 smi2 .
the reaction mixture was stirred at 0 c for 
 40 min to 1 h and then quenched by the addition of sat aq nahco3 ( 5 ml ) at 0 c .
the organic layer was separated , and 
 the aqueous layer was extracted with etoac ( 5 ml  4 ) .
the solvent was removed by rotary evaporation to give a light - yellow 
 solid .
the h nmr spectrum of the crude reaction mixture 
 showed that it was a mixture of 19a and 23a in a ratio of 1.4:1 .
purification by silica - gel chromatography ( 18 
  250 mm , 1:1:4.6 diethyl ether / hexanes / ch2cl2 as eluent ) afforded ( s)-19a as a white solid ( mp 7577 c ) in 55% isolated yield 
 ( 33.6 mg , 0.11 mmol ) and 23a as a colorless oil in 32% 
 isolated yield ( 19.2 mg , 0.065 mmol ) .
the optical purity of ( s)-19a was determined to be 78% ee by hplc analysis ( chiralcel od - h column , 98:2 hexanes / iproh at 222 
 nm , flow rate : 1.0 ml / min ) ; retention times of rt = 6.24 min ( minor enantiomer ( r)-19a ) and rt = 7.08 min ( major 
 enantiomer ( s)-19a ) . tlc and spectral 
 data for ( s)-19a : rf = 0.24 ( 5:1 hexanes / etoac ) ; h nmr ( cdcl3 , 300 mhz )  1.14 ( t , 3h , j = 7.1 hz ) , 
 1.40 ( s , 9h ) , 2.702.90 ( m , 2h ) , 4.05 ( q , 2h , j = 7.1 hz ) , 5.09 ( brs , 1h ) , 5.46 ( brs , 1h ) , 7.197.35 ( m , 
 5h ) ; c nmr ( cdcl3 , 150 mhz )  14.0 , 
 28.3 , 41.0 , 51.2 , 60.6 , 79.6 , 126.1 , 127.4 , 128.6 , 141.2 , 155.0 , 170.88 ; 
 [ ]d20 = 31.6 ( c 1.0 , etoac ) on 78% ee ( s)-19a . tlc and spectral data for 23a ( mixture of rotamers ) : rf = 0.34 ( 5:1 hexanes / etoac ) ; h 
 nmr ( cdcl3 , 300 mhz )  1.219 and 1.224 ( 2 t , 3h , j = 7.1 hz ) , 1.447 and 1.452 ( 2s , 9h ) , 3.75 and 3.89 ( 2s , 
 2h ) , 4.13 and 4.14 ( 2q , 2h , j = 7.1 hz ) , 4.49 and 
 4.52 ( 2s , 2h ) , 7.187.35 ( m , 5h ) ; c
nmr ( cdcl3 , 150 mhz )  14.1 , 14.2 , 28.2 , 28.3 , 47.7 , 48.1 51.0 , 
 51.5 , 60.9 , 61.0 , 80.4 , 80.6 , 127.37 , 127.43 , 127.5 , 128.1 , 128.5 , 
 137.4 , 137.6 , 155.6 , 155.8 , 169.90 , 169.94 .
the reaction was carried out according 
 to the general procedure described above , starting with racemic trans-11a ( 62.1 mg , 0.15 mmol , 1.0 equiv ) , 
 smi2 ( 5.5 equiv ) , n , n - dimethylethanolamine ( 0.17 ml , 1.7 mmol , 11.0 equiv ) , and dry thf 
 ( 1.5 ml for smi2 and 1.5 ml for aziridine , freshly distilled ) 
 held at 0 c for 1 h. the h nmr spectrum of the crude 
 reaction mixture showed that 12a(18 ) and 13a(18 ) were obtained 
 in a ratio of 16.7:1 .
the nmr yield of 12a was determined 
 to be 82% with the aid of ph3ch as an internal standard .
this reaction was carried out according 
 to the general procedure described above , starting with racemic trans-11b ( 62.7 mg , 0.15 mmol , 1.0 equiv ) , 
 smi2 ( 6.0 equiv ) , n , n - dimethylethanolamine ( 0.18 ml , 1.8 mmol , 12.0 equiv ) , and dry thf 
 ( 1.5 ml for smi2 and 1.5 ml for aziridine , freshly distilled ) 
 held at 0 c for 1 h. the nmr yield of 12b(18 ) was determined to be 73% with the aid of ph3ch as an internal standard .
the 
 reaction was carried out according 
 to the general procedure described above , starting with racemic trans-15a ( 58.3 mg , 0.2 mmol , 1.0 equiv ) , smi2 ( 6.0 equiv ) , n , n - dimethylethanolamine 
 ( 0.24 ml , 2.4 mmol , 12.0 equiv ) , and dry thf ( 1.8 ml for smi2 and 1.8 ml for aziridine , freshly distilled ) held at 0 c for 
 1 h. the h nmr spectrum of the crude reaction mixture 
 showed that 19a and 23a were present in 
 a ratio of 6.7:1 .
purification by silica - gel chromatography ( 18  
 250 mm , 1:1:4.6 diethyl ether / hexanes / ch2cl2 as eluent ) afforded 19a as a white solid ( mp 7577 
 c ) in 85% isolated yield ( 50.1 mg , 0.17 mmol ) and 23a as a colorless oil in 10% isolated yield ( 5.9 mg , 0.02 mmol ) .
the 
 spectral data for 19a and 23a are the same 
 as those obtained in the reductive ring opening of cis-15a .
the general procedure 
 for the reductive 
 ring opening described above was followed , starting with cis-15b , except that 4 equiv of smi2 and 8 equiv 
 of dmea were used .
starting from cis-15b ( 38 mg , 0.12 mmol ) , purification by 
 silica - gel chromatography ( 18 mm  150 mm , 1:5 etoac / hexanes 
 as eluent ) gave 19b as a white solid in 84% isolated 
 yield ( 30 mg , 0.1 mmol ) .
the h nmr spectrum of the crude 
 reaction mixture showed the ratio of 19b/23b > 99:1 .
tlc and spectral data for 19b : rf = 0.25 ( 1:5 etoac / hexane ) ; h nmr ( cdcl3 , 500 mhz )  0.830.99 ( m , 2h ) , 1.011.17 
 ( m , 3h ) , 1.21 ( t , 3h , j = 7.1 hz ) , 1.38 ( s , 9h ) , 
 1.311.40 ( m , 1h ) , 1.611.75 ( m , 5h ) , 2.382.51 
 ( m , 2h ) , 3.633.75 ( m , 1h ) , 4.08 ( q , 2h , j = 7.1 hz ) , 4.88 ( d , 1h , j = 7.1 hz ) ; c nmr ( cdcl3 , 125 mhz )  14.1 , 25.98 , 26.02 , 26.2 , 
 28.3 , 28.9 , 29.7 , 37.0 , 41.5 , 52.2 , 60.4 , 79.0 , 155.5 , 172.0 ; ir ( thin 
 film ) 3360 ( br , s ) , 2930 ( s ) , 1719 ( vs ) , 1504 ( m ) , 1173 ( s ) cm .
the h nmr spectral data match those 
 previously reported for this compound . the spectral data for 23b has been reported .
the reaction was 
 carried out according 
 to the general procedure described above , starting with racemic trans-15b ( 59.5 mg , 0.2 mmol , 1.0 equiv ) , smi2 ( 6.0 equiv ) , n , n - dimethylethanolamine 
 ( 0.24 ml , 2.4 mmol , 12.0 equiv ) , and dry thf ( 1.8 ml for smi2 and 1.8 ml for aziridine , freshly distilled ) held at 0 c for 
 1 h. -amino ester 19b was obtained in 84% nmr 
 yield with the aid of ph3ch as an internal standard .
the h nmr spectrum of the crude reaction mixture showed the ratio 
 of 19b/23b > 99:1 .
the reaction was carried out according 
 to the general procedure described above , starting with racemic trans-16a ( 51.9 mg , 0.15 mmol , 1.0 equiv ) , 
 smi2 ( 6.0 equiv ) , n , n - dimethylethanolamine ( 0.18 ml , 1.8 mmol , 12.0 equiv ) , and dry thf 
 ( 1.5 ml for smi2 and 1.5 ml for aziridine , freshly distilled ) 
 held at 0 c for 1 h. purification by silica - gel chromatography 
 ( 18  250 mm , 5:1 hexanes / etoac as eluent ) afforded 20a as a colorless liquid in 88% isolated yield ( 45.9 mg , 0.132 mmol ) . 

spectral data for 20a : rf = 0.25 ( 1:3 etoac / hexanes ) ; h nmr ( cdcl3 , 
 500 mhz )  1.10 ( t , 3h , j = 7.2 hz ) , 2.35 ( s , 
 3h ) , 2.72 ( dd , 1h , j = 16 , 6.0 hz ) , 2.81 ( dd , 1h , j = 16 , 6.0 hz ) , 3.944.05 ( m , 2h ) , 4.70 ( q , 1h , j = 6.7 hz ) , 5.67 ( d , 1h , j = 7.5 hz ) , 
 7.067.11 ( m , 2h ) , 7.127.19 ( m , 5h ) , 7.567.60 
 ( m , 2h ) ; c nmr ( cdcl3 , 125 mhz )  14.0 , 
 21.4 , 41.2 , 54.3 , 60.9 , 126.4 , 127.1 , 127.7 , 128.5 , 129.4 , 137.5 , 
 139.3 , 143.2 , 170.6 .
the h nmr 
 spectrum of the crude reaction mixture showed the ratio of 20a/24a > 99:1 .
the 
 general procedure for the reductive 
 ring opening described above was followed , starting with aziridine 
 ( 2r,3r)-16b ( 82% ee , 53.4 mg , 0.15 mmol , 
 1.0 equiv ) , smi2 ( 5.0 equiv ) , n , n - dimethylethanolamine ( 0.15 ml , 1.5 mmol , 10.0 equiv ) , 
 and dry thf ( 1.5 ml for smi2 and 1.5 ml for aziridine , 
 freshly distilled ) held at 0 c for 1 h. purification by silica - gel 
 chromatography ( 18  250 mm , 5:1 hexanes / etoac as eluent ) afforded 
 ( s)-20b as a colorless oil in 97% isolated 
 yield ( 52.1 mg , 0.147 mmol ) . the optical purity of ( s)-20b was determined to be 84% ee by hplc analysis ( chiralcel 
 od - h column , 98:2 hexanes / iproh at 222 nm , flow rate : 1.0 ml / min ) ; 
 retention times : rt = 12.73 min ( major 
 enantiomer ( s)-20b ) and rt = 16.94 min ( minor enantiomer ( r)-20b ) .
the h nmr spectrum of the crude 
 reaction mixture showed the ratio of 20b/24b > 99:1 .
spectral data for ( s)-20b : rf = 0.17 ( 4:1 hexanes / etoac ) ; h 
 nmr ( cdcl3 , 600 mhz )  0.78 ( qd , 1h , j = 12.0 , 3.2 hz ) , 0.87 ( qd , 1h , j = 12.0 , 3.2 ) , 
 1.001.17 ( m , 3h ) , 1.18 ( t , 3h , j = 7.1 hz ) , 
 1.371.45 ( m , 1h ) , 1.541.61 ( m , 2h ) , 1.631.70 
 ( m , 2h ) , 1.731.81 ( m , 1h ) , 2.25 ( dd , 1h , j = 16.0 , 5.6 hz ) , 2.37 ( dd , 1h , j = 16.0 , 5.6 hz ) , 
 2.39 ( s , 3h ) , 3.263.34 ( m , 1h ) , 4.01 ( m , 2h ) , 5.24 ( d , 1h , j = 9.3 hz ) , 7.26 ( d , 2h , j = 8.1 hz ) , 
 7.72 ( d , 2h , j = 8.1 hz ) ; c nmr ( cdcl3 , 150 mhz )  14.1 , 21.5 , 25.87 , 25.93 , 26.1 , 29.1 , 29.3 , 
 35.9 , 41.2 , 55.5 , 60.6 , 127.0 , 129.6 , 138.2 , 143.2 , 171.6 ; ir ( thin 
 film ) 3292 ( m ) , 2928 ( vs ) , 2854 ( m ) , 1734 ( vs ) , 1718 ( s ) , 1456 ( m ) , 
 1324 ( s ) , 1161 ( vs ) cm ; mass spectrum , m / z ( % rel intensity ) 354 ( mh ) ( 6.4 ) , 271 ( 31 ) , 270 ( 100 ) , 224 ( 50 ) , 198 ( 42 ) , 155 ( 86 ) , 91 ( 86 ) , 
 41 ( 12 ) ; anal .
calcd for c18h27no4s : c , 61.16 ; h , 7.70 ; n , 3.96 . found : c , 61.30 ; h , 8.12 ; n , 3.88 . 
 [ ]d20 = 10 ( c 0.4 , etoac ) on 84% ee ( s)-20b .
the reaction was carried out according 
 to the general procedure described above , starting with racemic trans-16b ( 53.3 mg , 0.15 mmol , 1.0 equiv ) , 
 smi2 ( 6.0 equiv ) , n , n - dimethylethanolamine ( 0.18 ml , 1.8 mmol , 12.0 equiv ) , and dry thf 
 ( 1.5 ml for smi2 and 1.5 ml for aziridine , freshly distilled ) 
 held at 0 c for 1 h. purification by silica - gel chromatography 
 ( 18  250 mm , 5:1 hexanes / etoac as eluent ) afforded 20b as a colorless oil in 95% isolated yield ( 51.0 mg , 0.144 mmol ) . 

the spectral data of 20b are the same as the product 
 obtained from the reductive ring opening of cis-16b .
the h nmr spectrum of the crude reaction 
 mixture showed the ratio of 20b/24b > 
 99:1 the general procedure for the reductive 
 ring opening described above was followed , starting with aziridine cis-17a ( 53.4 mg , 0.15 mmol , 1.0 equiv ) , smi2 ( 4.0 equiv ) , n , n - dimethylethanolamine 
 ( 0.12 ml , 1.2 mmol , 8.0 equiv ) , and dry thf ( 2.0 ml for smi2 and 1.5 ml for aziridine , freshly distilled ) held at 0 c for 
 1 h. the h nmr spectrum of the crude reaction mixture 
 showed that 21a and 25a were present in 
 a ratio of 23:1 .
purification by silica - gel chromatography ( 18  
 250 mm , 5:1 hexanes / etoac as eluent ) afforded ( s)-21a as a white solid in 84% isolated yield ( 45.2 mg , 0.126 
 mmol ) and 25a as a colorless oil in 4% isolated yield 
 ( 2.0 mg , 0.0056 mmol ) .
spectral data for 21a : white solid ; 
 mp 6061 c ; h nmr ( 500 mhz , cdcl3 )  0.14 ( s , 9h ) , 0.75 ( td , 1h , j = 
 14 , 4.5 hz ) , 0.84 ( td , 1h , j = 14 , 4.0 hz ) , 1.17 
 ( t , 3h , j = 7 hz ) , 2.52 ( td , 1h , j = 14 , 4.5 hz ) , 2.63 ( td , 1h , j = 14 , 4.0 hz ) , 2.792.90 
 ( m , 2h ) , 4.08 ( qd , 2h , j = 7.2 , 1.5 hz ) , 4.814.90 
 ( m , 1h ) , 5.57 ( d , 1h , j = 8 hz ) , 7.247.30 
 ( m , 1h ) , 7.307.39 ( m , 4h ) ; c nmr ( cdcl3 , 125 mhz )  2.2 , 10.2 , 14.0 , 41.9 , 49.9 , 54.5 , 61.0 , 
 126.6 , 128.2 , 128.9 , 140.3 , 170.5 ; ir ( thin film ) 3277 ( br , s ) , 2955 
 ( w ) , 1736 ( s ) , 1144 ( s ) cm ; hrms ( esi - tof ) m / z : [ m + h ] calcd for c16h28no4sis , 358.1508 ; found , 
 358.1509 ; [ ]d20 = 21.7 ( c 0.87 , ch2cl2 ) on 98% ee ( s)-21a .
spectral 
 data for 25a : h nmr ( 500 mhz , cdcl3 )  0.05 ( s , 9h ) , 1.111.16 ( m , 2h ) , 1.24 ( t , 3h , j = 7.2 hz ) , 3.053.10 ( m , 2h ) , 3.90 ( s , 2h ) , 4.16 
 ( q , 2h , j = 7.2 hz ) , 4.53 ( s , 2h ) , 7.277.36 
 ( m , 5h ) ; c nmr ( cdcl3 , 125 mhz )  2.0 , 
 10.3 , 14.2 , 46.9 , 50.0 , 51.8 , 61.3 , 128.1 , 128.5 , 128.8 , 135.5 , 169.6 ; 
 ir ( thin film ) 2955 ( w ) , 1746 ( s ) , 1333 ( s ) , 1142 ( s ) cm ; hrms ( esi - tof ) m / z : [ m + h ] calcd for c16h28no4sis , 358.1508 ; found , 358.1530 . the 
 general procedure for the reductive 
 ring opening described above was followed , except that 2.5 equiv of 
 sml2 and 5 equiv of dmea were used . starting from cis-18a ( 47 mg , 0.19 mmol ) ,
purification of 
 the product by silica - gel chromatography ( 18 mm  300 mm , 1:5 
 etoac / hexanes as eluent ) gave 22a as a colorless semisolid 
 in 52% isolated yield ( 24 mg , 0.1 mmol ) , along with the -amino 
 ester resulting from the cleavage of the n 
c3 bond as a colorless 
 semisolid in 13% isolated yield ( 6 mg , 0.025 mmol ) .
tlc and spectral 
 data for 22a : rf = 0.15 ( 1:5 
 etoac / hexane ) ; h nmr ( cdcl3 , 500 mhz )  
 1.12 ( t , 3h , j = 7.1 hz ) , 1.98 ( s , 3h ) , 2.77 ( dd , 
 1h , j = 15.4 , 6.0 hz ) , 2.87 ( dd , 1h , j = 15.7 , 6.0 hz ) , 4.04 ( q , 2h , j = 7.1 hz ) , 5.365.43 
 ( m , 1h ) , 6.60 ( d , 1h , j = 8.0 hz ) , 7.207.32 
 ( m , 5h ) .
the general procedure for the reductive 
 ring opening described above was followed , except that 5.0 equiv of 
 sml2 and 10 equiv of dmea were used .
starting from cis-27a(18 ) ( 19 mg , 
 0.10 mmol ) , purification of the product by silica - gel chromatography 
 ( 18 mm  300 mm , 1:1:4 et2o / ch2cl2/hexanes as eluent ) gave 31a as a colorless oil in 75% 
 isolated yield ( 14.4 mg , 0.0746 mmol ) .
spectral data for 31a : h nmr ( cdcl3 , 300 mhz , )  1.25 ( t , 
 3h , j = 7.1 hz ) , 3.39 ( s , 2h ) , 3.78 ( s , 2h ) , 4.17 
 ( q , 2h , j = 7.2 hz ) , 7.207.35 ( m , 5h ) ( n  h 
 proton not located ) .
the general procedure for the reductive 
 ring opening described above was followed , except that 5.0 equiv of 
 sml2 and 10 equiv of dmea were used .
starting from cis-29a ( 35 mg , 
 0.10 mmol ) , purification of the product by silica - gel chromatography 
 ( 18 mm  300 mm , 1:1:4 et2o / ch2cl2/hexanes as eluent ) gave 33a as a colorless oil in 69% 
 isolated yield ( 25 mg , 0.069 mmol ) .
spectral data for 33a : h nmr ( 300 mhz , cdcl3 )  1.17 ( t , 
 3h , j = 7.2 hz ) , 3.25 ( s , 2h ) , 3.82 ( s , 2h ) , 4.04 
 ( q , 2h , j = 7.2 hz ) , 5.27 ( s , 1h ) , 7.157.51 
 ( m , 15h ) ; c nmr ( 75 mhz , cdcl3 )  14.2 , 
 50.3 , 54.9 , 59.9 , 70.3 , 127.0 , 127.1 , 128.28 , 128.33 , 128.4 , 128.7 , 
 139.2 , 142.1 , 171.6 .
the general procedure 
 for the reductive 
 ring opening described above was followed , starting with cis-29b ( 44 mg , 0.12 mmol ) . 

purification of the product by silica - gel chromatography ( 18 mm  
 300 mm , 1:5 etoac / hexanes as eluent ) gave a 1:1.4 mixture of -amino 
 ester 30b ( 22% nmr yield ) and unreacted cis-29b ( 31% nmr yield ) .
the h nmr spectrum 
 of the crude reaction mixture indicated the formation of amine 34 in 39% yield . extending the reaction time from 40 min to 
 2 h for the ring - opening reaction of cis-29b ( 42 mg , 0.12 mmol ) at room temperature gave 30b ( 8.6 
 mg , 0.024 mmol ) in 22% isolated yield and amine 34 in 
 52% isolated yield .
spectral data for 30b : h nmr ( 600 mhz , cdcl3 )  0.901.04 
 ( m , 2h ) , 1.051.23 ( m , 2h ) , 1.20 ( t , 3h , j = 7.1 hz ) , 1.451.54 ( m , 1h ) , 1.601.80 ( m , 6h ) , 2.34 
 ( dd , 1h , j = 14.5 , 7.0 hz ) , 2.47 ( dd , 1h , j = 14.5 , 5.3 hz ) , 2.77 ( dt , 1h , j = 7.0 , 
 5.3 hz ) , 4.034.14 ( m , 2h ) , 4.94 ( s , 1h ) , 7.157.19 
 ( m , 2h ) , 7.237.28 ( m , 4h ) , 7.357.41 ( m , 4h ) ( n  h 
 proton not located ) ; c nmr ( 150 mhz , cdcl3 )  14.2 , 26.5 , 26.6 , 26.7 , 28.4 , 29.5 , 36.0 , 40.9 , 56.8 , 60.2 , 
 64.1 , 126.89 , 126.91 , 127.4 , 127.6 , 128.33 , 128.34 , 144.2 , 144.4 , 
 172.9 ; hrms ( esi - tof ) m / z : [ m + 
 h ] calcd for c24h32no2 , 366.2433 ; found , 366.2431 .
spectral data for 34 : h nmr ( 600 mhz , cdcl3 )  1.84 ( bs , 2h ) , 5.20 
 ( s , 1h ) , 7.187.23 ( m , 2h ) , 7.267.32 ( m , 4h ) , 7.337.37 
 ( m , 4h ) ; c nmr ( 150 mhz , cdcl3 )  59.7 , 
 126.88 , 126.92 , 128.4 , 145.6 .
the h and c 
 nmr spectral data for 34 match those provided by the 
 source for this compound .
the general procedure for the reductive 
 ring opening described 
 above was followed , starting with trisubstituted aziridine 35(20 ) ( 76 mg , 0.25 mmol , 99% ee ) and 5.0 
 equiv of smi2 .
the h nmr spectrum of the crude 
 reaction mixture indicated that a mixture of anti-36 , syn-36 , and 37 was present in a ratio of 1.28:0.28:1 , respectively .
purification 
 of the products by silica - gel chromatography ( 18 mm  200 mm , 
 1:10 to 1:6 etoac / hexanes as eluent ) gave anti-36 as a white solid ( mp 5355 c ) in 43% isolated 
 yield ( 32.7 mg , 0.106 mmol ) , syn-36 as 
 a white solid ( mp 8991 c ) in 9% isolated yield ( 6.6 
 mg , 0.021 mmol ) , and 37 as a colorless oil in 30% isolated 
 yield ( 23.2 mg , 0.0755 mmol ) .
spectral data for anti-36 : h nmr ( 300 mhz , cdcl3 )  
 1.09 ( t , 3h , j = 7.1 hz ) , 1.20 ( d , 3h , j = 7.0 hz ) , 1.39 ( s , 9h ) , 2.87 ( brt , 1h , j = 6.5 
 hz ) , 4.01 ( q , 2h , j = 7.1 hz ) , 4.81 ( brs , 1h ) , 5.81 
 ( brs , 1h ) , 7.167.33 ( m , 5h ) ; c nmr ( 125 mhz , 
 cdcl3 )  14.0 , 15.4 , 28.3 , 45.3 , 56.7 , 60.6 , 79.4 , 
 126.3 , 127.3 , 128.4 , 141.0 , 155.4 , 174.9 ; ir ( thin film ) 3355 ( br , 
 w ) , 2978 ( m ) , 1721 ( s ) , 1171 ( s ) cm ; hrms ( esi - tof ) m / z : [ m + h ] calcd for c17h26no4 , 308.1862 ; found , 
 308.1860 ; [ ]d20 = 40.1 ( c 0.5 , ch2cl2 ) on 99% ee material .
spectral data for syn-36 : h nmr ( 600 mhz , cdcl3 )  
 1.11 ( t , 3h , j = 7.2 hz ) , 1.13 ( d , 3h , j = 7.2 hz ) , 1.39 ( s , 9h ) , 2.87 ( brs , 1h ) , 3.964.08 ( m , 2h ) , 
 4.97 ( brs , 1h ) , 5.27 ( brs , 1h ) , 7.197.25 ( m , 3h ) , 7.267.31 
 ( m , 2h ) ; c nmr ( 150 mhz , cdcl3 )  13.1 , 
 14.0 , 28.3 , 45.4 , 56.5 , 60.6 , 79.6 , 126.8 , 127.4 , 128.4 , 140.2 , 155.1 , 
 173.7 ; ir ( thin film ) 3380 ( s ) , 2980 ( m ) , 1728 ( s ) , 1686 ( s ) , 1520 
 ( s ) , 1173 ( s ) cm ; hrms ( esi - tof ) m / z : [ m + h ] calcd for c17h26no4 , 308.1862 ; found , 308.1855 ; 
 [ ]d20 = 26.0 ( c 0.5 , ch2cl2 ) on 99% ee material .
spectral data for 37 ( compound 37 appeared to be a colorless - oil mixture of two rotamers 
 at room temperature in a ratio of 1.2:1 ) : h nmr ( 600 mhz , 
 cdcl3 )  1.21 ( t , 3h , j = 7.2 hz ) , 
 1.271.50 ( m , 12h ) , 3.824.64 ( m , 5h ) , 7.167.37 
 ( m , 5h ) ; c nmr ( 125 mhz , cdcl3 )  14.1 , 
 15.4 , 15.8 , 28.3 , 49.7 , 50.8 , 54.8 , 55.4 , 60.9 , 80.4 , 80.6 , 127.0 , 
 127.2 , 127.3 , 128.0 , 128.3 , 128.6 , 138.2 , 139.2 , 155.4 , 155.5 , 172.1 , 
 172.3 .
trifluoroacetic 
 acid ( 0.240 ml , 357 mg , 3.13 mmol , 35.6 equiv ) was added to a solution 
 of anti-36 ( 27 mg , 0.088 mmol , 1.0 equiv ) 
 in ch2cl2 ( 0.24 ml ) .
after the reaction mixture 
 was stirred at room temperature under nitrogen overnight , it was concentrated 
 and diluted with 0.3 ml of h2o .
the ph of the mixture was 
 adjusted to 10 with sat aq nahco3 ( ca .
10 ml ) , 
 and then the mixture was extracted with ch2cl2 ( 10 ml  3 ) . the combined organic layer was dried over na2so4 , filtered , and concentrated .
purification of 
 the product by silica - gel chromatography ( 18 mm  150 mm , 1:1 
 etoac / hexanes as eluent ) gave ethyl 3-amino-2-methyl-3-phenylpropanoate 60 as a colorless oil in 74% isolated yield ( 13.5 mg , 0.065 
 mmol ) .
spectral data for ethyl 3-amino-2-methyl-3-phenylpropanoate : h nmr ( 500 mhz , cdcl3 )  0.93 ( d , 3h , j = 7.2 hz ) , 1.26 ( t , 3h , j = 7.2 hz ) , 
 1.64 ( brs , 2h ) , 2.602.72 ( m , 1h ) , 4.00 ( d , 1h , j = 9.4 hz ) , 4.17 ( q , 2h , j = 7.2 hz ) , 7.217.34 
 ( m , 5h ) ; c nmr ( 125 mhz , cdcl3 )  14.2 , 
 15.4 , 48.1 , 59.1 , 60.4 , 127.0 , 127.5 , 128.5 , 143.6 , 175.9 .
the h nmr data match those previously reported for the anti isomer 
 but not those of the syn isomer . to a flame - dried 25 ml schlenk 
 flask equipped with a stir bar and filled with nitrogen
were added 
 ( r)-vapol ( 54 mg , 0.10 mmol ) , b(oph)3 ( 87 
 mg , 0.30 mmol ) , amine 52(7d ) ( 599 mg , 2.00 mmol ) ; dry toluene ( 4 ml ) was added to dissolve the 
 reagents .
the flask was then sealed , and the reaction mixture was 
 stirred at room temperature for 1 h. thereafter , 4  of powdered 
 molecular sieves ( 600 mg , freshly flame - dried ) were added to the reaction 
 flask , followed by the addition of aldehyde 50(39 ) ( 467 mg , 2.10 mmol , 1.05 equiv ) . to this solution 

was rapidly added ethyl diazoacetate ( eda ) 53 ( 0.30 ml , 
 2.4 mmol , 1.2 equiv ) .
after the resulting mixture was stirred for 
 20 h at room temperature , it was diluted by the addition of hexane 
 ( 12 ml ) .
the reaction mixture was then filtered through a celite pad 
 into a 100 ml round - bottomed flask .
the reaction flask was rinsed 
 with etoac ( 6 ml  3 ) , and the rinse was filtered through the 
 same celite pad . the combined filtrate was concentrated in vacuo , 
 followed by exposure to high vacuum ( 0.05 mmhg ) to afford the crude 
 aziridine as a yellow oil .
purification of the crude aziridine by 
 silica - gel chromatography ( 40 mm  210 mm column , 2:1 hexanes / etoac 
 as eluent ) afforded pure cis - aziridine 54 as a white solid ( mp 6567 c on > 98.5% ee material ) 
 in 98% isolated yield ( 1.15 g , 1.95 mmol ) .
the optical purity of 54 was determined to be > 98.5% ee by hplc analysis ( chiralcel 
 od - h column , 85:15 hexane/2-propanol at 222 nm , flow rate : 1 ml / min ) . 

retention times : rt = 7.18 min ( minor 
 enantiomer , ent-54 ) and rt = 8.46 min ( major enantiomer , 54 ) . 

spectral data for 54 : rf = 
 0.19 ( 1:2 etoac / hexane ) ; h nmr ( 500 mhz , cdcl3 )  1.02 ( t , 3h , j = 7.1 hz ) , 2.21 ( s , 6h ) , 
 2.25 ( s , 3h ) , 2.26 ( s , 6h ) , 2.27 ( s , 3h ) , 2.59 ( d , 1h , j = 6.8 hz ) , 3.09 ( d , 1h , j = 6.8 hz ) , 3.65 ( s , 3h ) , 
 3.68 ( s , 1h ) , 3.69 ( s , 3h ) , 3.914.03 ( m , 2h ) , 7.047.10 
 ( m , 3h ) , 7.17 ( s , 2h ) , 7.247.29 ( m , 2h ) ; c nmr 
 ( cdcl3 , 125 mhz )  14.0 , 16.15 , 16.22 , 20.59 , 20.60 , 
 46.4 , 47.2 , 59.5 , 59.6 , 60.8 , 76.8 , 122.6 , 122.9 , 126.0 , 127.3 , 127.7 , 
 130.6 , 130.8 , 134.2 , 137.5 , 137.6 , 141.2 , 141.4 , 155.9 , 156.2 , 167.7 , 
 168.0 , 168.2 ; ir ( thin film ) 2932 ( m ) , 1773 ( vs ) , 1746 ( s ) , 1213 ( vs ) 
 cm ; hrms ( esi - tof ) m / z : [ m + h ] calcd for c34h40no8 , 590.2754 ; found , 590.2769 ; [ ]d20 = 28.2 
 ( c 1.0 , ch2cl2 ) on > 98.5% 
 ee 
 ( by hplc ) material . the procedure 
 for the synthesis of aziridine 54 was followed , starting 
 with aldehyde 51(40 ) ( 643 mg , 
 2.10 mmol , 1.05 equiv ) .
purification of the crude product by silica - gel 
 chromatography ( 40 mm  210 mm column , 5:1 hexanes / etoac as eluent ) 
 afforded pure cis - aziridine 55 as a 
 white solid ( mp 6466 c on 98% ee material ) in 97% isolated 
 yield ( 1.31 g , 1.94 mmol ) .
the optical purity of 55 was 
 determined to be 98% ee by hplc analysis ( chiralpak ad column , 95:5 
 hexane/2-propanol at 222 nm , flow- rate : 0.7 ml / min ) .
retention times : rt = 8.68 min ( minor enantiomer , ent-55 ) and rt = 10.23 min ( major 
 enantiomer , 55 ) .
spectral data for 55 : rf = 0.21 ( 1:5 etoac / hexane ) ; h nmr 
 ( 500 mhz , cdcl3 )  1.04 ( t , 3h , j = 7.0 hz ) , 1.30 ( s , 9h ) , 1.32 ( s , 9h ) , 2.20 ( s , 6h ) , 2.24 ( s , 6h ) , 
 2.56 ( d , 1h , j = 6.8 hz ) , 3.08 ( d , 1h , j = 6.8 hz ) , 3.64 ( s , 3h ) , 3.66 ( s , 1h ) , 3.68 ( s , 3h ) , 3.904.03 
 ( m , 2h ) , 6.98 ( d , 1h , j = 8.0 hz ) , 7.07 ( s , 2h ) , 
 7.11 ( d , 1h , j = 1.5 hz ) , 7.16 ( s , 2h ) , 7.25 ( dd , 
 1h , j = 8.5 , 1.5 hz ) ; c nmr ( cdcl3 , 125 mhz )  14.0 , 16.18 , 16.22 , 27.18 , 27.23 , 39.0 , 
 39.1 , 46.2 , 47.3 , 59.5 , 59.6 , 60.7 , 76.9 , 122.6 , 122.8 , 125.6 , 127.3 , 
 127.7 , 130.6 , 130.7 , 133.7 , 137.55 , 137.61 , 141.7 , 141.9 , 155.9 , 156.1 , 
 167.8 , 175.6 , 175.8 ; ir ( thin film ) 2977 ( s ) , 1761 ( vs ) , 1482 ( s ) , 
 1119 ( vs ) cm ; hrms ( esi - tof ) m / z : [ m + h ] calcd for c40h52no8 , 674.3693 ; found , 674.3694 ; 
 [ ]d20 = 34.2 ( c 1.0 , ch2cl2 ) on 98% ee ( by hplc ) material . to a oven - dried 25 ml round - bottomed flask 
 equipped with a stir bar and filled with nitrogen
were added aziridine 55 ( 67.4 mg , 0.100 mmol , 98% ee ) , pd(oh)2 ( 28.0 
 mg , 0.020 mmol , pd(oh)2 on carbon 20% , moisture 50% ) , 
 ditert - butyl dicarbonate ( 33 mg , 0.15 mmol ) , and 
 methanol ( 10 ml ) .
the flask was sealed with a rubber septum , and a 
 needle connected to a vacuum line was used to apply vacuum in the 
 flask through the septum .
the vacuum was applied for a few seconds 
 with vigorous stirring of the reaction mixture .
then the vacuum was 
 stopped , and a hydrogen balloon was connected to the flask by a needle 
 through the septum .
the suspension 
 was stirred at room temperature under hydrogen for 17 h and then filtered 
 through a pad of celite .
the filter cake was washed with etoac ( 5 
 ml ) and dcm ( 3 ml  3 ) . the combined filtrate was concentrated 
 to give a light - yellow oil .
purification of the crude product by column 
 chromatography on silica gel ( 20 mm  160 mm , hexanes / etoac 5:1 ) 
 gave -amino ester 56 as a colorless oil ( 42.2 
 mg , 0.0855 mmol , 86% ) .
spectral data for 56 : rf = 0.20 ( 1:5 etoac / hexane ) ; h nmr 
 ( 500 mhz , cdcl3 )  1.20 ( t , 3h , j = 7.0 hz ) , 1.30 ( s , 18h ) , 1.41 ( s , 9h ) , 3.06 ( d , 2h , j = 6.0 hz ) , 4.074.18 ( m , 2h ) , 4.50 ( dt , 1h , j = 7.5 , 6.0 hz ) , 5.01 ( d , 1h , j = 7.5 hz ) , 6.87 
 ( s , 1h ) , 6.97 ( d , 1h , j = 8.2 hz ) , 7.02 ( d , 1h , j = 8.2 hz ) ; c nmr ( cdcl3 , 125 mhz ) 
  14.1 , 27.2 , 28.3 , 37.5 , 39.06 , 39.09 , 54.3 , 61.5 , 79.9 , 123.2 , 
 124.2 , 127.0 , 134.5 , 141.5 , 142.3 , 155.0 , 171.5 , 175.6 , 175.8 ( one 
 sp carbon not located ) ; ir ( thin film ) 2977 ( s ) , 1761 
 ( vs ) , 1482 ( s ) , 1119 ( vs ) cm ; hrms ( esi - tof ) m / z : [ m + h ] calcd for c26h40no8 , 494.2754 ; found , 
 494.2751 ; [ ]d20 = + 27.8 ( c 1.0 , ch2cl2 ) on 98% ee material . (
the optical purity was assumed to be 
 unchanged from that of 55 . ) to a flame - dried 100 ml round - bottomed 
 flask equipped with a stir bar and filled with nitrogen were added 
 room - temperature aziridine 54 ( 467 mg , 0.792 mmol ) and 
 anisole ( 4.1 ml ) . the resulting solution was cooled to 0 c in 
 an ice bath , and trifluoroacetic acid ( 4.1 ml ) was rapidly added . 
 the ice bath was then removed , and the reaction mixture was stirred 
 for 40 min at room temperature .
the reaction mixture was quenched 
 by careful addition of sat aq na2co3 ( 30 ml ) 
 and h2o ( 10 ml ) , followed by the addition of et2o ( 30 ml ) .
the organic layer was separated , and the aqueous layer 
 was extracted with et2o ( 30 ml  3 ) .
the combined 
 organic layer was dried with na2so4 , filtered , 
 and concentrated in vacuo , followed by exposure to high vacuum ( 0.05 
 mmhg ) for 4 h to give a yellow oil , to which was added 6.5 ml of ch2ci2/chcl3 ( 1:1 ) and et3n 
 ( 0.33 ml , 2.4 mmol ) .
the resulting solution was cooled to 0 c , 
 and a portion of tosyl chloride ( 228 mg , 1.20 mmol ) was added .
the 
 mixture was then stirred at 0 c for 15 h. thereafter , additional 
 portions of both tosyl chloride ( 228 mg , 1.20 mmol ) and et3n ( 0.33 ml , 2.4 mmol ) were added to the reaction mixture at room 
 temperature .
after the mixture was stirred for 26 h at room temperature , 
 the reaction was quenched with 12 ml of sat aq nh4cl and 
 2.5 ml of h2o .
the combined organic layer 
 was dried with na2so4 , filtered , and concentrated 
 to give a dark - brown oil .
purification by silica - gel chromatography 
 ( 25 mm  160 mm , 2:1 hexanes / etoac as eluent ) afforded cis-57 as a light - yellow oil in 70% yield ( 258 
 mg , 0.559 mmol ) .
spectral data for 57 : rf = 0.14 ( 1:2 etoac / hexane ) ; h nmr ( 500 
 mhz , cdcl3 )  0.96 ( t , 3h , j = 7.1 
 hz ) , 2.236 ( s , 3h ) , 2.240 ( s , 3h ) , 2.43 ( s , 3h ) , 3.66 ( d , 1h , j = 7.5 hz ) , 3.894.02 ( m , 2h ) , 4.03 ( d , 1h , j = 7.5 hz ) , 7.07 ( d , 1h , j = 8.3 hz ) , 
 7.13 ( d , 1h , j = 2.0 hz ) , 7.17 ( dd , 2h , j = 8.3 , 2.0 hz ) , 7.34 ( d , 1h , j = 8.0 hz ) , 7.88 
 ( d , 1h , j = 8.0 hz ) ; c nmr ( cdcl3 , 125 mhz )  13.7 , 20.55 , 20.60 , 21.7 , 43.4 , 44.3 , 61.9 , 
 122.7 , 123.3 , 125.8 , 128.1 , 129.9 , 130.0 , 133.7 , 141.8 , 142.3 , 145.4 , 
 164.1 , 167.8 , 168.0 ; ir ( thin film ) 2986 ( w ) , 1773 ( vs ) , 1734 ( m ) , 
 1210 ( vs ) , 1165 ( s ) cm ; hrms ( esi - tof ) m / z : [ m + h ] calcd for c22h24no8s , 462.1223 ; found , 
 462.1234 ; [ ]d20 = + 15.6 ( c 1.0 , ch2cl2 ) on > 98.5% ee material . ( the optical purity was assumed 
 to 
 be unchanged from that of 54 . ) to a flame - dried 100 ml round - bottomed 
 flask equipped with a stir bar and filled with nitrogen were added 
 room - temperature aziridine 54 ( 366 mg , 0.621 mmol ) and 
 anisole ( 3.1 ml ) .
the resulting solution was cooled to 0 c in 
 an ice bath , and trifluoroacetic acid ( 3.1 ml ) was rapidly added . 

the ice bath was then removed , and the reaction mixture was stirred 
 for 40 min at room temperature .
the reaction mixture was quenched 
 by careful addition of saturated aq na2co3 ( 25 
 ml ) and h2o ( 10 ml ) , followed by addition of et2o ( 30 ml ) .
the organic layer was separated , and the aqueous layer 
 was extracted with et2o ( 30 ml  3 ) .
the combined 
 organic layer was dried with na2so4 , filtered , 
 and concentrated in vacuo followed by exposure to high vacuum ( 0.05 
 mmhg ) for 4 h to give a yellow oil , which was then dissolved in a 
 mixture of ch2cl2 ( 2 ml ) and et3n 
 ( 0.9 ml ) . after the solution was cooled to 0 c in an ice bath , 
 2-(trimethylsilyl)ethanesulfonyl chloride ( 0.12 ml , 0.93 mmol ) was 
 added dropwise to the reaction mixture at 0 c .
the ice bath 
 was then removed , and the reaction mixture was stirred at room temperature 
 for 17 h. thereafter , additional portions of both 2-(trimethylsilyl)ethanesulfonyl 
 chloride ( 0.12 ml , 0.93 mmol ) and et3n ( 0.9 ml ) were added 
 to the reaction mixture at room temperature . after the mixture was 
 stirred for 23 h at room temperature , the reaction was quenched with 
 2.5 ml of sat aq nh4cl and 1 ml of h2o .
the 
 organic layer was separated , and the aqueous layer was extracted with 
 ch2cl2 ( 4 ml  3 ) .
the combined organic 
 layer was dried with na2so4 , filtered , and concentrated 
 to give a dark - brown oil .
purification by silica - gel chromatography 
 ( 25 mm  160 mm , 3:1 hexanes / etoac as eluent ) afforded cis-58 as a light - yellow oil in 78% yield ( 0.228 
 g , 0.483 mmol ) .
spectral data for 58 : rf = 0.20 ( 1:3 etoac / hexane ) ; h nmr ( 500 mhz , 
 cdcl3 )  0.05 ( s , 9h ) , 1.03 ( t , 3h , j = 7.0 hz ) , 1.121.20 ( m , 2h ) , 2.26 ( s , 6h ) , 3.163.24 
 ( m , 2h ) , 3.66 ( d , 1h , j = 7.5 hz ) , 3.974.09 
 ( m , 2h ) , 4.02 ( d , 1h , j = 7.5 hz ) , 7.15 ( d , 1h , j = 8.2 hz ) , 7.25 ( d , 1h , j = 1.9 hz ) , 
 7.30 ( dd , 1h , j = 8.2 hz , j = 1.9 
 hz ) ; c nmr ( 125 mhz , cdcl3 )  2.1 , 
 9.5 , 13.8 , 20.57 , 20.62 , 43.5 , 43.6 , 49.5 , 62.0 , 122.8 , 123.4 , 125.8 , 
 130.1 , 142.0 , 142.4 , 164.2 , 167.9 , 168.0 ; ir ( thin film ) 2955 ( m ) , 
 1777 ( s ) , 1208 ( s ) , 1177 ( s ) cm ; hrms ( esi - tof ) m / z : [ m + h ] calcd for c20h30no8sis , 472.1461 ; found , 
 472.1449 ; [ ]d20 = + 27.5 ( c 1.0 , ch2cl2 ) on > 98.5% ee material .
( the optical purity was assumed 
 to 
 be unchanged from that of 54 . ) to a flame - dried 
 100 ml round - bottomed flask equipped with a stir bar and filled with 
 nitrogen were added room - temperature aziridine 55 ( 674 
 mg , 1.00 mmol ) and anisole ( 8.9 ml ) .
the resulting solution was cooled 
 to 0 c in a ice bath , and trifluoroacetic acid ( 8.9 ml ) was 
 rapidly added .
the ice bath was removed , and the reaction mixture 
 was stirred for 30 min at room temperature .
the reaction mixture was 
 quenched by the careful addition of saturated aq na2co3 ( 68 ml ) and h2o ( 35 ml ) , followed by the addition 
 of et2o ( 50 ml ) .
the organic layer was separated , and the 
 aqueous layer was extracted with et2o ( 100 ml  3 ) . 

the combined organic layer was dried with na2so4 , filtered , and concentrated in vacuo , followed by exposure to high 
 vacuum ( 0.05 mmhg ) for 4 h to give a yellow oil , which was then dissolved 
 in a mixture of ch2cl2 ( 3.5 ml ) and et3n ( 1.5 ml ) . after the solution was cooled to 0 c , 2-(trimethylsilyl)ethanesulfonyl 
 chloride ( 0.20 ml , 1.5 mmol ) was added dropwise to the reaction mixture 
 at 0 c
. the ice bath was removed , and the reaction mixture was 
 stirred at room temperature for 14 h. thereafter , additional portions 
 of both 2-(trimethylsilyl)ethanesulfonyl chloride ( 0.20 ml , 1.5 mmol ) 
 and et3n ( 1.5 ml ) were added to the reaction mixture at 
 room temperature .
after the mixture was stirred for 22 h at room temperature , 
 the reaction was quenched with 4 ml of sat aq nh4cl and 
 1.5 ml of h2o .
the organic layer was separated , and the 
 aqueous layer was extracted with ch2cl2 ( 6 ml 
  3 ) . the combined organic layer was dried with na2so4 , filtered , and concentrated to give a dark - brown oil . 

purification by silica - gel chromatography ( 25 mm  160 mm , 5:1 
 hexanes / etoac as eluent ) afforded cis-59 as a light - yellow oil in 86% yield ( 0.475 g , 0.855 mmol ) .
spectral 
 data for 59 : rf = 0.20 ( 1:5 
 etoac / hexane ) ; h nmr ( 500 mhz , cdcl3 )  
 0.05 ( s , 9h ) , 1.06 ( t , 3h , j = 7.1 hz ) , 1.111.21 
 ( m , 2h ) , 1.31 ( s , 9h ) , 1.32 ( s , 9h ) , 3.173.26 ( m , 2h ) , 3.66 
 ( d , 1h , j = 7.5 hz ) , 3.984.07 ( m , 2h ) , 4.02 
 ( d , 1h , j = 7.5 hz ) , 7.09 ( d , 1h , j = 8.3 hz ) , 7.18 ( d , 1h , j = 1.8 hz ) , 7.27 ( dd , 
 1h , j = 8.3 hz , j = 1.8 hz ) ; c nmr ( 125 mhz , cdcl3 )  2.1 , 9.5 , 
 13.8 , 27.10 , 27.14 , 39.0 , 39.1 , 43.2 , 43.7 , 49.4 , 61.9 , 122.7 , 123.3 , 
 125.4 , 129.5 , 142.4 , 142.9 , 164.2 , 175.4 , 175.6 ; ir ( thin film ) 2977 
 ( m ) , 1761 ( vs ) , 1117 ( s ) cm ; hrms ( esi - tof ) m / z : [ m+nh4 ] calcd 
 for c26h45n2o8sis , 573.2666 ; found , 573.2675 ; [ ]d20 = + 26.9 ( c 1.0 , ch2cl2 ) on 98% ee material . (
the general procedure for the reductive ring opening described 
 above was followed , starting with aziridine 57 ( 228 mg , 
 0.494 mmol ) , 2.5 equiv of smi2 , and 5 equiv of dmea .
the h nmr spectrum of the crude reaction mixture indicated a complex 
 mixture of several products due to partial cleavage of the acetate 
 group on the benzene ring . to this mixture
after the reaction was 
 stirred at room temperature for 30 min , it was quenched by the addition 
 of etoh ( 0.1 ml ) and h2o ( 2.5 ml ) .
the combined organic layer 
 was dried with na2so4 , filtered , and concentrated 
 to give a yellow oil .
purification by silica - gel chromatography ( 20 
 mm  160 mm , 1:1.5 etoac / hexanes as eluent ) gave 61a as a colorless oil in 76% isolated yield ( 173 mg , 0.373 mmol ) and 61b as a light - yellow oil in 8% isolated yield ( 17.5 mg , 0.0377 
 mmol ) .
spectral data for 61a : rf = 0.23 ( 1:1.5 etoac / hexane ) ; h nmr ( 500 mhz , cdcl3 )  1.11 ( t , 3h , j = 7.1 hz ) , 2.22 
 ( s , 6h ) , 2.33 ( s , 3h ) , 2.68 ( dd , 1h , j = 16.2 , 6.2 
 hz ) , 2.75 ( dd , 1h , j = 16.2 , 6.4 hz ) , 3.99 ( q , 2h , j = 7.1 hz ) , 4.70 ( dt , 1h , j = 7.5 , 6.2 
 hz ) , 5.97 ( d , 1h , j = 7.8 hz ) , 6.906.98 ( m , 
 3h ) , 7.14 ( d , 2h , j = 8.0 hz ) , 7.54 ( d , 2h , j = 8.0 hz ) ; c nmr ( 125 mhz , cdcl3 )  13.9 , 20.5 , 20.6 , 21.4 , 41.0 , 53.6 , 61.0 , 121.8 , 123.3 , 
 124.5 , 126.9 , 129.5 , 137.1 , 138.0 , 141.4 , 141.8 , 143.4 , 167.8 , 167.9 , 
 170.4 ; ir ( thin film ) 3279 ( m ) , 2984 ( w ) , 2930 ( w ) , 1773 ( s ) , 1734 
 ( s ) , 1211 ( s ) , 1161 ( s ) cm ; hrms ( esi - tof ) m / z : [ m + h ] calcd for c22h26no8s , 464.1379 ; found , 
 464.1381 ; [ ]d20 = + 45.2 ( c 1.0 , ch2cl2 ) on > 98% ee material . ( the optical purity was assumed 
 to 
 be unchanged from that of 54 . )
spectral data for 61b : rf = 0.38 ( 1:1.5 etoac / hexane ) ; h nmr ( 500 mhz , cdcl3 )  1.13 ( t , 3h , j = 7.1 hz ) , 2.26 ( s , 6h ) , 2.42 ( s , 3h ) , 3.93 ( s , 2h ) , 3.99 
 ( q , 2h , j = 7.1 hz ) , 4.46 ( s , 2h ) , 7.09 ( s , 1h ) , 
 7.12 ( s , 2h ) , 7.30 ( d , 2h , j = 8.2 hz ) , 7.73 ( d , 
 2h , j = 8.2 hz ) ; c nmr ( 125 mhz , cdcl3 )  14.0 , 20.6 , 20.7 , 21.6 , 46.8 , 50.5 , 61.2 , 123.5 , 
 123.6 , 126.5 , 127.4 , 129.6 , 134.0 , 136.7 , 141.9 , 142.2 , 143.6 , 168.1 , 
 168.2 , 168.6 ; ir ( thin film ) 2984 ( w ) , 2934 ( w ) , 1773 ( vs ) , 1213 ( s ) 
 cm ; hrms ( esi - tof ) m / z : [ m + h ] calcd for c22h26no8s , 464.1379 ; found , 464.1381 . the general 
 procedure for the reductive ring opening described 
 above was followed , starting with aziridine 58 ( 236 mg , 
 0.500 mmol ) , 4 equiv of smi2 , and 8 equiv of dmea .
the h nmr spectrum of the crude reaction mixture indicated a complex 
 mixture of several products due to partial cleavage of the acetate 
 group on the benzene ring . to this mixture
after the reaction was 
 stirred at room temperature for 40 min , it was quenched by the addition 
 of etoh ( 0.32 ml ) and h2o ( 9 ml ) .
the combined organic layer 
 was dried with na2so4 , filtered , and concentrated 
 to give a yellow oil .
purification by silica - gel chromatography ( 20 
 mm  160 mm , 1:2 etoac / hexanes as eluent ) gave 62a as a colorless oil in 69% isolated yield ( 164 mg , 0.346 mmol ) and 62b as a light - yellow oil in 19% isolated yield ( 45 mg , 0.095 
 mmol ) .
spectral data for 62a : rf = 0.21 ( 1:2 etoac / hexane ) ; h nmr ( 500 mhz , cdcl3 )  0.09 ( s , 9h ) , 0.780.93 ( m , 2h ) , 
 1.19 ( t , 3h , j = 7.1 hz ) , 2.26 ( s , 6h ) , 2.592.78 
 ( m , 2h ) , 2.802.89 ( m , 2h ) , 4.064.13 ( m , 2h ) , 4.87 
 ( dt , 1h , j = 8.1 , 6.4 hz ) , 5.70 ( d , 1h , j = 8.1 hz ) , 7.16 ( d , 1h , j = 8.7 hz ) , 7.197.28 
 ( m , 2h ) ; c nmr ( 125 mhz , cdcl3 )  2.2 , 
 10.2 , 14.0 , 20.575 , 20.584 , 41.6 , 50.1 , 53.6 , 61.2 , 121.9 , 123.7 , 
 124.6 , 139.1 , 141.7 , 142.2 , 167.8 , 168.0 , 170.5 ; ir ( thin film ) 3283 
 ( m ) , 2955 ( m ) , 1773 ( vs ) , 1734 ( vs ) , 1211 ( s ) , 1143 ( s ) cm ; hrms ( esi - tof ) m / z : [ m+nh4 ] calcd for c20h35n2o8sis , 491.1883 ; found , 491.1894 ; [ ]d20 = + 27.0 
 ( c 1.0 , ch2cl2 ) on > 98.5% 
 ee 
 material ( the optical purity was assumed to be unchanged from 54 ) .
spectral data for 62b : rf = 0.27 ( 1:2 etoac / hexane ) ; h nmr ( 500 mhz , 
 cdcl3 )  0.04 ( s , 9h ) , 1.081.16 ( m , 2h ) , 
 1.24 ( t , 3h , j = 7.1 hz ) , 2.26 ( s , 6h ) , 3.043.11 
 ( m , 2h ) , 3.93 ( s , 2h ) , 4.15 ( q , 2h , j = 7.1 hz ) , 
 4.52 ( s , 2h ) , 7.127.21 ( m , 3h ) ; c nmr ( 125 mhz , 
 cdcl3 )  2.0 , 10.2 , 14.1 , 20.59 , 20.63 , 46.8 , 
 50.0 , 50.9 , 61.4 , 123.2 , 123.7 , 126.3 , 134.4 , 141.9 , 142.3 , 168.1 , 
 168.2 , 169.5 ; ir ( thin film ) 2955 ( w ) , 2930 ( w ) , 1773 ( s ) , 1742 ( s ) , 
 1211 ( s ) cm ; hrms ( esi - tof ) m / z [ m+nh4 ] calcd for c20h35n2o8sis , 
 491.1883 ; found , 491.1897 .
the general procedure for 
 the reductive ring opening described 
 above was followed , starting with aziridine 59 ( 111 mg , 
 0.200 mmol , 98% ee ) and 4.0 equiv of smi2 .
the h nmr spectrum of the crude reaction mixture indicated a mixture 
 of c  n cleavage product 63a and c  c cleavage 
 product 63b was obtained with a ratio of 4.3:1 .
purification 
 by silica - gel chromatography ( 20 mm  160 mm , 1:3 etoac / hexanes 
 as eluent ) gave 63a as a yellow oil in 74% isolated yield 
 ( 81.8 mg , 0.147 mmol ) and 63b as a light - yellow oil in 
 16% isolated yield ( 18.2 mg , 0.0326 mmol ) .
spectral data for 63a : rf = 0.25 ( 1:3 etoac / hexane ) ; h nmr ( 500 mhz , cdcl3 )  0.11 ( s , 
 9h ) , 0.750.90 ( m , 2h ) , 1.18 ( t , 3h , j = 7.2 
 hz ) , 1.29 ( s , 9h ) , 1.30 ( s , 9h ) , 2.552.75 ( m , 2h ) , 2.82 ( d , 
 2h , j = 6.5 hz ) , 4.07 ( q , 2h , j = 
 7.1 hz ) , 4.84 ( dt , 1h , j = 8.0 , 6.5 hz ) , 5.70 ( d , 
 1h , j = 8.0 hz ) , 7.09 ( d , 1h , j = 
 8.4 hz ) , 7.13 ( d , 1h , j = 2.0 hz ) , 7.19 ( dd , 1h , j = 8.4 , 2.0 hz ) ; c nmr ( 125 mhz , cdcl3 )  2.2 , 10.2 , 14.0 , 27.11 , 27.13 , 39.05 , 39.06 , 
 41.6 , 50.0 , 53.7 , 61.1 , 121.8 , 123.7 , 124.3 , 138.6 , 142.2 , 142.6 , 
 170.4 , 175.4 , 175.5 ; ir ( thin film ) 3283 ( m ) , 2977 ( s ) , 1763 ( vs ) , 
 1736 ( s ) , 1117 ( s ) cm ; hrms ( esi - tof ) m / z [ m+nh4 ] calcd 
 for c26h47n2o8sis , 575.2822 ; found , 575.2842 ; [ ]d20 = + 26.0 ( c 1.0 , ch2cl2 ) on 98% ee material . (
the optical 
 purity was assumed to be unchanged from that of 55 . ) 

spectral data for 63b : rf = 0.39 ( 1:3 etoac / hexane ) ; h nmr ( 500 mhz , cdcl3 )  0.04 ( s , 9h ) , 1.091.16 ( m , 2h ) , 1.24 ( t , 
 3h , j = 7.1 hz ) , 1.31 ( s , 18h ) , 3.043.13 
 ( m , 2h ) , 3.92 ( s , 2h ) , 4.15 ( q , 2h , j = 7.1 hz ) , 
 4.52 ( s , 2h ) , 7.067.11 ( m , 2h ) , 7.17 ( dd , 1h , j = 8.4 , 1.8 hz ) ; c nmr ( 125 mhz , cdcl3 )  
 2.0 , 10.2 , 14.1 , 27.18 , 27.21 , 39.10 , 39.13 , 46.7 , 50.0 , 50.9 , 
 61.4 , 123.4 , 123.7 , 126.1 , 133.9 , 142.4 , 142.8 , 169.5 , 175.7 , 175.8 ; 
 ir ( thin film ) 2977 ( s ) , 1761 ( vs ) , 1507 ( m ) , 1337 ( m ) , 1256 ( m ) , 
 1117 ( vs ) cm ; hrms ( esi - tof ) m / z [ m+nh4 ] calcd for c26h47n2o8sis , 
 575.2822 ; found , 575.2834 . to a oven - dried 10 ml schlenk flask equipped 
 with a stir bar and filled with nitrogen were added 63a ( 38 mg , 0.068 mmol , 1.0 equiv ) , 4-dimethylaminopyridine ( 0.9 mg , 
 0.007 mmol , 0.1 equiv ) , et3n ( 19 l , 14 mg ,
0.14 
 mmol , 2.0 equiv ) , and ch2cl2 ( 0.32 ml ) . the 
 flask was sealed , and the reaction mixture was stirred for 2 h at 
 room temperature and then stirred at 40 c for 15 h. after the 
 reaction mixture was cooled to room temperature , 0.5 ml of 1 n hcl 
 was added to the flask , followed by the addition of etoac ( 5 ml ) . 

the organic layer was separated , washed with brine ( 0.3 ml  
 2 ) , dried with na2so4 , and concentrated to give 
 a yellow oil , which was then dissolved in thf ( 0.65 ml ) in a 10 ml 
 schlenk flask filled with nitrogen . to this solution was dropwise 
 added tbaf ( 0.31 ml , 1 m in thf , 0.31 mmol ) at room temperature .
after 
 the reaction mixture was stirred at room temperature under nitrogen 
 for 1.5 h , it was concentrated by rotary evaporation and then high 
 vacuum ( 0.5 mmhg ) to give a bright - yellow oil .
this oil was dissolved 
 in a mixture of thf ( 0.2 ml ) and et3n ( 0.2 ml ) .
then trimethylacetyl 
 chloride ( 0.05 ml , 0.4 mmol ) was added to the solution at room temperature . 

after the resulting reaction mixture was stirred for 15 min at room 
 temperature under nitrogen , it was quenched by the addition of etoh 
 ( 0.1 ml ) and h2o ( 1.5 ml ) .
the combined organic layer was dried with 
 na2so4 , filtered , and concentrated to afford 
 a yellow oil .
purification by silica - gel chromatography ( 20 mm  
 120 mm , 1:3 etoac / hexanes as eluent ) gave 64 as a light - yellow 
 oil in 88% isolated yield ( 29.5 mg , 0.0598 mmol ) .
spectral data for 64 : rf = 0.27 ( 1:3 etoac / hexane ) ; h nmr ( 500 mhz , cdcl3 )  1.16 ( t , 3h , j = 7.2 hz ) , 1.30 ( s , 9h ) , 1.31 ( s , 9h ) , 1.39 ( brs , 9h ) , 
 2.622.92 ( m , 2h ) , 4.06 ( q , 2h , j = 7.2 hz ) , 
 5.06 ( brs , 1h ) , 5.47 ( d , 1h , j = 7.5 hz ) , 7.03 ( d , 
 1h , j = 1.6 hz ) , 7.06 ( d , 1h , j = 
 8.4 hz ) , 7.14 ( dd , 1h , j = 8.4 hz , j = 1.6 hz ) ; c nmr ( 125 mhz , cdcl3 )  
 14.0 , 27.20 , 27.22 , 28.3 , 39.10 , 39.12 , 40.7 , 50.6 , 60.9 , 79.8 , 121.4 , 
 123.5 , 124.0 , 139.7 , 141.8 , 142.5 , 154.9 , 170.7 , 175.6 , 175.8 ; ir 
 ( thin film ) 3387 ( m ) , 2978 ( s ) , 2936 ( m ) , 2874 ( w ) , 1761 ( vs ) , 1739 
 ( s ) , 1723 ( s ) , 1713 ( s ) , 1256 ( s ) , 1119 ( vs ) cm ; hrms ( esi - tof ) m / z
[ m + h ] calcd for c26h40no8 , 494.2754 ; found , 494.2758 ; [ ]d20 = + 23.6 ( c 1.0 , ch2cl2 ) on 98% ee material .
( the optical 
 purity was assumed to be unchanged from that of 55 . )
 a general study is undertaken to 
 examine the scope of the reductive 
 ring opening of aziridine-2-carboxylates with samarium diiodide . the 
 competition between c  c and c  n bond cleavage is examined 
 as a function of the nature of the n - substituent of the aziridine , 
 the nature of the substituent in the 3-position of the aziridine , 
 and whether the substituent in the 3-position is in a cis or trans 
 relationship with the carboxylate in the 2-position . 
 the desired c  
 n 
 bond cleavage leads to -amino esters that are the predominant 
 products for most aziridines with an n - activating group . 
 however , 
 c  c cleavage products are observed with an aryl group in the 
 3-position ; this can be particularly pronounced with cis - aziridines where a nearly equal mixture of the two is observed . 
 
 exclusive formation of the c  n cleavage product is observed 
 for all aziridines with the strongly n - activating p - toluene sulfonate group . similarly high selectivity is observed 
 for the 2-trimethylsilylethyl sulfonate group ( ses ) , which is easier 
 to remove . the utility of these methods is illustrated in the synthesis 
 of protected forms of ( r)-3-dopa 
 and l - dopa from the same aziridine , the former by smi2-mediated reductive opening at c-2 and the latter by palladium - mediated 
 reductive opening at c-3 . 
Introduction
Results
and Discussion
Conclusions
Experimental Section