this invention relates to a process for preparing herbicidally active imidazolidinone amine compounds represented by the formula i : ## str1 ## wherein a is ## str2 ## wherein : x is ch or n ; r is up to c 6 alkyl , haloalkyl or cycloalkyl , up to c 5 alkenyl or alkynyl , -- r 2 -- o -- r 3 or -- r 2 -- s -- r 3 wherein r 2 is up to c 6 alkylene and r 3 is up to c 6 alkyl or optionally substituted phenyl or benzyl ; and r 4 is up to c 3 alkyl or allyl . the process of this invention involves reacting a 3 - ( or 5 -) isocyanato isoxazole of the formula or a 3 - ( or 5 -) isocyanato oxadiazole of the formula ii : wherein a is as previously defined , with a substituted aminoacetonitrile of the formula iii : wherein r 4 is as previously defined , to obtain a novel imidazolidinone 4 - imine of the formula iv : ## str3 ## wherein a and r 4 are as previously defined . the imine of formula iv is then hydrogenated to obtain a formula i compound . more particularly , equivalent amounts of the formula ii and formula iii compounds are reacted at up to reflux temperature typically in the presence of an inert solvent and a tertiary amine catalyst , for a time sufficient to assure complete conversion of starting material . some suitable solvents include toluene , tetrahydrofuran , chloroform , benzene or the like . triethylamine , tributylamine , diethylaniline and the like are exemplary of suitable catalysts . the novel formula iv compound thus obtained is then hydrogenated to obtain the desired formula i compound . hydrogenation may be effected by contacting the formula iv compound with gaseous hydrogen in the presence of a suitable solvent and a suitable catalyst . exemplary solvents include benzene , ethyl acetate , ethanol , glacial acetic acid or the like . palladium , palladium on carbon or metallic sodium are exemplary of suitable catalysts . hydrogenation could also be effected by electrochemical reduction . ( a ) to a flask provided with a reflux condenser a magnetic stirring bar and a drying tube is charged with 5 -( t - butyl )- 3 - isocyanato isoxazole , dry toluene and a catalytic amount of dry triethylamine . to this stirred mixture is added an equivalent amount of methaminoacetonitrile . the reaction mixture is then heated to reflux and maintained at reflux until hplc analysis indicates complete consumption of starting material . the reaction mixture is then cooled , transferred to a separatory funnel , diluted with ethyl acetate and washed with saturated aqueous sodium bicarbonate and saturated aqueous sodium chloride solutions . the organic layer is dried over anhydrous magnesium sulfate , filtered and concentrated in vacuo affording 3 -[ 5 -( t - butyl )- 3 - isoxazolyl ]- 1 - methyl - 4 - imino - 2 - imidazolidinone . ( b ) the 4 - imino compound prepared as described in paragraph ( a ) is charged to a parr hydrogenation bottle along with glacial acetic acid and a catalytic amount of 10 percent palladium on carbon hydrogenation catalyst . the bottle is charged with hydrogen and rocked in a parr hydrogenation apparatus until tlc analysis indicates completeness of reaction . the bottle is then flushed with air , the catalyst removed by filtration and the reaction mixture is concentrated in vacuo to remove the acetic acid solvent . the residue is then dissolved in chloroform , dried over anhydrous magnesium sulfate , filtered and concentrated in vacuo to afford the desired product , 3 -[ 5 -( t - butyl )- 3 - isoxazolyl ]- 1 - methyl - 4 - amino - 2 - imidazolidinone . preparation of a particular formula i and formula iv compound is illustrated by the foregoing and it is to be understood that other formula i and formula iv compounds can be readily prepared using the process of this invention simply by varying the choice of starting materials . the formula i compounds prepared by the process of this invention are useful as herbicides and are described in u . s . pat . no . 4 , 426 , 527 and copending , commonly assigned u . s . application ser . no . 606 , 810 filed may 3 , 1984 , the teachings of which are incorporated by reference herein respecting the structure and utility of said compounds .