ortho-Substituted aryl aldehyde complexes undergo diastereoselective nucleophilic addition with organometallic reagents and other nucleophiles. Equation (8) is an example of a diastereoselective Morita-Baylis-Hillman reaction.
Pinacol coupling and the corresponding diamine coupling are possible in the presence of a one-electron reducing agent such as samarium(II) iodide.
Benzylic cations of chromium arene complexes are conformationally stable, and undergo only exo attack to afford S1 products stereospecifically, with retention of configuration. Propargyl and oxonium cations undergo retentive substitution reactions, and even β carbocations react with a significant degree of retention.
Benzylic anions of chromium arene complexes exhibit similar reactivity to cations. They are also conformationally restricted and undergo substitution reactions with retention of stereochemistry at the benzylic carbon. In the example below, complexation of the pyridine nitrogen to lithium is essential for high stereoselectivity.
Nucleophilic addition to styrenes followed by quenching with an electrophile leads to cis products with essentially complete stereoselectivity.
Diastereoselective reduction of styrenes is possible with samarium(II) iodide. A distant alkene is untouched during this reaction, which provides the reduced alkylarene product in high yield.
Complexation of a haloarene to chromium increases its propensity to undergo oxidative addition. Suzuki cross coupling of a planar chiral chromium haloarene complex with an aryl boronic acid is thus a viable method for the synthesis of axially chiral biaryls. In the example below, the syn isomer is formed in preference to the anti isomer; when R is the formyl group, the selectivity reverses.
Tetralones complexed to chromium may be deprotonated without side reactions. Alkylation of the resulting enolate proceeds with complete diastereoselectivity to afford the exo product.