Asymmetric Synthesis Using Chirally Modified Borohydrides. Part 1. Enantioselective Reduction of Aromatic Ketones with the Reagent Prepared from Borane and (S)-Valinol
The asymmetric reduction of aromatic ketones with the reagents prepared from borane and chiral aminoalcohols was studied under various conditions.The ratio of borane to (S)-valinol was found to be optimum at 2-3:1, when up to 65-73percent selectivity was obtained in the reduction of n-propyl phenyl ketone.The amino-alkoxy-amine-boranes (2) and/or (3) were tentatively proposed as the reaction species responsible for asymmetric induction.