Catalytic enantioselective reactions. Part 16. Oxazaborolidine-catalyzed asymmetric borane reduction of α-keto acetals

Asymmetric reductions of α-keto acetals using various oxazaborolidines and borane reagents as catalyst and the hydride source, respectively, were compared. The reduction catalyzed by Corey’s CBS reagents with N-phenylamine–borane reagents provided α-hydroxy acetals with very high enantioselectivities for most aromatic analogues.