Enantioselectivity Switch in Direct Asymmetric Aminoxylation Catalyzed by Binaphthyl-Based Chiral Secondary Amines

Abstract

Binaphthyl-based amino acids ( S)- 1 and an aminosulfonamide ( S)- 2 were appliedfor direct asymmetric aminoxylation with nitrosobenzene. In thepresence of either ( S)- 1 or( S)- 2, the aminoxylationof aldehydes proceeded smoothly, and subsequent reduction with NaBH 4 gave2-aminoxyl alcohols with good to excellent enantioselectivities.In each case, binaphthyl-based chiral amine catalysts ( S)- 1 and ( S)- 2, whichhave the identical axial chirality, gave opposite enantiomers asthe major product. This method represents a rare example of thedirect asymmetric aminoxylation by a non-proline type catalyst.