Increasing enantioselectivity in reductions with borane reagents

Abstract

A method of increasing enantioselectivity in a reduction reaction of a prochiral substrate with a borane reagent including a borohydride species (for example, a borohydride stabilized borane-tetrahydrofuran complex) catalyzed by a chiral catalyst includes the step of maintaining the concentration of borohydride species in the borane reagent below approximately 0.005 M during the reduction of the prochiral substrate. A method of increasing enantioselectivity in a reduction reaction of a prochiral substrate with a borane reagent including a borohydride species that is catalyzed by a chiral catalyst includes the step of reducing the detrimental effect the borohydride species has on enantioselectivity by adding a Lewis acid. For example, the prochiral substrate can be a ketone and the chiral catalyst can be a chiral oxazaborolidine.

Dependencies are inferred from the claim text.