Recent Development and Improvement for Boron Hydride-Based Catalytic Asymmetric Reduction of Unsymmetrical Ketones

Catalytic asymmetric reduction of prochiral ketones with hydrides such as boranes and borohydrides is one of the simplest and the most convenient methods for obtaining chiral alcohols. This tutorial review describes the most significant advances recently achieved for enhancing the enantioselectivity and practicability of the reduction using this methodology. The review covers the development of new homogeneous and/or immobilized catalysts for asymmetric reduction using borane or borohydride reagents and practical improvement of the well-known oxazaborolidine (OAB)-catalysed reduction through developing more stable, cost effective and recoverable OABs, scalable and environmental friendly borane sources, and one-pot procedures for the reduction.