Chiral Spiroaminoborate Ester as a Highly Enantioselective and Efficient Catalyst for the Borane Reduction of Furyl, Thiophene, Chroman, and Thiochroman-Containing Ketones.

Abstract Prochiral heteroaryl ketones containing furan, thiophene, chroman, and thiochroman moieties were successfully reduced in the presence of 1–10 mol % of spiroaminoborate ester 1 with different borane sources to afford non-racemic alcohols in up to 99% ee. In addition, modest enantioselectivity, around 80% ee, was achieved in the reduction of linear α,β-unsaturated heteroaryl ketones.