Enantioselective reductions by chirally modified alumino- and borohydrides

Fifty years after the first report on the reduction of carbonyl compounds using chiral LiAlH4-derived hydrides (Bothner-By, A. A. J. Am. Chem. Soc. 1951, 7-3, 846), the field of enantioselective aluminohydride and borohydride reagents modified by chiral additives is reviewed. The first section deals with the Preparation. scope, limits. mechanism of action and synthetic applications of chiral alluminohydrides, classified according to the chemical nature of the stereogenic modifier. The second covers the field of chiral borohydrides, which have been further classified according to the boron sources, namely metal borohydrides (via reaction with chiral additives or in the presence of chiral catalysts), or chiral boranes (by reduction with alkyllithiums or metal hydrides). (C) 2001 Elsevier Science Ltd. All rights reserved.