Achiral additives dramatically enhance enantioselectivities in the BINOL–Ti(IV) complex catalyzed aldol condensations of aldehydes with Chan’s diene

Abstract

Achiral additives can dramatically enhance the enantioselectivities in the BINOL–Ti(IV) complex catalyzed aldol condensations of aldehydes with Chan’s diene. The best results were obtained by using 2.0 equiv of LiCl with respect to ( S)-BINOL/Ti(O i-Pr) 4 as the additive. In the presence of 4.0 mol % of LiCl and 2.0 mol % of BINOL/Ti(O i-Pr) 4, all aldehydes tested gave δ-hydroxy-β-ketoesters as almost pure single enantiomers. Moreover, the present catalyst system was highly effective on reducing the catalyst loadings to 0.1 mol %.