Asymmetric induction in Michael addition reactions mediated by C₂-symmetric aluminate

Abstract

The C₂-symmetric chiral amino-diol, (1 R, 5R)-3-aza-3- benzyl-1 ,5-diphenylpentan-1,5-diol (1) is available readily from the reaction of benzylamine with a twofold excess of enantiopure R(+)-styrene epoxide. We have recently shown that the titanoate complexes formed from these promote Diels-Alder and ene reactions. The adducts are obtained in high enantiomeric excess under extremely mild reaction conditions. However, this Lewis acid complex was incapable of promoting Michael addition reactions. But the corresponding aluminate of the amino diol 1 was found to act as efficient catalyst for Michael addition reactions and the homochiral aluminate was capable of inducing high enantiomeric excess in the corresponding Michael addition products. In this paper the synthesis of 1, the complexation with LiAIH₄and its ability to promote a chiral variant in the Michael addition of various donors and acceptors (Eq.l) are discussed.