Asymmetric reduction of imines with lithium butyl(hydro)dipinan-3α-yl-borate and related reagents

Abstract

Asymmetric reductions of a series of cyclic imines, 2-n-propyl-, 2-ethyl-, and 2-methyl-3,4,5,6-tetrahydropyridine, and also 3,4-dihydropapaverine with lithium butyl(hydro)dipinan-3α-ylborate and with the related methyl and phenyl compounds are described. A transition state which correlates the chirality of the reagents with that generated at the incipient chiral centre is proposed. Reductions with these reagents are shown to give amines of higher optical purity and opposite preferred chirality to those obtained by reductions with di- or tri-pinan-3α-yl-borane.