Asymmetric synthesis of propargylic alcohols via aldol reaction of aldehydes with ynals promoted by prolinol ether–transition metal–Brønsted acid cooperative catalysis

Abstract

A catalytic and highly stereoselective entry to propargylic alcohols and products derived thereof is reported based on an unprecedented cross-aldol coupling between unmodified aldehydes and ynals. The method requires an amine–metal salt–Brønsted acid ternary catalyst system and implies synergistic activation of the donor aldehyde via enamine and of the acceptor carbonyl via unique and reversible metal–alkyne complexation. Specifically, by using a combined α,α-dialkylprolinol silyl ether–CuI–PhCO2H catalyst system, remarkably high levels of diastereo- and enantioselectivity (anti/syn up to >20 : 1, ee up to >99%) are achieved.