Combined α,α-dialkylprolinol ether/Brønsted acid promotes Mannich reactions of aldehydes with unactivated imines. An entry to anti-configured propargylic amino alcohols

Abstract

The first enamine mediated anti-selective and highly enantioselective Mannich reaction of aldehydes and unactivated imines is reported. The key for success is the combined use of a Brønsted acid with an α,α-dialkylprolinol ether catalyst that leads to adducts with good yields (typically 70–75%), anti : syn ratios greater than 90 : 10, and ee values usually above 95%. The method works particularly well with propargylic imines and, unlike previous catalytic routes to optically active propargylamines, provides adducts featuring two contiguous stereocenters and a functionalized side chain amenable for ulterior synthetic applications.