Salen as a chiral activator: Anti versus syn switchable diastereoselection in the enantio-selective addition of crotyl bromide to aromatic aldehydes

Abstract

To be syn or to be anti? This is an 'open' matter! A good degree of syn simple diastereoselection (up to 83:17) and high enantioselectivity (ee values up to 90%) were obtained with the addition of crotyl bromide to aromatic aldehydes promoted by the [Cr(salen)]/Mn/Me3SiCl catalytic system (see scheme, path B). The remarkable degree of syn simple diastereoselection obtained with organochromium reagents can be explained by an open transition state in a chromium-mediated process.