Efficient asymmetric hydrogenation of olefins with hydrazine-derived diphosphoramidites

Abstract

Enantiopure, BINOL-derived diphosphoramidites built upon an achiral hydrazine spacer are efficient ligands for the hydrogenation of 2-(acetylamino)-3-(aryl)-propenoic methyl esters. The activity and enantioselectivity of the hydrazine derivatives were shown to be markedly influenced by the nature of the two NR substituents, symmetrical but bulky R groups leading to the best results. A diphosphosphoramidite obtained from ^tBuHNNH^tBu resulted in ee's as high as 95%. The present results contradict previous reports on “short” diphosphoramidites.