Asymmetric Synthesis. Asymmetric Catalytic Hydrogenation Using Chiral Chelating Six-Membered Ring Diphosphines

Article abstract of DOI:10.1021/ja00399a023

Rhodium(I) catalysts formed by the two chiral chelating six-membered ring diphosphines, 2,4-bis(diphenylphosphino)pentane (skewphos) and 1,3-bis(diphenylphosphino)butane (chairphos), are efficient catalysts for the hydrogenation of amino acid precursors.The two chiral phosphines differ in that skewphos probably adopts a chiral conformation whereas chairphos probably adopts an achiral conformation.This comparison evidences the importance of ring conformations in determining optical yields.The mechanism of asymmetric hydrogenation is discussed, and a number of particular and general conclusions are drawn which may prove useful in predicting optical yields from asymmetric synthesis.