Asymmetric Hydrogenation Catalyzed by Rhodium Complex with a New Chiral Bisphosphine Derived from L-Threonine

Abstract

A new chiral bisphosphine, (2R,3S)-l,2-bis(diphenylphosphino)-3-tBoc-aminobutane (RS-5), was prepared from L-threonine. Mesylation of ’Boc-L-threonine methyl ester (2) and subsequent reduction with sodium borohydride gave the alcohol (10), which was treated with potassium carbonate to afford a key intermediate, (2S,3S)-l-tBoc-3-methyl-2-aziridinemethanol (SS-7b). Mesylation of SS-7b, followed by treatment with sodium diphenylphosphide afforded the new chiral bisphosphine (RS-5). The structure of RS-5 was confirmed by the X-ray analysis of its crystalline CuCl complex (RS-12). The cationic rhodium (I) complexes prepared from RS-5 and RS-12 are efficient asymmetric hydrogenation catalysts for N-acyldehydroamino acids, giving (S)-N-acylamino acids in high optical yields (83—94% ee). © 1985, The Pharmaceutical Society of Japan. All rights reserved.