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Note | Special issue | Vol 76, No. 2, 2008, pp.1633-1645
Published online, 12th June, 2008
DOI: 10.3987/COM-08-S(N)121
Catalytic Asymmetric Synthesis of (-)-Ritodrine Hydrochloride via Silyl Enol Ether Amination Using Dirhodium(II) Tetrakis[tetrafluorophthaloyl-(S)-tert-leucinate]

Masahiko Tanaka, Seiichi Nakamura, Masahiro Anada, and Shunichi Hashimoto*

*Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan

Abstract

A catalytic asymmetric synthesis of (-)-ritodrine hydrochloride was achieved, incorporating an enantioselective amination of (Z)-silyl enol ether derived from 4-benzyloxypropiophenone with [(2-nitrophenylsulfonyl)imino]phenyliodinane (NsN=IPh) and a chelation-controlled reduction of the ketone carbonyl group with Zn(BH4)2 as the key steps. The use of dirhodium(II) tetrakis[tetrafluorophthaloyl-(S)-tert-leucinate] as a catalyst produced the targeted α-amino ketone in 94% yield with 91% ee.