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Synthesis 2004(9): 1353-1358  
DOI: 10.1055/s-2004-822396
PAPER
© Georg Thieme Verlag Stuttgart · New York

Optically Active 1,1′-Di-tert-butyl-2,2′-diphosphetanyl and Its Application in Rhodium-Catalyzed Asymmetric Hydrogenations

Tsuneo Imamoto*a, Nobuhiko Ooharab, Hidetoshi Takahashia
a Department of Chemistry, Faculty of Science, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
b Research & Development Division, Nippon Chemical Co., Ltd, Kameido, Koto-ku, Tokyo 136-8515, Japan
Fax: +81(43)2902791; e-Mail: imamoto@faculty.chiba-u.jp;
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Publikationsverlauf

Received 2 May 2004
Publikationsdatum:
08. Juni 2004 (online)

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Abstract

(1S,1′S,2R,2′R)-1,1′-Di-tert-butyl-2,2′-diphosphetanyl was prepared from tert-butylphosphine via phosphine-boranes as intermediates. The rhodium complex of the ligand was used as a highly efficient catalyst in asymmetric hydrogenations of α-acetyl­aminoacrylates and α-substituted enamides.

Key words

chiral phosphine ligand - chiral phosphetane derivative - rhodium complex - asymmetric hydrogenation - phosphine-borane

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15

The purification of the C 2-compound to obtain enantiomerically pure 8 by recrystallization was not easily accomplished. The major reason is that the two enantiomers [(1R,1′R,2R,2′R) and (1S,1′S,2S,2′S)] readily associated to form a racemic compound (mp 250-252 °C; HPLC analysis: Daicel Chiracel OD-H, hexane-i-PrOH (95:5), 0.5 mL/min, t = 13.6 min; Anal. Calcd for C28H56P4S4: 52.15, H, 8.75. Found: C, 51.83; H, 8.79) which was less soluble than enantiomerically pure 8.