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Article

Catalytic Cycle of Rhodium-Catalyzed Asymmetric 1,4-Addition of Organoboronic Acids. Arylrhodium, Oxa-π-allylrhodium, and Hydroxorhodium Intermediates

Tamio Hayashi,* Makoto Takahashi, Yoshiaki Takaya, and Masamichi Ogasawara

Contribution from the Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan

J. Am. Chem. Soc., 2002, 124 (18), pp 5052–5058

DOI: 10.1021/ja012711i

Publication Date (Web): April 11, 2002

Corresponding author. E-mail: thayashi@kuchem.kyoto-u.ac.jp.

Abstract

The catalytic cycle of asymmetric 1,4-addition of phenylboronic acid to an α,β-unsaturated ketone catalyzed by a rhodium−binap complex was established by use of RhPh(PPh₃)(binap) as a key intermediate. The reaction proceeds through three intermediates, phenylrhodium, oxa-π-allylrhodium, and hydroxorhodium complexes, all of which were observed in NMR spectroscopic studies. The transformations between the three intermediates, that is, insertion, hydrolysis, and transmetalation, were also observed. On the basis of the catalytic cycle, a more active chiral catalyst, [Rh(OH)(binap)]₂, was found and used successfully for the asymmetric 1,4-addition reactions.

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