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Catalytic Asymmetric Epoxidation of Enones Using La-BINOL-triphenylarsine Oxide Complex: Structural Determination of the Asymmetric Catalyst

Catalytic Asymmetric Epoxidation of Enones Using La-BINOL-triphenylarsine Oxide Complex: Structural Determination of the Asymmetric Catalyst

T Nemoto, T Ohshima, K Yamaguchi, M Shibasaki

J Am Chem Soc. 2001 Mar 28;123(12):2725-32.

PMID: 11456958

Abstract:

The catalytic asymmetric epoxidation of enones using the La-BINOL-Ph(3)As=O complex generated from La(O-i-Pr)(3), BINOL, and Ph(3)As=O in a ratio of 1:1:1 is described herein. Using 1-5 mol % of the asymmetric catalyst, a variety of enones, including a dienone and a cis-enone, were found to be epoxidized in a reasonable reaction time, providing the corresponding epoxy ketones in up to 99% yield and with more than 99% ee. The possible structure of the actual asymmetric catalyst has been clarified by various methods, including X-ray crystal structure analysis. This is the first X-ray analysis of an alkali-metal free lanthanoid-BINOL complex. Although La(binaphthoxide)(2)(Ph(3)As=O)(2) (7) was observed as the major complex in the complexes' solution, generated from La(O-i-Pr)(3), BINOL, and Ph(3)As=O in a ratio of 1:1:1, the possible active species turned out to be the La-BINOL-Ph(3)As=O complex in a ratio of 1:1:1. A probable reaction mechanism of the catalytic asymmetric epoxidation of enones is also proposed, suggesting that preferential formation of a heterochiral complex is the reason for asymmetric amplification. Moreover, the interesting role of La(O-i-Pr)(3) for accelerating the epoxidations while maintaining high ee's is discussed.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP1153055	Triphenylarsine oxide		1153-05-5	Price

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