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Pure Appl. Chem., 2006, Vol. 78, No. 11, pp. 2029-2034

Catalytic asymmetric reactions using environmentally friendly reagents and catalyst: Asymmetric synthesis versus kinetic resolution

Kiyoshi Tomioka

Graduate School of Pharmaceutical Sciences, Kyoto University, Yoshida, Sakyo, Kyoto 606-8501, Japan

Abstract: Kinetic resolution of racemic compounds is a familiar method for the preparation of optically active compounds. However, an inevitable and critical drawback from the point of view of green chemistry is the consequent wastage of half of the starting compound. A catalytic asymmetric synthesis of 5-arylcyclohex-2-enones was developed starting from racemic 5-(trimethylsilyl)cyclohex-2-enone, which overcomes the drawback of kinetic resolution. A chiral amidophosphane- or BINAP-Rh(I)-catalyzed asymmetric conjugate arylation of racemic 5-(trimethylsilyl)cyclohex-2-enone with arylboronic acids in dioxane-water (10:1) afforded trans- and cis-3-aryl-5-(trimethylsilyl)cyclohexanones in reasonably high enantioselectivity. Dehydrosilylation of the product mixture with Cu(II) chloride in dimethylformamide (DMF) gave 5-arylcyclohex-2-enones with up to 93 % ee in high yield. Enantiofacial selectivity with chiral phosphane-Rh(I) overrides the trans-diastereoselectivity that is maintained in the achiral or racemic phosphane-Rh(I)-catalyzed conjugate arylation of 5-(trimethylsilyl)cyclohex-2-enone.