ON THE DIASTEREOFACIAL SELECTIVITY OF LEWIS ACID-CATALYZED CARBON-CARBON BOND FORMING REACTIONS OF CONJUGATED CYCLIC ENONES BEARING ELECTRON-WITHDRAWING SUBSTITUENTS AT THE GAMMA-POSITION

Lewis acid catalyzed reactions of several cyclic enones are described. The gamma-OTBS enones 1 and 2 give products where carbon-carbon bond formation at the beta carbon occurs with high stereoselectivity favoring attack syn to the resident OTBS group. In the case of enone 24 bearing an additional dioxolane ring, the products correspond to addition anti to the resident carbon-oxygen bond at the gamma carbon. The reaction of 24 with lithium dimethylcuprate also occurs in an anti sense. The starting materials in this study are available in quantity in optically pure form. Given the excellent stereoselectivity of the reactions, these compounds are useful intermediates for synthesis.