Silyl group-transfer-mediated serial Michael additions
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Three protocols have been developed for achieving ordered, multiple (serial) Michael reactions initiated by silyl enol ethers or silyl ketene acetals. Anion (fluoride or m-chlorobenzoate) catalysis was most effective for reactions of silyl ketene acetal 2 with bis diesters, as in the highly selective formation of 3. Lewis acid (ZnI2) catalysis was more general than anion catalysis and afforded stereochemically complementary products with lower selectivity. The use of SnCl2-trityl chloride was effective in reactions of both silyl ketene acetals and silyl enol ethers with bis enones. Very high stereoselectivity was generally observed in the formation of cyclopentanes. The products of serial Michael reactions of bis enones could be regiospecifically cyclized to bicyclic enones. Overall, it was found that the serial Michael reactions initiated by silyl enolates can be used to form efficiently and selectively complex cyclics from simple acyclic precursors. © 1992, American Chemical Society. All rights reserved.
author list (cited authors)
Klimko, P. G., & Singleton, D. A.