SmI₂-Promoted conjugate reduction of α,β-unsaturated esters and ketones studied in comparison with Mukaiyama-Michael reaction of ketene silyl acetal

SmI₂-promoted conjugate reduction of α,β-unsaturated esters and ketones proceeds in a manner quite similar to Mukaiyama-Michael reaction of ketene silyl acetal. The more substituted eaters are reduced more preferentially than the less substituted ones. The substrates with a 12 or 16 membered-ring structure undergo reduction smoothly. On the other hand, the 6-membered substrates completely fail to react under the same conditions. These results indicate generation of intermediate enolate radicals to be a key step for the conjugate reduction.