N-Heterocyclic Carbene-Catalyzed Diastereoselective Vinylogous Michael Addition Reaction of gamma-Substituted Deconjugated Butenolides

摘要

An efficient N-heterocyclic carbene (NHC)-catalyzed vinylogous Michael addition of deconjugated butenolides was developed. In the presence of 5 mol % of the NHC catalyst, both gamma-alkyl- and aryl-substituted deonjugated butenolides undergo vinylogaus Michael addition with various alpha, beta-unsaturated ketones, esters, or nitriles to afford gamma,gamma-disubstituted butenolides containing adjacent quaternary and tertiary carbon centers in good to excellent yields with excellent diastereoselectivities. In this process, the free carbene is assumed to act as a Strong Bronsted base to promote the conjugate addition.