Enantioselective all-carbon (4+2) annulation by N-heterocyclic carbene catalysis.

ABSTRACT

The enantioselective vinylogous Michael/aldol cascade is an underdeveloped approach to cyclohexenes. Herein we describe a highly enantioselective (most ≥ 982 er) and diastereoselective (all ≥ 151 dr) N-heterocyclic carbene catalyzed cycloisomerization of acyclic dienyl esters to cyclohexyl ß-lactones. Derivatizations avail cyclohexenes bearing four contiguous stereogenic centers, while mechanistic studies support olefin isomerization prior to cyclization.