Enantioselective All-Carbon (4+2) Annulation by N-Heterocyclic Carbene Catalysis

The enantioselective vinylogous Michael/aldol cascade is an underdeveloped approach to cyclohexenes. Herein we describe a highly enantioselective (most ≥ 98:2 er) and diastereoselective (all ≥ 15:1 dr) N-heterocyclic carbene catalyzed cycloisomerization of acyclic dienyl esters to cyclohexyl β-lactones. Derivatizations avail cyclohexenes bearing four contiguous stereogenic centers, while mechanistic studies support olefin isomerization prior to cyclization.