Enantioselective Tail-to-Head Cyclizations Catalyzed by Dual-Hydrogen-Bond Donors.

Chiral urea derivatives are shown to catalyze enantioselective tail-to-head cyclization reactions of neryl chloride analogues. Experimental data are consistent with a mechanism in which π-participation by the nucleophilic olefin facilitates chloride ionization and thereby circumvents simple elimination pathways. Kinetic and computational studies support a cooperative mode of catalysis wherein two molecules of the urea catalyst engage the substrate and induce enantioselectivity through selective transition state stabilization.