Enantioselective synthesis of 6-(Indole-2-yl)-3,4-dihydropyran-2-one skeletons by N-Heterocyclic carbene-catalyzed asymmetric [3 + 3] cycloaddition of α-bromocinnamaldehyde

Abstract

The enantioselective construction of chiral 6-(indole-2-yl)-3,4-dihydropyran-2-one skeleton was demonstrated by the formal [3 + 3] cycloaddition reaction of α-bromocinnamaldehyde with β-ketoester indole catalyzed by chiral N -heterocyclic carbene (NHC). The reaction proceeds smoothly via a vinyl acyl azolium intermediate (electron-poor enone) generated from NHC-aldehyde adducts, providing 6-(indole-2-yl)-3,4-dihydropyran-2-one derivatives in good yields with excellent enantioselectivities (up to 98% ee ).