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).

Keywords

Organocatalysis / enantioselective synthesis / N-heterocyclic carbene (NHC) / acyl azolium intermediate / 6-(indole-2-yl)-3 / 4-dihydropyran-2-one skeleton

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