Enantioselective construction of dihydropyranone-fused indoles by [3 + 3] annulation of in situ-derived indolin-3-ones and unsaturated carboxylic esters

Abstract

We have developed an N-heterocyclic carbene (NHC) and base-mediated [3 + 3] annulation reaction of unsaturated carboxylic esters and sulfonium salts for rapid and direct access to enantioselective dihydropyrano[3,2-b]indoles. Easily prepared sulfonium salts were used as precursors of indolin-3-ones to react with unsaturated acyl azolium in these reactions. The title transformation proceeds smoothly under mild reaction conditions and affords privileged indole-fused dihydropyranones with moderate to good isolated yields and excellent enantioselectivities.