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

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.

Automated summary

We have developed a N-heterocyclic carbene (NHC) and base-mediated [3 + 3] annulation reaction for the synthesis of enantioselective dihydropyrano[3,2-b]indoles. Easily prepared sulfonium salts were used as precursors and reacted with unsaturated acyl azolium to achieve this transformation. The reaction conditions are mild and result in privileged indole-fused dihydropyranones with moderate to good yields and excellent enantioselectivities.