An Enolate‐Structure‐Enabled Anionic Cascade Cyclization Reaction: Easy Access to Complex Scaffolds with Contiguous Six‐, Five‐, and Four‐Membered Rings

Abstract

Catalyst-free addition of ketone enolate to nonactivated multiple CÀCb onds involves non-complementary reaction partners and typically requires super-basic conditions. On the other hand, highly aggregated or solvated enolates are not reactive enough to undergo direct addition to alkenes or alkynes.Herein, we report an ew anionic cascade reaction for one-step assembly of intriguing molecular scaffolds possessing contiguous six-, five-, and four-membered rings,r epresenting af ormal [2+ +2] enol-allene cycloaddition. Reaction proceeds under very mild conditions and with excellent diastereoselectivity.D eeper mechanistic and computational studies revealed unusually slow proton transfer phenomenon in cyclic ketone intermediate and explained peculiar stereochemical outcome.