K3PO4-Promoted Cascade Annulation of ortho -Hydroxyphenyl-Substituted para -Quinone Methides and Vinylsulfonium Salts: An Access to 2 H -Chromenes

Abstract The compounds containing 2H-chromene scaffolds exhibit a broad spectrum of biological and pharmaceutical activities. Herein, a novel metal-free reaction of ortho-hydroxyphenyl-substituted p-QMs with vinylsulfonium salts has successfully been developed, leading to the formation of 2H-chromenes in a one-pot way, of which 2H-chromenes themselves could also be easily further transformed into valuable ring-contraction products, benzofurans, via a rearrangement strategy under mild conditions. The protocol circumvents several limitations of prior methods, including the use of transition metals (Pd, Co, Ag, Ni, etc.), equivalent levels of special agents, expensive ligands, the requirement of difficult-to-access starting materials, and harsh reaction environments.