Base‐Mediated [4+1] Annulation Strategy for Modular Assembly of Alkynyl/Carboxylated Dihydrobenzofurans

Abstract An efficient and operational [4+1] annulation strategy toward functional dihydrobenzofurans from 2‐bromomalonates and in situ generated alkynyl o ‐quinone methides (from o ‐hydroxyphenyl propargylamines) has been developed. Without the need for pre‐dried solvent and inert atmosphere protection, a broad range of substituted propargylamines are well‐tolerated, producing the expected alkynyl/carboxylated dihydrobenzofurans with good to high yields. Furthermore, a gram‐scale synthesis and valuable alkenyl/carboxylated dihydrobenzofurans construction were conducted to provide a great potential value in medicinal chemistry and other related disciplines.