Access to 5‐Hydroxybenzofurans via Formal [3+1+1] Annulation of Quinone Esters with Pyridinium Ylides

Abstract A base promoted formal [3 + 1 + 1] annulation of pyridinium salts and quinone esters has been developed. A series of highly functionalized biologically important benzofurans from readily available starting materials can be facilely and efficiently obtained in acceptable yields (up to 77%) under very mild reaction conditions. The utility of this protocol was demonstrated by gram‐scale synthesis. The possible mechanism was proposed. This protocol represents the first example of annulation reaction of pyridinium salts and quinone esters for the synthesis of benzofurans.