Synthesis of 2-acyl benzofurans and indoles based on nucleophile-intercepted Meyer–Schuster rearrangement of o-hydroxyphenyl and o-aminophenyl propargylic alcohols

Abstract

A metal-free synthetically useful catalytic approach for the preparation of 2-acyl benzofurans and indoles from easily accessible o-hydroxyphenyl and o-aminophenyl propargylic alcohols in the presence of pyridine N-oxide is disclosed. This protocol comprises the acid promoted formation of a carbocation and subsequent nucleophilic trapping by pyridine N-oxide, which leads to umpolung of the allenyl ether moiety. The following intramolecular attack at the umpolung allenyl carbon furnishes the final benzofurans and indoles via a nucleophile-intercepted Meyer–Schuster rearrangement.