Synthesis of 2-substituted 3-acylindoles via reductive cyclization – rearrangement of β-acyl β-alkyl-substituted 2-nitrostyrenes

Abstract

A short synthetic sequence to 2-substituted 3-acylindoles has been developed. The sequence starts with a Wittig or an aldol reaction of 2-nitrobenzaldehydes to give β-acyl-β-alkyl-substituted 2-nitrostyrenes. The styrenes are transformed into 2-substituted 3-acylindoles by a palladium – catalyzed, carbon monoxide – mediated, reductive cyclization with concurrent migration of the acyl group. In addition to indoles, quinoline-N-oxides and quinolines were sometimes obtained in low isolated yields.