Tandem C/N-Difunctionalization of Nitroarenes: Reductive Amination and Annulation by a Ring Expansion/Contraction Sequence

Abstract

A synthetic method for the reductive transformation of nitroarenes into <i>ortho</i>-aminated and -annulated products is reported. The method operates via the exhaustive deoxygenation of nitroarenes by an organophosphorus catalyst and a mild terminal reductant to access aryl nitrenes, which after ring expansion, are trapped by amine nucleophiles to give dearomatized 2-amino-3<i>H</i>-azepines. Treatment of these ring-expanded intermediates with acyl electrophiles triggers 6π electrocyclization to extrude the nitrogen atom and restore aromaticity of the phenyl ring, which delivers via C-H functionalization 2-aminoanilide and benzimidazole products.