A switchable reductive cyclization of o-alkyl nitroarenes: divergent synthesis of heterocycles

Abstract

Readily accessible o-alkyl nitroarenes have been developed for the divergent synthesis of heterocycles via temperature-controlled, base-mediated reductive cyclization. This protocol enables the rapid and selective transformation of o-alkyl nitroarenes into thiophenes or quinolines in moderate to good yields by simply adjusting the reaction temperature in the presence of elemental sulfur. Remarkably, removing sulfur shifts the selectivity toward a diverse range of N-hydroxyindoles. This metal-free strategy offers an environmentally benign approach with high chemoselectivity and a broad substrate scope. Additionally, several synthetic transformations of the products were achieved. A series of mechanistic studies demonstrates the transformation relationships and possible pathways among thiophenes, quinolines, and N-hydroxyindoles.