Three-Component Synthesis of Pyrrolo/indolo[1,2-a]quinoxalines Substituted with o-Biphenylester/N-arylcarbamate/N-arylurea: A Domino Approach Involving Spirocyclic Ring Opening.

A p-TsOH-mediated one-pot, three-component methodology has been developed for the synthesis of pyrrolo/indolo[1,2-a]quinoxalines substituted with o-biphenylester/N-arylcarbamate/N-arylurea at the C-4 position under open-air heating conditions. The protocol offers a transition-metal-free and external oxidant-free solvent-mediated pathway to afford a library of diversely substituted quinoxalines in moderate to good yields. Various water-miscible aliphatic alcohols and amines participate in the reactions both as solvent as well as reactant. X-ray crystal structure analysis suggests that some of the suitably substituted quinoxalines may exhibit atropisomerism at room temperature.