Facile synthesis of quinoxaline-2-thiol and quinoxaline from α-oxo sulfines and o-aryl diamines

A series of quinoxaline-2-thiol and quinoxaline were prepared in moderate to good yields from various phenacyl sulfoxides bearing 1-methyl-1H-tetrazole and o-aryl diamines. The proposed reaction mechanism involves generation of sulfines from the phenacyl sulfoxides bearing 1-methyl-1H-tetrazole through thermolysis elimination. Then, site-selectively carbophilic addition of sulfines by o-aryl diamines, followed by elimination, intramolecular nucleophilic addition and dehydration condensation. The current method provides a direct and simple strategy for the preparation of quinoxaline-2-thiols and quinoxalines.