Synthesis of quinoxalines by cyclization of α-arylimino oximes of α-dicarbonyl compounds

Heating the title compounds 1 at reflux in acetic anhydride yields quinoxalines 3 and 4 via a presumed aryliminoiminyl radical 5, resulting from homolytic cleavage of the NO bond in the intermediate ester 2. The observed regioselectivity of the reaction is also rationalized by implicating such a radical.