Heteroaromatic Fused-Ring Mesoionic Compounds. Sydno[3,4-a]quinoxalines

A number of derivatives of sydno[3,4-a] quinoxalines have been synthesized from 3-(o-nitropheny1)sydnone. Incorporation of the five-membered mesoionic sydnone ring into a conjugated fused-ring heteroaromatic system produces compounds of enhanced stability toward thermal and aqueous acid-catalyzed decomposition. Susceptibility toward base-catalyzed reaction is increased. SCF molecular orbital treatments were found to be useful in predicting electronic absorption spectra, relative stability of tautomers, and the probable site of O alkylation.