Quinoxaline derivatives. VIII. Betaine structures of dihydroquinoxalinium and benzimidazolium barbiturates formed from o-dialkylaminoanilines and alloxan

Abstract

Condensation of alloxan and o-dimethylaminoaniline gives 1,2,3,4.tetrahydro-4-methylquinoxaline-2-spiro-5-(hexahydro-2,4,6-trioxopyrimidine) (I) formed as a result of a unique ring-closure involving a methyl group of the o-dimethylamino substituent. The structure of the closely related compound previously formulated as its 3-hydroxy derivative (a carbinolamine) (II) is now revised to the corresponding betaine, a dihydroquinoxalinium barbiturate (III; R = H). The 6-methyl, 7-methyl, and 6,7-dimethyl analogues of the spiran (I), like the parent compound, were regarded as anils by Rudy and Cramer. Betaine structures (cf. III) may be assigned to the 6,7-dimethyl and 6,7-dichloro analogue of the barbiturate (III; R = H). o-Diethylaminoaniline reacts differently from o-dimethylaminoaniline with alloxan in giving a benzimidazolium barbiturate (VIII; R = H). We propose a similar benzimidazolium barbiturate structure for the analogous product from 4,5-dimethyl-2-dipropylaminoaniline. Mass spectra of the lowly volatile betaines and some of their deuterated derivatives were obtained and rationalized in terms of the assigned structures. Several dihydrobenzimidazoles have been prepared, and their N.M.R. and light absorption spectra recorded.