Heterocyclic compounds from alloxan and amines. XII. Tetrahydroquinoxalinespirobarbituric acids and 5-(1-Benzimidazolio)-4-barbiturates from 2-Dialkylaminoanilines

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Abstract
The betaine formed from 2-dimethylaminoaniline and alloxan is shown to be 5-(3-methyl-1-benzimidazolio)-4-barbiturate by synthesis from 1-methylbenzimidazole; it's N,S-dimethyl derivative (1,3-dimethylbarbiturate) was also synthesized. A number of analogous betaines was prepared from alloxan and 1-o-aminophenyl derivatives of secondary amines, and it was shown by tracer studies that enamines are not intermediates in the reaction. A probable mechanism is discussed. 2-Amino-N-mesityl-N-methylaniline and the N-ethyl analogue gave tetrahydroquinoxaline-spirohexahydrotrioxopyrimidines with alloxan instead of betaines, and alkaline hydrolysis led to the related 4-mesityltetrahydroquinoxalinohydantoins. Some of the betaines, and one of the spirans, were also obtained by oxidation of uramils. Mass spectra of the betaines are discussed, and N.M.R. data are reported. Ring expansion occurs during conversion of 5-(3-methyl-1-benzimidazolio)-4-barbiturate into the related tetrahydroquinoxalinespirobarbituric acid by reduction with sodium borohydride.

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