SIGMA-COMPLEXES IN THE PYRIMIDINE SERIES. 11. 5-ARYLAZO-5-NITRO-2,5- AND -4,5-DIHYDROPYRIMIDINES FROM ANIONIC SIGMA COMPLEXES OF 5-NITROPYRIMIDINE

Article abstract of DOI:10.1007/BF00531663

We have studied the reaction of acetonyl anionic sigma complexes of 5-nitropyrimidines with aryldiazonium salts. We have established that, independently of the position of the geminal unit in the sigma complex, electrophilic attack by the diazonium ion occurs at the C₍₅₎ atom with formation of 5-arylazo-5-nitro-2,5- and -4,5-dihydropyrimidines. The latter are unstable and upon isolation are converted to N-methoxycarbonyl-N'-(1-acetonyl-2-nitro-2-arylhydrazono)ethyl-O-methylisourea. The structure of one of these compounds has been proven by x-ray diffraction. Under alkaline conditions, aromatization of 2,5-dihydropyrimidines to 5-arylazo-2-acetonylpyrimidines occurs.