v-Triazolo[4,5-d]pyrimidines (8-azapurines). Part XVII. Preparation of 1,6-dihydro-8-azapurines by heating 4-amino-5-aminomethyl-N-alkyl-1,2,3-triazoles with orthoesters or amidines

Abstract

Treatment of salts of 4-amino-5-aminomethyl-3-benzyl-1,2,3-triazole (6a) with triethyl orthoformate and orthoacetate gave 9-benzyl- and 9-benzyl-2-methyl-1,6-dihydro-8-azapurine (1b and c), respectively. Small variations in the experimental conditions diverted these reactions to by-products, which illuminated the course of the normal reaction. These by-products were NN′-bis-(5-aminomethyl-3-benzyl-1,2,3-triazol-4-yl)formamidine (7) and 5-acetamidomethyl-3-benzyl-4-(α-ethoxyethylideneamino)-1,2,3-triazole (8a).

For straightforward production of 1,6-dihydro-8-azapurines, a new reaction is recommended in which amidines replace the orthoesters. With its aid, high yields were obtained of 9-benzyl-, 9-benzyl-2-methyl-, 7- and 8-methyl-, 2,7- and 2,8-dimethyl-, and 9-benzyl-2-trichloromethyl-1,6-dihydro-8-azapurine (1b–h). Ionization constants, and u.v., i.r., and ¹H n.m.r. spectra of this stable class of compounds are reported and discussed. All these dihydro-compounds were oxidised with manganese reagents to the corresponding 8-azapurines in high yields.