v-Triazolo[4,5-d]pyrimidines (8-azapurines). Part 24. The 3-alkyl derivatives

Abstract

4-Methylamino-1,2,3-triazole-5-carboxamide (2e) and its 3-benzyl derivative (2b) were cyclized with hydrochloric acid and triethyl orthoformate to give 3-methyl-8-azapurin-6(1H)-one (1c) and its 9-benzyl derivative (1b). The reaction mechanism is discussed. The 8-azapurinone (1c) was converted by phosphorus pentasulphide into 3-methyl-8-azapurine-6(1H)-thione (9) and an extraordinary by-product, 5-amino-1,2,3-thiadiazole-4-N-(thioformyl)carbothioamide (10). Hydrogenation of the two 8-azapurinones (1c) and (1b) gave 1,2-dihydro-3-methyl-8-azapurin-6(3H)-one (7b) and its 9-benzyl derivative (7a), respectively.

4-Methylamino-1,2,3-triazole-5-carbonitrile (12c) was converted by formamidinium acetate into 6-amino-3-methyl-8-azapurine (13a). Hydrogenation of 3-benzyl-4-methylamino-1,2,3-triazole-5-carbonitrile (12b) produced 5-aminomethyl-3-benzyl-4-methylamino-1,2,3-triazole (14a) which gave formly (14b) and acetyl, formyl (14c) derivatives when cyclization was attempted. Several Dimroth retrogressions were encountered, in which a methyl group appeared to move from the exocyclic 4-amino-group to a nitrogen atom (N-3) in the ring, in one instance displacing a 3-benzyl group. Two other unusual by-products were the highly fluorescent diacylamine, 3-benzyl-4-methylamino-5-N-formylcarboxamide (6) obtained by ring-opening of the 8-azapurinone (1b), and bis-(3-benzyl-4-methylamino-1,2,3-triazol-5-carbonyl)amine (3) from the action of sodium ethoxide on the triazole (2d).

¹ H N.m.r., i.r., and mass spectra of the products are discussed. The ¹H n.m.r. spectra of three triazoles showed several twinned sets of signals due to stable rotamers. There were several unusual features in the i.r. spectrum of 3-methyl-8-azapurin-6(1H)-one.