v-Triazolo[4,5-d]pyrimidines (8-azapurines). Part 19. Stability of N-alkyl-8-azapurines. Degradation by cold, dilute acid and base to N-alkyl-4-amino-1,2,3-triazole-5-carbaldehydes and -triazol-5-yl ketones

Abstract

7-, 8-, and 9-Methyl and 8- and 9-benzyl derivatives of 8-azapurine (5) were hydrolysed by cold, aqueous N-hydrochloric acid to 1-, 2-, and 3-methyl and 2- and 3-benzyl (respectively) derivatives of 4-amino-1,2,3-triazole-5-carbaldehyde (6), mostly in high yield. Prior methylation in the 2-position prevented the hydrolysis. 6,9-Dimethyl-8-azapurine gave the analogous ketone (7a). Cold, aqueous N-sodium hydroxide behaved similarly expect that the presence of a 2-methyl group did not prevent reaction. From some of the alkaline hydrolyses, the same aldehydes (6) were isolated, as such or as their N-formyl or -acetyl derivatives which are intermediates, but in other cases self-condensation of the aldehyde occurred. Some of the 8-azapurines (5) were hydrolysed by simply boiling with water. 8-Azapurine disintegrated in acid but resisted alkali by forming an anion (Coulombic repulsion). These reactions, which have preparative value, were found by u.v. spectroscopy to show first-order behaviour. The half-lives of the starting materials were calculated. I.r and n.m.r. spectra and ionization constants are discussed.