3-Alkylthio-s-triazolo[3,4-i]purines and 9-Alkylbis-s-triazolo[3,4-b:3',4'-i]purines

Purin-6-ylhydrazine (la) reacted with carbon disulfide to give s-triazolo[3,4-i]purine-3(2H)-thione (tautomer, 2b) which underwent alkylation to yield its S-methyl (2c) and S-carbamoylmethyl (2d) derivatives. In contrast, purin-8-ylhydrazine (lb) and triethyl orthoacetate gave only the intermediate N-(1'-ethoxyethylidene)-9-methylpurin-8-ylhydrazine (lc) which resisted cyclization. Purine-2,6-diyldihydrazine (1f) reacted with trimethyl orthoacetate, triethyl orthoacetate and triethyl orthopropionate to give 3,7,9-trimethyl-, 9-ethyl-3,7-dimethyl- and 3,7,9-triethyl-bis-s[ 3,4-b:3',4'-i]purine (4a-c), respectively. The unexpected extra N-alkyl group was shown to occupy the 9-rather than the 11-position by unambiguous synthesis of (4c) from 9-ethylpurine-2,6-diyldihydrazine (1h). Structures were confirmed by n.m.r. spectra.