v-Triazolo[4,5-d]pyrimidines (8-azapurines). Part 18. Three new reactions for synthesizing 8-azapurinethiones from 4-amino-5-cyano-1,2,3-triazoles
4-Amino-5-cyano-1,2,3-triazole (2d) and its 1-, 2-, and 3-methyl and 3-benzyl derivatives were, variously, subjected to (a) condensation with triethyl orthoformate followed by treatment with sodium hydrogen sulphide, (b) condensation with O-ethyl dithiocarbonate, and (c) condensation with phenyl isothiocyanate, to give (respectively) 8-azapurine-6-thiones (4), 8-azapurine-2,6-dithiones (6), and 6-anilino-8-azapurine-2-thiones (9). Several of the dithiones were characterized by di-S-methylation to give 2,6-bismethylthio-8-azapurines. The reversible isomerisation of 8-azapurine-2,6-dithione (6d) to 7-amino[1,2,3]thiadiazolo[5,4-d]pyrimidine-5-thione (7) was explored. I.r. and 1H n.m.r. spectra are discussed.