Transformation of 6-methylthiopyrimidines. Preparation of new pyrimidine derivatives and fused azolopyrimidines

2,4‐Diamino‐6‐methylthiopyrimidines 1 reacted with sodium methoxyde and benzylamine to give the corresponding 6‐methoxypyrimidine and 6‐benzylaminopyrimidine derivatives 2 and 4 respectively. The reaction of 1 with hydrazine hydrate, in ethanol, gave 6‐hydrazino derivatives 6. However, by treating pyrimidines 1 in boiling hydrazine hydrate 3,6‐diamino‐4‐hydrazino‐1H‐pyrazolo[3,4‐d]pyrimidine 5 was obtained. The 6‐hydrazinopyrimidines 6 could be converted into the pyrazolo[3,4‐d], triazolo[4,3‐c] and tetrazolo‐[1,5‐c]pyrimidines 7, 8 and 9 by the action of heating, trimethyl orthoformate and nitrous acid, respectively.