The synthetic utility of heteroaromatic azido compounds. Part VII. Preparation of some 2‐ and 4‐substituted thieno[3,2‐d]pyrimidines

Synthetically useful scission reactions of some 1H‐1,2,3‐triazolo[1,5‐a]thieno[3,2‐d]pyrimidines have been studied. The net result of these reactions is an elimination of nitrogen, and a 1,1‐addition of the cleaving agent, forming 2‐substituted thieno[3,2‐d]pyrimidines. The mechanism of the scission is discussed, and a concomitant nucleophilic attack and expulsion of nitrogen is proposed. An unusual reaction between the unsubstituted triazole‐fused parent compound (1) and bromine in alkaline medium is also reported.