The azide/tetrazole equilibrium: an investigation in the series of furo- and thieno[2,3-e]tetrazolo[3,2-d]pyrimidine derivatives

Abstract Starting from 7(8)-chlorofuro(thieno)[3,2- d ]pyrimidines 1 , the corresponding 7(8)-hydrazinofuro(thieno)[3,2- d ]pyrimidines 2 were obtained by reaction with hydrazine. By treatment with nitrous acid, compounds 2 gave fused furo- and thieno[2,3- e ]tetrazolo[1,5- c ]pyrimidines 3 T and 4 T in excellent yields, which in solution exist in equilibrium with 7(8)-azidofuro(thieno)[3,2- d ]pyrimidines 3 A and 4 A . Compounds 3 T / 3 A and 4 T / 4 A represent useful substrates for investigating the azide/tetrazole equilibrium: it has been examined as a function of solvent, temperature, and their structure. We have observed that, in solution, in both 3 and 4 the equilibrium was strongly …