Thiazolo(oxazolo)thieno[b]pyrimidines. Preparation from 2-allylthio(oxy)thieno[2,3-d]pyrimidines and hydrolysis

Heterocyclization of 5,6-disubstituted 2-allylthio(oxy)-4-oxothieno[2,3-d]pyrimidines by treatment with halogens affords thieno[3,2-e]thiazolo[3,2-a]pyrimidine iminium salts. Treatment of these salts with aqueous sodium acetate results in cleavage of the thiazoline ring.