[1]Benzothienopyrimidines. I. Etude de la 3H-benzothieno[3,2-d]pyrimidone-4

3H-benzothieno3,2-d]pyrimidin-4-one (3) was synthesized by bimolecular cyclising the 3-amino-2-carbethoxybenzothiophene (1) with formamide. The electrophilic substituion of 3 afforded N-methylated lactam derivavtives, the structure of which was assigned by 'H nmr and unequivocal synthesis. The sysnthesis of benzothieno3,2-d]pyrimidine (7) was achieved by desulphurization of the 3H-benzothieno3,2-d]-3,2-d]pyrimisine-4-thione (6) or by oxydation of the 4-hydrazinobenzothieno3,2-d]primidine (5).