The nucleophilic substitution of 4-chloro thieno [3.2-d] pyrimidine has been studied. The synthesis of thieno [3.2-d] pyrimidine was made via catalytic reduction of the 4-chloro thieno [3.2-d] pyrimidine and by oxidation of the 4-hydrazino thieno [3.2-d] pyrimidine. Electrophilic substitution of thieno [3.2-d] pyrimidine yielded derivatives bearing substituents at C-7. NMR spectral data are given for various thieno [3.2-d] pyrimidines, and the structures assigned ...