Fused thieno[2,3-b]pyridines: synthesis and characterization of new condensed pyridothienopyrimidines

Reaction of cyanopyridine-2(1H)-thiones 2a,b with chloroacetonitrile gave the corresponding 3aminothieno[2,3-b]pyridine-2-carbonitriles 4a,b. Condensation of 4a,b with triethyl orthoformate produced the methanimidate derivatives 6a,b which upon treatment with hydrazine hydrate resulted in the formation of 3-amino-4-iminopyrido[3 ',2 ':4,5]thieno[3,2-d]pyrimidines 7a,b. Aminothieno[2,3-b]pyridine-2-carboxamide 5 was prepared and reacted with triethyl orthoformate to give pyrimidine-4(3H)-one derivative 14. Chlorination of 14 with phosphorus oxychloride gave 4-chloropyrimidine 15, which in turn was reacted with hydrazine hydrate to produce 4-hydrazinopyrido[3 ',2 ':4,5]thieno[3,2-d]pyrimidine 17. Compounds 7a,b and 17 were used as precursors for synthesizing other new pyridothienopyrimidines as well as triazolopyrido-thienopyrimidines, and pyridothienopyrimidotriazinoindoles. Structural formulas of all newly synthesized compounds were confirmed by elemental and spectral (IR, NMR, and mass) analyses. [GRAPHICS]