New derivatives of thioxo-2, 5-dihydro-1H-pyrano [2,3-d] pyrimidine 3 was obtained from the reaction of compound 1a with acetic anhydride. Compound 1a was treated with acetic anhydride for 5 min and (or) acid chloride to yield the corresponding pyrano [2,3-d] pyrimidin-7-yl-acetamide 5a and pyrano [2,3-d] pyrimidin-7-yl benzamide 5b derivatives. Treatment of compound 1a with bifunction compounds such as hydrazine hydrate, hydroxylaminehydrochloride, orthophenylene diamine, urea and ammonium thiocyanate to give compounds 6, 8, 10 and 12 respectively. Fusion of isolated compounds 6, 8, 10 and 12 in basic medium afforded the condensed pyrazolo, chromeno, pyrimido and thiopyrimidine 7, 9, 11 and 13 respectively. Treatment of compound 1b with ethylcyanoacetate afforded cyanoacetamide derivatives 15. The reactivity of compound 15 towards some electrophilic and nucleophilic reagents was also investigated. The structures of the products and conceivable mechanisms are discussed; the newly synthesized compounds were characterized by IR, 1H-NMR and mass spectral studies.