Base catalyzed reaction of 2-acetyl-3,5-dimethyl-isothiazolo[2,3-a]pyrimidin-7-one (1) with malononitrile yielded the corresponding compound (2) which is cyclized with sulphur to give (3), also, compound (1) reacted with 2- cyanoacetohydrazide in acetic acid to give (4). On the other hand, by treatment of compound (1) with 2-amino-2- (hydroxy methyl) propane-1,3 diol gives (5) which reacted with phosphorous oxychloride to give (6).Finally, chalcone (7) is formed by the reaction of compound (1) with trimethoxy benzaldehyde (scheme.1). Compound (3) is reacted with ρ.nitrobenzaldehyde to give compound (8) which is reacted with thioglycolic acid in the presence of anhydrous Na2SO4 to give compound (9). Compound (3) is cyclized by ethylenediamine to give (10), also compound (3) reacted with chloroacetylchloride to give chloroderivative (11) which under heating with potassium thiocyanate yielded (12) (scheme 2). Compound (3) under heating with formic acid, formamide, malononitrile and ethylcyanoacetate yielded the compounds (13-16) respectively (scheme 3). Diazotization of the compound (3) with concentrated HCl and sodium nitrite at 0-5 °C yielded azodye derivative (17). On the other hand, Coupling of (3) with diazotized p.nitroaniline gave (18).Finally (3) is condensed with acetic anhydride and phthalic anhydride to give (19,20) respectively(Scheme 4).