SYNTHESIS AND SPECTROPHOTOMETRIC STUDIES OF SOME NEW COUMARINDERIVATIVES

The current study was designed to investigate the reactivity of 3-acetyl-6-bromocoumarintowards a variety of electrophilic and nucleophilic reagents such as aromatic aldehydes to give 3-cinnamoyl coumarins 2a,b. The reaction of2b with guanidine hydrochloride gave 6-bromo-3-(substituted pyrimidine)coumarin-3-yl 3. Other6-bromo-3-(substituted pyrimidine) coumarin-3-ylderivatives 5a and 5b were synthesized from treatment of 1 with thiosemicarbazide then treating the product 4 with active methylene compounds namely diethyl malonate and/or ethyl acetoacetate. Treating 4 with phenacyl bromide yielded the corresponding phenyl thiazole derivative 7. Alkylation of 4 with acetic anhydride and/or benzoyl chloride yielded the corresponding diacetyl-and/or di benzoyl derivatives6a,b. The reaction of 4 with ethyl chloroacetate and/or chloro acetic acid in different media yielded two isomers 8a and 8b. The reaction of 1 with nitriles such as malononitrile and/or ethyl cyanoacetatefollowed by treatment with sulfur gave corresponding coumarin -3-y?thiophene derivatives 10a,b. The structures of the newly synthesized derivatives were elucidated by means of microanalysis, IR, 1H-NMR, 13C-NMR and MS measurments. The UV-Vis absorption spectra of the various newly 3-substituted-6-bromo coumarin derivatives 1-10were investigated in expectation of the shift to the longer wavelength region by the extension of the conjugated system. The absorption properties of the prepared compounds were investigated spectrophotometrically by dissolving in chloroform in the range 200-800 nm using 1cm quartz cells, showed good UV absorption properties and were discussed from the view point of the intermolecular charge transfer (ICT) between push- and pull- substituents.