4-oxo-5-(3,4,5-trimethoxy-benzylidene)-4,5-dihydrothiazol-2-yl)-acetonitrile 1 was prepared and treatment with sodium azide, phenyl isothiocyanate, 5-bromosalicylaldehyde, thioacetamide and ethylacetate to give the corresponding 2-substitute-4-oxo-5-(3,4,5-Trimethoxy benzylidene-4,5-dihydrothiazole-2-yl) derivatives 2,3,5,6 and 8. Treatment of 3 and 6 with phenacylbromide gave 4 and 7a also 4-oxo-2-[4-oxo- 5-(3,4,5-trimethoxy benzylidene)-4,5-dihydro-thiazol-2-yl)-butyronitrile 8 when reacted with malononitrile, 2-cyanoacetohydrazide, hydrazine hydrate, benzaldehyde and 2-amino-2-(hydroxylmethyl) propane-1,3-diol afforded 9,13,15, 16 and 17. Treatment of compound 9 with sulfur gave 10 which in turn treated with p-nitrobenzaldehyde to give Schiff base 11, which on further treatment with thioglycollic acid gave 12. Cyclization of compound 13 with acetic acid gave 14. The newly synthesized compounds screened for their in vitro antitumor activity against human cancer cell line.