Ethyl 2-(3-allylthioureido)-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylate (1) was used as a building block for synthesis of new heterocycles. Pyrimidine and thiazole moieties were achieved upon condensation of compound 1 with various reagents such as chloroacetic acid, dietyl malonate, ninhydrin, 2,3-epoxy-2,3-dihydro-1,4-naphthoquinone, and hydrazine hydrate. The structures of the newly synthesized compounds were confirmed using spectral measurements. The prepared products were evaluated for their anticancer activity against colon HCT-116 human cancer cell line. Compounds 6, 9, 10a, 11, 12, 15 have displayed potent activity.