Some novel thiazolo[3,2-a]pyrimidines, pyrimidino[1',2':3,2]thiazolo[4,5-b] pyridines,pyrimidino[1'',2'':3',2']thiazolo[4',5':2,3]pyrido-[2,3-d]pyrimidines, pyrimidino [1',2':3,2]thiazolo[4,5-d]pyrimidines, pyrimidino[1',2':3,2]thiazolo[4,5-d][1,2,4] triazolo[3,4-b]pyrimidines (2-10) were prepared starting with 2-(arylmethylene) trimethylthiazolo [3,2-a]pyrimidin-3-one(2). Also, some, S-alkylated thiazolo[4,5-d] pyrimidine derivatives were synthesized via reaction of 4-substited-7,7,9-trimethyl-1,3,4-trihydropyrimidino[1',2':3,2]thiazolo[4,5-d]pyrimidin-2-thione (6b) with different reagents. Furthermore, some of the prepared products were selected and tested for activity against HCT116 and MCF-7 (human colon carcinoma and human breast carcinoma).