Treatment of 1-(benzothiazol-2-yl-thio)-acetonitrile 1 with 5,5-dimethyl-1,3-cyclohexanedione-(dimedone) 2 and aromatic aldehyde 3a, b in refluxing ethanol containing a catalytic amount of piperidine lead to bisdimedone derivatives 5a and b in short periods of times with excellent yields and not 4H-chromen-5(6H)-one derivatives 8. The compound 5a was then cyclized to 1,8 dioxo-octahydroxanthene derivative 6. The structures of the synthesized compounds were elucidated by elemental analysis 1 H NMR and 13C NMR spectra, COSY, HSQC, HMBC, MS, and X-ray crystallographic investigations. The cytotoxicity of the synthesized compounds 5a, b, and 6 were studied and evaluated. Three human tumor and three normal cell lines, namely as breast adenocarcinoma (MCF-7), non-small cell lung cancer (NCI-H460) and CNS cancer (SF-268), human fibroblast (WI-38), normal prostate epithelial cells, and normal colon mucosal, NCM 460 cells, respectively. The tested compounds were found to exhibit higher inhibitory effects toward the tumor and normal cell lines than the reference drug, doxorubicin.