A wide variety of indole, substituted benzaldehyde linked keto hydrazide-hydrazone analogues were designed, synthesized and evaluated for their cytotoxicity against eight human cancer cell lines HeLa, A549, MCF-7, K562, HEK293, HT29, SF295 and HL60. All these synthesized compounds showed potent antitumor activities on the above eight human cancer cell lines. Among them, 6a and 6h compounds exhibited potent antitumor activity on HL 60 and A549 cancer cell lines with IC50 value of 3.913 and 4.838 µM than the standard drug cisplatin with IC50 values of 27 and 36 µM, respectively.

General. Amines, CS2, DIB, Et3N, Pyridine, KOH, and NaOH were purchased from Aldrich and used without further purification. The solvents were purchased and dried according to standard procedure prior to use. 1 1 H NMR (400 MHz) spectra were recorded with a Varian 400 spectrometer. Infrared (IR) spectra recorded on a Perkin Elmer Spectrum one FT-IR spectrometer.General Procedure for Aryl/Alkyl isothiocyanate: In a 10 mL round bottom flask containing a magnetic stir bar, Amine (1.0 equivalent), NaOH (1.5 equivalent) and TPGS-750-M/H2O (1wt%, 0.4 mL, 1.0 M) were sequentially added. The reaction mixture was stirred at room temperature for 2h. After starting material was completely consumed, as monitored by TLC, DIB (1.5 equivalent) and NaOH (1.5 equivalents) were sequentially added and stirring continued for 60 minutes. Then ethyl acetate (2 x 1mL) was added to the reaction mixture, which was stirred for 5 minutes. The organic layer was transferred using a Pasteur pipet and evaporated under reduced pressure to give the crude product. The residue was purified by column chromatography over silica gel by using 100% hexane as eluent to obtain isothiocyanate derivative .

Scheme 8. Proposed mechanism for the synthesis of (2-Oxy/Thio)benzothiazole. Scheme 9. Bulk Scale Synthesis of Substituted benzothiazoles.

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The synthesis of 2‐aminobenzothiazoles has been demonstrated in the presence of transition metal under mild reaction conditions. In this paper, disubstituted thioureas have also been reported from isothiocyanates at room temperature. Subsequently, C−S cross‐coupling reaction was described for the construction of benzothiazoles using cheap, readily available and air stable Iron catalyst. Moreover, no other byproducts could be observed except target products. Furthermore, control experiments were performed for reveal the mechanism. In addition, a broad range of substrate scope has been explored.