Spectroscopic, X-ray, mechanistic and DFT studies on formation of novel benzoimidazole-4-ones from cyclohexenyl carbothioamides

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Spectroscopic studies of cyclohexenyl carbothioamides 2, obtained from condensation of 1,3-cyclohexandione with aryl isothiocyanates, predicted the proton transfer behaviour in solid, solution and gaseous phases. DFT studies in gaseous and solution phase shows good congruence with the experimental findings. Condensation of cyclohexenyl carbothioamide 2a with hydrazine hydrate unexpectedly embellished novel 2-(4-chlorophenyl)amino)-2,5,6,7-tetrahydro-4H-benzo[d]imidazol-4-one 4a and 2-(bis((4-chlorophenyl)amino)methylene)cyclohexane-1,3-dione 3a instead of the presumable 2H and 1H-indazole derivatives 5a and 6a, respectively. The proposed mechanism of formation of unconventional products 3a and 4a supported by experimental results is described. Spectroscopic investigations such as FT-IR, Mass and NMR (1H, 13C, DEPT-135, HSQC, COSY, NOESY) along with X-ray crystallographic results established the structure of two derived novel products 3a and 4a. The interesting feature of this study is NN bond cleavage of strained transit diazetidine ring and formation of CN bond leading to generation of novel benzoimidazol-4-one derivative 4a. Hirshfeld surface analysis of entitled compounds is reported.