Spectroscopic, X-ray and DFT studies of prototropic tautomerism and photophysical properties of regioselectively designed new 3-, 2,3-substituted tetrahydro[4H]indazol-4-ones

Synthesis, prototropic tautomerism studies of indenocarbothioamides and their conversion to biologically active indenothiazole derivatives

Indenocarbothioamides 2, obtained from reaction of indane-1,3-dione with aryl isothiocyanates, on condensation with 3-chloropentane-2,4-dione and chloroacetyl chloride furnished 1,3-indanedione coupled thiazole and thiazolidin-5-one derivatives, respectively. The structure of the obtained products was assigned on the basis of spectral data (IR, NMR and Mass). Prototropic tautomerism studies of carbothioamides 2 were carried out in solution (¹H NMR, ¹³C NMR and UV-vis), gas phase (Mass) and solid state (IR and X-ray). X-ray diffraction studies of carbothioamide 2a have revealed the existence of enolic form in the solid state. DFT studies of various possible tautomeric forms in gas phase as well as in solution state corroborated by the experimental results. Antibacterial studies of indenothiazole and indenothiazolidin-5-one derivatives have been reported.