Regioselective synthesis of some new pyrazole and isoxazole derivatives incorporating benzothiazole moiety: Experimental and theoretical studies.

Nitrile imine derivative 3 added regioselectively to α-(benzothiazol-2-yl)cinnamonitrile derivatives 1a–c to afford 5-(benzothiazol-2-yl)-5-cyano-4,5-dihydro-1H-pyrazole derivatives 4a–c. Compound 4a underwent thermal elimination of hydrogen cyanide in sodium ethoxide solution to give the pyrazole derivative 6. The isoxazole derivative 10 was synthesized by reacting nitrile oxide 8 with cinnamonitrile derivative 1d. The structures of the synthesized compounds were characterized by FT-IR, NMR, and MS spectroscopic techniques. The reaction mechanism was studied via density functional theory (DFT) quantum chemical calculations at the B3LYP/6-31G (d) level of theory. [ABSTRACT FROM AUTHOR]