Abstract
4,5'-Bipyrazoline-5-carboxylate ester 4 was regioselectively obtained from 1,3-dipolar cycloaddition reaction of nitrilimine 2 with ethyl 2-cyano-5-phenylpenta-2,4-dienoate (3). The bipyrazoline-5-carboxylate ester 4 underwent thermal elimination of hydrogen cyanide upon heating in DMF to afford bipyrazole 10. Heating the 4,5'-bipyrazole derivative 4 in ethanolic sodium ethoxide solution afforded the bipyrazole 11 via concurrent decarboxylation and hydrogen cyanide elimination. Oxidation of the latter product with tetrachloro-1,4-benzoquinone gave the 4,5'-bipyrazole 12. The regioselectivity of the reaction was studied in the light of some theoretical reactivity indices and the frontier molecular orbital (FMO) theory using the B3PW91/6-31G(d) level of calculation as well as some thermodynamic properties using the PM6 semi-empirical level of calculation. The analysis of the data obtained reveals that the dipolar cycloaddition reactions in the present study can be classified in the normal electron demand category.