Solvent-Free Regioselective Synthesis of Novel Isoxazoline and Pyrazoline N-Substituted Saccharin Derivatives Under Microwave Irradiation

Novel isoxazoline and pyrazoline derivatives of N-substituted saccharin were synthesized in good yields by 1,3-dipolar cycloaddition of N-crotonoyl- or N-cinnamoylsaccharin as dipolarophile to arylnitrile oxides or nitrile imines using p-HAP300 as catalyst under solventfree microwave conditions. In this process, the yields were significantly improved compared to classical conditions without alteration of the selectivity. The regioselectivity as well as the nonthermal specific microwave effect are discussed.