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