A cascade reaction between N-alkyl-N-methacryloylbenzamide and aryl aldehydes was developed to generate isoquinoline-1,3(2H,4H)-dione derivatives. The reaction involves oxidative cross-coupling of the activated alkene from the N-alkyl-N-methacryloylbenzamide with the aldehyde functional group (-CHO), followed by radical addition to the aromatic ring to afford isoquinoline-1,3(2H,4H)-dione derivatives in good yields under mild reaction conditions without either metal catalysts or organic solvents involved.