This page covers common cycloaddition reactions, including the Diels-Alder reaction, ene reaction, photo [2+2], ketene [2+2], and 1,3-dipolar cycloadditions, and discusses why some are promoted by hea...This page covers common cycloaddition reactions, including the Diels-Alder reaction, ene reaction, photo [2+2], ketene [2+2], and 1,3-dipolar cycloadditions, and discusses why some are promoted by heat and others by light.