Enone–alkene cycloadditions often suffer from side reactions, e.g. those associated with the diradical intermediate. These side reactions can often be minimized by a judicious choice of reaction conditions.
Dissolved oxygen is avoided since it is photo reactive.
A variety of solvents can be used. Acetone is a useful solvent, because it can serve as a triplet sensitizer. Alkane-based solvents are selected to be free of alkenes. Excitation wavelength is important. For intermolecular reactions, excess of the alkene can be employed to avoid competitive dimerization of the enone.