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Energy transfer vs Lewis acid photocatalysis dependent product selectivity is reported for the photochemical reaction of maleimides with alkenes. The photoproduct selectivity depends on the mode of photocatalysis that was deciphered using photochemical and photophysical studies. Under energy transfer conditions, hydroxy maleimides undergo a 3+2-photocycloaddition, while in the presence of Lewis acids 2+2-photocycloaddition was observed. Synergistic interactions between the Lewis acid, triplet sensitizer, and the substrate dictate both the outcome and efficiency of 2+2-photocycloaddition.
Parthiban et al. (Wed,) studied this question.