Synergistic Excited State Photocatalysis: Divergent Energy Transfer vs Lewis Acid Mediated Phototransformations

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.