Are Triplet Exciplexes Involved in (2 + 2) Photocycloaddition of Cyclic Enones to Alkenes

摘要

There is no correlation between quantum yields for photocycloaddition of four representative cyclic enones to a variety of alkenes and rate constants for quenching of triplet states of these enones by the alkenes. Laser flash experiments show that electron deficient alkenes have the highest rates of interaction with eneone triplets, and generally the lowest quantum yields. These data are incompatible with formation of an anone alkene exciplex, as proposed many years ago by Corey and generally accepted in the literature. Biradical reversion is proposed to be responsible for the discrepancy between the efficiency of enone triplet capture by alkenes and product yields. Alkenes; Exciplex; Cyclic compounds, Reprints. (mjm)