Photocycloaddition of ketones to olefins as radiationless transitions

The tunnel effect theory is applied to study the photocycloaddition of ketones to olefins. This theory can quantitatively explain the reactivity, regioselectivity, stereospecificity and efficiency of the photocycloadditions studied. The study covers a large diversity of olefins (electron rich and electron poor) and ketones (alkyl, alkylphenyl and phenyl), in both their ¹(n,π*) and ³(n,π*) states. The theory does not need to postulate the questionable intermediacy of an exciplex to explain the characteristics of these reactions. Evidence for the dominancy of tunnelling over thermal activation is presented. The results of this study are in line with previous applications of tunnel effect theory and complete the explanation of ketone photoreactivity in solution under the framework of the general intersecting-state model.