Spin-polarized conceptual density functional theory study of the regioselectivity in the [2+2] photocycloaddition of enones to substituted alkenes

The regioselectivity of the photochemical [2+2] cycloaddition of triplet enones with a series of ground-state electron-rich and electron-poor alkenes is investigated using density functional theory (DFT)-based reactivity description. The spin philicity concept is used to interpret the regioselectivity as resulting from the interaction of the site on the alkene with the highest spin philicity with the site showing the highest change of spin number on the enone expected to result in the largest stabilization of this species.