Regioselectivity of the Intramolecular Photocycloaddition of α,β-Butenolides to a Terminal Alkene

Abstract The intramolecular [2+2] photocycloaddition of α,β-butenolides to a terminal double bond tethered to the lactone through the γ-position and located at a suitable distance has been studied. The regioselectivity of the photoisomerization depends on the substitution pattern of the substrate and can be rationalized by simple theoretical calculations performed on the diradical intermediates.