A Study on the Photochemistry of α,β-Unsaturated γ-Lactones. I. The Structures of the Photodimers of 4-Hydroxycrotonic Acid γ-Lactone

The structures of the photodimers obtained from 4-hydroxycrotonic acid γ-lactone under several conditions were determined. The products of irradiations in the solution were a pair of anti dimers: one is a head-to-head cyclo-adduct, and the other a head-to-tail adduct. The corresponding product in the solid, state, on the other hand, was a head-to-head cyclo-adduct in the syn form.