Photochemical addition of benzophenone to ethyl-penta-2, 3-dienoate (), ethyl hexa-2,3-dienoate () and ethyl 4-methylhexa-2,3-dienoate () furnish various mono- and dioxetanes. Novel oxetanes () result in the reactions of () through addition of benzophenone to electron deficient C2-C3 π-bond of the respective esters. A rationalization of the obtained modes of photoaddition has been offered.