Photosensitized intramolecular cyclization of furan and non-activated alkene: pathway switching by the substituent on the furan ring

A photosensitized reaction of furan with a non-activated simple alkene was investigated. Intramolecular Diels–Alder-type cycloaddition reactions between furan and a trisubstituted alkene were found to proceed in high yield in the presence of 9,10-dicyanoanthracene under UV irradiation to afford oxabicyclo[2.2.1]heptane derivatives in high stereoselectivity when the furan was alkyl substituted. On the other hand, the aryl-substituted furan cyclized via a completely different pathway to give spirocyclic and tricyclic products.