Photochemistry of 3-alkoxychromones I - Photocyclisation of 6-chloro-3-alkoxy-2-(furan-3-yl)-4H-chromen-4-ones

3-Alkoxy/allyloxy-6-chloro-2-(furan-3-yl)-4H-chromen-4-ones yield angular tetracyclic products involving the 2-furyl group on photoirradiation through the intermediacy of 1,4-biradicals. The nature of the 3-alkoxy/allyloxy group influenced the photoproduct distribution. The stereochemical dispositions of the products have been established using the J/Phi relationship and were corroborated by MM2 calculations.