Diastereoselective [4 + 4]-Photocycloaddition Reactions of Pyran-2-ones: Rapid Access to Functionalized 5−8−5 Skeletons

Fused bicyclic pyran-2-ones with pendant furan side chains and an oxygenated stereogenic center adjacent to the pyranone ring oxygen were
prepared via FeCl3-catalyzed Michael addition. Irradiation furnished the corresponding lactone-bridged tricyclic [4 + 4]-cycloadducts with
good facial selectivity. Surprisingly, the major isomer resulted from approach of the furan from the same face as the protected alcohol.