Intramolecular [2+2] Photocycloaddition

Significance

Bach and co-workers report a [2+2] photocycloaddition of 4-(3′-butenyloxy)quinolone using xanthone 4 as catalyst. In this reaction two products can be obtained, the straight product 2 and the crossed product 3. By increasing the reaction time the conversion could be improved to up to 90% with a regiomeric ratio 2/3 of >99:1, but the isolation became difficult due to decomposition of the sensitizer.