Chemical transformations of the photochemical 1,3-adducts of benzene and anisole to cyclobutenes

The photochemical 1,3-adduct of benzene to cis-3,4-dichlorocyclobutene has been transformed in four steps to 2,5-endo-10-oxotricyclo[4.3.1.02,5]deca-3,8-diene 1. The key reaction is the acid catalyzed addition of water to the photoadduct 2 which gives the 3,4-dichloroalcohol 3 corresponding to 1. Similarly the photochemical 1,3-adduct of benzene to cyclobutene has also been cleaved with acid. A more convenient synthesis of 1 is provided by the photochemical 1,3-addition of anisole to cis-3,4-dichlorocyclobutene and the treatment of the adduct with acid. The 3,4-dichloro derivative of 1 is thereby obtained directly. Probable mechanisms for these transformations are discussed. © 1975.