Photoinduced transannular reaction of 1,3-dimethylcyclooctapyrimidine-2,4-diones.

This article reports further elaboration of the authors' investigations on the acid-catalyzed photorearrangements undergone by derivatives of 1,3-dimethylcyclooctapyrimidine-2,4-dione. In this case the results are represented for compounds containing a simple methyl or fluorine substituent at different positions in the eight-membered ring. Upon photolysis in frozen benzene containing trifluoroacetic acid, the monomethylated compounds give varying yields of pentalenopyrimidinedione products that are not generated from the fluorinated compounds, which are either inert or undergo hydration accompanied by dehyrofluorination. Plausible mechanisms are advanced to account for the formation of the observed photoproduct species. The work represents an interesting extension and uncovered new aspects of the photorearrangement process.