sensitizers employed. The cyclopropene derivatives were produced in the cases of the DCA and TPP+ sensitizations and a solventadduct was obtained for the TPP+ sensitization reaction. The difference in products is explained by the rates of the back electrontransfer from the electron accepted sensitizers to the radical cation intermediates. In the DCA sensitization, the absorption band of the diazoalkene
3-Dimethyl-3H-pyrazoles were photolyzed, and in the presence of 2,4,6-triphenylpyrylium tetrafluoroborate (TPP+) as a sensitizer in acetonitrile; in addition to cyclopropenes, 2H-pyrroles were obtained as solventadducts to 1,3-radical cation intermediate.