Photolysis of 10,10-difluorophenanthren-9(10H)-one. Evidence for solvent-assisted α-cleavage

The photolysis of 10,10-difluorophenanthren-9(10H)-one 1 in different solvents shows that the major competing reaction of the diradical formed by α-cleavage: recombination and hydrogen atom abstraction depends on the hydrogen atom donating ability of the solvent. Photolysis of 1 in cyclohexane in the presence of air or oxygen leads mainly to α-cleavage while photoreduction with the formation of 10-fluoro-9-phenanthrol occurs when the solution is deaerated prior to irradiation. In acetonitrile, a poor hydrogen donor, recombination of the diradical back to starting compound 1 is the sole process.