Abstract The photochemical reaction of 1, 3-diphenylcyclopenta [l] phenanthrene-2-one 5 (phencyclone) with oxygen in acetone leads to the formation of 1, 2, 3-trihydro-1, 2, 3- triphenylcyclo-penta [l] phenanthrene 7 (9, 10-dibenzoylphenanthrene) along with a trace of the lactone 1, 4-diphenylcyclo-3-pyran [l] phenanthrene-2-one 8. An independent synthesis of 8 was achieved by the reaction of 5 with FeCl 3 in CHCl 3. The treatment of 5 with ...