Abstract: The photochemical behavior of six P, y-unsaturated ketones (5a-e, 19), whose double bond is incorporated into rings of four to eight members, has been studied under acetone sensitization and direct irradiation. In the triplet manifold, the four and five- membered rings undergo the oxadi-a-methane (ODPM) rearrangement, but the larger rings do not. Only the four-membered compound (5a) shows CY cleavage upon direct ...
