The photochemical behavior of six 0,7-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-ir-methane (ODPM) rearrangement, but the larger rings do not. Only the four-membered compound (5a) shows a cleavage upon direct irradiation, but all of the others give cyclobutanols. The seven-and eight-membered compounds yield oxetanes, a reaction which is favored by high olefin electron density and the ability of the olefin to twist in the excited state. Several thermal rearrangements of the products to starting ketone and to one another have been noted.

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