Irradiation of 2,6-cyclooctadienone (1) in inert solvents affords in modest yield tricyclo[3.2.1 .02a6]octan-8-one, whose structure was proven by chemical degradation. Irradiation of 1 in reactive solvents such as methanol or furan gives addition products derived from a ground-state intermediate, 2-fruns,6-cis-cyclooctadienone.Photolysis of 2,4-cyclooctadienone, 2, in inert solvents gives low yields of the trans, head-to-head, 2 + 2 dimer, 16, resulting from dimerization at the a,@ positions of each dienone molecule. In methanol and furan adducts resulting from trapping of a mono-trans-dienone are formed. Possible pathways for the formation of the various products are discussed. s part of the tremendous amount of investigation A into the photochemistry of carbonyl compounds, cyclic enones of various ring sizes have received considerable attention.* Recent studies of the photochemical behavior of medium-ring unsaturated ketones have uncovered a multitude of interesting transforma-(1) Supported in part by a grant from the Robert A. Welch Foun-( 2 ) See, for example, R. 0. Kan, "Organic Photochemistry," Mc-dation. Graw-Hill Book Co., Inc., New York, N. Y., 1966, Chapters 3 and 4.tions. The eight-membered ring conjugated enones 2-cycloocten-1-one3 and 2,4,6-cyclooctatrien-l -one4 have been found to undergo isomerization to strained trans enones, which in turn undergo thermal cycloadditions and dimerizations, and in the latter case,(3) (a) P. E. Eaton and I<. Lin,
