A STUDY OF PHOTOADDITION REACTIONS OF NORBORNADIENE WITH 2-CYCLOHEXENONES

To gain mechanistic information on photoaddition reactions of 2-cyclohexenones, the additions of 2- and 3-methyl-2-cyclohexenone and 2-cyclohexenone to bicyclo[2.2.1]heptadiene have been studied. The products are of the following types: (i) cyclobutane derivatives (cis- and irans-fused structures are formed); (ii) α- and β-ncrtricyclyl-2-cyclohexenones; and (iii) α- and β-(7-anti-norbornenyl)-2-cyclohexenones. The nortricyclyl compounds were prepared by independent routes, and one of the norbornene derivatives was degraded to 7-norbornanecarboxylic acid. Other structure assignments rest on infrared and nmr spectra. In the reaction of 3-methyl-2-cyclohexenone and norbornadiene a 16% yield of 9-methyl pentacyclo [7.4.0.02,7.03,5.044,8]tridecan-13-one (9) is obtained. It is proposed that this and the cyclohexenone derivatives are formed via biradical intermediates. Hydrogen shifts are involved in the formation of the latter products, and a deuterium-labeling experiment showed that one such shift is intramolecular and stereospecific. Naphthalene quenching experiments imply that the cyclohexenone derivatives are formed by a triplet-state reaction. © 1969, American Chemical Society. All rights reserved.