Abstract
This thesis describes the studies on the photochemical reactions of 1,3,3-trimethylbicyclo[2.2.2]octa-5,7-dien-2-ones (35) which were synthesized by making use of the methodology developed in our laboratory. Cycloadducts 38a-e were obtained via the Diels-Alder reaction of 4-trifluoromethanesulfonyloxy-2,6,6-trimethylcyclohexa-2,4-dienone (37) with dimethyl acetylenedicarboxylate, diphenylacetylene, phenylacetylene, and ethyl propiolate in the yields of 73-96%. The cycloadduct 38f was derived from the Diels-Alder reaction of 37 and phenyl vinyl sulfoxide followed by elimination reaction. The palladium catalyzed reduction of cycloadducts 38a-f furnished dienones 35a-f in36-97% yields. The photochemical reactions of 35a-f were examined under the condition with or without a photosensitizer to find out the modes of reactions including the competitivity of di-π-methane(DPM)rearrangement and oxa-di-π-methane(ODPM) rearrangement. Thereactions of 35a, 35b, and 35e under the sensitized condition underwent DPM rearrangement, but in contrast, 35c, 35d, and 35f did not undergo DPM rearrangement under the similar condition. The proposed mechanism suggests that substituents R of the bicyclo[2.2.2] adducts that stabilize the radical intermediates favor the pathway leading to the DPM products. Under the conditions of direct irradiation in various solvents, the products 40a-f were obtained from 35a-f via the α-cleavage of bicyclo[2.2.2] system. In the case of 35b, DPM rearrangement products was generated in 15 to 18% yields, this may be due to the reason that the first excited singlet state of 35b undergoes the intersystem crossing at a rate competitive to that of the Norrish type Ι cleavage for the excited singlet state of 35b.