Photoisomerization of bicyclooctanones in solution

The photolysis of bicyclo(3.2.1)octan-2-one (XVII), bicyclo(2.2.2)octan-2-one (XXV), and 1,8,8-trimethyl-bicyclo(3.2.1)octan-2-one (homocamphor) (IX) in nucleophilic solvents (methanol, water, cyclohexylamine) is reported. The structures of the products were established by synthesis and comparison with authentic materials, and, in the case of XVII, the two aldehydes (XVIII, XIX) were isolated and the position of the double bond established by nuclear magnetic resonance shift measurements and confirmed by degradation. The spectroscopic properties of the products were recorded. -- The photochemical products were predominantly derived from aldehydes and ketenes and the product ratios are tabulated. The results are rationalized in terms of conformational analysis of the diradical intermediates involved. A potential general method of altering the product ratio using cyclohexylamine is described, as are various synthetic approaches to these ketones.