SYNTHESIS AND STRUCTURE OF METHANOBENZOCYCLOOCTENE DERIVATIVES

10-Oxo-5,9-methanobenzocyclooctene-8-carboxylic acid 4a was prepared b y the intramolecular cyclization of 4t-phenylcyclohexane-1r,2c-dicarbo xylic acid 1a in concentrated H2SO4 or in the reaction of 4t-phenylcyc lohexane-1r,2c-dicarboxylic anhydride 2 in 80% H2SO4. To improve the y ield, the esters 3a,b were cyclized to the methanocyclooctene isomers 5a,b, in a 1:5 ratio from 3a, and in a 5:4 mixture (54%) from 3b at el evated temperature. After separation, 5a was hydrolysed, the keto grou p of 4a was reduced by the Wolff-Kishner method and the resulting cis and trans methylene-bridged benzocyclooctenes 6a,b (1:2) were separate d. From 4a with hydrazine, the tetracyclic pyridazinone derivative 7 w as obtained. The structures were determined by H-1 and C-13 NMR method s and for 4a also by X-ray crystallography.