Acid-catalysed cyclisation of 2-methyl-2[3-(2,4-dimethoxyphenyl)-5-methoxypent-2-enyl]-cyclopentane-1,3-dione: Structure of a novel product

Acid-catalysed reaction of the title compound (3a) with boiling ethanolic HCl afforded a complex mixture of compounds from which a crystalline keto alcohol was isolated. On the basis of spectral data (UV, IR, NMR and MS), this keto alcohol was assigned the tricyclodecane structure 7a. Acetylation of the keto alcohol followed by hydrogenation gave the dihydro keto acetate 8b which was brominated using dioxane dibromide to give the bromo compound 8c. X-ray crystal structure analysis of the bromo compound confirmed the structure of this compound as well as the parent keto alcohol 7a.