Correction of the structure of a new sesquiterpene from Cistus creticus ssp. creticus

In an attempt to identify the structure of a sesquiterpene from Cistus creticus ssp. creticus proposed in the literature as 1,1,4a,6-tetramethyl-5-methylene-1,2,3,4,4alpha,5,8,8alpha-octahydronaphthalene, the synthesis of its cis isomer 2 was carried out in 11 steps and 9.5% yield. Comparison of the spectra of 2 and those reported earlier for the synthetic trans isomer 1 with the spectral profile of the isolated natural product indicated that the latter was not compatible with either 1 or 2. The correct structure was assigned, by detailed spectroscopic analysis of the natural product, as 6-isopropenyl-4,4a-dimethyl-1,2,3,4,4a,5,6,7-octahydronaphthalene (3).