Terpenes and terpene derivatives, XXXIII. Synthesis of rac‐cis‐ and ‐trans‐dracunculifoliol and their 10‐epimers

The cis‐aldehyde 9, a key intermediate in the total synthesis of cis‐dracunculifoliol (1) previously isolated from Vassoura oil, was prepared starting from the bicyclic enone 5 via the nitrile 8. Grignard reaction of 9 led exclusively to epi‐1. Oxidation to the ketone 10 followed by reduction gave a separable mixture of the natural isomer 1 and epi‐1. – The synthesis of trans‐dracunculifoliol (2) starts with the 6‐methoxytetralone 14. After some usual steps, the trans‐octalin 17 was obtained. MMPP‐HIO4 oxidation gave compound 19 which was transformed into the iodo ester 26, precursor of the hydrindane ester 27. Analogously to the synthesis of epi‐1 the epi‐trans‐dracunculifoliol (epi‐2) was formed via alcohol 28 and aldehyde 29. Oxidation ( 30) and reduction furnished the natural trans alcohol 2. – Olfactory evaluation of the purified isomers 1, epi‐1, 2, and epi‐2 showed that all of them possess only a weak, woody odor. Therefore, the dracunculifoliols 1 and 2 are not responsible for the typical earthy, leathery, and spicy odor of the Vassoura oil.