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-HI04 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 I, 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.From the commercial Vassoura oil (ex Baccharis dracunculifolia) we isolated, besides more than hundred other compounds[*], several unkown sesquiterpene alcohols as minor or trace constituents. Most interesting were the isohumbertiols possessing the humbertane skeleton which was found in nature only once up to and the dracunculifoliols with the rare axane or oppositane -an 8(7 + 6)-abeo-eudesmane -skeleton. These results were presented brieflyL41. Meanwhile we published the synthesis of the isohumbertiol~[~I, and now we present the synthesisf61 and complete stereochemical assignment of the dracunculifoli01s. 2Only relative configurations are shown.Despite the fact that the isolated dracunculifoliols 1 and 2 from the Vassoura oil (total amount 0.05%) could not be purified completely (due to the very low percentage) the structure of a cis-hydrindane 1 (an axane) and a transhydrindane 2 (an oppositane) was assigned by extended NMR spectroscopy. Whereas the stereochemistry at C-1, C-6, and C-7m was undoubtfully elucidated, the stereocenter at (2-10 remained unclarified[61. That means the isolated alcohols could also possess the structure of epi-1 or epi-2.Thus, by the synthesis of the various diastereoisomers an unambiguous assignment could be expected. A second reason was given by the olfactory evaluation of the isolated mixture of the dracunculifoliols (GC purity: 30% of 1 and 50% of 2) smelling earthy, sweet, fruity, rooty, typical of Vassoura oil. Synthesis of 1 and epi-1Key compound on the way to the dracunculifoliols should be the known[g] bicyclic enone 5. Michael-type addition of an appropriate C1 building block should generate an intermediate with an aldehyde, nitrile or ester function at C-7, from where the end products should readily be formed. If the addition to 5 furnished a mixture of cis-and trans-hydrindane derivatives both 1 and 2 could be prepared by this approach.The addition of the Grignard compound from 2-(2-bromoethyl)-1,3-dioxane to the cyclohexenon...

Alkylation of ethyl geranate (5) with the bromo esters 7 and 8 gave the P,y-unsaturated esters 10 and 11, which could be isomerized to 13 and 14 by treatment with DBU. The u,p-unsaturated esters 12 -14 were cyclized to 15-17, and subsequent reduction of 15 -17 led to the diols 18 -20. Final cyclization afforded the spiro ethers 2-4. -The olfactive properties (intensity and quality) of the theaspirane analogs 1 -4 are determined by the conformational flexibility of the respective molecule. Thus, the rigid 1 and 2 have strong camphoraceous odors. Augmenting flexibility (-3, -4) results in weaker, fruity-woody notes.Recently, we investigated the structure-odor correlation of various theaspirane analogs [']. We found that the odor of the theaspirane derivatives A-C in strength and quality is strongly dependent on the size of the heterocyclic ring. The odor intensity is rapidly decreasing from strong (A) to medium (B) and weak (C), and the quality varies from dominating camphoraceous with a herbaceous undertone (A) to camphoraceous-herbaceous green with a fruity undertone (B) and to floral-woody-fruity (C). We explained these results with the large difference of conformational flexibility of the heterocyclic four-, five-or six-membered ring. Since A -C possess both similar shapes and polarities, rigidity should be responsible for the strong camphoraceous-herbaceous odor, flexibility for the weak fruity-floral-woody tonality.This hypothesis should be supported by the synthesis and olfactory evaluation of the analogs 1-4. The odor of the rigid molecules 1 and 2 should be similar to that of A, and the increasing flexiblity of 3 and 4 should be expressed by an olfactory similarity to B and C. In other words, our Scheme 1. The atom numbering in the schemes is used for comparison purposes of the NMR data in Tables 1 -3 and does The alkylation of 5 with the halo esters 6-8 in THF in the presence of LDA/HMPT leads primarily to the P,y-diesters 9-11 in moderate (9, 11) to very good (10) yield. The

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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.