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

Abstract

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...

Five New Sesquiterpenoids and a New Diterpenoid from Erigeron annuus (L.) PERS., Erigeron philadelphicus L. and Erigeron sumatrensis RETZ.

“…The IR spectrum showed the presence of a hydroxyl group (3599, 3445 cm Ϫ1 ). The 1 H-and 13 C-NMR spectra of 2 were similar to those of 16, 14) except for the presence of one more hydroxyl group. The position of this hydroxyl group was determined to be attached at C-1 by the HMBC spectrum, in which a cross peak was observed between H 3 -14 at d 0.67 and C-1 at d 79.0.…”

“…14) From the above data, the structure of 2 was determined to be (7R*)-opposit-4(15)-ene-1b,7-diol. Compound 3 was isolated as a colorless amorphous solid, [a] D ϩ48.8°, and the molecular formula was determined to be C 16 H 28 O 2 by HR-EI-MS.…”

Constituents of Brazilian Vassoura oil

“…6 We also described the structure elucidation of three sweet, fruity smelling sesquiterpene ethers 1,l l-epoxycadina-4,9-diene (52b), 1,6-epoxyeudesm-4( 15)-ene (59), and 5,ll-epoxycadinl(l0)-ene (70a), and of some other compounds 2,2-dimethyl-6-vinylchromene (42a), 4-epimaaliol (a), and 10-epi-globulol (a), see by liquid-liquid partition (Normag mixerseparator apparatus) with MeOH/10% HzO (8 1) and n-hexane to give a non-polar part (320g) and a polar part (290g).…”

Essential oil variability in Baccharis uncinella DC and Baccharis dracunculifolia DC growing wild in southern Brazil, Bolivia and Uruguay

“…4 The only previous phytochemical study reported for this species was published by Frizzo et al 5 By contrast, the essential oil of B. dracunculifolia, commercially known as vassoura oil, has been studied by several authors. [6][7][8][9][10][11][12][13][14][15][16][17][18] This oil has importance in the perfumery industry, mainly due to the presence of the sesquiterpene alcohol (E)-nerolidol, responsible for the herbaceous and green notes of the oil. The differences observed in the composition of this oil for populations of Brazil, Bolivia and Uruguay suggest the existence of chemotypes.…”