- Synthesis of Furanoid Terpenes via an Efficient Palladium-Catalyzed Cyclization of 4,6-Dienols
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The total syntheses of marmelo oxides A and B and a terpene alcohol found in peppermint oil are described.The key steps in these syntheses are the regioselective palladium-catalyzed allylic substitution of 4 and 11 to 6a and 12, respectively, and the regioselective palladium-catalyzed cyclization of 8 and 14 to 9a, 9b, and 15, respectively.The relative stereochemistry of marmelo oxides A and B was established by NOE measurements.
- Andersson, Pher G.,Baeckvall, Jan-E.
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p. 5349 - 5353
(2007/10/02)
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- Etude des phenomenes physico-chimiques intervenant lors du procede d'hydrodistillation
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During the steam distillation of aromatic plants, some terpenic compounds undergo various chemical reactions (hydrolysis, elimination, cyclisation rearrangement) which depend on the acidity of the water in which the plant is soaked.In order to study the physical and chemical phenomena involved in this process and in particular the formation of artefacts, we have performed steam distillation experiments on lavender flowers in a buffered aqueous medium.The essential oils collected are rich in linalol and linalyl acetate, two monoterpenic compounds known for their propensity to undergo heat induced transformations.At pH 4 or 7, the chromatograms of the essential oils are similar whereas in a more acidic medium (pH = 2), the degradation of linalyl acetate gives rise to a number of terpenic products (α and γ terpinenes; 2,6,6-trimethyl 2-vinyl tetrahydropyran; 1,4-cineol, cis and trans ocimenols, myrcenol, terpin 1-en 4-ol, etc.).A study of the reactions involved during the thermal degradation of linalyl acetate in a model experiment (heating to reflux) as well as the determination of the kinetic parameters, show that some terpenes, present in lavender oil originate in part from the transformations of linalyl acetate during steam distillation.Furthermore, the decomposition of this ester is directly and quantitatively related to the concentration of acid in the medium (pseudo first order rate constant is 0.008 min-1 at pH 7 and 0.0147 min-1 at pH 2).It is therefore necessary to control and maintain the pH of the water during steam distillation to avoid the alteration of the essential oils by formation of artefacts and preserve the integrity of the oil originally present in the plant.The study of the various steam distillation fractions gives informaiton on the kinetics of the steam distillation of the various components which apparently do not depend only on the boiling point but also on their polarity (hydrodiffusion phenomenon).
- Morin, Ph.,Gunther, C.,Peyron, L.,Richard, H.
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p. 921 - 930
(2007/10/02)
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