Terpene ketones

Santenone, CgHj O, is a lower homologue of the regular terpenic ketones of the formula It occurs naturally in sandalwood oil,... 

The student should be warned against confusing chemical endings and case endings for example, -en may be equivalent to the English -ene or only a plural sign Terpenen means not terpenene but terpenes Ketone means not ketone but ketones Terpene, not terpene but terpenes. 

Behinderte Terpen-Ketone der Campher-Reihe ergeben mit komplexen Metallhydri-den hauptsachlich exo-Alkohole1, unbehinderte bicyclische Ketone in der Regel endo-Al-kohole2. 

Teisseire and co-workers (149) have also shown that the reduction of several terpene ketones with excess TIBA involved preferential hydride transfer from the less hindered side of the substrate. 

Unlike the terpene alcohols, aldehydes, and esters, acyclic terpene ketones are not particularly important as fragrance or flavor substances thus, they are not discussed here in detail. 

Cyclic terpene aldehydes occur in essential oils only in low concentration. These aldehydes are seldom used as single fragrance substances. A few of the cyclic terpene ketones are commercially important as fragrance and flavor substances, for example, menthone and carvone, which have the / -menthane skeleton, and the ionones, which have a (trimethylcyclohexenyl)alkenone skeleton. The ionones and... 

E. J. Enholm and S. Jiang, Highly stereoselective coupling of carbohydrate lactones with terpene ketones promoted by SmI2, Tetrahedron Lett. 55 6069 (1993). 

Camphor is a particularly well-known bicyclic terpene ketone, which has uses in medicine and as a plasticizer for nitrocellulose (Section 20-7) ... 

Compounds with carbon-nitrogen multiple bonds were also successfully used in the Barbier procedure. Allylic groups add to imines in high yields (> 77% in the examples published), even enolizable substrates, possibly due to the low basicity of the medium.37 Additions to nitriles occur in THF in the presence of the zinc-silver couple.38 Terpenic ketones were prepared by this method. 

Representative procedure. To a solution of Sml2 in THF (5 mmol) and HMPA (300 pi) at — 78 °C was added the lactone substrate (lmmol) and the terpene ketone (2 mmol) in THF and the reaction mixture was warmed to room temperature. When TLC showed that the lactone starting material had been consumed, aqueous saturated NaHC03 and ethyl acetate were added and the resulting mixture stirred for 30 min. After filtration through Celite and concentration in vacuo, the crude product was purified by column chromatography. 

Many terpenes contain additional functional groups, especially carboxyl groups and hydroxyl groups. A terpene aldehyde, a terpene alcohol, a terpene ketone, and a ter-pene acid are shown next. 

For both terpene ketones, pulegone and camphor, the A ( C-ASIS) has been estimated by a chemical shift comparison method using t-butylcyclohexane as an additional reference compound [409], By comparing the A (ASIS) of both and nuclei it seems that the carbonyl plane rule is also valid for aromatic solvent-induced NMR chemical shifts of carbonyl compounds [409], Obviously, the particular geometrical arrangement of the aromatic solvent molecules around the carbonyl dipole inhu-ences both the and nuclei in the same way. 

Camphene is a solid terpene. The dextro variety d-camphene is found in camphor, ginger and spike oils, and the levo variety, 1-camphene is in citrondla and valerian oil and in French and American turpentine. Bornylene does not occur in nature but has been prepared from the alcohol corresponding to it known as Borneol or Borneo camphor. This, as previously stated, may be prepared from pinene so that Bornylene itself may be made from pinene. Fenchene, also, is not found in nature but is obtained by reduction of fenchone a terpene ketone found in fennel oil and in Thuja oil. 

Stereoselective hydrosiiyiation of terpene ketones such as camphor and menthone catalyzed by Rh(PPh3)3Cl followed by hydrolysis produces different stereochemistry from reductions using metal hydrides . Bulky hydrosilanes favor the production of the more stable alcohols ... 

The a-siloxyalkylrhodium complex plays a key role in the catalytic cycle for the asymmetric hydrosiiyiation of prochiral ketones . The intermediacy is suggested in the hydrosiiyiation of cyclic terpene ketones catalyzed by Rh(PPh3)3CP, supported by spin trapping experiments in which spin adducts such as 4 are detected . 

With chiral ketones, asymmetric induction takes place at a silicon center even with an achiral catalyst such as Rh(PPh3)3Cl, which is an application of the stereoselective hydrosiiyiation of cyclic terpene ketones (see 14.4.4.2). Double asymmetric induction is also effective and achieves a high optical yield ... 

Katsuhara has discussed the mechanism of opoxidation of endocyclic ocfi-unsaturated terpene ketones and reached the conclusion that the oxygen atom is introduced stereoselectively in such a way that the most favourable transition state involves the best orbital overlap stabilisation. He predicted the formation of lK,4i ,5/ -menth-4-en-3-one epoxide (161) from the unsaturated ketone, a prediction that was subsequently confirmed. 

Baeyer obtained some dimeric nitroso compounds in the terpene series by the action of ethyl or pentyl nitrite on terpene ketones in the presence of small amounts of acetyl chloride or by means of pentyl nitrite and a few drops of concentrated hydrochloric acid in light petroleum solution 273 and similar procedures have been used by some other workers.274,275... 

Recent studies revealed that, in addition to aldehydes in such systems, there may also exist terpenes, ketones, acetone and hexanal [42-44]. This finding has initiated a growing interest for other possible non-formaldehyde based VOC emissions from wood and wood products. 

Stereoselective reduction of terpene ketones via hydrosilylation [36] exhibited significant difference in stereochemistry from other reduction by metal hydrides. Results of the reduction of camphor and menthone via hydrosilylation are listed in Table 6. Included also in the Table are reported selectivities obtained by using conventional reducing agents. It is seen in the Table that the bulkiness of silanes exerts remarkable influence on the stereochemical course of the reduction, i.e., a bulky hydrosilane favors the production of the more stable alcohols. This trend is quite... 

These facts may well imply that the stereoselectivity for addition of a hydrosilane to the enantiotopic faces of a ketone is different from that of an olefin which is undoubtedly tr-coordinated to the chiral catalyst the difference is again explained in terms of the intermediacy of an a-siloxyalkyl-platinum complex similar to the a-siloxyalkyl-rhodium complex described in the hydrosilylation of terpene ketones (see Scheme 4). 

Since the intermediacy of a-siloxyalkyl rhodium complex III (see Scheme 4) is strongly suggested in the hydrosilylation of terpene ketones catalyzed by chlorotris-(triphenylphosphine)rhodium(I) (7), such an intermediate most likely plays a key role in the asymmetric induction of the present system. The fundamental premise is to assume a square-pyramidal structure of the a-siloxyalkyl-rhodium intermediate VI, as shown in equation (18), on the basis of the established structures of dihydrido [46] and of silylhydrido [14, 32c, 47] complexes derived from the Wilkinson s rhodium(I) complex. 

In 1958, Russian chemists [31] reported that chloroplatinic acid-catalyzed hydrosilylation of a,/3-unsaturated carbonyl compounds takes place in a 1,4-fashion. Recently, it has been disclosed [35] that highly selective 1,2- as well as 1,4-addition of hydrosilanes to ajS-unsaturated terpene ketones can be achieved by using chloro-tris(triphenylphosphine)rhodium(I) (7), the selectivity depending markedly on the nature of the hydrosilane employed as described in Section 4.1. This achievement has resulted in studies on two kinds of selective asymmetric hydrosilylation of a, unsaturated carbonyl compounds by making use of either selective 1,4-addition or 1,2-addition the 1,4-addition induces asymmetry on a jS-carbon to afford optically active saturated carbonyl compounds, while the 1,2-addition gives optically active allylic alcohols. 

Perfumes are composed of hundreds of aromatic chemicals, namely, fragrance chemicals, or just simply fragrances. Among these compounds, it is very common to find compounds with the characteristic five-carbon isoprene unit, giving them the names of terpenes, such as terpene aldehydes, monoterpene alcohols, sesquiterpene alcohols, terpene ketones, terpene esters, monoterpene hydrocarbons, or sesquiterpene hydrocarbons. In addition, other compounds, such as aldehydes, alcohols, ketones, esters, phenols, or lactones, are also very common. 

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