Sesquiterpenes cedrene

Semmler considers /3-gurjunene to resemble the tricyclic sesquiterpene, cedrene, so that it is doubtful whether it is bicyclic or tricyclic. 

It yields a phenylurethane if it is heated almost to boiliog-point with phenyl-isocyanate. This compound melts, at 106° to 107°. On dehydration with phosphoric acid it yields the sesquiterpene cedrene. The relationship between cedrene and cedrol is probably as follows —... 

In addition to cedrol and pseudocedrol, cedar-wood oil contains a third alcohol, of the formula Cj5H. 40, which has been named cedrenol. This alcohol was isolated by Semmler and Mayer, who found it to exist to the extent of about 3 per cent, in the oil. It is a tricyclic unsaturated alcohol, closely related in constitution to the sesquiterpene cedrene, as shown hy the following formulae —... 

The first example of the triplication of the arene- ene meta cycloaddition in complex molecule synthesis was the total synthesis of the sesquiterpene cedrene (82 Scheme 8). This taiget was selected for... 

Cyclic sesquiterpenes having the cedrene skeleton have also been isolated. When R = COOH, this stmcture (11) has been named sheUoflc acid. 

Important commercial sesquiterpenes mosdy come from essential oils, for example, cedrene and cedrol from cedarwood oil. Many sesquiterpene hydrocarbons and alcohols are important in perfumery as well as being raw materials for synthesis of new fragrance materials. There are probably over 3000 sesquiterpenes that have been isolated and identified in nature. 

Cedrene is the naturally occurring sesquiterpene of cedar wood oil of which it forms the principal constituent. It is a tricyclic compound having the following characters —... 

Semmler and Hoffmann have examined this sesquiterpene in considerable detail. It was dissolved in acetone and oxidised with potassium permanganate, and the indifferent products thus obtained were separated by fractional distillation. Cedrene glycol, Cj Hj O, was obtained to the extent of 12 to 15 per cent. it crystallises from acetone in prisms, melting at 160°. 

Semmler and Mayer have isolated from the oil of cedar wood an alcohol, pseudocedrol. There also exists in the oil a sesquiterpene alcohol, cedrol. The latter, on dehydration yields cedrene, which is probably identical with, or very closely allied to, natural cedrene, whilst pseudocedrol yields a mixture, when heated in a sealed tube, of cedrene and dihydrocedrene. Dihydrocedrene is a colourless oil having the following characters —... 

No crystalline halogen derivatives of cedrene have been prepared, only liquid compounds being obtained when the sesquiterpene is treated by the usual processes. 

The second chemotype (their Type 1) had, in addition to the Type 0 array, substantial amounts of a-longipinene [297] and an unidentified sesquiterpene alcohol. The third chemotype (their Type 2) was distinguished by the presence of, among other compounds, cedrene isomers, [a-cedrene is shown as 298], and large amounts of the isomeric sesquiterpene alcohols a-acorenol [294] and its P-isomer [295]. The acora-diene isomers [295 and 296] were also identified. Some geographic patterning was observed in the Type 0 chemotype when the data were subjected to numerical analysis a trend in the reduction of caryophyllene content was revealed in a west to east direction. The data sets for Types 1 and 2 were too small to allow for similar analysis. 

Although cedranoid sesquiterpenes have earlier been synthesized, a renewed interest in alternative methods for elaborating these frameworks has arisen. The stereo-specific approach to (x-cedrene and a-patchoulene skeletons designed by Deslong-champs and summarized in Scheme XLIII is a case in point Beginning with the Stork-Clarke intermediate 559, the tetracyclic cyclopropyl diketone 560 was elaborated via a series of standard transformations. Treatment of 560 with three equivalents of sodium methoxide in methanol at room temperature for 20 min... 

C17H26O, Mr 246.39, is a long-lasting wood fragrance which is prepared by acetylation of cedarwood oil fractions that contain sesquiterpene hydrocarbons, mainly a-cedrene and thujopsene. Acetylation is carried out in the presence of an acidic... 

Cedrene and Gedrol. Cedarwood oil is one of the essential oils whose production is large and provides a source for synthesizing a number of derivatives. Cedrene (91) and thujopsene (92) are the two main sesquiterpene hydrocarbons found in the oil, along with a number of minor components (187). Cedrol [77-53-2] (93) is the main alcohol component of the oil. 

The new red algal species Laurencia mariannensis from the Great Barrier Reef provides the novel sesquiterpene 297, along with the known pacifenol and deoxy-prepacifenol, which are now fully characterized by NMR for the first time (539). The Philippine Laurencia majuscula has furnished 13 novel halogenated sesquiterpenes 298-310, of which the major components are the majapolenes A (298, 299) (two diastereomers), which are also found in Laurencia caraibica (540). Most of these compounds occur as inseparable diastereomers. A collection of Laurencia majuscula from the South China Sea has yielded the cedrene-type sesquiterpene majusin (311) (541). A new sesquiterpene dichloroimine, stylotellane A (312), was isolated from the sponge Stylotella aurantium (Fig. 3.3) (542). 

Fig. 5-3. Examples of mono- and sesquiterpenes and their derivatives in softwood. 1, a-Pinene 2, /3-pinene 3, 3-carene 4, camphene 5, borneol (R = H), bornyl acetate (R = COCH3) 6, limonene 7, a-terpineol 8, dipentene 9, a-muurolene 10, 8-cadinene 11, a-cadinol 12, a-cedrene 13, longifolene 14, juniperol.

Before entering into a discussion of synthesis, it should be pointed out that the sesquiterpene class is particularly rich in molecules that have bicyclo[3.3.0]octane subunits. Cedrene (262) and 7-patchoullene (264) are representative examples as... 

The presence of a quaternary carbon atom is frequently encountered in sesquiterpene natural products and it often creates a synthetic challenge when two or more quaternary carbon atoms are present contiguously. The synthetic strategies for the construction of quaternary carbon centers involve sigmatropic rearrangements/ intramolecular cycloaddition/ and the reaction of tertiary carbon nucleophiles with a carbon electrophile. Recently, radical cyclization strategies turned out to be very effective for this purpose. For example, Srikrishna utilized the radical cyclization reaction to prepare tricyclo[6.2.1.0 - ]undecane system, which is present in several sesquiterpenes such as zizaenes and prelacinanes, and Chen demonstrated that a tandem radical cyclization approach is an efficient method for constructing the two quaternary carbon centers in the cedrene skeleton. ... 

The sesquiterpene cedrol (46) can be hydroxylated regio- and stereo-selectively with Beauveria sulfu-rescens (equation 13). This transformation serves to illustrate the general principle that substrates with an electron rich substituent, to serve as an anchor at, or close to, the active site of the hydroxylating enzyme system, generally are transformed with improved selectivity over those with no such anchor. For example, in the above system the unsaturated substrate cedrene (47) gives low yields of a mixture of products. ... 

Another instance of the use of a natural intermediate in the sesquiterpene series is illustrated by the synthesis of o-cedrene... 

Sesquiterpene chemistry is always full of surprises. For example, an attempt to use titanic chloride in place of aluminium chloride to produce acetylcedrene resulted in a previously unknown compound (McAndrew et al., 1983). In this case, as shown in Scheme 4.32, the carbocation produced by addition of the acetyl cation to cedrene, instead of eliminating a proton as normal, underwent a Wagner-... 

Shortly after these communications, the alcohol (127), named a-acorenol, was found to occur naturally in the wood of Juniperus rigida and Tomita and Hirose also demonstrated its facile cyclisation with formic acid to ( — )-(z-cedrene (123) in greater than 90% yield. The corresponding diene (132), a-acoradiene, which was also converted to (—)-a-cedrene, was found in the same source. Subsequently, Hirose et al. isolated four other related sesquiterpenes from the same species. These are j5-acoradiene (133), y-acoradiene (134), -acoradiene (135), and )3-acorenol (136). The above authors also reported a tricyclic alcohol... 

Selinene is another sesquiterpene found in woods. Its behaviour in the Vilsmeier-Haack-Arnold reaction is, like that of the acylation of cedrene using titanic chloride as a catalyst, another interesting and surprising piece of sesquiterpenoid carbocation chemistry. 

The isocedrenes are considered to be analogs of the tricyclic sesquiterpene cedrol (2) which has been synthesized by G. Stork. Cedrene and its derivatives, most notably the 9 and 10- oxy derivatives have found applications in the cosmetics field as additives to perfumes, and in other fields as plant growth stimulators. ... 

It is clear from these and previous results obtained over the past two or three years that the spiro-sesquiterpenes provide an important link between certain monocyclic and tricyclic sesquiterpenes. This is further exemplified by the recent work of Andersen and SyrdaP who have now reappraised the absolute stereochemistries of (-)-a- (137) and (- )-/3-alaskene (138). It now appears that 5-acoradiene, isolated by Hirose et is, in fact, (-I-)- -alaskene. Andersen and Syrdal also made the interesting observation that phthalic anhydride dehydration of the diols derived from iso-acorone (139) gave rise to small amounts of (-f )-a-cedrene (126 R = Me) and (— )-2-epi-a-cedrene (136). Subsequently these authors found that (-t- )-nerolidol (140) and a number of its derivatives undergo acid-catalysed cyclization to a mixture of a- and -bisabolenes (141), of which the... 

A useful variant of this chemistry involves the radical cyclization onto an A-aziridinyl hydrazone. Fragmentation of the intermediate nitrogen-centred radical to release nitrogen gas and an alkene (typically styrene or stilbene) results in the formation of a new carbon radical at the original hydrazone carbon atom. Thus, in a synthesis of the sesquiterpene a-cedrene, the radical species 80, formed from the thiocarbonyl compound 79, cychzes onto the hydrazone to give the nitrogen-centred... 

Production By steam distillation from the wood of the Chinese red pine Chamaecyparis funebris (Cupressaceae). The annual production amounts to ca. 200-3(X) t. CompositionThe main components of all mentioned oils are the sesquiterpene compounds a- cedrene (ca. 10-25%), tIiM/opsene(ca.20-35%),and cedrol(c. 20-40%, in Chinese oil only 10-15%). 

Phytochemistry Fresh branches contain 0.45-0.75 % essential oils with d-pinene, d-camphene, myrcene, cedrene, and other sesqueterpenes. The bark, young branches, and umipe fruits contain 7-8 % tannins. Ripe fruits contain yellow pigments and up to 18.6 % sugar. Leaf samples from Tajikistan contained 120-140 mg% vitamin C (Khalmatov et al. 1984). A variety of compounds, including diterpenes and sesquiterpenes, has been isolated from the dried fruits (Okasaka et al. 2006). 

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