A-Selinene

Many teipenes contain one or more rings, but these also can be viewed as collections of isoprene units. An exfflnple is a-selinene. Like fainesol, it is made up of three isoprene units linked head-to-tail. 

Semmler deduces from these results that natural selinene is composed of a mixture containing principally the hemicyclic pseudo-(yS)-selinene, together with a small quantity of ortho-(a)-selinene. By passing through the dihydrochloride it is possible to convert the pseudo-(y8)-selinene into the ortho-(a)-selinene or regenerated selinene, which contains only a. small proportion of the (3 form. Both yield the same solid dihydrochloride. Selinene affords a typical example of the possibility of the displacement of the double bond from the side chain into the nucleus. 

The protic reaction on occasion is a useful method of alkene formation, but is far from general because the cation intermediate tends to undergo rearrangements.Further, even for cases in which elimination to an alkene is the predominant pathway, the regioselectivity of the process is often mediocre. A key step in the synthesis of (+)-a-eudesmol and (-)-a-selinene exemplifies this point (Scheme 60). There are, however, isolated examples of excellent selectivity, such as the reaction of a 3-ketotetrahydrofuran tosyl-hydrazone salt to give the corresponding cyclic enol ether as the major product (Scheme 61), the intro-... 

The protic Bamford-Stevens reaction has been successfully utilized in the asymmetric synthesis of the naturally occurring sesquiterpenes (+)-a-eudesmol and (-)-a-selinene. Here, the more-substituted alkene was formed preferentially (equation 4,1). ... 

Synaclenium compactum N. E. Br. var compactum The oil from the dried stem bark of S. compactum var compactum (0.2%) contained 55 constituents, of which a-selinene (30%) and p-sehnene (19%) were major (58). Decoctions of the leaves and the white latex of this plant are widely used for treatment of East Coast Fever in cattle (35). The plant is rare in the wild and it is endemic to central Kenya, where the plants are used for marking farm boundaries (48). 

Synadenium compactum N. E. Br. var. compactum Stem bark D 0.2 a-selinene, P-selinene 58... 

Japanese female peach fruit moth have been synthesised (Scheme 10).2 9 The phosphine oxide starting material (51) was obtained from a Wittig reaction of the ylide derived from 1,1-diphenylphospholanium perchlorate. The reaction of (l-methyl-2-propenyl)diphenylphosphine oxide carbanion (55) with the optically active aldehyde (54) is the key step in a short synthesis of the sesquiterpenes (-)-a-selinene (58) and (-t-)-a-helmiscapene... 

The methodology was extended to provide synthetic routes to the sesquiterpenes eudesmane (209), a-selinene (212a), and a-eudesmol (212b) [43,68] (Scheme 6.68). The intermediate diene (208) was found to be a single isomer, presumed to have ( )-geometry. 

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