A-farnesene

PALLADIUM-CATALYZED SYNTHESIS OF 1.4-DIENES BY ALLYLATION OF ALKENYLALANES a-FARNESENE... 

Several natural products (Scheme 60) have been synthesized in vitro via singlet oxygen ene reactions. For example, clavukerin C was prepared in racemic form, in a biomimetic synthesis by Kim and Pak, whereas a-farnesene hydroperoxide was obtained starting from geraniol. 

Many sesquiterpenes which are not highly oxygenated are also found in essential oils. Several of these are reported to possess activity. a-Farnesene from apples is an attractant and oviposition stimulant for the codling moth ( ) and farnesol has been demonstrated to be an active feeding deterrent to gypsy moth larvae (Lymontria dispar) (69). 

Farnesene 69 is a constituent of hops oil and many other oils. a-Farnesene 70 is the structural isomer. Structural representations of a-farnesene and -farne-sene are illustrated in Structure 4.17. 

Nine compounds from branches with leaves and green fruit from apple consistently elicited an antennal response in codling female moths (Cydia po-monella, Lepidoptera), including methyl salicylate, ( )-/3-farnesene, /3-caryo-phyllene, 4,8-dimethyl-f,3( )-7-nonatriene, (3Z)-hexenol, (Z, )-a-farnesene, ( , )-a-farnesene, linalool and germacrene D [378]. 

In female Heliothis sp. (Lepidoptera) moths, four colocated receptor neurone types were identified, of which three types responded most strongly to the inducible compounds ( )- -ocimene and ( , )-a-farnesene. The fourth type responded most strongly to geraniol, which is a common floral volatile [383]. 

The flavour of distillates from apple and pear is characterised by typical aroma compounds from these fruits formed by enzymatic degradation of fatty acids to C6-fragments like hexanol, trans-2-hexenol, as well as ethyl esters and acetates of hexanoic acid. In distillates of pears, especially of the variety Bartlett pear, the characteristic pear flavour is mainly dominated by the ethyl and methyl esters of frans-2-czs-4-decadienoic acid and trans-2-trans-A-decadienoic acid [27-29], The biogenesis of these monounsaturated, diunsaturated, and triunsaturated esters may be explained by -oxidation of unsaturated linoleic and linolenic acid in the fruits. The sesquiterpene compound a-farnesene, which is formed during postharvest ripening and storage of Bartlett pears [28], shows that quality and intensity of distilled pear spirits is mainly influenced by the quality and degree of ripeness of the fruits. 

Higher oxygenated terpenes include the sesquiterpene alcohol, famesol, which has a lily-of-the-valley odor and occurs in ambrette-seed oil. On acid dehydration it gives a-farnesene (Table 30-1) under some conditions, and bis-abolene (a component of oil of bergamot) under others ... 

Figure 3.3 Sesquiterpenes (C15H24). (A) Farnesene (3,7,11-trimethyl-2l6l10-dodeeatriene) (acyclic). (B) Caryophyllene (bicyclic). Courtesy Spiring Enterprises Ltd.

PALLADIUM-CATALYZED SYNTHESIS OF 1,4-DIENES BY ALLYLATION OF AUENYLALANES a-FARNESENE (1,3,6,10-Dodecatetraene, 3,7,11-trlmethyl-)... 

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