Isoprene/farnesene

Nickel-catalysed trimerization of isoprene has been shown to provide a mixture of natural /S-trans-farnesene (8) (cf. Vol. 1, p. 82) and the isomeric compound (9). ... 

Further studies on the controlled oligomerization of isoprene (5) have shown that treatment with a nickel alkoxide catalyst provides tran5-/3-farnesene (6) in -60% yield. ... 

Palladium-catalysed reaction of trans-j8-farnesene, formed by catalytic tri-merization of isoprene, resulted in regioselective head-to-head coupling to a dimer which yielded squalene on hydrogenation. A detailed n.m.r. study of functionalized squalane derivatives and model compounds suggests the presence of precoiled conformations. ... 

Dienic carboxylic acids. Prater has described a method for addition of an isoprene unit to an allylic alcohol. The method is iUustrated for the conversion of the ester (1) of geraniol into farnesenic acid (3). The ester is treated with lithium N-isopropylcyclohexylamide (LilCA, 4, 306-309) and then with trimethylchlorosilane. The resulting trimethylsilylketene acetal (a) undergoes... 

Some common terpenes include geraniol, found in geraniums limonene, oil of orange a-pinene, or oil of turpentine a-farnesene, oil of cintronella zingiberene, oil of ginger farnesol, found in lily of the valley P-selinene, oil of celery and caryophyllene, oil of cloves. Isoprene is also produced in animal bodies and is said to be the most common hydrocarbon present in the human body. By one estimate, a 70-kilogram (150-pound) person produces about 17 milligrams of... 

By the outlines in the formulas above, we can see that the monoterpene (myrcene) has two isoprene units the sesquiterpene (a-farnesene) has three. In both compounds the isoprene units are linked head to tail ... 

Terpenes are classified based on units of 10 carbon atoms (two isoprene units). For example, a terpene with 10 carbon atoms is called a monoterpene, while a terpene with 20 carbon atoms is called a diterpene. As seen in Table 26.4, a compound with 15 carbon atoms is called a sesquiterpene. An example of a sesquiterpene is a-farnesene, found in the waxy coating on apple skins. 

Several aphid apecies of economic importance use ( )-P-farnesene as an alarm pheromone 304—307). Bowers et al. 308) have studied the activity of various famesene and nor-famesene analogs in an attempt to define the structural requirements necessary for alarm activity. They concluded that the following properties were important 1) there should be an JE -configurational double bond in the central position of the molecule, 2) the double bond in the terminal isoprene unit acts as an activator, 3) a rt-bond of 1.34 to 1.39 A must be located ten carbon... 

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