7- Bisabolene

Saturated hydrocarbons were a problem because they have no functionality. It can be just as bad when a molecule has several functional groups aU apparently unrelated. Bisabolene (TM 384) has three double bonds, aU rather widely separated. Comment on possible strategies in terms of the hkely origin of each double bond and the probable order of events. 

This is the synthesis carried out by Vig and his group. (J. Indian Chem. Soc.. 1966, 43, 27). Bisabolene has been made in several other ways. 

Birch leaf extract Birch reduction Birch-type reactions Bird feathers Bird repellents Bireactive dyes Birkeland-Eyde process Birnessite [1244-32-5] b-Bisabolene [495-61-4]... 

Aerial parts of N. sintenisii yielded 0.3% of a clear yellowish oil. Forty constituents (96.5% of the total oil) were identified. The main components were 4aP,7a,7aP-nepetalactone (23.4%), elemol (16.1%), E- -farnesene (9.5%), 1,8-cineole (8.2%), cw-sabinene hydrate (6.5%), P-bisabolene (4.2%), germacrene-D (3.5%), P-sesquiphellandrene (2.8%), P-bourbonene (1.5%) and a-epi-cadinol (1.3%). According to available data, Nepeta species can be divided into two groups of nepetalactone-containing and nepetalactone-free species. The results of this study indicate that the compositions of volatile oil of N. sintenisii are similar to the other Nepeta genus and this plant could be classified in the group which 4aP,7a,7aP-nepetalactone is the major component of their oils. 

The stereoselective synthesis of y-bisabolenes was made possible by the development of a new method for the carbosilylation and double alkylation of an acetylenic function coupled with ring closure, overall addition of three carbon substituents to two acetylenic carbons. 

An alternative route to ( )-Y-bisabolene was demonstrated starting from the acetylene B, which was made from 5-hexyn-2-one as shown ... 

The acetylenic alcohol A, which was used as a key intermediate in the synthesis of ( )-7-bisabolene, served as the starting point of this synthesis. 

As far as we are aware, abscisin II is the only known sesquiterpene possessing the carbon skeleton of structure A. All the other mono-cyclic sesquiterpenes are thought to arise by way of ion D (the example given is bisabolene) or E (the example given is elemol) (21). 

Both E- and Z-isomers of the terpene y-bisabolene have been isolated from natural sources. The synthesis of these compounds can be achieved by stereoselective alkene syntheses using borane intermediates. An outline of each synthesis is given below. Indicate the reaction conditions that would permit the stereoselective synthesis of each isomer. 

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