Y -Bisabolene

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 ... 

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. 

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

Several interesting compounds (Scheme 27) have been identified from insects in this family, but no pheromones have been conclusively demonstrated. For example, homo-y-bisabolene 154 has been identified from male Sunn bugs, Eurygaster integriceps, but nothing is known of its biological activity [149]. 

Teroenes in G. barbadense and Upland race stocks. Different cultivars of Upland cotton have similar profiles of volatile terpenes, but barbadense and certain insect-resistant Texas race stocks of G.. hirsutum (15 - 17) have profiles different from the cultivars. 1. barbadense lacks myrcene, y-bisabolene and B-bisabolol, which are major components in cultivated Upland cotton, but it has greater concentrations of a-copaene (18 Table II). 

This cation does many tilings but it takes its name from the three fairly random proton losses that lead to the a-, P-, and y-bisabolenes. 

Two new sesquiterpenoids isolated from the roots of Ptilostemon chamaepeuce have been assigned structures (38) and (39) on the basis of their spectroscopic properties and chemical behaviour.18 The isomeric y-bisabolenes (40a and b), postulated... 

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