B-pinene

The (-)-B-pinene used in this procedure was obtained from Glidden Organics. It was purified before use by distillation from lithium aluminum hydride small increments of hydride were added to pinene stirred under nitrogen until an excess was present as determined by observing gas evolution on addition of a few drops of methanol to an aliquot of the slurry. The purified material had [ajjp -21.0" (neat, 92.1% ee). GLC analysis (10% SE-30 on Chromosorb W, 100°C) showed only one peak. Use of dry, peroxide-free... 

Charles A. Brown and Prabhakav K. Jadhav 224 (-)-a-PINENE BY ISOMERIZATION OF (-)-B-PINENE... 

For a general discussion on methods of isomerization of B-pinene to a-pinene see Brown, C. A. Synthesis 1978, 754. 

B-Pinene Is an important auxiliary for directed chiral syntheses. It has been used for preparation of mono- and diisopinocampheylborane 8-allyldiisoplnocampheylborane,6 B-pinanyl-9-bora[bicyclo]nonane, els-... 

Two pinene cyclases have been isolated from sage (19,35). Electrophoretically pure pinene cyclase I converts geranyl pyrophosphate to (+)-a-pinene and to lesser quantities of (+)-camphene and (+)-limonene, whereas pinene cyclase II, of lower molecular weight, converts the acyclic precursor to (-)-B-pinene and to lesser quantities of (-)-a-pinene, (-)-camphene and (-)-limonene. Both purified enzymes also utilize neryl and linalyl pyrophosphate as alternate substrates for olefin synthesis. The availability of enzyme systems catalyzing formation of enantiomeric products from a common, achiral substrate has provided an unusual opportunity to examine the stereochemistry of cyclization. 

Qccurance and Identification. An early report of cotton volatile composition by Minyard et al. (44) involved steam distillation of large quantities of leaves and flowers. Major compounds identified included the monoterpenes a-pinene, B-pinene, myrcene, trans-B-ocimene, and limonene ( 4). Several other monoterpene hydrocarbons were also present in low concentration. Since that report, many other terpenes have been identified in cotton essential oil steam distillates and solvent extracts. These compounds include cyclic hydrocarbons such as bisabolene, caryophyllene, copaene and humulene (45-47), the cyclic epoxide caryophyllene oxide (45), cyclic alcohols such as bisabolol, spathulenol, and the aromatic compound... 

Polymerization of terpenes using acidic catalysts such as AICI3 and BF3 is another major reaction for terpenes. B-Pinene and dipentene yield almost quantitative amounts of polymer in the 600-2000 MW range, while a-pinene yields only about 60% polymer in this range (32). More recently, it was claimed that an all a-pinene resin can be prepared by using chlorosilane as a catalyst (33). Monoterpenes condense with phenol in the presence of BF3 to form terpene-phenolic resins. 

The quantitative conversion of dipentene and 3-pinene to form polymers stirred interest in (1) the pyrolysis of a-pinene to dipentene and allo-ocimene (34) and (2) the synthesis of B-pinene from a-pinene (35). However, due to the availability of citrus limonene as a supplemental source for dipentene, the pyrolysis scheme is no longer economically attractive. 

Perhaps the most intriguing and fast-growing area of terpene chemistry is in speciality chemicals. A wide range of flavor and fragrance materials can be synthesized from terpenes. Figures 10 and 11 Illustrate some of the reaction routes. A major expansion has recently been completed in this area, including a new route to some of these derivatives using a- Instead of B-pinene (11). 

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