Terpene derivatives, from pinenes

In several important cases, new synthetic strategies have been developed into new production schemes. An outstanding example of this is the production of an entire family of terpene derivatives from a-pinene (29), the major component of most turpentines, via linalool (3) (12). Many of these materials had been produced from P-pinene, a lesser component of turpentine, via pyrolysis to myrcene and further chemical processing. The newer method offers greater manufacturing dexibiUty and better economics, and is environmentally friendly in that catalytic air oxidation is used to introduce functionality. 

C, b.p. 156 C. The most important of the terpene hydrocarbons. It is found in most essential oils derived from the Coniferae, and is the main constituent of turpentine oil. Contains two asymmetric carbon atoms. The (- -)-form is easily obtained in a pure state by fractionation of Greek turpentine oil, of which it constitutes 95%. Pinene may be separated from turpentine oil in the form of its crystalline nitrosochloride, CioHigClNO, from which the ( + )-form may be recovered by boiling with aniline in alcoholic solution. When heated under pressure at 250-270 C, a-pinene is converted into dipentene. It can be reduced by hydrogen in the presence of a catalyst to form... 

Among chiral dialkylboranes, diisopinocampheylborane (8) is the most important and best-studied asymmetric hydroborating agent. It is obtained in both enantiomeric forms from naturally occurring a-pinene. Several procedures for its synthesis have been developed (151—153). The most convenient one, providing product of essentially 100% ee, involves the hydroboration of a-pinene with borane—dimethyl sulfide in tetrahydrofuran (154). Other chiral dialkylboranes derived from terpenes, eg, 2- and 3-carene (155), limonene (156), and longifolene (157,158), can also be prepared by controlled hydroboration. A more tedious approach to chiral dialkylboranes is based on the resolution of racemates. /n j -2,5-Dimethylborolane, which shows excellent enantioselectivity in the hydroboration of all principal classes of prochiral alkenes except 1,1-disubstituted terminal double bonds, has been... 

Organic aerosols formed by gas-phase photochemical reactions of hydrocarbons, ozone, and nitrogen oxides have been identified recently in both urban and rural atmospheres. Aliphatic organic nitrates, such dicarboxylic acids as adipic and glutaric acids, carboxylic acids derived from aromatic hydrocarbons (benzoic and phenylacetic acids) and from terpenes emitted by vegetation, such as pinonic acid from a pinene, have been identified. The most important contribution in this held has been that of Schuetzle et al., who used computer-controlled... 

Many terpenes are derived from renewable plant oil resources like essential oils. a-Pinene and -pinene from turpentine may be the best known examples, because they represent a very large volume. Turpentine was originally obtained from pine trees by tapping gum oleoresin from the stem of the living trees followed by steam distillation of the crude oleoresin and subsequently separation into rosin and turpentine by distillation. The ratio of a-pinene to -pinene in this turpentine varies considerably and depends a lot on the pine species from... 

The name pinanyl is recommended for the univalent saturated radical (CjqH ij-j derived from pinane because in the terpene literature the name pinyl (which would be the name formed by replacing the ending ane of pinane by yt) has been used exclusively and frequently for a 10 15—radical (with point of attachment at position 3) derived from /S-pinene. Since pinanyl must be an exception to the general rules, the names of the other two saturated radicals in the pinane-group series, that is, pinanylidene and pinanylene, should also be exceptions for consistency. In the series of nor- names, however, it does not seem necessary to insert the "an syllable because the radical names norpinyl and the like have not been used in the literature. 

Terpenes are a class of naturally occurring olefins found in many plants. They are biosynthetically derived from isoprene, CsHg, and therefore consist of Cs-building blocks and are found in both cyclic and acyclic forms. An important subgroup is the monoterpenes, which consist of two isoprene units and are of the molecular formula Ci0H16. Of the monocyclic monoterpenes, by far the most industrially relevant is limonene, which is abundantly present as a fragrance in various household products. From the bicyclic monoterpenes, a-pinene, p-pinene, camphene, and carene are of industrial relevance and are also mostly used in the fragrance industry [44]. 

Planar chiral compounds should also be accessible from the chiral pool. An example (with limited stereoselectivity) of such an approach is the formation of a ferrocene derivative from a -pinene-derived cyclopentadiene (see Sect. 4.3.1.3 [81]). A Cj-symmetric binuclear compound (although not strictly from the chiral pool, but obtained by resolution) has also been mentioned [86]. Another possibility should be to use the central chiral tertiary amines derived from menthone or pinene (see Sect. 4.3.1.3 [75, 76]) as starting materials for the lithiation reaction. In these compounds, the methyl group at the chiral carbon of iV,iV-dimethyl-l-ferrocenyl-ethylamine is replaced by bulky terpene moieties, e.g., the menthane system (Fig. 4-2 le). It was expected that the increase in steric bulk would also increase the enantioselectivity over the 96 4 ratio, as indicated by the results with the isopropyl substituent [118]. However, the opposite was observed almost all selectivity was lost, and lithiation also occurred in the position 3 and in the other ring [134]. Obviously, there exists a limit in bulkiness, where blocking of the 2-position prevents the chelate stabilization of the lithium by the lone pair of the nitrogen. 

More typically, mixtures of products are formed. Terpene epoxides that have been subjected to ZnBr2-catalyzed rearrangement include the oxiranes derived from limonene, carvomenthene, other pinenes, 2,3-carvene, pulegone and piperitone. ZnCh is rarely employed, but has been compared with AICI3 in a study involving sever epoxides. In most instances there appears to be no evidence for special advantages of zinc halides compared with other more commonly used Lewis acids. 

Complex volatile hquids derived from flowers, stems, and leaves, and often the entire plant. They contain terpenes (pinene, dipentene, etc.) and are used chiefly for perfumery and flavorings. Usually resinous products are admixed with them. Turpentine is a highly resinous essential oil. 

P-pinene. (nopinene). C10H16. A terpene hydrocarbon derived from sulfate wood turpentine. 

Terpenes are are a class of compounds whose chemical structures are based on a number of isoprene units , derived from the hydrocarbon CH2=C(CH3)-CH=CH2 they may themselves be hydrocarbons, but may also contain alcohol (OH), aldehyde/ketone (CO) and carboxylic acid (COOH) groups. Monoterpenes are Cm compounds derived from two isoprene units, sesquiterpenes (Cu) are derived from three isoprene units, diterpenes (C20) from four and tritepenes (C30) from six. Terpenes are widespread in plants, where they are largely responsible for the odor, and they are the major constituents of plant-derived essential oUs . Among the best known terpenes are 3-pinene (turpentine), camphor, menthol and citroneUal (aU monoterpenes) and farnesol (a sesquiterpene that is a constituent of the essential oils of many plants). Certain terpenes have important biological roles vitamin A, for example, is a diterpene, and steroid hormones have a structure related to triterpenes (and are biosynthesized by a similar route). 

Tea tree oil is derived from leaves of Melaleuca alternifolia and M. linearifolia (Myrtaceae), native to the east coast of New South Wales. To meet the Australian standard for tea tree oil the terpinen-4-ol content must be at least 30% while that of the oxidised terpene 1,8 dneole must not exceed 15% (Williams et al. 1988). The chemo-types of tea tree oil from natural stands is genetically determined, so that all commercial plantations are started from seed known to be of the right chemotype. Other terpene constituents of tea tree oil are the alcohol a-terpineol, hydrocarbons a-pinene and (3-pinene, p-cymene and y-terpinene, and sesquiterpenes including the unique compound viridflorene (Penoel 1990). Terpenin-4-ol is also a major ingredient in marjoram—Marjorana hortensis (Lamiaceae). 

Monoterpenoids with Cio skeleton is not the most diverse group of terpenoids, but they can be considered to be the most important because of their abundance and frequent appearance in nature. Most common monoterpenes e.g., a-pinene can be detected from nearly every green plant since chloroplasts produce monoterpenes, even by those species which do not synthesize isoprene. Plastids of other cells such as epithelial cells of resin duct in conifers produce a-pinene and other monoterpenoids in storage structures. Resin of conifers is a mixture of monoterpenes and diterpenes. The word terpene is derived from the word turpentine, which is mostly an essential oil containing a-pinene distilled from tree resins, originally from turpentine tree Pistacia terebinthus. 

Crude wood turpentine differs from normal turpentine primarily in that it contains additional terpenes, and terpene derivatives, t< ether with other non-terpene derivatives. In that obtained by the destructive distillation of longdeaf yellow pine, dipentene, pentane, pentene, toluene, heptine, etc., have been identified, in addition to pinene. 

The chemistry of this oil is in need of further elucidation, as it is -clear that thei-e are several constituents present which have, so far, escaped identification. The terpene dipentene is present, and probably small quantities of pinene or camphene cadinene is present, as well as a second sesquiterpene not yet identified. There is also present, especially in the oil distilled from old fruit, which has doubtless become partially oxidised, a small amount of the so-called cubeb-camphor. This b y, C H gOH, appears to be a crystalline sesquiterpene alcohol derived from the sesquiterpenes (or one of them) by oxidation. From a mixture of ether and alcohol it crystallises in rhombs, melting at 65 and is laevo-rotatory. It boils at 248 , with decomposition. The nature of the blue oil found in the higher fractions is unknown. 

As a final example of a process in which enantioselective synthesis is achieved using an optically active reagent, let us consider some of the results of hydroboration with optically active boranes. The boranes are normally prepared by reaction of diborane with one of several available terpene-derived alkenes. One such reagent is diisopinocampheylborane, which is prepared from diborane and a-pinene. ... 

---