Pinane monoterpenoids

Also the biotransformation of a-pinene derivatives and other pinane monoterpenoids by Cephalosporium aphidicola has been described [101]. The best conversion was the oxidation of verbenol to verbenone (yield 61%). 

Additional chemical diversity of monoterpenes is apparent from the natural occurrence of their bicyclic analogs that bear cyclopropane (carane and thujane types), cyclobutane (pinane type), and cyclopentane (camphene/bornane, isoeamphane and fenchone types) rings (Figs. 6 and 7). The carane type of bicyclic monoterpenoids in plants is represented by (+)-3-carene... 

Pinane-type bicyclic monoterpenoids (Fig. 6) occur in the wood of several species of Pinus. The most abundant are a- and p-pinenes (F7 and F8, respectively). Ally lie hydrox-ylation products of pinenes, (+)-verbenol (F9), (+)-myrtenol (FIO), and (—)-pinocarveol (Fll) also occur in nature together with their products of oxidation (-f-)-verbenone (F12), (-h)-myrtenal (F13), and (-)-pinocarvone (F14). (-h)-Verbenol is a constituent of the oil of turpentine. Its regioisomers, (-h)-myrtenol and (—)-pinocarveol, occur in oils of orange Citrus sinensis, Rutaceae) and eucalyptus Eucalyptus globulus, Myrtaceae), respectively. 

The diastereoselectivity of the hydrogenation of pinene monoterpenoids and related systems depends on the location of the double bond. The endocyclic double bond in a-pinene (5) is reduced from the less hindered face yielding pinane (6) in a 93 7 (cis/trans) ratio56. 

Some other common monoterpenoid hydrocarbons are shown in Figure 3.4. Citronellene is also known as dihydromyrcene. It does not occur in nature but is prepared by pyrolytic cracking of pinane. Hydration of the trisubstituted bond of citronellene produces dihydro-myrcenol which is used to provide fresh notes in perfumery. Further details of both of these processes are given in Chapter 9. a-Ocimene occurs in various essential oils such as those of basil, catnip and magnolia, while the P-isomer occurs in the leaf oils of lemon, orange and grapefruit and also in narcissus flowers. Allo-ocimene occurs in the leaves of sequoia trees and is the thermodynamically most stable of the three ocimenes since the double bonds are all in conjugation and as heavily substituted as possible. Double bonds can be isomerised under... 

---