Sesquiterpene bicyclic

Cadinene is a bicyclic sesquiterpene, whose constitution is not definitely understood. 

Selinene is a bicyclic sesquiterpene occurring in essential oil of celery. Its presence was first indicated by Ciamician and Silber who announced the isolation of a sesquiterpene boiling at 262° to 269°, but no characteristic derivatives were prepared. Schimmel Co. examined this sesquiterpene to which they assigned the name selinene. They prepared a solid dihydrochloride melting at 72° to 74° and ha-ving a specific rotation -h 18°. The pure sesquiterpene, regenerated from the dihydrochloride by means of sodium ethylate had the following characters —... 

By dehydrating guaiol, the sesquiterpene alcohol present in guaiac wood oil, Wallach and Tuttle obtained a bicyclic sesquiterpene which they called guaiene. It has been obtained by different methods by other observers from guaiol, and its characters are recorded as follows... 

Tapia has prepared this bicyclic sesquiterpene by distilling capar-rapiol, the sesquiterpene alcohol present in caparrapi oil, with phosphoric ai ydride. It is a colourless oil having the following characters —... 

It is a doubly unsaturated bicyclic sesquiterpene from which no crystalline derivatives have, so far, heen prepared. 

It yields a chloride, CjjHjgCl, of specific gravity 0-990 at 20°. a bicyclic sesquiterpene alcohol, with one double bond. 

Costol is a diolefinic bicyclic sesquiterpene alcohol, which, on oxidation by chromio acid in acetic acid yields an aldehyde, CjgH jO, which jrields a semi-carbazone, melting at 217° to 218°. This aldehyde, which U triolefinic has the following characters —... 

This alcohol has, however, been quite recently reinvestigated by Semmler, Jonas, and Eichter. They consider that it is a bicyclic sesquiterpene alcohol whose characters are as follows —... 

About 20 years ago, Bohlmann and co-workers examined South American plants of the widespread Vemonia species and found the first and (until now) only naturally occurring endocydic allenes (Scheme 18.32) [97]. These are the bicyclic sesquiterpene lactones 100-102 bearing a 10-membered ring [98], in which the E-double bond of the larger ring can also be present in its oxidized form (101, 102). As in other cases, these fasdnating natural products have not been synthesized until now. 

R)- and (S)-LBA 52 were also applied to the diastereoselective cychzafion of optically acttve hydroxypolyprenoid 53 to afford after several steps the natural bicyclic sesquiterpene ethers (-)-caparrapi oxide and (-i-)-8-epicaparrapi oxide, respectively (Scheme 5.69) [130]. Notably, LBAs 52 and ent-52 were able to... 

Table 1. Bicyclic Sesquiterpene Isothiocyanates Isolated from Sponges...

Among the other terpenes that have been used as substrate in the MTO-catalyzed oxidation reactions are the bicyclic monoterpenes carene and camphene, the acyclic monoterpene myrcene, fi-citronellene (the reduced form of myrcene), and the bicyclic sesquiterpene (i-caryophyllene (Fig. 6). 

The two major adducts obtained in the reaction of 9a with cyclopentadiene were used by Koizumi et al. in the synthesis of bicyclic sesquiterpenes [31]. From... 

Bicyclic sesquiterpenes include a variety of bioactive compounds including the Solanaceae phytoalexins capsidiol (G61G6) from Capsicum frutescms (pepper) and the Solanum tuberosum (potato) antifungals rishitin (G61C6) and solavetivone (G6-G5) the Ipomoea batatus... 

Application of this methodology to the synthesis of ( + )-a-amorphene (zizazene, bicyclic sesquiterpene with a cadinane skeleton) shows that only the (.EJ-isomer 7 undergoes [3,3] sigmatropic shift. Obviously, steric interactions in the transition state of the corresponding (Z)-isomer suppress the rearrangement987. 

S. F (1989) A new stereochemical class of bicyclic sesquiterpenes from Eremophila virgata W V. Fitzg. (Myoporaceae). Tetrahedron 45,6297-6308. 

Metz et al. have also demonstrated the use of sulfonate tethers in the preparation of the bicyclic sesquiterpene lactone, ivangulin 68 [25f]. The sulfonate derived from vinyl sulfonyl chloride and diene 69 underwent smooth IMDA reaction affording a mixture of exo cycloadducts 70 and 71 in a 1 1.4 ratio. Heating this mixture in toluene at reflux allowed... 

Eudesmanes (selinanes). Bicyclic sesquiterpenes with 7-isopropyl-1,4a-dimethyldecalin skeleton. 

GermacranoBdes. Bicyclic sesquiterpene lactones derived from the germacranes. The lactone ring is usually in the 7/3,8a-position as in pyrethrosin it can also be in the 7, 6a-position but is only rarely seen in the 4,6-position as in linderalactone. 

Bicyclic sesquiterpenes caryophyllenes in essential oils, as perfume and fragrance products, chewing gum, synthesis of other perfumes typical odor (clove)... 

Independently, Koizumi et al. also reported [160] the use of nonracemic 3-p-tolylsulfinylacrylates as dienophiles in highly diastereoselective Diels-Alder reactions. The functionalized bicyclo[2.2.1]heptane derivatives such as (186), obtained by asymmetric Diels-Alder cycloaddition of ethyl p-tolylsulfinylmethylenepropionate with cyclopentadiene, have been used as intermediates for the synthesis of bicyclic sesquiterpenes such as (+)-epi-P-santalene (187) [161,162] (Scheme 5.61). 

Betuleitols optically active, isomeric, bicyclic sesquiterpene alcohols from birch bud oil. They arc derived from caryophyllene, and their structures are spedes-spedfic for Betula alba and Betula lento. 

The structure of the frequently occurring bicyclic sesquiterpene 6-caryophyllene was for many years a matter of doubt. After numerous investigations W. Treibs (1952) has been able to isolate the crystalline caryophyllene epoxide from the autoxidation products of clove oil and F. Sorm et al. (1950) suggested caryophyllene to have a 4- and 9-membered ring on bases of infrared (IR) investigations. This suggestion was later confirmed by the Fnglish chemist D. H. R. Barton (Barton and Lindsay, 1951), who was awarded the Nobel Prize in Chemistry in 1969. 

Figure 11.23. A few typical examples of the thousands of bicyclic sesquiterpenes found in nature.

In addition to common six-membered rings such as in the cadinenes, one classic bicyclic sesquiterpene is caryophyllene, which has a nine-membered ring and cyclobutane ring. Additional unsaturation provides aromatic bicyclic sesquiterpenoids such as vetivazulene and guaiazulene. Examples are caryophyllene, y-muurolene, petasin, Ipomeamarone, carotol, helminthosporal, avocettin, alkaloids of Nuphar, and mycophenolic acid. 

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