Acyclic monoterpene

Acyclic diperoxyketals, 14 287 18 457 Acyclic diyne metathesis (ADIMET), 26 951 Acyclic monoterpenes, aroma chemicals, 3 237... 

While earlier it was generally thought that the acyclic monoterpene alcohols 242-245 are derived from the host tree s oleoresin component, myreene [453], more recent results clearly show that at least in some species they are produced denovo [454-456]. 

For Instance, many terpene derivatives mimic insect hormone actioa Juvabione (15) is the classical example of a juvenile hormone (JH) mimic that prevents egg maturation in Pyrrhocoris bugs. Aromatic terpene ethers (16), methylene dloxyphenyl terpene ethers (17), and other farnesyl derivatives also have JH activity and the latter ones (18) also cause sterility in Pyrrhocoris. For the most part JH active terpenes are among the sesquiterpenes but several monoterpenes also have insect sterilizing effects (19. 20). The acyclic monoterpene cltral reduces the fertility of rats by causing follicular degeneration (21). 

Z-Tagetone (82a) -Tagetone (82b) Z-Ocimenone (83a) -Ocimenone (83b) Fig. (13). Acyclic monoterpene ketones tagetone and ocimenone... 

As in the discussion of the acyclic monoterpene ketones (see 1.1.3) instead of the sesquiterpene ketones, the structurally related compounds neryl-(176) and geranylacetone (169) will be reviewed. Indeed, as mentioned before, neryl- and geranylacetone are the norsesquiterpene -analogues of 6-methyl-5-hepten-2-one, which is the /1-oxidation product of nerol and geraniol, just like neryl- and geranylacetone are the bioconversion products of famesol (see 2.1.1). 

An early example is the fascinating rearrangement802 of acyclic monoterpenes geraniol 195 and nerol 196 to a stable observable oxonium ion in HSO3F—SO2—CS2 at —78°C, which represents yet another dramatic example of altered course of terpene rearrangement in superacid medium. Careful quenching of this ion led to the isolation of 3/3,6a,6a/3-trimethyl- s-perhydrocyclopenta[b]furan 197 in excellent yield (Scheme 5.76). 

Stierle, D. B., Wing, R. M., and Sims, J. J., Marine natural products XVI. Polyhalogenated acyclic monoterpenes from red alga Plocamium of Antarctica, Tetrahedron, 35, 2855, 1979. 

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). 

Acyclic monoterpene alcohols are present in many essential oils and can be isolated by distillation, although nowadays, they are often synthesized from other sources. Geraniol and linalool (Fig. 7) are the most important monoterpene alcohols and together with nerol are the primary products in terpene biosynthesis [44]. a-Terpineol is a frequently used cyclic monoterpene alcohol in the fragrancing industry because of its typical lilac odor and is also partly responsible for the typical... 

Figure 3.2 Monoterpenes (C10H16). (A) Myreene, an acyclic monoterpene. (B) a-Pinene, a dicyclic structure. (C) d-Limonene, a monocyclic structure. Courtesy Spiring Enterprises Ltd.

Different acyclic monoterpenes are made up of two isoprene units, but the positions of the three double bonds vary. 

V.B. (2007) Oxidation of acyclic monoterpenes by P450 BM-3 monooxygenase influence of the substrate B/Z-isomerism on enzyme diemo- and regio-selectivity. Tetrahedron, 63, 9413-9422. 

Monoterpenoids are responsible for fragrances and flavors of many plants and thus their products are used in perfumery and as spices. To date over 1,500 monoterpenoids are known, and these constitute acyclic, monocyclic, and bicyclic monoterpenoids (32), which occur in nature as hydrocarbons, alcohols, aldehydes, and carboxylic acids and their esters. Several acyclic monoterpenoid hydrocarbons are known, and these include trienes such as 3-myrcene (Cl), a-myrcene (C2), (Z)-a-ocimene (C3), ( )-a-ocimene (C4), (Z)-3-ocimene (C5), and ( )-P-ocimene (C6). 3-Myrcene and 3-ocimene are constituents of basil (Oci-mum basilicum, Labiatae) and bay (Pimenta acris, Myrtaceae), pettitgrain (Citrus vulgaris, Rutaceae) leaves, strobiles of hops (Humulus lupulus, Cannabaceae), and several other essential oils. Unsaturated acyclic monoterpene alcohol constituents of plants and their derived aldehydes play a signihcant role in the perfume industry. Some common acyclic monoterpene alcohols and aldehydes include geraniol (C7), linalool (C8) (a... 

N,N-Diethy1gerany1am1ne is a key intermediate for the synthesis of Industrially Important acyclic monoterpenes such as geranyl acetate, llnalooicitral and cltronellal... 

Boidron (71) showed that there was a decrease in the concentration of acyclic monoterpene alcohols and oxides in grape juice which was fortified with these compounds and then inoculated with B. cinerea. After 25 days of fungal growth none of the added monoterpenes could be detected in the juice. Two proposals were put forward to account for these observations - (a) B. cinerea metabolized acyclic monoterpenes to oxides and a-terpineol, then degraded these postulated metabolites or (b) a chemical oxidation paralleled the attack by the fungus (71). 

There are several cyclic ethers derived from acyclic monoterpenes which are of importance at lower levels in fragrances. Allylic oxidation of citronellol can be used to introduce a leaving group which allows cyclization to form the pyran, rose oxide. Chlorination was one of the first oxidation techniques employed various others, including electrochemical methods, have since been developed. An outline of the synthesis is given in Scheme 4.16. Rose oxide occurs in rose and geranium oils, to which it imparts a characteristic dry, green, rosy top-note. 

As in the 1960s the demand for (3-pinene far exceeded its availability owing to its versatile applications, a large part of the more commonly occurring a-pinene was isomerized to (3-pinene using, for example, basic catalysts such as calcium amide and alkaline earth metal oxides. A major amount of (3-pincnc is converted to resins with adhesive properties and by pyrolysis to the acyclic monoterpene myrcene. 

CHronellols (3,7-dimethyloct-6- and -7-en-l-ol). CioHjoO, Mr 156.27, formula, see citronellals. Acyclic monoterpene alcohols, of which the /8-forms of both enantiomers occur in nature (3/ )(+)-/S- and (35)(-)-/S-C., bp. 224-224.5 °C, [a]o 5 (neat). Both have strong, rose-like odors. 

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