Linalool formation

However, the lower fatty acid esters (particularly the acetates) of the acyclic terpene alcohols geraniol, linalool, and citronellol are extremely important both as fragrance and as flavor substances. The acetates occur in many essential oils, sometimes in rather high amounts. Formates, propionates, and butyrates occur less frequently. As a result of the development of large-scale production processes for terpenes, the esters of acyclic terpene alcohols are nearly always made synthetically. All acyclic terpene esters that are used as fragrance and flavor materials can be prepared by direct esterification of the appropriate alcohols. However, special precautions are required for the esterification of linalool. 

Because the lower fatty acid esters of geraniol, linalool, and citronellol are important contributors to the odor of many essential oils, these esters are widely used in the reconstitution of such oils, as well as in perfume and flavor compositions. The acetates, particularly linalyl acetate, are most widely used. The use of formates is limited by their relative instability. Higher esters are not important in terms of quantity, but are indispensable for creating specific nuances. 

Esterification of linalool requires special reaction conditions since it tends to undergo dehydration and cyclization because it is an unsaturated tertiary alcohol. These reactions can be avoided as follows esterification with ketene in the presence of an acidic esterification catalyst below 30 °C results in formation of linalyl acetate without any byproducts [71]. Esterification can be achieved in good yield, with boiling acetic anhydride, whereby the acetic acid is distilled off as it is formed a large excess of acetic anhydride must be maintained by continuous addition of anhydride to the still vessel [34]. Highly pure linalyl acetate can be obtained by transesterification of tert-butyl acetate with linalool in the presence of sodium methylate and by continuous removal of the tert-butanol formed in the process [72]. 

Heating (cooking) seems to produce certain terpenoids. In some vegetables, such as tomatoes and potatoes, there is a considerable increase in the formation of some terpene alcohols, including linalool, a-terpineol and terpinen-4-ol during heat treatments. 

Recently a practical and convenient synthesis was described starting from linalool via linalyl acetate [8]. It involves the ene-type chlorination of linalyl acetate prepared from linalool which results in the formation of y-chloro-a-linalyl acetate (Scheme 13.8). Dehydrochloronation with lithium bromide and lithium carbonate in dimethylformadide followed by hydrolysis of dehydro-a-linalyl ac-ylate results in hotrienol. 

The transformation of Arabidopsis thaliana with a cDNA from strawberry fruits encoding a dual (S)-linalool/(S)-nerolidol synthase also led to the production of both (S)-linalool and its glycosylated and hydroxylated derivatives in the leaves [14]. Surprisingly, the formation and emission of (S)-nerolidol was detected as well, suggesting that a small pool of its precursor farnesyl diphosphate is present in the plastids. The newly emitted (S)-linalool and (S)-nerolidol showed the same diurnal emission pattern as the pristine volatiles. 

Scheme 26.1 Catalytic formation of (S)-linalool from geranyl diphosphate. OPP denotes the diphosphate moiety...

Flowery Anisyl alcohol Benzyl acetate, phenylaceiate Cinnamic acid Cinnamyl acetate Citronellyl formate Crcsyl acetate Decanal Dimethyl benzyl carbinol Dimethyl benzyl carbinyl acetate Ethyl anthranilate Geranyl acetate Hydroxycitronellal dimethyl acetate Linalool Linalyl acetate Methyl benzoate Pcnethyl acetate 2-Phcnylpropionaldehyde 3-Phenylpropionaldehvde. 

Peana, A. T., Marzocco, S., Popolo, A., and Pinto, A. (2006a). (—)-Linalool inhibits in vitro NO formation Probable involvement in the antinociceptive activity of this monoterpene compound. 

Oliver (2003) reported pure (S)-(+)-linalool from oil of coriander by formation and recrystallization of its 3,5-dinitroben-zoate ester, followed by regeneration and distillation. Fathima et al. (2001) noted that microwave drying affected the colour, appearance and odour properties of coriander. 

The Ti,Al-Beta shows both acidic and oxidative properties which is reflected in unwanted side-reaction. The group of Corma used the bifunctionality in the epoxidation/rearrangement of cx-terpineol to cineol alcohol and in the formation of furans from linalool.81,82 Similarly van Klaveren et al. applied Ti,Al-Beta in the one-pot conversion of styrene to phenyl acetaldehyde.83 Sato et alM solved the unwanted acid-catalyzed side reaction by neutralizing the acid site by ion exchange with alkali metals. Nevertheless the bifunctionality restricts the use of this catalyst to a limited number of reactions. 

Dimethoxy Phenol 3,4-Dimethyl 1,2-Cyclopen tandione 5-Ethyl 3-Hydroxy 4-Methyl 2(5H)-Furanone 3-Ethyl Pyridine Furfuryl Mercaptan Geranyl Isovalerate 2,3 -Heptandione (Z)-3-Hexenyl Butyrate (Z)-3-Hexenyl Formate Hexyl Butyrate Hexyl Hexanoate Isoamyl Isobutyrate Isobutyl Formate Isobutyl Hexanoate Linalool Oxide... 

Three new monoterpenoid lactones, (28)—(30), isolated from the urine of koala bears fed on Eucalyptus punctata, appear to have arisen from the cyclization of carboxylic acids formed as hydrolysis products of glucuronide conjugates from the metabolism of a- and /3-pinenes.70 Linalool injected into various plant species has been claimed to be converted into a-terpineol and other monoterpenoids.71 However, direct interconversions cannot be inferred from this type of non-radioactive tracer study. The terpenoids alleged to be produced may well be stress metabolites or be formed b secondary processes that perturb the usual pattern of terpenoid formation. 

The reaction was carried out in acetonitrile at 353 K using TBHP as oxidant. Conversions as high as 80 % were obtained. As shown in Scheme 6, it was postulated that the reaction takes place via epoxidation over Ti sites foUowed by acid catalyzed intramolecular opening of the epoxide ring by the 3-hydroxy group. Ti-6 zeolite gave somewhat lower conversions in addition to the preferential formation of furans over pyrans (ratio of ca. 1.5) due to shape selectivity. Ti-MCM-41 and gave furan to pyran ratios of ca. 0.9, comparable to those obtained by the epoxidase conversion of linalool. 

In their strategy, three methods were investigated for the synthesis of aldehyde 86. Initially, linalool was selected as the starting material (Scheme 19). Cyclization with TBCO afforded a mixture of tetrahydropyrans (89 and 90, 10 6.9) and tetrahydrofurans (88) in 56% and 24% yields respectively. The preference for the stereoselective formation of pyran 89 over the desired compound 90 was postulated to be associated with the chair transition states shown in Scheme 19. Presumably, the diaxial interaction between the Ci methyl group and the vinyl substituent R in intermediate 92 is less severe than those between the two methyl groups in intermediate 93, leading to the undesired tetrahydropyran 89 as the major product [51]. 

Scheme 2) 84 treatment of (24) and its analogues with dissolving metals or peracids also led to novel, functionalized but regular structures.85 Methods for the formation of allylsilanes from geraniol, linalool, and myrtenol86 and... 

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