Ketones nootkatone

Some examples of conjugate addition reactions of allylic silanes are given in Scheme 9.5. Entries 1 to 3 illustrate the synthesis of several (3-allyl ketones. Note that Entry 2 involves the creation of a quaternary carbon. Entry 4 was used in the synthesis of a terpenoid ketone, (+)-nootkatone. Entry 5 illustrates fluoride-mediated addition using tetrabutylammonium fluoride. These conditions were found to be especially effective for unsaturated esters. In Entry 6, the addition is from the convex face of the ring system. Entry 7 illustrates a ring closure by intramolecular conjugate addition. 

The sesquiterpene ketone nootkatone is primarily responsible for the characteristic aroma of grapefruit oil [370a], [370d], [372-379a]. 

The sesquiterpene (C15) molecules include structures like hydrocarbons () -bisabolene, j3-caryophylene), alcohols (famesol, carotol, patchoulol), ketones (nootkatone) and aldehydes (anisaldehyde, valerenal). 

Two bacterial strains, one from soil and the other from infected local beer, which utilised calarene as the sole source of carbon and energy have been isolated by enrichment culture techniques [149]. Both these bacteria were adapted to grow on valencene as the sole carbon source. Fermentations of valencene (5) by these bacteria of the genus Enterobacter in a mineral salts medium yielded several neutral metabolic products dihydro alpha-agarofuran (200) (7.5%), nootkatone (6) (12%), another ketone (201) (18%) and a-cyperone (202) (8%), Fig. (40). 

Some reported odor threshold values for nootkatone were considerably lower than the taste threshold values. Odor thresholds of 0.8 ppm in water and 30 ppm in air were reported for (+)-nootkatone, the enantiomer of this sesquiterpene ketone present in grapefruit (35). An odor threshold of 0.15 ppm in water was reported for crystalline nootkatone isolated from grapefruit oil (36). In that study, mother liquor from crystallization of nootkatone was 30 times more potent (odor threshold of mother liquor 5 ppb) than nootkatone alone and the panel felt that the aroma of the mother liquor more closely resembled grapefruit aroma... 

The 1,5-diketone formation by the Michael addition of allylsilane (48) to a, -unsaturated ketones was applied to the synthesis of (+)-nootkatone. Reaction of the keto group of keto aldehyde (58) with allyl Orignard reagent and dehydration gave the diene aldehyde (59). The selective oxidation of the terminal double bond afforded the 1,5-dica nyl compound (60), which is not stable and converted directly to pyridines and phenols (Scheme 18). ... 

The flavour properties of the citrus oils are based on compounds like aldehydes, esters and alcohols. Aldehydes play the most important role in citrus flavours. Mainly the saturated C-8, C-10 and C-12 long-chain constituents as well as the terpenoid aldehydes citral (a mixture of neral and geranial) and citronellal form the basic notes of the fresh and pleasant citms flavour. Also sesquiterpene aldehydes and ketones, such as sinensal or nootkatone, are significant for citms flavours. The aldehyde content, therefore, is frequently used as a quality criterion for citms oils. Important citms alcohols are linalool, octanol, a-terpineol (especially in distilled lime oil) and ter-pinen-4-ol. Furthermore, esters contribute to the flavour properties of citms oils. Especially the acetates of geraniol and nerol and, to a lesser extent, citronellol are... 

In connection with potential routes to sesquiterpenoids of the eremophilane and valencane classes, Marshall and Ruden have found that acid-catalysed cleavage of the cyclopropyl ketone (284) gives exclusively the enone (285). This is in contrast to the epimeric ketone (286) which yields predominantly (287). Leitereg has found that Robinson annelation of (-H )-dihydrocarvone with frans-3-penten-2-one gives as a major compound the bicyclic enone (288) which is isomeric with (-f- )-nootkatone (242). The full paper on the structures of a- (289) and j -rotunol (290) has been published. 

Ketones quantitated in orange oil are carvone, an oxidation product of limonene, found at 0.1% or less, and nootkatone, found at extremely low levels of < 0.01% of peel oil. 

The eremophilane derivative (-h)-nootkatone (195) has been valued for its most important contribution to the distinctive flavor of many citrus oils, in particular of grapefruit peel oil Citrus paradisi, Macfayden) 371, 372). Qualitative 211, 313, 453, 591) and quantitative 38, 211, 313, 591, 630) aspects of this aroma compound have been treated. The naturally occurring (-h)-nootkatone (195) is detectable at 1 ppb in water (33). The both enantiomeric forms of ketone (195) differ not only... 

An example of monocyclic sesquiterpenic alcohols is (-l-)-o(-bisabolol (8-24). It occurs in citrus essential oils along with other sesquiterpenic alcohols, and represents the major component of the essential oil of chamomile flowers (Matricaria chamomilla, Asteraceae). a-Bisabolol (0.26%) and other sesquiterpenoids, such as monocyclic sesquiterpenic alcohol (Z)-lanceol (1.7%), bicyclic sesquiterpenic alcohol (Z)-a-essential components of white sandalwood oil (Santalum album, Santa-laceae) used in perfumery, cosmetics and aromatherapy. (Z)-Lanceol is also a component of sage species (Salvia spp., Lamiaceae) essential oil. Sesquiterpenic bicyclic alcohol (-F)-P-nootkatol is the precursor of ketone (-F)-nootkatone, an important component of grapefruit essential oil. Trivial and systematic names of the main sesquiterpenic alcohols are listed in Table 8.7. 

Monocyclic sesquiterpenic ketone (-f)-flr-turmerone (8-52) is the main component (25-50%) of turmeric essential oil (see Table 8.32). It is formed by oxidation of hydrocarbon (-l-)-flr-curcumene, which is present in turmeric rhizomes at a level of about 6%. Bicyclic sesquiterpenic ketone is (-l-)-nootkatone (8-52), which is an important odorous compound of grapefruits formed by oxidation of hydrocarbon (-l-)-valencene via alcohol (-l-)-P-nootkatol. Another oxidation product of valencene is... 

The nootkatones are bicyclic ketones that contribute to the flavor and aroma of grapefruits [in addition to 2-(4-methyl-3-cyclohexenyl)-2-propanethiol. Section 9-11]. Nootkatone is also an environmentally friendly insecticide repellent against ticks, mosquitos, and termites. Fill in the missing reagents in the partial synthetic sequence for the preparation of isonootkatone shown below. More than one synthetic step may be needed for each transformation. 

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