Of damascones

The synthetic chemistry of damascones and damascenones has been reviewed. New syntheses have been reported of /8-damascenone (141) from dimedone, of 3-hydroxy-/3-damascone (142) and 3-hydroxydihydro-/3-damas-cone (143),and of various damascones and their demethyl analogues. ... 

Methods for the synthesis of damascones by cross-aldol reactions and from a-cyclocitral (144) by treatment with ethyl diazo(lithio)acetate or 1-diazo-lithioacetone have been described. Eighteen new sesquiterpenoid theas-pirane derivatives, e.g. (145) and (146), have been prepared from the dehydro-jS-cyclonerolidol epoxide (147). Racemic theaspirane (148) and dihydroedulan (149) have been synthesized by photosensitized oxidation of dihydro-a-ionol (152) via (150) and (151). Other carotenoid-like compounds for which syntheses have been reported include 3/8-bromo-8-epicaparrapi oxide (153), ... 

The biogenesis of damascone starts from jS-carotene, which is enzymatically degraded. [32-34] The oxidative degradation of carotenoids [37] leads, for... 

With a-haloepoxides, ring opening occurs faster than addition, leading to an allylic alcohol.305 The overall transformation is an allylic transposition, which was used in the synthesis of damascone from ionone, 06 nd of an isomer of the antiviral Neplanocin (Fig. 58). ... 

Noma, Y, T. Etashimoto, and Y. Asakawa, 2001a. Microbiological transformation of damascone. Proc. 45th TEAC 93-95. 

Snowden has used the terminus fragmentation in his earlier papers for the P-cleavage of homoallylic alkoxides (Scheme 72). Such a reaction sequence (Scheme 73) has been used in particular for the synthesis of damascones (e.g. y-damascone 203) and related compounds. 

One of the most important discoveries recently made in the field of carotenoid aroma compounds relates to the class of damascones. Seven naturally occurring members (266) to (272) of this class are known today. The discovery of these new compounds started with the isolation of damascenone (268) from Bulgarian rose oil in 1970 120). Later, the same compound was detected in various tobacco brands 5, 110, 306), tea 491), raspberry oil 708), cooked apples 442), various grape and wine varieties 546, 549), beer 598), coffee oil 179), buchu leaf oil 283) and Roman camomile 638). 3-Hydroxy-(3-damascone (269) was shown to be an important aroma component of tobacco 108, 169, 285) in which it develops a green, rose-floral and sweet Burley-like note (556). (3-Damascone (267) was found in Burley tobacco 110) and rose oil 108), whereas a-damascone (266), accompanied by (3-compound (267) and damascenone (268), was exclusively observed in tea oil 491). Among the known cyclization products (270) to (272), the last two compounds were found in tobacco (779), while ketone (270) was detected in tea 491). 

Aldehydes (RCHO) react with 1-diazo-l-lithioacetone to give a-diazo- -hydroxyketones (48). These latter compounds can then be converted to P-diketones by the addition of rhodium(il) acetate a procedure which has been applied in the synthesis of -damascone. 1,6,6A -Trithiapentalene and a metal salt catalyse the lithiation of unactivated alkenes to alkenyl-lithiums by lithium metal, constituting a very useful method for preparing such compounds since in the past the preparation of alkenyl-lithiums from lithium metal has been confined to alkenes containing relatively acidic protons. Finally, the allenyl-lithium reagent (49) can be converted to various functionalized allenes by simple electrophiles. ... 

Of all these, probably P-phenethyl alcohol (2) comes closest to the odor of fresh rose petals however, mixing all these components does not reproduce the total fine character of the natural oil. It has been determined that a number of trace constituents representing less than 1% of the volatiles are critical to the development of the complete rose fragrance (10). These include cis- and trans-i.ose oxide (1), nerol oxide (12), rose furan (13), /)i7n7-menth-l-en-9-al (14), P-ionone (15), P-damascone (16), and P-damascenone (3). 

KH/HMPT is also useful for selective 3-cleavage of tris(homoallylic) alcohols, as shown by a new synthesis of a-damascone (4). In general, l,l-dimethyl-2-pro-penyl and benzyl groups are cleaved more readily than a l-methyl-2-propenyl group,... 

Examination of the flavour constituents of the passion fruit Passiflora edulis has yielded the novel ionone derivatives (47) and (48). Edulans 1 and II, (49) and (50), and dihydroedulans I and II, (51) and (52), from the same source have been characterized fully. Two bicyclodamascenones, (53) and (54), have been identified as components of the flavour of Virginia tobacco, and several ionone, damascone, and cyclocitral derivatives are present amongst the many volatile compounds produced during flue-curing of this tobacco. ... 

The acid-catalyzed cyclization of the chiral enamine (134) produces (R)-a-cyclocitral (135) and hence (R)-trans-a-damascone (136) in 33 % enantiomeric excess 152). 

Although a small amount of acyclic terpene acids such as geranic acid and citronel-lic acid occurs in many essential oils, often as esters, they are rarely used in perfume and flavor compositions. Methyl geranate is an intermediate in a-damascone synthesis and is sometimes needed in the reconstitution of essential oils. 

C13H20O, Mr 192.30, are ionone isomers. Depending on the position of the double bond in the ring, various isomers may exist. Commercially important are a-, (3-and -damascone. 

One synthetic route to the damascones starts with an appropriate cyclogeranic acid derivative (halide, ester, etc.). This is reacted with an allyl magnesium halide to give 2,6,6-trimethylcyclohexenyl diallyl carbinol, which on pyrolysis yields the desired l-(2,6,6-trimethylcyclohexenyl)-3-buten-l-one. Damascone is obtained by rearrangement of the double bond in the side-chain [98]. 

The material is prepared by Diels-Alder reaction of 1,3-pentadiene and mesityl oxide and subsequent aldol condensation of the resulting acetyl trimethyl cyclohexene with acetaldehyde [99]. 5-Damascone is used in perfumes to create masculine notes. 

Werkhoff P, Bretschneider W, Giintert M, Hopp R, Surburg H (1991) Chirospecific analysis in flavor and essential oil chemistry. Part B. Direct enantiomer resolution of trans-a-ionone and trans-a-damascone by inclusion gas chromatography. Z Lebensm Unters Forsch 192 111 Larsen M, Poll L (1990) Odour thresholds of some important aroma compounds in raspberries. Z Lebensm Unters Forsch 191 129... 

Zenoni G, Qrattrini F, Mazzotti M, Fuganti C, Morbidelli M (2002) Scale-up of analytical chromatography to the shmdated moving bed separation of the enantiomers of the flavor nor-terpenoids a-ionone and a-damascone. Flavour Fragr J 17 195... 

Such routes have been used for the synthesis of natural products terpenes such as egomaketone (3-(4-methyl-3-pentenoyl)furan, perillene, ar-turmerone and iso-ar-turmerone [341], ar-curcumene [152], artemisia and isoartemisia ketones [342, 343], damascone [344], macrolides such as maysine [345], and pheromones with the sex attractant of the pine saw-fly [346],... 

Hydrogenation of 2,4,4-trimethyl-2-cyclohexenone with rrans-RuCl2(tolbinap)(dpen) and (CH3)3COK under 8 atm of hydrogen gives 2,4,4-trimethyl-2-cyclohexenol quantitatively with 96% ee (Scheme 1.70) [256,275,276]. In this case, unlike in the reaction of aromatic ketones, the combination of the R diphosphine and S,S diamine most effectively discriminates the enantiofaces. The chiral allylic alcohol is a versatile intermediate in the synthesis of carotenoid-derived odorants and other bioactive terpens such as a-damascone and dihydroactinidiolide [277]. 

Dihydroxylation of allylsilanes with OSO4 has been investigated extensively. The reaction has been used for the synthesis of /J-damascone 179 (equation 152)270. 

Amrollah-Madjdabadi and Stella used a similar approach for the rapid and concise synthesis of y-damascone (30) in three steps starting from allyl bromide (28) and dimethylaminoacetonitrile (29).21 These investi-... 

Today there are several thousand synthetically produced aroma chemicals potentially available to the perfumer. Many of these—for example, vanillin, the rose oxides, and the damascones—were first discovered in nature and subsequently synthesized. Others are the fruit of a chemist s imagination and have never been found in nature. Of course not all are of equal value to the perfumer, and the number that are widely used runs into the hundreds rather than into the thousands. 

Paris also contains fruity notes, including alpha damascone and gamma-decalactone, which contrast with the green side of the violet accord. Violet and raspberry, both of which can contain ionones, form a natural association, and a trace of Frambinone can also work well in this context. 

Table 20.1 shows the detection thresholds of a number of perfume materials in air and in water. Note the tremendous range (from 0.002 parts per billion for beta-damascenone to 10,000 parts per billion for phenylacetic acid—both taken in water solutions), the large difference between optical isomers of the same substance (e.g., Nootkatone and alpha-damascone), and the large differences in thresholds reported by different investigators (e.g., benzaldehyde and vanillin). In substances with relatively high water solubility such as vanillin and ethyl vanillin, benzaldehyde, phenylethyl alcohol, and phenylacetic acid, the thresholds in water are very much higher than in air. In poorly water-soluble substances such as pinene and the macrocyclic musk cyclopentadecanolid, the reverse is true. The relative thresholds of a substance in different solvents indicate its performance in different application environments. Substances whose thresholds in water solution are much... 

Low-slope odorants typically do not seem very powerful when examined undiluted on a blotter and for this reason their value may be overlooked in the initial screening of new perfumery materials. They show their mettle only when used in actual applications. We suspect that materials such as the synthetic musks, Hedione, and the damascones are, among others, of this kind. 

Enantioselective protonation. (R)- and (S)-a-Damascone (4) have been prepared by a Grignard reaction followed by enantioselective protonation with l1 and 2,3 both available from (-)- or (+ )-ephedrine. Thus protonation of the ketone enolate 3 with (+ )-l or (- )-2 furnishes (S)- or (R)-a-damascone (4), respectively. 

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