6-Damascone synthesis

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. 

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,... 

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-... 

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

The damascones are a group of materials related to the ionones, but in which the enone unit is transposed. They are components of rose oils and have very intense fruity-floral odours. The damascenones, which contain a second double bond in the ring, are also very much sought after. One synthesis of a-damascone from methyl a-cyclogeranate is shown in Scheme 4.40. A double Grignard addition gives the tertiary alcohol. Heating of this in the presence of base, to prevent elimination... 

So, for example, the natural product a-damascone (9) cydises to (10) in add solution. The disconnection is of the bond (a in 11) opposite the carbonyl group in the five-membered ring and the synthesis is carried out by treating the dienone (12) with add or Lewis add. ... 

Diels-Alder catalyst (4, 10-11). Details for the synthesis of j3-damascone and 3-damascenone by the Diels-Alder reaction are now available. ... 

The ready availability of ionones as potential starting materials, was exploited by Btichi in an elegant synthesis of p-damascone (8.69) and... 

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), ... 

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