Pseudoionone, synthesis

Finally, we remark that precisely because of its strong basicity, low coordination oxygen atoms O " are very reactive and may reconvert to surface OH" in the presence of water formed during the pseudoionone synthesis (see reachon scheme 1). Recent reports confirm that the surface of metal oxides with basic character are often restructuring during the reaction (15). Thus, the formation of pseudoionones on Li-doped MgO may be accompanied by the gradual modification of the catalyst surface, by reconverting... 

The isophytol side chain can be synthesized from pseudoionone (Fig. 5) using chemistry similar to that used in the vitamin A synthesis (9). Hydrogenation of pseudoionone (20) yields hexahydropseudoionone (21) which can be reacted with a metal acetyUde to give the acetylenic alcohol (22). Rearrangement of the adduct of (22) with isopropenyknethyl ether yields, initially, the aHenic ketone (23) which is further transformed to the C g-ketone (24). After reduction of (24), the saturated ketone (25) is treated with a second mole of metal acetyUde. The acetylenic alcohol (26) formed is then partially hydrogenated to give isophytol (14). 

Fig. 5. Synthesis ofisophytol (14) pseudoionone [141-10-6] (20), hexahydropseudoionone [1604-34-8] (21), C -acetylenic alcohol [1604-35-9] (22), C g-aUenic ketone [16647-10-2] (23), C g-diene ketone [1604-32-6] (24), C g-saturated ketone [16825-16-4] (25), and C2Q-acetylenic alcohol [29171-23-1] (26).

Pseudoionones (PS) are valuable intermediate compounds for the synthesis of a and P-ionones, which are widely used as pharmaeeuticals and fragranees. In partieular, P-ionone is the preferred reactant for different synthesis proeesses leading to vitamin A (1). Pseudoionones are commercially produced via the aldol eondensation of eitral with acetone in a liquid-phase process involving the use of diluted bases, sueh as NaOH, Ba(OH)2, LiOH, which pose problems of high toxieity, eorrosion, and spent base disposal (2). The eonsecutive cyelization of pseudoionones to yield a and P-ionones is catalyzed by strong liquid aeids. The two-step proeess for ionone synthesis is depicted in equation (1). 

Synthesis of Pseudoionones by Aldol Condensation of Citral with Acetone on... 

Methyl-5-hepten-2-one is an important intermediate in the synthesis of terpenoids. Its odor properties are not impressive. It occurs in nature as a decomposition product of terpenes. Tagetone [6752-80-3] is a major component of tagetes oil. Solanone [1937-45-8] and pseudoionone [141-10-6] are acyclic Cn ketones with a terpenoid skeleton. Solanone is one of the flavor-determining constituents of tobacco, pseudoionone is an intermediate in the synthesis of ionones. 

In the synthesis of vitamin A, the dependence on natural sources as well as steadily increasing production via /3-ionone as an intermediate have led to the development of a method for synthesizing citral from dehydrolinalool (see p. 37). More recent routes employ dehydrolinalool as the starting material for pseudoionone. Dehydrolinalool is converted into pseudoionone by using either diketene [92] or a suitably substituted acetoacetate (Carroll reaction) [93] ... 

The raw material, myrcene (15 FF/Kg), is significantly cheaper than linalool (40 FF/Kg), the feedstock in the existing process.54 Furthermore, the intermediate P-ketoesters can be used for the synthesis of pseudoionone a key intermediate for the manufacture of vitamin A (world market for vitamin A 3 000 t/a at a price of 40-50 /kg).54>504... 

The biomimetic-type cyclization of polyisoprenoids is an important industrial process for terpene synthesis. In most cases, a large excess of coned. H SO and SnCl. has been employed For example, ionone, a precursor of vitamin A, is prepared by coned. H2SO4 catalyzed cyclization of pseudoionone. The disadvantage of this process is undoubtedly the requirement of bases to neutralize the large excess of acid. The EGA method offers a promising alternative for this purpose. Thus, Electrolysis of 15 and 17 in a ClCHjCH Cl—LiClO —Et NClO — (Pt) system provides 16 and 18, respectively in reasonable yields and the neutralization of the reaction solution can be performed simply by addition of a small amount of pyridine... 

Rehydrated Mg/Al LDH have also been used successfully for the synthesis of several fine chemicals of industrial or pharmacological interest, i.e. jasminaldehyde (a-M-amylcinnamaldehyde), chalcones such as vesidryl (2, 4,4 -trimethoxychalcone) and pseudoionones (6,7-dimethyl-3,5,9-undecatrien-2-one) by aldol and Claisen-Schmidt condensations/13,1091... 

Climent, M. J., Corma, A., Iborra, S. and Velty, A. Synthesis of pseudoionones by acid and base solid catalysts, Catal. Lett., 2002, 79, 157-163. 

The synthesis of dehydro-linalool (28) lehes on the basic chemicals acetone and acetjiene. Addition of a metal acetyhde to acetone yields methylbutynol (33). Semihydiogenation affords the alkene (34) which is reacted with i-propenylmethyl ether. A Cope rearrangement of the adduct yields methylheptenone (35). Addition of a second mole of metal acetyhde to dehydto-hnalool (28) is followed by a second Cope rearrangement to yield pseudoionone (26) (9,21) (Fig. 7). 

The reaction provides a useful synthesis of pseudoionone (6) from dehydrolinalool (4). 

The selective synthesis of pseudoionone is achieved by the acetylenic oxy-Cope rearrangement of 4-isopropenyl-3,7-dimethyl-6-octen-l-yn-3-ol (37) in A-methylpyrrolidone (NMP) as solvent containing a trace of hydrobromic acid, or iodine772,1127. 

Pseudoionone, which is an important starting material for the synthesis of vitamin A, can be prepared in 50% yield from citral and acetone in the presence of sodium ethoxide in ethanol.938... 

Some other products of interest are pseudoionones [54, 243, 260] and methyl pscudoionones [181], resulting from aldol condensation between citral and acetone or methyl ethyl ketone, respectively Fij ttre 16). Subsequent cyclalion of (methyl) pseudoionones over acid catalysts yields (methyl) ionones. lonones are cyclic terpenoids which have extensive uses as medicinal products, fragance materials and as intermediates in vitamin A synthesis. 

Diez. VK Capiianich, M Apesteguia, CR Di Cosimo, Jl. Liquid-phase synthesis of pseudoionones by aldol condensation of ciiral with acetone on Mg-based catalysts. Proceedings of the Sth ICC. Paris f France) 2004. Reference P5-I33. 

All industrial syntheses of ionones proceed by way of pseudoionones. These maybe obtained either hy the still employed Tiemarm synthesis, i.e. aldol condensation of citral with acetone, or by the Saucy-Marbet reaction starting from dehydrolinalool. 

Rhone-Poulenc has developed a route to pseudoionone along a three-stage synthesis based on myrcene, which itself is obtainable in one step from isoprene (cf. section 3.4 Menthol). Myrcene is treated with methyl acetoacetate in presence of a rhodium catalyst thereby the terminal double bond is isomerised into the chain. After transesterification with aUyl alcohol, there follows a palladium-catalysed decarboxylation. All by-products are readily volatile. [62]... 

Cyclization of pseudoionone to P-ionone is an important reaction used in the synthesis of vitamin A. Conventionally, pseudoionone is slowly dosed to a stirred tank reactor containing a biphasic mixture of concentrated sulfuric acid and an organic solvent to control the temperature of the highly exothermic reaction [88]. The reaction takes place in the acid phase, where by-products are formed very quickly. The by-product formation is observed to increase with increasing temperature. The product yield obtained in conventional semibatch reactors is in the range of 70%. 

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