Tishchenko aldehyde-ester

Metal alkoxides cataly2e the Tishchenko condensation of aldehydes (62), the transesterification of carboxyhc esters, the Meerwein-Poimdorf reaction (63), and other enolization and condensation reactions. 

When aldehydes are reduced, the Tishchenko reaction may be a side-reaction. It is the result of an attack of the oxygen atom of the alkoxide on the carbonyl function of the aldehyde. In particular, aldehydes lacking an a-hydrogen atom such as benzaldehyde are prone to form esters (Scheme 20.24) [108]. It has been reported that many aldehydes can be converted into Tishchenko esters at room temperature, almost quantitatively and with high turnovers, using Sml2 catalysts [109] or a bi-aluminum catalyst [8],... 

The dimerization of aldehydes to form esters is a completely atom-efficient process known as the Tishchenko reaction, which involves no net oxidation or reduction. Suzuki, Katoh, and coworkers have used complex 77 to catalyze the Tishchenko reaction of a range of aldehydes, including dihydrocinnamaldehyde 91 and benzaldehyde 14 (Scheme 22) [81]. The same catalyst has been used for an intramolecular variant of the reaction, where keto-aldehyde 92 isomerizes to lactone 93 via an intramolecular Tishchenko reaction. The oxidized product is formed as a by-product,... 

In the aldol-Tishchenko reaction, a lithium enolate reacts with 2 mol of aldehyde, ultimately giving, via an intramolecular hydride transfer, a hydroxy ester (51) with up to three chiral centres (R, derived from rYhIO). The kinetics of the reaction of the lithium enolate of p-(phenylsulfonyl)isobutyrophenone with benzaldehyde have been measured in THF. ° A kinetic isotope effect of fee/ o = 2.0 was found, using benzaldehyde-fil. The results and proposed mechanism, with hydride transfer rate limiting, are supported by ab initio MO calculations. 

The coupling of two molecules of aldehydes into esters (Tishchenko reaction) has been used as an efficient method for the industrial preparation of dimeric esters. Although a number of systems for such reactions using transition-metal catalysts have been reported [73], there is stiU great room for improvement of the synthetic efficiency. 

The first report on organolanthanide-promoted Tishchenko reactions, that is, the transformation of aldehydes or mixed aldehydes into the corresponding esters, including a mechanistic proposal appeared in 1996 [catalyst Cp2 LnCH(SiMe3)2 with Ln = La and Nd] [233]. Two years later, lanthanide silylamide complexes Ln[N(SiMe3)2]3 were found as easily accessible and even more active catalysts (Scheme 12.24) [234, 235]. 

The Tishchenko reaction is a dimerization of aldehydes to the corresponding esters, which is classically carried out in homogeneous media using aluminum... 

When aldehydes, with or without a hydrogen, are treated with aluminum ethoxide, one molecule is oxidized and another reduced, as in 9-69, but here they are found as the ester. The process is called the Tishchenko reaction. Crossed Tishchenko reactions are also possible. With more strongly basic alkoxides, such as magnesium or sodium alkoxides, aldehydes with an a hydrogen give the aldol reaction. Like 9-69, this reaction has a mechanism that involves hydride transfer.751 The Tishchenko reaction can also be catalyzed752 by ruthenium complexes.753 by boric acid,754 and, for aromatic aldehydes, by disodium tetracarbonylferrate Na2Fe(CO)4,755 OS I, 104. 

Aldehydes and Ketones. Esters are obtained readily by condensation of aldehydes in the presence of alcoholate catalysis such as aluminum ethylate, AI(OC H5) , by the Tishchenko reaction. 

TISHCHENKO REACTION. Formation of esters from aldehydes by an oxidation-reduction process in the presence of aluminum or sodium alkoxidcs. 

An outstanding input into the chemistry of metal alkoxides was made by the dissertation of V. E. Tishchenko, which was devoted to aluminium alkoxides. It was published in 1899 (unfortunately only in Russian) [1585] and—in contrast to his works on organic chemistry — is practically unknown by foreign chemists. A number of general synthetic approaches to metal alkoxides have been developed. The main regularities for the variation of the properties in the homologous sales and ramification of the radical were found to determine the main directions of the thermal decomposition. He made also the proposal to use the Al(OR)3 in ester condensation of aldehydes (Tishchenko reaction) (see also Chapter 12, Section 12.5). 

The Tishchenko Reaction is a disproportionation reaction that allows the preparation of esters from two equivalents of an aldehyde. 

The mixed Tishchenko reaction involves the reaction of the aldol prodnct 113 from one aldehyde with another aldehyde having no a-hydrogens to yield an ester The products were proposed to be formed through an aldol step (equation 33), followed by addition of another aldehyde (equation 34) and an intramolecular hydride transfer (equation 35). However, several aspects of this mechanism need to be clarified. As part of the continuing mechanistic studies carried out by Streitwieser and coworkers on reactions of alkali enolates ", it was found that the aldol-Tishchenko reaction between certain lithium eno-lates and benzaldehyde proceeded cleanly in thf at room temperature". Reaction of the lithium enolate of isobutyrophenone (Liibp) with 1 equiv of benzaldehyde in thf at — 65 °C affords a convenient route to the normal aldol product 113 (R = R" = Ph, R = Me). At room temperature, however, the only product observed after acid workup was the diol-monoester 116, apparently derived from the corresponding lithium ester alcoholate (115, R = R" = Ph, R = Me), which was quantitatively transformed into 116 after quenching. As found in other systems", only the anti diol-monoester diastereomer was formed. 

Sarains A-C are a family of alkaloids isolated from marine sponges. J.K. Cha and co-workers accomplished the synthesis of the western macrocyclic ring of sarain To establish the C3 quaternary stereocenter, they treated the aldehyde substrate with formaldehyde in the presence of sodium carbonate. The aldehyde substrate underwent an aldol reaction followed by a Tishchenko reaction to provide the formate ester of the 1,3-diol product. This ester was hydrolyzed in situ under the reaction conditions and the 1,3-diol was isolated. 

Tishchenko reaction Conversion of aldehydes to the corresponding esters in the presence of metal alkoxides. 456... 

Tishchenko, W. The effect of aluminum alcoholates on aldehydes. The ester condensation as a new condesationform of aldehydes. Chem. Zentr. 1906, II, 1309-1311. 

Yokoo, K., Mine, N., Taniguchi, H., Fujiwara, Y. Chemistry of organolanthanoids lanthanoid-catalyzed Tishchenko condensation of aldehydes to esters. J. Organomet. Chem. 1985, 279, C19-C21. 

Tishchenko reaction When aldehydes are treated with aluminium ethoxide, one molecule is reduced while the other is oxidised, and the product is the resulting ester.This reaction involves a hydride anion transfer. With more basic alkoxides, aldehydes with an a-hydrogen undergo the aldol reaction. 

Tishchenko reaction Various aldehydes undergo Tishchenko reaction to give esters. 

RuH2(PPh3)4 reacts with aldehydes to give esters via Tishchenko-type dimerization. For example, benzaldehyde is converted to benzyl benzoate by RuH2(PPh3>4(eq (45)) [166-167]. This reaction involves C—H bond activation of the formyl proton followed by formation of a ruthenium acyl alkoxide complex Ru(OCH2Ph)(COPh)(PPh3)4. 

When this polymerization reaction was studied for monomers such as 2,3-epoxypropanal (above) or 2,3-epoxybutanal, however, an unusual Initiation step was found to take place by the Tishchenko-Claisen reaction, which is a well-known disproportionation reaction of aldehydes to esters, and an intermediate product, the dlepoxyester was identified. This intermediate product on polymerization formed, up to about 20% conversion, linear polyethers with both oxlrane and ester side groups by an epoxy ring-opening reaction, as follows ... 

Alkoxides can cause dimerization of aldehydes. Thus, according to observations by Tishchenko,508 the catalytic action of aluminum or magnesium alkoxides provides a method of preparing esters whose alcoholic and acidic components have the same number of carbon atoms the general scheme, according to a reaction ... 

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