Esters to aldehydes with

In 1990, Fukuyama and co-workers established a palladium-mediated reduction of thiol esters to aldehydes with Et3SiH (Eq. 19) [40]. 

Unique properties of solubility and reactivity are encountered when certain functionalized alcohols interact with lithium aluminum hydride. Sodium bis(2-methoxyethoxy)aluminum hydride ( Redal ), for example, is soluble in benzene even at —70°. It is possible to reduce esters to aldehydes with this reagent ... 

Another important transformation, the reduction of esters to aldehydes with lithium diisobutyl-tert-butoxyaluminum hydride (LDBBA) in flow, was performed in the laboratory of Janssen Pharmaceuticals [45]. DIBAL-H applied in their previous research [44] proved to be unsuccessful in reducing ethyl benzoate (la) to benzaldehyde (2a). LDBBA appeared to be the most general and effective alternative to DIBAL-H. The selective reduction of an ester group in the presence of an aldehyde, the selective reduction of a single ester group, and the selective reduction of a primary ester in the presence of a secondary ester are achieved with the efficiency that cannot be achieved under traditional batch conditions. 

Oxidation of Functionalized Alkenyl Boionic Esters to Aldehydes with Trimethylamine... 

The reduction of esters to aldehydes is carried out with hydrides such as NaH2Al(0CH2CH20CH2)2, NaALH, or... 

Carboxylic esters have been reduced to aldehydes with DIBALH at — 70°C, with... 

Hydrogenolysis of esters to aldehydes or alcohols needs high temperatures and high pressures. Moreover, it leads to the formation of acids, alcohols, and hydrocarbons. In contrast, bimetallic M-Sn alloys (M = Rh, Ru, Ni) supported on sihca are very selective for the hydrogenolysis of ethyl acetate into ethanol [181]. For example while the selectivity to ethanol is 12% with Ru/Si02, it increases up to 90% for a Ru-Sn/Si02 catalyst with a Sn/Ru ratio of 2.5 [182]. In addition, the reaction proceeds at lower temperatures than with the classical catalysts (550 K instead of temperatures higher than 700 K). The first step is the coordination of the ester to the alloy (Scheme 46), and most probably onto the tin atoms. After insertion into the M - H bond, the acetal intermediate decomposes into acetaldehyde and an ethoxide intermediate, which are both transformed into ethanol under H2. 

Similarly, esters are also reduced to aldehydes with DIBAL-H. 

Hydrogenolysis of esters to aldehydes or alcohols is difficult to attain either by homogeneous or heterogeneous catalysis. In fact, high temperatures and high pressures are required to achieve the reaction, leading to a non-selective hydrogenolysis with formation of acids, alcohols, CO2, CO and hydrocarbons. 

Desulfurization by refluxing with Raney nickel in 70% ethanol for 6 hours converted thiol esters to aldehydes in 57-73% yields (exceptionally 22% yield) [1101] ( Procedure 6, p. 205). Desulfurization of a dithioester, methyl dithio-phenylacetate, by refluxing with Raney nickel in 80% ethanol for 1 hour afforded 65% yield of ethylbenzene [1102]. 

To access anti-l,2-diols, indirect methods are required for the preparation of geometrically pure, chiral E-3-alkoxy reagents. To this end, the isomerization of alkenylboronic esters described above (Eq. 41), provides a reliable route to tartrate-derived E-3-siloxy allylboronate 99 (Fig. 7). The latter shows variable enantioselectivities in additions to aldehydes, with cyclohexanecarboxaldehyde affording the highest selectivity (Eq. 70). ... 

A methyl ester was formed by methanolysis of a trihalide (Equation 32) <2007S225>. Decarboxylation of the /3-ketoacid resulting from hydrolysis has also been reported (Equation 33) <1980LA1917>. A carboxylic acid substituent was reduced to aldehyde with LAH (Equation 34) <1974J(P1)2092>. Thiazine nitrogen probably participates in this reaction. 

Carboxylic esters have been reduced to aldehydes with DIBALH at -70°C, with di-aminoaluminum hydrides,1224 with LiAlH E NH,1226 and with NaAlH4 at -65 to -45°C, and (for phenolic esters) with LiAlH(0-/-Bu)3 at (fC.1227 Aldehydes have also been prepared by reducing ethyl thiol esters RCOSEt with Et3SiH and a Pd-C catalyst.1228... 

Preparation Essentially this reaction involves the preparation of a low-valent titanium reagent that then couples carbonyl groups, including esters to aldehydes/ketones. Generally, TiCLt is reduced with some reducing agent (LiAIH4, Zn, Mg). 

Fig. 14.53. Mechanism of the DIBAL reduction of carboxylic esters to aldehydes and further to alcohols. In nonpolar solvents the reaction stops with the formation of the tetrahedral intermediate A. During aqueous workup, A is converted into the aldehyde via the hemiacetal. In polar solvents, however, the tetrahedral intermediate A quickly decomposes forming the aldehyde via complex B. In the latter situation the aldehyde successfully competes with unreacted ester for the remaining DIBAL. The aldehyde is reduced preferentially, since the aldehyde is the stronger electrophile, and it is converted into the alcohol.

Originally devised as a method for the conversion of amino acids or amino acid esters to aldehydes. The Akabori reaction has been modihed for use in the determination of C-terminal amino acids by performing the reaction in the presence of hydrazine and for the production of derivatives useful for mass spectrometric identihcation. See Ambach, E. and Beck, W., Metal-complexes with biologically important ligands. 35. Nickel, cobalt, palladium, and platinum complexes with Schiff-bases of... 

The method has been used to prepare isotopically labelled amino acids. While Boc-BMI enolate adds to aldehydes with only moderate diastereoselectivity, reduction of the acylation products (5) gives allothreonine derivatives (6). Michael additions to o(,p-unsaturated esters, ketones, and nitro compounds lead to products of type (7) and (8) (for a general discussion see Suzuki and Seebach ). 

Enantioselective Addition of Dialkylzincs to Aldehydes with Functional Groups. Enantioselective and chemoselective addition of dialkylzincs to formyl esters using (15,2R)-DBNE as a catalyst affords optically active hydroxy esters. The subsequent hydrolysis of the esters affords the corresponding optically active alkyl substituted lactones with up to 95% ee (eq 13). ... 

The reduction method applied is typically used for the selective reduction of carboxylic esters to aldehydes. The reaction is carried out in non-coordinating solvents such as toluene or dichloromethane. In the first step the addition of a hydride takes place, which results in the formation of stabilized tetragonal intermediates. These intermediates withstand further reductions, because the essential elimination of an aluminum alkoxide species is unfavored in non-coordinating solvents. Finally, the Al-0 bond is broken during aqueous workup, yielding a hemiacetal, which equilibrates with the aldehyde. The mode of action is depicted in the margin. ... 

Allenylboronic acid, readily accessible from propargylic halides, on esterification with tartaric acid esters can also be induced to add to aldehydes with high enantioselectivity to give homopropargylic alcohols (Scheme 82). ... 

A device for getting extended enolates of esters to combine with aldehydes and ketones in the y position is to use a Wittig approach. The bromo-ester 28 is commercially available. Reaction with a trialkyl phosphite gives the phosphonate ester 29 that gives dienes such as 30 with aldehydes.11 Phosphonium salts can also be used.12... 

Reduction. At -78°, selective reduction of l-alkylindole-2,3-dicarboxylic esters at the C-2 substituent (to a CHO group) by Dibal-H is observed. Generally, the ester to aldehyde conversion can be performed at 0° with alkali metal diisobutyl(t-butoxy)aluminum hydride, which is formed by adding t-BuOM (M = Na, Li) to Dibal-H in THF. ... 

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