Esters reductive carbonylation

Esters. Reductive carbonylation in the presence of an alcohol or phenol leads to an ester. Substrates include organoiodonium salts and allylic alcohols. p,y-Unsaturated thioesters can be generated by the method or from allenes. Note that y-lactones are formed when allylic alcohols are carbonylated without additives. ... 

The mechanism of the reaction is as shown in equations (13.139) and (13.140). This reaction is also catalyzed by compounds of other metals of groups 8 and 9 such as ruthenium and iridium. Higher alcohols EtOH, Pr"OH, Pr OH also undergo carbonylation to give corresponding carboxylic acids.However, the rate of the reaction is lower. It is assumed that in this case, the oxidative addition of alkyl iodide to the rhodium(I) complex proceeds according to a radical mechanism. Hydrocarboalkoxylation, carbonylation of esters, reductive carbonylation of... 

Carbonylation glycolic acid, gfycolic acid esters Reductive carbonylation ethylene gfycol, gfycolaldehyde... 

Reduction of anilines containing acid, ester, or carbonyl functions provides a convenient entry to bi- and tricyclic systems, cyclization occurring once the rigidity of the aromatic ring has been lost through saturation (1,2,61,77). 

Enantiomerically pure /J-keto sulfoxides are prepared easily via condensation of a-lithiosulfinyl carbanions with esters. Reduction of the carbonyl group in such /J-keto sulfoxides leads to diastereomeric /J-hydroxysulfoxides. The major recent advance in this area has been the discovery that non-chelating hydride donors (e.g., diisobutylaluminium hydride, DIBAL) tend to form one /J-hydroxysulfoxide while chelating hydride donors [e.g., lithium aluminium hydride (LAH), or DIBAL in the presence of divalent zinc ions] tend to produce the diastereomeric /J-hydroxysulfoxide. The level of diastereoselectivity is often very high. For example, enantiomerically pure /J-ketosulfoxide 32 is reduced by LAH in diethyl ether to give mainly the (RR)-diastereomer whereas DIBAL produces exclusively the (.S R)-diastereomer (equation 30)53-69. A second example is shown in... 

Rhodium compounds have also been used as catalysts since the late 1960s and mechanistic studies date from the 1970s.534,578-582 The binuclear rhodium complex [(Ph3P)4Rh2(//-OH)2] was found to be an effective catalyst for the reductive carbonylation of nitrobenzenes to carbamate esters. Electron-withdrawing groups at the para-position enhance the reactivity of the substrate.583... 

Carbon-carbon double bonds alkene to alkane reductions, trisubstituted alkenes, 40 ketone-alcohol reduction, 77, 86-87 a,p-unsaturated ester reduction, 93-96 Carbonyl compounds ... 

Treatment of the /3-keto ester 220 with sodium ethoxide at elevated temperature triggered off an epoxide ring opening by / -elimination that was followed by the desired Knoevenagel condensation to afford the tricyclic product 206 (Scheme 34). The enone moiety in the intermediate 221 did not show a propensity for deprotonation and, therefore, the ketone carbonyl function of the enone moiety was available for a Knoevenagel condensation. The reduction of the p-keto ester (206) to the corresponding diol was the next objective. Treatment of the TES-protected -keto ester (TES-206) with DIBAH afforded the diastereomeric diols 222 and 223 in a moderate diastereoselec-tivity in favour of the undesired diastereomer 222. The diastereomers were separated and the undesired diastereomer 222 was epimerized to 223 by a sequence that consists of Mitsunobu inversion and benzoate ester reduction [98, 99]. 

Acetaldehyde Production by Reductive Carbonylation of Methanol, Methyl Ketals, and Methyl Esters... 

Acetaldehyde is obtained from the reaction of synthesis gas with methanol, methyl ketals or methyl esters. The reactions are carried out with an iodide-promoted Co catalyst at 180-200 °C and 2000-5000 psig. In comparing the various feedstocks, the best overall process to make acetaldehyde involves the reductive carbonylation of methyl esters. In this case, acetaldehyde selec-tivities are > 95% ut acceptable rates and conversion. 

Me have studied the Co-I-PPh catalyzed reductive carbonylation of methanol, dimethyl ketalsf dimethyl carbonate and methyl esters ( 10 JL5 >2 ) 0 goal was to achieve high acetaldehyde... 

Reductive Carbonylation of Methyl Esters. The best alternative, and in our opinion, the best reported synthesis gas based process to produce acetaldehyde, is the reductive carbonylation of methyl esters. Equation 15 (16). 

Rhodium(II) acetate catalyzes C—H insertion, olefin addition, heteroatom-H insertion, and ylide formation of a-diazocarbonyls via a rhodium carbenoid species (144—147). Intramolecular cyclopentane formation via C—H insertion occurs with retention of stereochemistry (143). Chiral rhodium (TT) carboxamides catalyze enantioselective cyclopropanation and intramolecular C—N insertions of CC-diazoketones (148). Other reactions catalyzed by rhodium complexes include double-bond migration (140), hydrogenation of aromatic aldehydes and ketones to hydrocarbons (150), homologation of esters (151), carbonylation of formaldehyde (152) and amines (140), reductive carbonylation of dimethyl ether or methyl acetate to 1,1-diacetoxy ethane (153), decarbonylation of aldehydes (140), water gas shift reaction (69,154), C—C skeletal rearrangements (132,140), oxidation of olefins to ketones (155) and aldehydes (156), and oxidation of substituted anthracenes to anthraquinones (157). Rhodium-catalyzed hydrosilation of olefins, alkynes, carbonyls, alcohols, and imines is facile and may also be accomplished enantioselectively (140). Rhodium complexes are moderately active alkene and alkyne polymerization catalysts (140). In some cases polymer-supported versions of homogeneous rhodium catalysts have improved activity, compared to their homogenous counterparts. This is the case for the conversion of alkenes direcdy to alcohols under oxo conditions by rhodium—amine polymer catalysts... 

Ketones are more reactive toward nucleophiles than esters. Reduction therefore occurs at the ketone carbonyl group, to give... 

In dissolving-metal ester reduction, the ester carbonyl is believed to accept an electron to form a radical oxyanion 37 (Scheme 12.12). Chelation with a lithium counterion then ensues to produce a tertiary radical 38 which then captures a second electron to become a carbanion. Protonation of 39 next yields 40, whose fate is to collapse to aldehyde 41. Another multiple electron transfer/protonation sequence subsequently yields the product alcohol 46. 

One-Electron Reductions of Carbonyl Compounds and Esters Reductive Coupling... 

Alternatively, the electron-withdrawing properties of the a-heteroatom and its ability to coordinate Sml2 may facilitate reduction of the ester carbonyl group and formation of ketyl radicals 37 (Scheme 4.22). Once the activating heteroatom group has been removed, no further ester reduction is possible. A similar mechanism is possible for the reduction of a-heteroatom-substituted amides. 

Mechanism The mechanism of acids and esters reduction with LiAlH4 is shown in Schemes 6.9 and 6.10, respectively. The acidic hydrogen in acid reacts first. Then the reduction of carbonyl group proceeds via the usual alkoxyaluminate intermediate. 

Diels-Alder cycloadditions occur on the endo face when the unsaturated bicyclic lactam is treated with 1,3-dienes such as Iso-prene (eq 10). Ester reduction followed by organolithium addition to the lactam carbonyl group and subsequent hydrolysis affords a variety of enantiopure functionalized cyclohexenes. ... 

Ester reduction. A method for the conversion of dicarboxylic acids to CD-hydroxycarboxylic acids involves formation and reduction (with NaBH ) of dilactones in which the two carbonyl residues are linked by tm OCH2O chain. Arylpyruvic esters can be reduced to either the a-hydroxy esters or 1,2-diols. ... 

The reductive carbonylation of propargyl alcohols in the presence of thiols which results in P,y-unsaturated thioesters is in contrast to the formation of 5-hydroxy-2,3-alkadienoic esters from ethynyloxiranes. 

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