Palladium aldehyde hydrogenation

To ensure complete oxidation of aldehydes to carboxylic acids, Aulin-Erdtman and Tomita (1963) treated the ozonation products of lignin model compounds with hydrogen peroxide. Soteland (1971) applied hydrogen peroxide to a groundwood ozonation product and found that it degraded the components to unidentified volatile substances. To simplify the product mixture, reduction is sometimes used to stop further oxidation. Tanahashi et al. (1975) applied palladium-catalyzed hydrogenation, while Kondo et al. (1987) added dimethyl sulfide. 

Heteroatom-substituted carbohydrates are efficiently assembled by the enzymatic aldol condensation of DHAP with an appropriately appended aldehyde. Iminocyclitols that are inhibitors of glycosidases, such as deoxynojirimycin and deoxymannojirimycin, are simply prepared by condensation of azo-substituted aldehydes under the FDP protocol followed by dephosphorylation and palladium mediated reductive animation (Scheme 5.18a).39 In addition a number of polyhydroxylated pyrrolidines that are efficient glucosidase inhibitors have been synthesized by this chemo-enzymatic strategy (Scheme 5.18 ).1" 30,40 If the palladium mediated hydrogenation is done in the presence of hydrochloric acid, an amino-sugar intermediate is formed as its hydrochloride salt. Treatment with base then forms polyhydroxylated imines, instead of iminocyclitols (Scheme 5.19).41... 

Treatment of 2 with 3 equiv of 3-phenyl-2-propenal in refluxing toluene-cfe while the reaction progress was monitored by H NMR spectroscopy resulted in the disappearance of the aldehyde hydrogen peak (5 1.56). The IR spectrum of 4 shows a new absorption due to a vC-o stretch at 1448 cm 1. The mass spectrum of the product shows a molecular ion at m/z 538. To our surprise, an X-ray study of 4 showed it to be the insertion product of the two carbonyl ligands into the C-Si bond in 2. The reaction has the potential for developing a new method for double C-C bond formation between the carboranyl unit and carbonyl compounds. Such an insertion of the carbonyl functionality into the o-carborane has been observed in Yamamoto s work on the chemoselective addition of o-carborane to the aldehyde groups by a palladium-catalyzed9 or a fluoride-promoted reaction.10... 

In these catalytic carbonylation reactions, metallic palladium and hydrogen halides are essential for the catalysis. Furthermore, olefins react with carbon monoxide and hydrogen in benzene in the presence of metallic palladium to form aldehydes in a low yield (19). 

Based on the fundamental studies, conversion of anhydrides to corresponding aldehydes and carboxylic acids has been found to be catalyzed by a Pd(0) complex in the presence of H2 (Eq. 30) [75]. Prior to the report of palladium-catalyzed hydrogenation of acyclic anhydrides, cobalt carbonyl was found to convert anhydrides into aldehydes and carboxylic acids under more severe conditions [76]. 

Palladium is usually the prefeired metal of choice for aromatic aldehyde hydrogenation in neutral non-polar solvents such as hexane, DMF, or ethyl acetate (5-100 °C and 1-10 bar) although ruthenium, which is less active, can be considered and run in aqueous alcohol at similar temperatures and pressures. If higher pressures are accessible ruthenium may be preferable because of its lower (historical) cost. Its use has recently been reviewed [4]. Although platinum and rhodium could... 

A stereochemical study reported by Henry illustrated that the formation of aldehyde and formation of chlorohydrin occur with different stereochemistry, and this result implies that one process occurs by syn addition and one by anti addition of water and palladium across the olefin. This study is summarized in Scheme 16.24. Oxidation of the non-race-mic, chiral allyl alcohol in the absence of added chloride forms the (R)-(E)-alcohol, whereas reaction of the allyl alcohol in the presence of added chloride forms the product with stereochemistry resulting from the opposite mode of attack. Because it is known that the allylic alcohol binds to palladium with hydrogen bonding between the hydroxyl group and the bound chloride, Henry concluded that the reaction conducted in the presence of high concentrations of added diloride occurs by external attack of the oxygen nucleophile, while the reaction with low concentrations of added chloride occurs by insertion of the olefin into a Pd-0 bond. ... 

Several reduction methods are available to convert nitriles (Stephen reaction) or acyl chlorides (Rosenmund reduction) or amides to aldehydes. The use of lithium aluminum hydride at low temperatures or lithium triethoxyaluminum hydride appears to be a more effective means of reduction than the stannous chloride-HCl used in the Stephen method or palladium and hydrogen used in the Rosenmund reduction. 

The most obvious way to reduce an aldehyde or a ketone to an alcohol is by hydro genation of the carbon-oxygen double bond Like the hydrogenation of alkenes the reac tion IS exothermic but exceedingly slow m the absence of a catalyst Finely divided metals such as platinum palladium nickel and ruthenium are effective catalysts for the hydrogenation of aldehydes and ketones Aldehydes yield primary alcohols... 

The reaction is used for the chain extension of aldoses in the synthesis of new or unusual sugars In this case the starting material l arabinose is an abundant natural product and possesses the correct configurations at its three chirality centers for elaboration to the relatively rare l enantiomers of glucose and mannose After cyanohydrin formation the cyano groups are converted to aldehyde functions by hydrogenation m aqueous solution Under these conditions —C=N is reduced to —CH=NH and hydrolyzes rapidly to —CH=0 Use of a poisoned palladium on barium sulfate catalyst prevents further reduction to the alditols... 

Aromatic Aldehydes. Carbon monoxide reacts with aromatic hydrocarbons or aryl haHdes to yield aromatic aldehydes (see Aldehydes). The reaction of equation 24 proceeds with yields of 89% when carried out at 273 K and 0.4 MPa (4 atm) using a boron trifluoride—hydrogen fluoride catalyst (72), whereas conversion of aryl haHdes to aldehydes in 84% yield by reaction with CO + H2 requires conditions of 423 K and 7 MPa (70 atm) with a homogeneous palladium catalyst (73) and also produces HCl. 

Rosenmund reaction is the action between acid chloride and hydrogen in the presence of palladium catalyst to produce aldehydes... 

According to Skita, the reaction proceeds in a different manner if the reduction be effected with palladium chloride and hydrogen. In this case the citral in alcoholic solution is mixed with an aqueous solution of palladium chloride and the whole thickened with gum-arabic. Hydrogen gas is then forced into this solution under pressure. The products of the reduction include citronellal and citronellol and a di-molecular aldehyde, C Hj O, which probably has the following constitution —... 

Reduction of unsaturated carbonyl compounds to the saturated carbonyl is achieved readily and in high yield. Over palladium the reduction will come to a near halt except under vigorous conditions (73). If an aryl carbonyl compound, or a vinylogous aryl carbonyl, such as in cinnamaldehyde is employed, some reduction of the carbonyl may occur as well. Carbonyl reduction can be diminished or stopped completely by addition of small amounts of potassium acetate (i5) to palladium catalysts. Other effective inhibitors are ferrous salts, such asferroussulfate, at a level of about one atom of iron per atom of palladium. The ferrous salt can be simply added to the hydrogenation solution (94). Homogeneous catalysts are not very effective in hydrogenation of unsaturated aldehydes because of the tendencies of these catalysts to promote decarbonylation. 

Anhydrides are reduced with relative ease. McAlees and McCrindle 20) established the following increasing order of difficulty for various carbonyls acid chlorides > aldehydes, ketones > anhydrides > esters > carboxylic acids > amides. Reduction may proceed by 1,2-addilion of hydrogen or by cleavage of an oxygen-carbonyl bond. If 1,2-addition to the carbonyl occurs, as in the presence of strong protic acids over palladium, 1,1-diesters are formed by acylation 26). 

Isomerization of the double bond in allylic alcohols may result in aldehydes or ketones (I07a). The reaction can have synthetic value (8bJ3c). If isomerization is desired, palladium is probably the preferred catalyst, operated best under hydrogen-poor conditions (/47fl). Allylic ethers can be converted to alcohols by isomerization with (Ph3P)3RhCl at pH 2 to the vinyl ether, which undergoes hydrolysis (36a). 

Aldehydes, both aliphatic and aromatic, can be decarbonylated by heating with chlorotris(triphenylphosphine)rhodium or other catalysts such as palladium. The compound RhCl(Ph3P)3 is often called Wilkinson s catalyst.In an older reaction, aliphatic (but not aromatic) aldehydes are decarbonylated by heating with di-tert-peroxide or other peroxides, usually in a solution containing a hydrogen donor, such as a thiol. The reaction has also been initiated with light, and thermally (without an initiator) by heating at 500°C. 

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