Palladium aliphatic ketones

Because of the industrial magnitude of these processes, many catalysts have been examined with variations in metal distribution, pore size, and alkalinity. In most synthetic work where catalyst life and small variations in yield are not of great importance, most palladium-on-carbon or -on-alumina powder catalysts will be found satisfactory for conversion of phenols to cyclohexanones. Palladium has a relatively low tendency to reduce aliphatic ketones, and a sharp decrease in the rate of absorption occurs at about 2 mol of consumed hydrogen. Nickel may also be used but overhydrogenation is more apt to occur. 

Chitosan (Fig. 27) was deposited on sihca by precipitation. The palladium complex was shown to promote the enantioselective hydrogenation of ketones [80] with the results being highly dependent on the structure of the substrate. In the case of aromatic ketones, both yield and enantioselectiv-ity depend on the N/Pd molar ratio. Low palladium contents favored enan-tioselectivity but reduced the yield. Very high conversions were obtained with aliphatic ketones, although with modest enantioselectivities. More recently, the immobilized chitosan-Co complex was described as a catalyst for the enantioselective hydration of 1-octene [81]. Under optimal conditions, namely Co content 0.5 mmolg and 1-octene/Co molar ratio of 50, a 98% yield and 98% ee were obtained and the catalyst was reused five times without loss of activity or enantioselectivity. 

Ruthenium-on-carbon in aqueous ethanol or platinum oxide also is used but to a much lesser extent than Pd. Palladium shows a low activity for hydrogenation of nonactivated aliphatic ketones, but all the platinum metals can be used in addition to Cu chromite and Ni catalysts. Platinum catalysts have been widely used, platinum-on-carbon in aqueous acid is satisfactory. Rhodium is active under mild conditions and leads to a-hydroxy steroids in excellent yields ... 

For related palladium-catalyzed cyclizations of enolates, see Ciufolini, M.A. Qi, H.B. Browne, M.E. Intramolecular arylations of soft enolates catalyzed by zerovalent palladium. J. Org. Chem. 1988, 53, 4149 151. Muratake, H. Natsume, M. Nakai, H. Palladium-catalyzed intramolecular -arylation of aliphatic ketone, formyl, and nitro groups. Tetrahedron 2004, 60, 11783-11803. Muratake, H. Natsume, M. Palladium-catalyzed intramolecular -arylation of aliphatic ketones. Tetrahedron Lett. 1997, 38, 7581-7582. 

Ethylene and other olefins can also be copolymerized with carbon monoxide to form polymers of aliphatic ketones, using transition metal catalysts, like paUadium(ll) coupled with non-coordinating anions. There are numerous reports of such catalysts in the literature. One example is a compound composed of bidentate diarylphosphinopropane ligand and two acetonitrile molecules coordinating Pd coupled with BF3 counterions. This compound, bis(acetonitrile)palladium(II)-l,3-bis(diphenyl-phosphino)propane-(tetrafluoborate), can be illustrated as follows [97] ... 

In 2006, Griebenow and coworkers [31] described the palladium-catalyzed a-arylation of ketones on a solid support using modified Buchwald-Hairtwig reaction conditions. The coupling of immobilized 4-bromobenzamide (prepared from polystyrene Rink amide resin and 4-bromobenzoic acid chloride) with several aromatic, heteroaromatic, and aliphatic ketones was investigated. 

The treatment of carbonyl compounds with Sml2 and methyl chloroformate in the presence of molecular sieves affords the cyclic carbonates or biscarbonates of pinacols. This one-pot reaction proceeds rapidly even with aliphatic ketones. The stereochemistry of the reaction run by this procedure is different from that of conventional pinacolic couplings. Trifluoromethylated five-membered cyclic carbonates were prepared through the palladium-promoted reaction of tertiary trifluoromethylated propargylic alcohols and sodium carbonate (Scheme 6). ... 

Nitrilimines react with hydrazones of aliphatic aldehydes and ketones to yield addition products 9 which cyclise when treated with palladium charcoal at room temperature to give 1,6-dihydro-j-tetrazines 10 <96JCR(S)174>. 

Wacker (1) A general process for oxidizing aliphatic hydrocarbons to aldehydes or ketones by the use of oxygen, catalyzed by an aqueous solution of mixed palladium and copper chlorides. Ethylene is thus oxidized to acetaldehyde. If the reaction is conducted in acetic acid, the product is vinyl acetate. The process can be operated with the catalyst in solution, or with the catalyst deposited on a support such as activated caibon. There has been a considerable amount of fundamental research on the reaction mechanism, which is believed to proceed by alternate oxidation and reduction of the palladium ... 

Ruthenium is commonly used with other platinum metals as a catalyst for oxidations, hydrogenations, isomerizations, and reforming reactions. The synergetic effect of mixing ruthenium with catalysts of platinum, palladium, and rhodium lias been found for the hydrogenations of aromatic and aliphatic nitro compounds, ketones, pyndine, and nitriles. 

Lower aliphatic amines are widely used as intermediates for the synthesis of herbicides, insecticides and drugs or can be applied as rubber accelerators, corrosion inhibitors, surface active agents etc. [l]. The most widespread method for the preparation of lower aliphatic amines involves the reaction of ammonia with an alcohol or a carbonyl compound in the presence of hydrogen. The most common catalysts used for reductive amination of alcohols, aldehydes and ketones contain nickel, platinum, palladium or copper as active component [ I — 3 ]. One of the most important issues in the reductive amination is the selectivity control as the product distribution, i.e. the ratio of primary to secondary or tertiary amines, is strongly affected by thermodynamics. 

The most conspicuous property of aliphatic amines, apart from their fishy smell, is their high basicity, which usually precludes N-alkylations under acidic reaction conditions (last reaction, Scheme 6.3). Hence, alkylation of amines with tertiary alkyl groups is not usually possible without the use of highly stabilized carbocations which can be formed under basic reaction conditions. Rare exceptions are N-alkyla-tions of amines via radicals (Scheme 4.2), copper-catalyzed propargylations (Scheme 6.3), and the addition of amines to some Michael acceptors and allyl palladium or iridium complexes. Better strategies for the preparation of tert-alkylamines include the addition of Grignard reagents to ketone-derived imines [13] or the reduction of tert-alkyl nitro compounds. 

Pd(II) catalysts have been widely used for aerobic oxidation of alcohols. The catalytic systems Pd(OAc)2-(CH3)2SO [14] and Pd(OAc)2-pyridine [15] oxidize allylic and benzylic alcohols to the corresponding aldehydes and ketones. Secondary aliphatic alcohols, with relatively high water solubility, have been oxidized to the corresponding ketones by air at high pressure, at 100 °C in water, by using a water-soluble bathophenanthroline disulfonate palladium complex [PhenS Pd(OAc)2] [5d]. The Pd catalyst has also been successfully used for aerobic oxidative kinetic resolution of secondary alcohols, using (-)-sparteine [16]. 

Aromatic aldehydes and ketones can also be deoxygenated with hydrogen over a palladium charcoal catalyst. The reaction occurs because the aromatic ring activates the carbonyl group towards reduction. Aliphatic aldehydes and ketones are not reduced in this. 

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