Palladium catalyzed oxidations aliphatics

Similarly, chelation-assisted palladium-catalyzed oxidative functionalizations of C—H bonds with, for example, hypervalent iodine(III) reagents turned out to be particularly valuable. These protocols allowed for, inter alia, regioselective acetoxyla-tion or etherification of aromatic and aliphatic C— H bonds [17-19], and also halogenations of arenes (Scheme 9.3) [20, 21]. 

Carbonyl Compounds by Oxidation of Alcohols and Aldehydes. A critical assessment of the use of palladium catalysts in the aerobic oxidation of alcohols has concluded that Pd(OAc)2-Et3N is the most versatile and convenient catalyst system and that this often functions under especially mild conditions.There have been many other recent advances in this field and such that there is now a wealth of methods available for effecting the palladium-catalyzed oxidation of alcohols. A procedure using pyridine under an oxygen atmosphere has been shown to convert benzylic and aliphatic alcohols into the corresponding aldehydes or ketones. The yields of product are frequently over 90%. Replacing pyridine with (—)-sparteine in such processes allows for the oxidative kinetic resolution of chiral secondary alcohols. 

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 ... 

Esters 106 (R = Me, Et or Pr = Et, Pr, r-Bu or PhCHi) of aliphatic carboxylic acids react with lithium acetylides 107 (R = H, C5 Hi i or Ph) in the presence of boron trifluoride etherate in THE to give acetylenic ketones 108 (equation 18). Palladium-[tetrakis(triphenylphosphine)]-copper(I) iodide catalyses the oxidative addition-decarboxylation of propargyl methyl carbonates, e.g. 109, with terminal alkynes to yield 1,2-dien-4-ynes (allenylacetylenes) 110. The regiochemistry of the palladium-catalyzed addition of phenylacetylene to the allenic ester 111 depends on the nature of the catalyst used palladium(III) acetate-triphenylphosphine yields a 81 19 mixture of adducts 112 and 113, while in the presence of tetrakis(carbomethoxy)palladacyclopentadiene-tris(2,4,6-trimethoxyphenyl)phosphine the ratio is reversed to 9 91 k... 

Heck carbonylation involving the oxidative addition of aryl halides is not applicable to aliphatic halides, since alkyl halides react directly with nucleophiles. Tsuji developed a process of carbonylating allyl carbonates to form carboxylic esters by palladium-catalyzed carbonylation that is applicable to aliphatic substrates [60]. The process probably involves (a) the oxidative addition of allyl carbonates to Pd(0) species to form r/ -allyl palladium species, (b) CO insertion into the allyl-Pd bond to give acylpalladium species, (c) decarboxylation of the carbonate ligand to give alkoxide, and (d) liberation of butenoate esters by combination with the alkoxides as shown in Scheme 1.21. 

Related strategies have been successfully applied to the halogenation of aliphatic and aromatic C-H bonds. Yu reported iodination of alkyl chains attached to an oxazoline that binds the palladium catalysts (Equation 18.19a). In this iodination, the combination of PhI(OAc)j and are used as the reagents to effect iodination and oxidation. The use of directing groups on arenes has also made possible the regioselective halogenation of arenes. As illustrated by the catalyzed and uncatalyzed processes in Equation 18.19b, the palladium-catalyzed process can occur faster than the uncatalyzed process to form a product directed by the catalyst, rather than the electronic properties of the arene. Under microwave conditions, directed fluorination of arene C-H bonds can also occur (Equation 18.19c). ... 

Carbonylation Reactions. A three-component palladium-catalyzed amidocarbonylation reaction provides IV-acylamino acids from aromatic and aliphatic aldehydes or acetals with amides under elevated CO pressure (60 bar) in the presence of PdBr2, PPhs, LiBr, an acid additive (typically H2SO4), and iV-methyl-2-pyrrolidone. Mechanistically, the palladium-catalyzed amidocarbonylation reaction is proposed to proceed through the in situ formation of an a-haloamide and Pd(0) species, which can undergo oxidative addition, followed by CO insertion, and lastly hydrolysis of the acyl palladium complex to afford the product and regenerate the catalyst (eq 45). 

Activated alkanes, such as cyclohexanone, acetone, and aliphatic nitro compounds, can react with carbon dioxide even without metal catalysis. A typical example is the phenolate-catalyzed reaction of acetophenone with C02 to the corresponding carbon add. A catalytic conversion of the non-activated methane with C02 to give acetic acid was reported by Fujiwara and co-workers [72], The reaction was carried out in the presence of palladium and copper acetate and also stoichiometric amounts of the oxidant K2S208. 

In his pioneering contributions Moiseev has shown that giant cationic palladium clusters , e.g. Pd56iL6o(OAc)i8o (L = phenanthroline, bipyridine), characterized by use of high-resolution TEM, SAXS, EXAFS, IR and magnetic susceptibility data, catalyze, under mild conditions (293 363 K, 1 bar), the oxidative acetoxylation of ethylene into vinyl acetate, propylene into allyl acetate, and toluene into benzyl acetate. The oxidation of primary aliphatic alcohols to esters, and the conversion of aldehydes into acetals were also studied. ... 

Intramolecular oxidative aminations of olefins have alsobeen studied, and many of these intramolecular processes were observed prior to the analogous intermolecular variants. The oxidative aminations of alkenes with arylamines and arylamine derivatives catalyzed by palladium complexes were shown by Hegedus to form indoles (Equation 16.120). These reactions were conducted with orf/io-allylaniline and ort/zo-allylaniline derivatives as substrate, Pd(NCMe)jCl2 as catalyst, and benzoquinone as oxidant. Intramolecular reactions of N-tosylated aliphatic amines were reported by Larock. ° For example, the tosylamide in Equation 16.121 imdergoes cyclization in high yield in the presence of dioxygen with Pd(OAc)j as catalyst in DMSO. A related reaction (Equation 16.122) was reported recently in toluene solvent with added pyridine. ... 

Increase of temperature is the simplest way of reaction rate acceleration, but some drawbacks can be associated with CH, such as, drop of selectivity toward desired products and degradation of the catalyst. Utilization of MW irradiation instead of CH, can present marked advantages relative to the latter method, as described herein for some homogeneous alcohol oxidations, allowing to achieve higher and faster conversions of alcohols with acceptable selectivities. However, the activity of the catalytic systems, even under MW irradiation, is usually still low for the oxidation of aliphatic alcohols, except in a few cases, for example, the anaerobic oxidation catalyzed by some palladium(II) complexes. 

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