Palladium-Catalyzed Carbonylative Oxidation

VI.7.1 Palladium-Catalyzed Carbonylative Oxidation of Arenes, Alkanes, and Other Hydrocarbons... 

VI.7.2 Palladium-Catalyzed Carbonylative Oxidation Other than Those Involving Migratory Insertion... 

Oxidative Carbonylation of Ethylene—Elimination of Alcohol from p-Alkoxypropionates. Spectacular progress in the 1970s led to the rapid development of organotransition-metal chemistry, particularly to catalyze olefin reactions (93,94). A number of patents have been issued (28,95—97) for the oxidative carbonylation of ethylene to provide acryUc acid and esters. The procedure is based on the palladium catalyzed carbonylation of ethylene in the Hquid phase at temperatures of 50—200°C. Esters are formed when alcohols are included. Anhydrous conditions are desirable to minimize the formation of by-products including acetaldehyde and carbon dioxide (see Acetaldehyde). 

Palladium catalysts, 10 42 14 49 16 250 Palladium-catalyzed carbonylation, 13 656 Palladium chloride/copper chloride, supported catalyst, 5 329 Palladium compounds, 19 650-654 synthesis of, 19 652 uses for, 19 653-654 Palladium films, 19 654 Palladium membranes, 15 813 Palladium monoxide, 19 651 Palladium oxide, 19 601... 

In an alternative strategy functionalized phenols, such as iodophenol, were involved in palladium-catalyzed carbonylation of alkynes or allenes, producing coumarin or chromone derivatives (Scheme 23) [130-133]. After oxidative addition of the iodoarene to the Pd(0) catalyst the order of insertion of either CO or the unsaturated substrate mainly depends on the nature of the substrate. In fact, Alper et al. reported that CO insertion occurs prior to allene insertion leading to methylene- or vinyl-benzopyranone derivatives [130]. On the contrary, insertion of alkynes precedes insertion of CO, affording couma-rine derivatives, as reported by Larock et al. According to the authors, this unusual selectivity can be explained by the inability of the acyl palladium species to further react with the alkyne, hence the decarbonylation step occurs preferentially [131-133]. 

The mechanism of palladium-catalyzed carbonylation of organic halides is generally assumed to involve oxidative additon of R-X to a Pd(0) species which is formed from the precursors on the action of CO + OH . Migratory insertion of R onto a coordinated CO followed by reaction with a nucleophile generates the product and gives back the catalytically active palladium(O) species (Scheme 5.4 A). 

Trifluoroalanine has also been prepared by reducing trifluoropyruvate imines (ethyl trifluoropyruvate is available commercially it is prepared either from per-fluoropropene oxide or by trifluoromethylation of ethyl or f-butyl oxalate). These imines are obtained by dehydration of the corresponding aminals or by Staudinger reaction. They can also be obtained by palladium-catalyzed carbonylation of trifluoroacetamidoyl iodide, an easily accessible compound (cf. Chapter 3) (Figure 5.4). Reduction of the imines affords protected trifluoroalanines. When the imine is derived from a-phenyl ethyl amine, an intramolecular hydride transfer affords the regioisomer imine, which can further be hydrolyzed into trifluoroalanine. ... 

Palladium-catalyzed allylic oxidations, in contrast, are synthetically useful reactions. Palladium compounds are known to give rise to carbonyl compounds or products of vinylic oxidation via nucleophilic attack on a palladium alkene complex followed by p-hydride elimination (Scheme 9.16, path a see also Section 9.2.4). Allylic oxidation, however, can be expected if C—H bond cleavage precedes nucleophilic attack 694 A poorly coordinating weak base, for instance, may remove a proton, allowing the formation of a palladium rr-allyl complex intermediate (89, path by694-696 Under such conditions, oxidative allylic substitution can compete... 

In the metallic palladium-catalyzed carbonylation of olefins, some hydrogen sources are essential hydrogen halide and molecular hydrogen were found to be the most eflFective. The following sequence of reactions was proposed for the reaction mechanism of the ester and aldehyde formation catalyzed by palladium (23). The first step of the metallic palladium-catalyzed carbonylation seems to be the formation of a palladium-hydrogen bond by the oxidative addition of hydrogen chloride... 

In the laboratory of L.S. Hegedus, the total synthesis of (+)-ep/-jatrophone was accomplished using a palladium-catalyzed carbonylative coupling as the key step. In the endgame of the synthesis, a 3-hydroxy ketone moiety was oxidized in excellent yield to the corresponding 1,3-dione using the mild Corey-Kim protocol. 

P-Lactones can be obtained by oxidative carbonylation of alkenes in the presence of water. Ethylene, for example, is converted to p-propiolactone by carbonylation in aqueous acetonitrile at -20 C using a catalytic amount of PdCh and a stoichiometric quantity of copper(II) chloride (equation 37). Palladium-catalyzed carbonylation of halides can also be used to prepare p-lactones under mild conditions. The reaction takes place at room temperature and pressure in the presence of [PdCl2(PPh3)2] and has been applied to both bromides and chlorides (equations 38 and 39). 

Compared with the synthesis of five-membered rings relatively little has been done on the synthesis of 8-lactones. Homoallylic alcohols can be converted into 8-lactones by rhodium-catalyzed hydroformyla-tion followed by oxidation (equation 48). The thallation and subsequent palladium-catalyzed carbonylation described earlier can also be used for the synthesis of six-membered rings (equation 49). ... 

Advantage has been taken of the aforementioned observations in the synthesis of a terthiophene natural product, arctic acid (250) [168]. Palladium-catalyzed carbonylation of bromobisthiophene 37, obtained from the Kumada coupling of 2-thienylmagnesium bromide and 2,5-dibromothiophene, gave bithiophene ester 247, which was converted to iodide 248 by reaction with iodine and yellow mercuric oxide. Subsequent propynylation of 248 was then realized using the Sonogashira reaction with prop-l-yne to give bisthienyl alkyne 249, which was subsequently hydrolyzed to 250, a natural product isolated from the root of Arctium lappa. 

Palladium-catalyzed carbonylation of 2-chloropyrazine 1-oxide failed, whereas that of... 

Ruthenium complexes catalyze the reaction of primary alcohols with o-phenylenediamine. The catalyst apparently has dual roles in promotion of cyclization and oxidation of the alcohol to aldehyde <91CL1275>. A novel palladium-catalyzed carbonylation of iodobenzene has been linked to base-induced coupling and cyclization with o-phenylenediamine to give 2-arylbenzimidazoles without having to use an arylcarboxylic acid (Scheme 152) <93JOC7016>. 

Palladium-catalyzed carbonylation of chloropyrazines in methanol and in amines yields the pyrazine carboxylic methyl esters and carboxamides, respectively. This procedure has been successfully applied to the synthesis of 2,5-pyrazinedicarboxylic acid derivatives and 3-methoxy-carbonylpyrazine 1-oxide from the corresponding dichloropyrazines and A-oxides <908923 >. 

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. 

In the palladium-catalyzed carbonylation process, allyl formate, prepared by the reaction of allyl alcohol with formic acid, oxidatively adds to Pd(0) species with the C-0 bond cleavage to give allyl palladium formate. The CO insertion into the allylpalladium bond produces butenoyl palladium formate, which reductively ehminates butenoic formic anhydride with regeneration of the catalytically active Pd(0) species. Spontaneous decarbonylation of the mixed anhydride yields 3-butenoic acid, which isomerizes to 2-butenoic acid [61]. The process to give the butenoic acid proceeds only under CO pressure, suggesting that the CO insertion into the allyl-Pd bond is favored under CO pressure. When the reaction is carried out under normal pressure of CO, decarboxylation of the formate to give palladium hydride takes place. Reductive elimination of the allylpalladium hydride yields hydrogenation product of the allyl moiety [62]. 

Finally, Pd2(dba)3 has been utilized as a Pd(0) precatalyst for the palladium-catalyzed carbonylation of triarylstibines using ceric(IV) ammonium nitrate (CAN) as the bulk oxidant. Numerous oxidants were surveyed and CAN gave optimal results. It is believed that CAN serves the same role as molecular oxygen, in... 

In the case of a palladium-catalyzed carbonylative activation of C-X bonds, a general reaction mechanism is shown in Scheme 1.8. Normally this type of reaction starts from Pd(0) and is followed by the oxidative additional step and the coordination and insertion of CO to form the acylpalladium complex as the key... 

---