Oxidative carbonylations palladium bromide

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). 

The reaction of alcohols with CO was catalyzed by Pd compounds, iodides and/or bromides, and amides (or thioamides). Thus, MeOH was carbonylated in the presence of Pd acetate, NiCl2, tV-methylpyrrolidone, Mel, and Lil to give HOAc. AcOH is prepared by the reaction of MeOH with CO in the presence of a catalyst system comprising a Pd compound, an ionic Br or I compound other than HBr or HI, a sulfone or sulfoxide, and, in some cases, a Ni compound and a phosphine oxide or a phosphinic acid.60 Palladium(II) salts catalyze the carbonylation of methyl iodide in methanol to methyl acetate in the presence of an excess of iodide, even without amine or phosphine co-ligands platinum(II) salts are less effective.61 A novel Pd11 complex (13) is a highly efficient catalyst for the carbonylation of organic alcohols and alkenes to carboxylic acids/esters.62... 

The brownish-colored solid is air sensitive and should be handled and stored under inert gas atmospheres. Solutions are very air sensitive with precipitation of colloidal palladium. The 31P NMR (109.3 MHz, D20, 5°C) exhibits a singlet at <522.6 ppm. The IR displays the characteristic SO-vibrations at 1225 (sh, vst), 1200 (vst), 1039 (vst), and 622 (vst) cm-1. The compound has been intensively utilized for carbonylation of benzylic chlorides,26 aryl bromides,27 and 5-hydroxymethylfurfural,28 Heck-reactions,29 allylic substitution reactions,30 and oxidations.16... 

The catalytic carbonylation of allyl chloride to form 3-butenoate proceeds through a 7r-allyl complex which is formed by the oxidative addition of allyl chloride to metallic palladium. The 7r-allyl complex formation has been reported by Fischer and Burger (4) with allyl bromide and palladium as a supporting evidence. The carbonylation then proceeds by the insertion of carbon monoxide as before. 

Relatively limited work on profene synthesis via carbonylation of benzyl-X derivatives has been reported from university groups. One exception is the stero-selective carbonylation of racemic benzylic bromides. The asymmetric reaction toward enantiomerically pure profenes could a priori proceed either by a kinetic resolution or by true asymmetric induction via the intermediacy of a trigonal substrate. Results from Arzoumanian et al. [35] strongly suggest that the carbonylation of 1-methylbenzyl bromide with oxazaphospholene-palladium complexes is a kinetic resolution process with a discriminative slow oxidative addition step. Best enantiomeric excess is about 64 % ee at 9 % chemical yield. Another possible way to synthesize enantiomerically pure profenes is to start from optically pure benzyl derivatives. Baird et al. investigated the carboxylation of optically active benzyl carbonates with palladium catalysts. The enantiomeric excess was only modest [36]. Thus, the development of an efficient catalytic asymmetric carbonylation of C-X derivatives is still an existing challenge. 

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. 

Oxidative insertion into the aryl bromide, carbonylation, and nucleophilic attack on the carbonyl group with eUmination of Pd(0) form the catalytic cycle. No doubt the palladium has a number (1 or 2 ) of phosphine ligands complexed to it during the reaction and these keep the Pd(0) in solution between cycles. 

Carboxylic acids have been prepared from carbonylation of aUyl bromide over palladium catalysts supported by polyphenol, polyvinylpyrrolidone,polyacrylamide (PAA), modified poly(2,6-dimethyl-l,4-phenylene oxide), and polysulfone- It is unclear under these reducing conditions if gel form metal cluster is involved as the active catalyst. Palladium acetate immobilized on the clay montmoriUonite has proved to be an effective catalyst for the carbonylation of secondary aUylic alcohols, affording a,/3-unsaturated carboxylic acids in moderate yields. However, triphenylphosphine was needed for the acliviva-tion of the catalyst. Palladium catalyst bound to a platinum cluster has been used up to three times for allylic alkylation without a significant loss of its activity. Preliminary study indicated that the Pd—Pt bond remains intact during the catalytic cycle. 

In the palladium-catalysed carbonylation of aryl bromides to yield benzaldehyde derivatives, IV-formylsaccharin is used as the source of the acyl function. A double carbonylation has been observed in the reaction of aryl halides with carbon monoxide and terminal alkenes which yields 4-arylfuranones such as (152). The proposed mechanism involves oxidative addition of the aryl halide to palladium and insertion of the carbon monoxide to give an acyl palladium species. This is followed by coordination and insertion of the alkene. A second carbon monoxide insertion is faster than -hydride elimination and, after intramolecular attack, leads to the product. The palladium-catalysed reaction of aryl iodides with simple ketones such as acetone in the presence of carbon monoxide has been shown to yield 1,3-diketones such as... 

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