Aromatic compounds palladium catalysts

Arene(tricarbonyl)chromium complexes, 19 Nickel boride, 197 to trans-alkenes Chromium(II) sulfate, 84 of anhydrides to lactones Tetrachlorotris[bis(l,4-diphenyl-phosphine)butane]diruthenium, 288 of aromatic rings Palladium catalysts, 230 Raney nickel, 265 Sodium borohydride-1,3-Dicyano-benzene, 279 of aryl halides to arenes Palladium on carbon, 230 of benzyl ethers to alcohols Palladium catalysts, 230 of carboxylic acids to aldehydes Vilsmeier reagent, 341 of epoxides to alcohols Samarium(II) iodide, 270 Sodium hydride-Sodium /-amyloxide-Nickel(II) chloride, 281 Sodium hydride-Sodium /-amyloxide-Zinc chloride, 281 of esters to alcohols Sodium borohydride, 278 of imines and related compounds Arene(tricarbonyl)chromium complexes, 19... 

Polymerization by G—G Goupling. An aromatic carbon—carbon coupling reaction has been employed for the synthesis of rigid rod-like polyimides from imide-containing dibromo compounds and aromatic diboronic acids ia the presence of palladium catalyst, Pd[P(CgH )2]4 (79,80). 

ArSnRs, and with arylmercury compounds. Aryl triflates react with arylbo-ronic acids ArB(OH)2, or with organoboranes, in the presence of a palladium catalyst, to give the arene in what is called Suzuki couplingCyclopropyl groups can be attached to aromatic rings by this reaction. Even hindered boronic acids give good yields of the coupled product. 

In another nonelectrolytic process, arylacetic acids are converted to vi c-diaryl compounds 2A1CR2COOH —> ArCR2CR2Ar by treatment with sodium persulfate (Na2S20g) and a catalytic amount of AgNOs." Both of these reactions involve dimerization of free radicals. In still another process, electron-deficient aromatic acyl chlorides are dimerized to biaryls (2 ArCOCl —> ArAr) by treatment with a disilane RsSiSiRs and a palladium catalyst." " ... 

With palladium catalysts aromatic chlorides are rather unreactive, however, nickel is able to catalyze the reactions of these substrates, too. The water-soluble catalyst was generated in situ from the easily available [NiCl2(DPPE)] and an excess of TPPTS by reduction with Zn in mixtures of 1,4-dioxane and water. Although it had to be used in relatively large quantities (10 mol %), the resulting compound catalysed the cross-coupling... 

Sodium or potassium phenoxide can be carboxylated regioselectively in the para position in high yield by treatment with sodium or potassium carbonate and carbon monoxide.316 14C labeling showed that it is the carbonate carbon that appears in the p-hydroxybenzoic acid product.317 The CO is converted to sodium or potassium formate. Carbon monoxide has also been used to carboxylate aromatic rings with palladium compounds as catalysts.318 In addition, a palladium-catalyzed reaction has been used directly to prepare acyl fluorides ArH — ArCOF.31 ... 

Ring Acyloxylation. Soluble and supported palladium catalysts are suitable reagents used to achieve ring acyloxylation of aromatic compounds.499 503 693 780 Reaction conditions, however, are critical since coupling and side chain substitution also occur. 

The oxidative carbonylation of arenes to aromatic acids is a useful reaction which can be performed in the presence of Wacker-type palladium catalysts (equation 176). The stoichiometric reaction of Pd(OAc)2 with various aromatic compounds such as benzene, toluene or anisole at 100 °C in the presence of CO gives aromatic acids in low to fair yields.446 This reaction is thought to proceed via CO insertion between a palladium-carbon (arene) allyl chloride, but substantial amounts of phenol and coupling by-products are formed.447... 

Benzene and other aromatic compounds don t normally react with hydrogen in the presence of a palladium catalyst. If very high pressures (200 atm) and high temperatures are used, however, benzene will add three molecules of H2 to give an addition product. What is a likely structure for the product ... 

Deoxygenation of pyridine A-oxides has been achieved using dimethyldioxiran <95CC1831> and palladium with sodium hypophosphite <95GCI(124)385>. Pyridine A-oxides, with ruthenium porphyrin catalysts, have been used as an oxidant of aromatic compounds <95JA(117)8879> or olefins, alcohols, sulfides and alkanes <95FI(40)867>. 

During their work on the arylation of aromatic compounds by substitution, Fujiwara, et al. observed biaryl formation when aromatic compounds were placed in the presence of olefin-palladium complexes and silver nitrate.80 Developing this reaction as a method for biphenyl synthesis, these authors showed that the more stable the olefin-palladium complex was, the lower the yield. Ethylene dichloropalladium proved to be the best choice, when used with silver nitrate. However, the reaction required stoichiometric amounts of both catalysts (Scheme 10.47). Benzene derivatives substituted by electron-donating or -withdrawing groups reacted as well, but a mixture of regioisomers was produced, except for nitrobenzene, which only gave m,m -dinitrobiphenyl. 

Various aromatic dibromides have been cross-coupled with difunctional tributyltin aromatic compounds in the presence of palladium-based catalysts to yield poly(arylene)s [scheme (12)] [149-151]. The mechanistic pathway of this coupling, known as Stille coupling [152], follows an oxidative addition-trans-metallation-reductive elimination sequence. 

In Section 16.5, a few other C,C coupling reactions of alkenes and of aromatic compounds, which contain an sp2—OTf, an sp2—Br, or an sp2—Cl bond, will be discussed because these C,C couplings and the preceding ones are closely related mechanistically. These substrates, however, react with metal-free alkenes. Palladium complexes again serve as the catalysts. 

The palladium-catalyzed formation of diarylamines has been used in several contexts to form molecules of biological relevance. The ability to prepare haloarenes selectively by an ortfio-metalation-halogenation sequence allows the selective delivery of an amino group to a substituted aromatic structure. Snieckus has used directed metalation to form aryl halides that were subsequently allowed to react with anilines to form diarylamines (Eq. (34)) [209]. Frost and Mendonqa have reported an iterative strategy to prepare, by the palladium-catalyzed chemistry, amides and sulfonamides that may act as peptidomimetics. Diaryl-amine units were constructed using the DPPF-ligated palladium catalysts, and the products were then acylated or sulfonated with 4-bromobenzoyl or arylsulfonyl chlorides [210]. Le-miere has coupled primary arylamines with 4-chloro-3(2H)-pyridazinones to form compounds with possible analgesic and antiinflammatory properties. 

Palladium catalysts, in particular, in the form supported on carbon have frequently been employed for the hydrogenation of aromatic nitro compounds and are often preferred to platinum oxide because of their high activity as well as less tendency toward hydrogenation of the aromatic ring.85,86 3,4-Dimethoxynitrobenzene was hydrogenated to 4-aminoveratrole in a 97% yield over 5% Pd-C in ethanol at room temperature and 0.2 MPa H2 (eq. 9.40). 

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