Arenes palladium catalysts

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. 

The authors propose that the influence of the phenyl group is not an electronic effect, as no product formation is observed with palladium catalysts known to be highly active in disilane systems substituted with electronegative elements. Rather, the phenyl group may allow for precoordination via a w-arene complex, which would accelerate the oxidative addition of an Si-Si bond to platinum, a key step in the proposed catalytic cycle. 

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... 

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... 

Alkyltrifluoroborates (RBF3K, see 12-28) react with aryl triflates or aryl halides,or aryliodonium salts with a palladium catalyst, to give the arene. The reaction is compatible with sensitive functionality, such as an epoxide unit. 

Vinyl halides add to allylic amines in the presence of Ni(cod)2 where cod=l, 5-cyclooctodine, followed by reduction with sodium borohydride. Aryl iodides add to alkynes using a platinum complex in conjunction with a palladium catalyst. A palladium catalyst has been used alone for the same purpose, and the intramolecular addition of a arene to an aUcene was accomplished with a palladium or a GaCl3 catalyst, " AUcyl iodides add intramolecularly to aUcenes with a titanium catalyst, or to alkynes using indium metal and additives. The latter cyclization of aryl iodides to alkenes was accomplished with indium and iodine or with Sml2. " ... 

Arenes add to nitriles in the presence of a palladium catalyst in DMSO/trifluor-oacetic acid to give a diaryl ketone. ... 

The less reactive chlorobenzene and arene sulfonates coupled with phenylindole in the presence of a palladium catalyst generated from X-phos (31, Figure 8). For example, 4-tezt-butylphenyl tosylate reacted to give quantitative yields of ZV-(4-tezt-butylphenyl)indole in the presence of 2 mol% Pd, 5 mol% X-phos and K3PO4 as the base98. 

The imidazole, benzoxazole, and benzthiazole derivatives in Table 7-3 are rather moisture-sensitive.92 On the whole, however, the heteroarylstannanes show the same reactions that characterise the homoarylstannanes. With a palladium catalyst, they undergo coupling112 and cross-coupling reactions68 and indeed much of the recent interest in the heteroarylstannanes stems from their applications in the Stille reaction (see Section 22.2). One aspect of this is the synthesis of oligomers and polymers or copolymers, for example by the cross-coupling of 2,5-distannylthiophene with a 1,4-diiodo-arene.113,114... 

The most common mechanism of C-H bond cleavage in the arylation examples discussed above has been assumed to be electrophilic aromatic substitution involving reaction of an electrophilic palladium catalyst with an electron rich, nucleophilic aromatic ring. In order to effect direct arylation on simple, electron deficient arenes, a basic directing group or intramolecular reaction is usually necessary to enable formation of a metalocycle. As a brief introduction to the effect of this area on the functionalization of indoles and pyrroles, we provide an overview of the mechanistic... 

Since the intermolecular oxidative coupling of benzene to biphenyl using stoichiometric amounts of PdCl2 was first described by van Helden and Verberg in 1965 [41], the intramolecular oxidative coupling of two arenes mediated by a palladium catalyst to synthesize cyclic compounds has also attracted great attention. 

Intermolecular direct arylations of heteroarenes with aryl halides were thus far predominantly accomplished with palladium or rhodium complexes [31, 39,75, 76], Hence rhodium catalysts proved applicable to various electron-rich heteroarenes. In contrast, less expensive and more versatile palladium catalysts allowed for direct arylations of both electron-rich and electron-deficient substrates. Generally, the problem of achieving regioselectivities in direct arylation reactions of heteroarenes is less pronounced than it is for simple arenes, since in many cases the heteroatom can be considered as an endocyclic directing group. 

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