Palladium catalysis phenylation

The palladium-catalyzed arylation of 2-phenylphenols and naphthols shows an interesting feature of arylation of C-H bonds, leading to the formation of an (aryl)(aryloxy)palladium(n) intermediate.65,65a,65b The phenolates are suitable as precoordinating groups. The reaction of 2-hydroxybiphenyl with an excess of iodobenzene occurs regioselectively at the two ortho-positions of phenyl group under palladium catalysis (Equation (57)). In the case of 1-naphthol, the peri-position is phenylated (Equation (58)). 

According to a recent Organic Syntheses procedure, fluoromethyl phenyl sul-fone, which can be prepared on a large scale [90] (Eq. 23), undergoes a number of useful reactions. A Wadsworth-Emmons-type procedure affords a-fluoro-vinylsulfones [91], which undergo tin-sulfur exchange under free radical conditions (Eq. 24). The products maybe protodestannylated [92],fluorinated [93],or coupled under palladium catalysis [94]. The difluoromethyl phenyl sulfone also shows some useful chemistry. 

Other unsaturated substrates arylated by various diaryl iodonium salts included butenone, acrylic acid, methyl acrylate and acrylonitrile [46]. Allyl alcohols with diaryliodonium bromides and palladium catalysis were arylated with concomitant oxidation for example, from oc-methylallyl alcohol, aldehydes of the general formula ArCH2CH(Me)CHO were formed [47]. Copper acetylide [48] and phenyl-acetylene [49] were also arylated, with palladium catalysis. 

An interesting reaction between the bis phenyl iodonium triflate of acetylene and the silyl enol ether of acetophenone afforded an allene (PhCOCH=C=C=CHCOPh, 84%) [6], Also, alkynyl iodonium tosylates and carbon monoxide in methanol or ethanol, with palladium catalysis, furnished alkyne carboxylates [53]. 

Using nickel(O), generated from nickel(II) chloride with diisobutylaluminum hydride, as catalyst, cyanotrimethylsilane underwent addition to l-methylene-2-phenylcyclopropanes to give 2-phenyl-l-(trimethylsilylmethyl)cyclopropane-l-carbonitriIes 1 in poor yield. Palladium catalysis led to opening of the cyclopropane ring as the major process. 

With palladium catalysis, refluxing in nitrobenzene or xylene dehydrogenates 3-substituted 5,6,7,8-tetrahydropyrido[4,3-rf]pyrimidin-4(3//)-ones to yield the corresponding aromatic compounds. Thus, the 3-phenyl compound is dehydrogenated by heating in nitrobenzene with palladium on carbon at 125 130°C for 17 hours.509... 

The a-allylpalladium intermediate 135a, which must be formed on coupling of l,3-dicyclopropyl-l,2-propadiene (134), with, for example, iodobenzene under palladium catalysis rapidly undergoes rearrangement to the homoaUylpalladium species 135b and subsequent P-hydride elimination to yield the 1,3,5-hexatriene 136 [152g,h]. This in turn undergoes [4 + 2] cycloaddition with an added dienophile to furnish the 3-(2-cyclopropyl-l-phenyl)cyclohexene derivatives 138 as a mixture of trans,trans- and ds,trows-diastereomers (Scheme 8.31). 

Anion Source for Palladium Catalysis. The reagent serves as a source of weakly coordinating anions in the palladium-catalyzed formation of mixed phenyl ureas, a known class of commercially available herbicides, using palladium(II) acetate, copper(II) toluenesulfonate, and 2,2 -dipyridyl as the catalyst system. Other studies have suggested that use of this reagent to form palladium salts may have useful applications in the reductive carbonylation of nitroaromatic compounds to give isocyanates via initial carbamate formation (eq 2). ... 

Palladium-mediated catalysis has only been exploited relatively recently in the synthesis of substituted PPV derivatives. The use of aryl dibromides as monomers is particularly useful as it allows the synthesis of PPVs substituted with alkyl rather than alkoxy sidechains. The Suzuki [53, 54], Heck [55], and Stille [56] reactions have been used in the synthesis of new PPV derivatives, but attaining high molecular weight PPV derivatives by these methodologies has proved problematic. A phenyl-subslilutcd PPV material PPPV 31 was synthesized by a Suzuki coupling (Scheme 1-10) of dibromoethene and fo/.v-boronic acid 30. Its absorption (2ni ix=385 nm) and emission (2max=475 nm) maxima were strongly... 

Application of the complexes 63 in the Mizoroki-Heck reaction did not reveal higher activity than the previously examined palladium(II) complexes. However, in the Suzuki-Miyaura reaction, a drastically increased activity was observed with complex 63. Catalysis starts without a measurable induction period at mild temperatures accompanied by an extraordinarily high turnover frequency (TOF) of 552 [mol product x mol Pd x h ] at the start of the reaction for the coupling of p-chlorotoluene and phenyl boronic acid [Eq. (48)]. ... 

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