Bonding aryls

In presence of—C=C— or of aromatic ring In presence of—C=0 bond In presence of two carbon-oxygen bonds In presence of two carbon-carbon double bonds Aryl-C=0... 

Chiral sulfoxides with at least one sulfur-bonded aryl group have been separated by liquid chromatography into the enantiomers26. Some of the columns employed, which are commercially available, used 3,5-dinitrobenzoyl)phenylglycine bonded to silica... 

Historically, one of the most important limitations of the Suzuki-Miyaura reaction was the poor reactivity of organic chlorides, attributed to the strength of the C-Cl bond. Aryl chlorides are very attractive halides due to their low cost and wider diversity of available compounds. Prior to 1998, reports of effective palladium-catalyzed Suzuki reactions of aryl chlorides were limited to activated substrates, and generally employing very high temperatures. In that year. 

Palladium (II)-Nucleophile Addition across Olefins. Adding palladium complexes to olefins, either in the presence of an external nucleophile or a ligand which is attached to palladium, produces a palladium-carbon sigma-bonded complex which is not usually isolated in the case of monoolefins. Instead it decomposes and in doing so oxidizes the olefin to an organic carbonyl compound or a vinyl compound, exchanges a substituent group on the olefin, isomerizes the double bond, arylates (alkylates) the olefin, or carboxylates the olefin (2, 3). 

As to the next step, namely, the reaction of aryl radicals with nucleophiles, we should take into account the fact that air molecular orbital, which initially accommodates the incoming electron, is available in the aryl halide. The electron is subsequently transferred in-tramolecularly from the it to the o molecular orbital of the carbon-halogen bond. Aryl radicals effectively scavenge H atoms. Therefore, an abstraction of a hydrogen atom from the solvent may occur. However, in the case of nucleophiles that can act as effective traps of aryl radicals, the addition of a nucleophile to the phenyl radical takes place. At this point, let us focus on the step of addition of the nucleophile (Y ) to the intermediate radical (Ph). When a new a bond begins to form between the sp3 carbon-centered radical (H5C6) and... 

Consequently, we were faced with the task of formulating a widely acceptable and consistent definition of bond activation . Our research, discussions, and analyses led to a conclusion that bond activation should refer to a process of increasing the reactivity of a bond in question and as such encompasses an entire spectrum of possible mechanisms. Also, we argue that activation is not equivalent to reaction or, in other words, that activation of a bond is not the same as cleavage of a bond. For the latter process we proposed the general term bond transformation . It should be emphasized that both bond activation and bond transformation are general terms and, therefore, information about the reaction and mechanism category should be specified by additional descriptors (cf. C-H bond arylation via electrophilic metalation, C-H bond metalation via concerted metal insertion). 

As an example, Schiff base 1, with its bidentate chelation separated by a three-carbon fragment (the correct distance for formation of a six-membered metalla-cycle) from the C-H bond, can undergo palladium-catalyzed C-H bond arylation... 

Fig. 14 Tetrameric capsule made of L-shaped components held together by 16 hydrogen bonds. Aryl and OH groups have been removed for clarity...

Fig. 16.30. Pd(0)-catalyzed arytation of a copper acetytide at the beginning of a three-step synthesis of an ethynyt aromatic compound. Mechanistic details of the C,C coupling Step 1 formation of a complex between the catalytically active Pd(0) complex and the arylating agent. Step 2 oxidative addition of the arylating agent and formation of a Pd(II) complex with a cr-bonded aryl moiety. Step 3 formation of a Cu-acetylide. Step 4 trans-metalation the alkynyl-Pd compound is formed from the alkynyl-Cu compound via ligand exchange. Step 5 reductive elimination to form the -complex of the arylated alkyne. Step 6 decomposition of the complex into the coupling product and the unsaturated Pd(0) species, which reenters the catalytic cycle anew with step 1.

Oxidative addition to Pd (0) is the oxidation of choice used in several methods to form C— C bonds. Aryl and alkenyl halides react with alkenes in the presence of catalytic amounts of Pd and substitute the halide with the alkenyl group. This is called the Heck reaction (see Welton, 1999) ... 

Carbonyl group Nitroaromatic group A-oxide function Carbon-carbon double bond Aryl halide... 

The hydrogenolysis of aryl halides proceeds more readily than the cleavage of alkyl-halogen bonds. Aryl chlorides are rather stable to hydrogenolysis in neutral medium and bromides are dehalogenated only to a moderate extent 24,132 but iodides are readily lost. Aryl fluorides, however, are hydrogenolyzed only under... 

The enantioselectivities obtained in the first catalytic AD process (Table 2) reveal that the best results are obtained with trans-substituted alkenes with at least one aromatic substituent (entries 2 and 3). If the aromatic substituent is moved further away from the alkene, the ee drops sharply (entry 6). Furthermore, terminal alkenes give moderate ee provided a directly bond aryl group is present (entry 1). 1,1-Disubstituted (entry 4) and frans-dialkyl-substituted alkenes... 

Palladium and copper-catalyzed arylation of C-H bonds by aryl halide reagents is reviewed. The emphasis of the review is on directing-group-containing arene and alkane arylation catalyzed by palladium and on sp2 C-H bond arylation catalyzed by copper. Literature up to early 2009 is covered. 

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