Aryl compounds reactions

Pd(II) salts promote the carbonylation of organomercury compounds. Reaction of phenylmercury chloride and PdCh under CO pressure affords benzophenone (429)[387]. Both esters and ketones are obtained by the carbonylation of furylmercury(Il) chloride in alcohol[388]. Although the yields are not satisfactory, esters are obtained by the carbonylation of aryl- and alkylmercuryfll) chlorides[389,390]. One-pot catalytic carbonylation of thiophene, furan, and pyrrole (430) takes place at the 2-position via mercuration and transmetallation by the use of PdCb, Hg(N03), and CuCl2[391]. 

Cesium forms simple alkyl and aryl compounds that are similar to those of the other alkah metals (6). They are colorless, sohd, amorphous, nonvolatile, and insoluble, except by decomposition, in most solvents except diethylzinc. As a result of exceptional reactivity, cesium aryls should be effective in alkylations wherever other alkaline alkyls or Grignard reagents have failed (see Grignard reactions). Cesium reacts with hydrocarbons in which the activity of a C—H link is increased by attachment to the carbon atom of doubly linked or aromatic radicals. A brown, sohd addition product is formed when cesium reacts with ethylene, and a very reactive dark red powder, triphenylmethylcesium [76-83-5] (C H )2CCs, is formed by the reaction of cesium amalgam and a solution of triphenylmethyl chloride in anhydrous ether. 

Tetrazole, l-(p-substituted phenyl)-antimicrobial activity, 5, 835 Tetrazole, 5-thio-rearrangements, 5, 823 Tetrazole, 2-thioacyl-reactions, 5, 109 Tetrazole, 5-(o-tolyl)-tautomerism, 5, 804 Tetrazole, 5-(p-tolyl)-dipole moments, 5, 795 tautomerism, 5, 804 Tetrazole, 5-(trimethylsilylamino)-synthesis, 5, 832 Tefrazolecarbaldehydes reactions, 5, 820 Tetrazole-5-carbaldehydes reactions, 5, 820 Tetrazolecarbonitriles reactions, 5, 820 Tetrazole carbonyl compounds reactions, 5, 820 Tetrazolecarboxylic acid, 5-aryl-acidity, 5, 816... 

The results in the ionic liquid were compared with those obtained in four conventional organic solvents. Interestingly, the reaction in the ionic liquid proceeded with very high selectivity to give the a-arylated compound, whereas variable mixtures of the a- and (3-isomers were obtained in the organic solvents DMF, DMSO, toluene, and acetonitrile. Furthermore, no formation of palladium black was observed in the ionic liquid, while this was always the case with the organic solvents. 

In the presence of a precious metal catalyst, aryl halides can undergo dehalo-dimerization to give biaryl products, with varying degrees of selectivity. The major byproduct of this reaction is usually the dehalogenated aryl compound. This type of chemistry is currently one of the very few viable means for the large scale preparation of biaryl compounds. 

The alkylation of heterocyclic nitrogen compounds with alkyllithium reagents is called Ziegler alkylation. Aryllithium reagents give arylation. The reaction occurs... 

The course of the reaction of phosphinous amides with carboxylic acid chlorides is dependent on the characteristics of the iV-residue. Thus with N-aryl compounds this reaction gives chlorophosphanes and carboxamides. With AT-alkyl analogs the primary reaction products have not been identified but they hydrolyzed to carboxaldehydes [120]. 

The arylation of heteroaromatic compounds is also achieved by aryl-aryl coupling reaction. The arylation of A-methylimidazole with bromobenzene occurs under palladium catalysis (Equation (62)).72 The arylation of thiazole with aryl iodide occurs at the 2-position under PdCl2(PPh3)2/CuI catalysis.73 In this case, tetrabutylammonium fluoride improves the activity of the catalyst. Alternatively, thiazoles and benzothiazole are efficiently arylated... 

Palladium chemistry involving heterocycles has its unique characteristics stemming from the heterocycles inherently different structural and electronic properties in comparison to the corresponding carbocyclic aryl compounds. One example illustrating the striking difference in reactivity between a heteroarene and a carbocyclic arene is the heteroaryl Heck reaction (vide infra, see Section 1.4). We define a heteroaryl Heck reaction as an intermolecular or an intramolecular Heck reaction occurring onto a heteroaryl recipient. Intermolecular Heck reactions of carbocyclic arenes as the recipients are rare [12a-d], whereas heterocycles including thiophenes, furans, thiazoles, oxazoles, imidazoles, pyrroles and indoles, etc. are excellent substrates. For instance, the heteroaryl Heck reaction of 2-chloro-3,6-diethylpyrazine (1) and benzoxazole occurred at the C(2) position of benzoxazole to elaborate pyrazinylbenzoxazole 2 [12e]. 

Palladium chemistry of heterocycles has its idiosyncrasies stemming from their different structural properties from the corresponding carbocyclic aryl compounds. Even activated chloroheterocycles are sufficiently reactive to undergo Pd-catalyzed reactions. As a consequence of a and y activation of heteroaryl halides, Pd-catalyzed chemistry may take place regioselectively at the activated positions, a phenomenon rarely seen in carbocyclic aryl halides. In addition, another salient peculiarity in palladium chemistry of heterocycles is the so-called heteroaryl Heck reaction . For instance, while intermolecular palladium-catalyzed arylations of carbocyclic arenes are rare, palladium-catalyzed arylations of azoles and many other heterocycles readily take place. Therefore, the principal aim of this book is to highlight important palladium-mediated reactions of heterocycles with emphasis on the unique characteristics of individual heterocycles. 

The facile homogeneous catalysed reduction of acid chlorides to alcohols has many advantages over reduction with sodium borohydride in hydroxylic solvents where rapid reaction of the acid chloride with the solvent can occur [10]. The procedure has been incorporated into a simple one-pot conversion of aroyl chlorides into the corresponding benzyl chlorides (Scheme 11.1) under liquidrliquid or solid-liquid two-phase conditions [11], The reduction of a limited number of aryl compounds was reported with ca. 70% overall yields, although poorer yields result from the reduction of 4-nitro-, 2-cyano- and 2,4-dichlorobenzoyl chlorides, and the reduction failed completely with terphthaloyl chloride and with its 2,3,5,6-tetrafluoro derivative [11]. 

Domino-Heck Reactions-General Procedure 5.6 mg (25 pmol) of palladium(II) acetate and 55 pmol of the arsine ligand were dissolved in 3 ml of dry dimethyl formamide and the solution was stirred at 65°C (40°C for trimethylsilylacetylene) for 15 mitt Then, 127 mg (1.35 mmol) N-Benzoyl-2-azabicyclo[2.2.1]hept-5-en-3-one, 1 mmol of the aryl compound. Four hundred and eighty-eight microliters (3.50 mmol) of triethylamine, and 3.00 mmol of the phenylacetylene (or silylmethyl-acetylene) were added rapidly in one portion. The mixture was heated at the same temperature for 24 h. After cooling down to room temperature 50 ml of brine were added, the reaction mixture was extracted with ethyl acetate and dried over MgSO. The solvent was evaporated, the residue purified by column chromatography (n-Hexan-Ethyl acetate 4 1). 

The electrophilic substitution of the 3-aryl compounds (265, R = Ar, R = H) exemplified by the formation of 5-bromo- (265, R = Ar, R = Br) and 5-nitro derivatives (265, R = Ar, R = NOj) has been put forward as evidence against the meso-ionic formulation 265. lliis approach is unacceptable since ground state charge distribution cannot be deduced from reaction products. The aluminum-amalgam reduction of meso-ionic l,2,3-thiadiazol-4-ones (265) yields either N-mercaptoacetyl-A-arylhydrazines or Ar-acyl-A-arylbydrazines. Triethyl-oxonium tetrafluoroborate and meso-ionic l,2,3-thiadiazol-4-ones (265) yield 1,2,3-thiadiazolium tetrafluoroborates (267). The effect of solvent on the ultraviolet spectra of meso-ionic l,2,3-thiadiazol-4-ones (265) has been reported. ... 

Reactions of a number of l-phenylimidazole-2-carboxamides with chlorine in acetic acid, NCS, or hypochlorite failed to introduce chlorine into the 4- or 5-positions (80JHC409). Chlorination of a variety of 2,4-disubstituted imidazoles, however, was quite facile, Thus, 2,4-diesters [83JCS(P1)809] and 2-amino-4-aryl compounds [80IJC(B)526] were readily 5-chlorinated, and even when both the 4- and the 5-positions were blocked, as in 5-aminoimidazole-4-carboxamide, 2-chlorination with iodine monochloride was possible (89MI5). When all three carbons were substituted (e.g., in 2,4,5-triphenyl-, 2-chloro-4,5-diphenyl-, and 2-trichloromethyl-... 

The development of ferrocene 9 was part of our studies on planar-chiral compounds, which also involved the synthesis of other scaffolds such as chromium-tricarbonyl arenes [15], sulfoximidoyl ferrocenes [16], and [2.2]paracyclophanes [17]. In aryl transfer reactions, however, ferrocene 9 proved to be the best catalyst in this series, and it is still used extensively today. 

Later, the oxazolines 25 were examined to study the effects of matched/mismatched combinations of stereogenic centers on catalyzed aryl transfer reactions to aldehydes. Of these mandelic acid-derived catalysts, 25b gave the best results in terms of enantioselectivity (up to 35% ee), while diastereomer (l ,S)-25b proved to be superior to (S,S)-25b with respect to catalyst activity [29]. With both compounds, the absolute configuration of the product was determined by the oxazo-line moiety. 

After screening several compounds, including ferrocene 9 or cyrhetrene 14, which had previously been applied in the aryl transfer reactions to aldehydes and led to excellent enantioselectivities, we found, in collaboration with Erase, that only [2.2]paracyclophane 48 was capable of forming a catalyst system (Scheme 2.1.2.15). Subsequently, the substrate scope was evaluated, and several diaryl-methylamines 47 were obtained with excellent enantioselectivities (up to 97% ee) [69, 70]. 

E. Asymmetric Aryl Transfer Reaction to Carbonyl Compounds. 566... 

The reaction of isatin cr-chloride (160a) with electron-rich aryl compounds, in the presence of a Lewis acid, gives indolone salts (161) from which the indolones (162) can be liberated on treatment with base.49, 108, 109 The reaction of 160a with various amines, under these conditions, has been reported108 to give the unstable indolones (163) although later attempts to repeat the synthesis were unsuccessful.49... 

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