With Arylating Agents

With Arylating Agents 6.2.1. With Aryl Halides or Tolylsulfonylazohenzenes 

Unsymmetrical diaryl tellurium compounds generally cannot be prepared from arenetel-lurolates and aromatic halides under conditions suitable for aliphatic halides. Special conditions appear to be needed. Several methods have thus far been discovered for the arylation of arenetellurolates. 

Moderately activated iodobenzenes such as iodonitrobenzenes react with sodium benezenetellurolate in hexamethylphosphoric triamide at 90° in the presence of copper(I) iodide to give diaryl telluriums in yields of 50 to 60% In other aprotic solvents such as DMSO and DMF the reaction does not occur. 

2- Nitrophenyl Phenyl Tellurium Under nitrogen, 0.29 g (0.70 mmol) of diphenyl ditellurium are reduced with 0.03 g (0.73 mmol) of sodium borohydride in 5 ml of hexamethylphosphoric triamide at 70-80° with stirring for 0.5 h. Then 0.14 g (0.73 mmol) of copper(l) iodide are added whereupon the mixture turns black. 0.18 g (0.73 mmol) of l-iodo-2-nitrobenzene are added and the mixture is stirred well and heated at 80-90° for 1.5 h. The mixture is cooled, water is added, the whole is extracted with diethyl ether, the extract is washed with concentrated sodium chloride solution, and the organic layer is dried with anhydrous sodium sulfate. The solvent is evaporated under vacuum and the residue is chromatographed on a short column of alumina with hexane as eluent. Fractions containing the product are combined and evaporated to dryness and the residue is rccrystallized from ethanol yield 0.22 g (95%) m.p. 94°. 

Irgolic Organo Tellurium Compounds with 2 Te —C Bonds or 1 Te = C Bond 

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Halogenated pyridazines are generally inert as arylating agents in Friedel-Crafts reactions. The only example is the reaction of 3,6-dichloropyridazine with resorcinol and hydroquinone to give 3-aryl-6-chloropyridazines. 

The mfluoromethyl group activates the fluorine in position 4 ofperfluorotolu ene toward reaction with carbon nucleophiles Examples on che use of perfluoro-toluene as an arylation agent abound, and in all cases, the 4-fluonne atom is replaced predommantly or exclusively [% 87,88,89, 90 (equation 48) In perjluoromesity-lene, the aromatic fluorine atoms are activated toward Ar reaction, and a reaction... 

By comparison of the hydrolysis rate for the chloro- and bromobenzene catalyzed with cuprous oxide (Fig. 16), it is easy to show that the reactivity of bromobenzene as arylating agent is much higher than the reactivity of chlorobenzene the yields in phenolate is higher than 90 % after half an hour at 230 °C for the bromobenzene whereas the chlorobenzene affords only about 65 % after 15 hours, even at higher temperature (250°C). 

Reactions of the ferrocyanide ion with alkylating agents, and reactions of iron(II) salts with alkyl or aryl isocyanides, have led to complexes of several types including [FeLJ, [FeLjX], cis- and tranf-FeL4(CN)2 and FeL4X2 this chemistry is reviewed by Malatesta and Bonati (90). There has been some extension of this work. 

Arylcopper can be used as arylation agent to react with diorganotin dibromides, providing interesting aryl-substituted organotin bromides324 ... 

In Group IV metal complexes, metallocene complexes are the main catalyst precursors for hydrogenation. Two major catalytic systems have been used 1) Cp2MR2 (R=H, Alkyl, Aryl) and 2) Cp2MX2 in combination with alkylating agent or an hydride (Table 6.1). The catalytic tests are typically run with 50 equiv. of substrate per metal, but in some cases turnover numbers (TONs) exceeding 1000 can be achieved [35]. 

Dibromo-l,4-xylene or its 2,5-dichloro derivative is obtained by bromination or, correspondingly, chlorination of 1,4-xylene. It is oxidized to form 2,5-dibro-moterephthalic acid or its dichloro derivative 59. Subsequent reaction with aryl-amine, for instance in the presence of copper acetate, affords 2,5-diarylamino-terephthalic acid 60. It is also possible to replace the halogen atoms stepwise by arylamino moieties [11]. Cyclization to form linear trans-quinacridones, as in the above-mentioned method, is achieved by using acidic condensation agents ... 

The catalysed alkylation of l//,4//-pyrazol-5-ones is solvent dependent. In benzene, bis-alkylation occurs at the 4-position whereas, in a carbon disulphide benzene mixture, O-alkylation is observed, although the major product (4, Scheme 5.22) results from nucleophilic attack by the pyrazolone on the carbon disulphide, followed by alkylation of the dithiolate dianion [92]. The catalysed reaction of 2-thiono-3-aryl-thiazolidin-4-ones with alkylating agents under soliddiquid two-phase conditions results in alkylation at the 5-position (60-80%) [93]. The aldol condensation of the thiazolidinones with aryl aldehydes is also catalysed by quaternary ammonium salts. 

In summary, a number of effective chiral reducing agents have been developed based on the modification of LAH. Excellent results have been obtained with aryl alkyl ketones and a,p-acetylenic ketones. However, dialkyl ketones are reduced in much lower enantiomeric excess. This clearly indicates that steric effects alone do not control stereoselectivity in these reductions. Systematic studies have been carried out with the objective of designing improved reagents. A better understanding of the mechanisms and knowledge of the active species is required in order to provide more accurate models of the transition states of the key reduction steps. 

Three main routes have been well established for the preparation of diorganyl ditellurides (1) The reaction of sodium ditelluride with alkylating or arylating agents. 

Cyclizations with perfluoroacylating agents seem to be quite general for the synthesis of 5(2i7)-oxazolones with aromatic substituents directly bonded to the heterocyclic ring. For example, perfluoroacylation of a solution of an arylgly-cine containing a phosphorus trihalide affords 4-aryl-2-(perfluoroalkyl)-5(2//)-oxazolones (Table 7.1, Fig. 12) Similar results were obtained when amino nitriles were used as starting materials. ... 

Mowery and DeShong reported on the use of siloxanes 72 (Figure 16) as versatile transmetallation agents for Pd(dba)3-catalyzed couplings with aryl halides and allylic alcohol derivates, in the presence of TBAF and at high temperature (95 They later used aryl silatrane 73 (Figure 16) as a suitable partner for the fluoride-promoted... 

Mowery and DeShong used the commercially available hypervalent silicate complex TBAT as a phenylating agent for the cross-coupling reaction with allylic esters. They later reported on the use of the same organosilane for the coupling with aryl iodides and triflates and electron-deficient aryl bromides. The reactions were catalyzed by either Pd(dba)2 or [Pd(allyl)Cl]2 without the need of added phosphine ligands. 

Palladium-catalyzed arylation of the electron-rich olefin bntyl vinyl ether has been accomplished in the ionic liquid l-butyl-3-methylimidazolium tetrafluoroborate using as the arylating agents aryl iodides and bromides instead of the commonly used, but commercially unavailable and expensive, aryl triflates. The reaction proceeds with high efficiency and remarkable regioselectivity, leading almost exclnsively to substitution by various aryl groups at the olefinic carbon a to the heteroatom of butyl vinyl ether (Xu et ak, 2001). 

Arylation of alkenes catalyzed by palladium compounds is known as the Heck reaction [65]. While these reactions are very sensitive to steric effects, subtle electronic contributions to the regiochemical outcome may be assessed by comparing reactions of alkenes with similar substitution patterns. The arylating agents, being the nucleophilic arylpalladium species, tend to dictate the facility of their reaction with unsym-metrical, electron-deficient alkenes. 

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