With arenediazonium salts

TeCl4 in concentrated hydrochloric acid reacts with arenediazonium chlorides giving bis(arenediazonium) hexachlorotellurates that are decomposed by copper powder in acetone to give diaryltellurium dichlorides in low to medium yields.  

Bis(p-methoxyphenyl)tellunum dichloride (typical procedure) TeCl4 (27 g, 0.1 mol) or Te02 (16 g, 0.1 mol) dissolved in concentrated HCl (75 mL) is added to a stirred solution of (p-MeOCgH4N2) CL (0.2 M, from aminobenzene (24.6 g, 0.23 mol), half-concentrated HCl (150 mL) and NaN02 (14 g. 0.21 mol) in H2O (20 mL)) at -5°C. The mixtnre is stirred at -5°C for 20 min and then filtered. The filter cake is washed snccessively with acetone (3X50 mL), ether and petroleum ether. The diazonium hexachlorotellurate product is dried in air (52.8 g (86%)). 

Of the above product, 18.3 g (30 mmol) is carefully ground and suspended in acetone (95 mL). The snspension is vigoronsly stirred at -15°C while Cu powder (11.5 g, 180 mmol) is added over 40 min (the temperature must not exceed - 10°C). The mixtnre is stirred for a farther 20 min and is then allowed to warm at 20°C. The dark-colonred mixtnre is filtered to remove CuCl, the filter cake is washed with acetone and the filtrate and washings are combined. The acetone solntion is warmed at 20°C until a grey precipitate forms. The precipitate is collected and extracted repeatedly with boiling toluene. Activated charcoal is added to the tolnene extracts, the mixtnre is heated at reflux and filtered and most of the toluene is distilled from the filtrate. Petrolenm ether is added to precipitate the prodnct (p-MeOCgH4)2TeCl2, which is recrystallized from benzene (6.8 g (52%) m.p. 182°C). 

Like tellurium tetrachloride, aryltellurium (and alkyltellurium) trichlorides (and tribromides) nndergo condensation reactions with reactive organic substrates or metallo-organic reagents as well as addition reactions to C=C bonds, giving rise to tellnrinm dichlorides. 

Arenetellurolates, prepared from diaryl ditellurium compounds via reduction with sodium borohydride in organic media, interact with arenediazonium chlorides and arenediazonium tetrafluoroborates to produce unsymmetrical diaryl tellurium products in yields below 50%. The arenediazonium chlorides were added as aqueous solutions to the tellurolates. Arenediazonium tetrafluoroborates were used as solids. 

2-CarboxyphenyI Phenyl Tellurium 27.2 g (0.2 mol) of 2-aminobcnzoic acid arc dissolved in a mixture of 25 ml of concentrated hydrochloric acid and 70 ml of water. 13.8 g of sodium nitrite dissolved in 20 ml of water are added dropwise to the stirred amine solution cooled in an ice/water bath. Sodium hydrogen carbonate is added until the solution of the diazonium salt is slightly basic. 23 g (56 mmol) of diphenyl ditellurium are dissolved in a mixture of 30 ml of ethanol and 60 ml of THF. To this solution are added 2.3 g (60 mmol) of sodium borohydride dissolved in 33 m/of 1 M aqueous sodium hydroxide. The diazonium salt solution is quickly added to the warm benzenetellurolate solution. 10 /n/ of 1 M sodium hydroxide are then added and, after the evolution of nitrogen has ceased, the mixture is heated to complete the reaction. The mixture is poured onto ice and diphenyl ditellurium is extracted with benzene. The aqueous phase is acidified with 1 M hydrochloric acid and the product precipitates in analytically pure form yield 28.2 g (43%) m.p. 185° (from toluene). 

2-carboxyphenyl 4-methylphenyl tellurium 2-carboxyphenyl 3-thienyl tellurium 4-chlorophenyl phenyl tellurium 4-methylphenyl phenyl tellurium 4-methoxyphenyl 4-methylphenyl tellurium  

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Reaction with arenediazonium salts Adding a phe nol to a solution of a diazonium salt formed from a primary aromatic amine leads to formation of an azo compound The reaction is carried out at a pH such that a significant portion of the phenol is pres ent as its phenoxide ion The diazonium ion acts as an electrophile toward the strongly activated ring of the phenoxide ion... 

Arylhydrazones from reaction of /3-dicarbonyl compounds with arenediazonium salts... 

Many different nucleophiles—halide, hydride, cyanide, and hydroxide among others—react with arenediazonium salts, yielding many different kinds of substituted benzenes. The overall sequence of (1) nitration, (2) reduction, (3) diazotization, and (4) nucleophilic substitution is perhaps the single most versatile method of aromatic substitution. 

The diazonio group of arenediazonium salts can be replaced by alkenes and alkynes or, seen from the other reaction partner, alkenes and alkynes can be arylated with arenediazonium salts. The reactions are catalyzed by copper salts and, as found more recently, also by salts of palladium and other metals. 

Meerwein reactions can conveniently be used for syntheses of intermediates which can be cyclized to heterocyclic compounds, if an appropriate heteroatom substituent is present in the 2-position of the aniline derivative used for diazotization. For instance, Raucher and Koolpe (1983) described an elegant method for the synthesis of a variety of substituted indoles via the Meerwein arylation of vinyl acetate, vinyl bromide, or 2-acetoxy-l-alkenes with arenediazonium salts derived from 2-nitroani-line (Scheme 10-46). In the Meerwein reaction one obtains a mixture of the usual arylation/HCl-addition product (10.9) and the carbonyl compound 10.10, i. e., the product of hydrolysis of 10.9. For the subsequent reductive cyclization to the indole (10.11) the mixture of 10.9 and 10.10 can be treated with any of a variety of reducing agents, preferably Fe/HOAc. 

A different synthesis of arylmercuric chlorides (10.67) was described recently by Hu and Yu (1989). They showed that chloromercuryacetaldehyde (10.66) reacts with arenediazonium salts in aqueous acetone as shown in Scheme 10-89. The reaction is catalyzed by cupric chloride (yield 66-88% twelve substituted benzenediazonium chlorides were investigated). 

Barbituric acid can be considered as a cyclized malonic acid diamide (malonyl-urea). It is therefore a cyclic diketone that may be classified, in the sense of the compounds discussed in Section 12.6, as a coupling component with a methylene group activated by two carbonyl groups in the a- and a -positions. The reaction with arenediazonium salts was studied by Nesynov and Besprozvannaya (1971). These authors obtained coupling products (in good yield) that they considered to be arylhydrazones. Coupling with 4-(phenylazo)benzenediazonium chloride was studied by Chandra and Thosh (1991). The lH NMR spectra of these compounds are consistent with the arylhydrazone structure 12.68. 

Perfluoroalkyl carbanions, generated by reversible nucleophilic addition of a fluoride anion to fluoroalkenes, react with dry benzenediazonium chloride in dimethyl formamide, giving phenylazoperfluoroalkanes in 41-53% yield (Dyatkin et al., 1972). The dianion obtained from 1,2-dinitrobenzene with dipotassium cyclo-octatetraenide reacts in a complex way with arenediazonium salts, forming 4-aryl-azo-2-nitrophenol in 46-58% yield (Todres et al., 1988). 

In a very recent work, the Pd-catalysed cross-coupling reactions with arenediazonium salts under aerobic conditions in the presence of a chiral monothiourea ligand were reported (Scheme 25) [106]. Even if this Hgand bears four chiral centres, no test in asymmetric Heck-type reaction has been described so far. 

Through the use of arenediazonium salts, the straightforward transformation of amines into cross-coupling products can be realized. Whenever the diazonium salts do not tolerate bases and strong nucleophiles (e.g., phosphines), base- and phosphine-free protocols have to be used. Heterocyclic carbene ligands serve well in cross-coupling of Aryl- and vinylboronic acids, or alkylboronates with arenediazonium salts.369,370 Several convenient phosphine-free protocols have been developed for the same purpose.371-373... 

Reactivity of crown ether complexes with arenediazonium salts 420... 

REACTIVITY OF CROWN ETHER COMPLEXES WITH ARENEDIAZONIUM SALTS... 

Another new catalyst was described by Leardini and coworkers158, namely FeSC>4 in DMSO. It was applied to a Meerwein reaction of phenylethyne and substituted phenylethynes with arenediazonium salts containing a thioether group in the 2-position. 

Reaction of diarylditellurides with arenediazonium salts (typical procedure). p-Methoxy phenyl p-tolyl telluride. With heating and stirring in an atmosphere of nitrogen, sodium tetrahydroborate was added in small portions to a solution of 9.4 g of bis(p-methoxyphenyl) ditelluride in a mixture of 50 mL of ethanol and 15 mL of benzene until the solution was decolourized completely (1.5 g was required). Then 8.24 g of p-toluenediazonium fluo-roborate was added rapidly and the mixture was stirred for 1 h and poured into dilute HCl. The oil formed was extracted with ether, and the extract was washed with water and dried over CaCl2. Ether was evaporated, and the residue was dissolved in benzene and chromatographed on alumina (eluent hexane). After the evaporation of hexane, 4.8 g (36%) of the telluride was isolated, m.p. 64-64.5°C (hexane). 

S.3 Reaction of diaryl ditelluride with arenediazonium salts/CuXj ... 

Condensation of ester (44e) with the anion of malononitrile gave the alkene (44g) <91JPR35>. Oxadiazole (43e) and triethyl phosphite gave a methane phosphate which underwent a Wittig reation with aldehydes ArCHO to form alkenes (43f). When the alkyl side chain contained an active methylene group, as in (43g), reaction with arenediazonium salts ArN2X yielded arylhydrazones (43h) <88LA909>. 

Only activated aryl halides (e.g. 2,4-dinitrochlorobenzene and picryl chloride) react with pyridine, and the facility of these reactions is subject to much the same steric and electronic controls as alkylation. Picryl chloride forms characteristic yellow TV-picryl derivatives with pyridines. These have been used to help separate, purify and characterize particular liquid pyridines. Pyridine also undergoes quaternization with diphenyliodonium fluoroborate (equation 19). Treatment of pyridine 1-oxides with arenediazonium salts yields aryloxy quaternary salts (equation 20). 

Dimethylfuran-3(2ff)-one undergoes coupling with arenediazonium salts at pH 0 and furnishes 2-arylazo-2,5-dimethylfuran-3(2//)-ones which are readily converted into 1 -aryl-5-methyl-3-pyrazolones (79S283). 

Another method for the arylation of ethylene involves its reaction with arenediazonium salts (equation 177). [Pd(DBA)2] (105) was used as catalyst for the reaction.627 These reactions can be carried out at room temperature, unlike the reactions of aryl bromides above. At ethylene pressures of 0.6-0.8 MPa, styrene derivatives were obtained in good yields. [Pd(PPh3)4] (103) and [Pd(DBA)2] (105) plus diphos were also used as catalysts, but were less effective than complex (105) alone. The mechanism proposed is similar to that for arylation with aryl bromides and is given in Scheme 66.628... 

Palladium catalysts have been found which are effective in the Suzuki coupling reaction of arylboronic acids with aryl chlorides carrying electron-withdrawing groups.73 Biaryls may also be synthesized by cross-coupling of arylboronic acids with arenediazonium salts.74,75 There has been a report of the polymer-bound palladium-catalysed Suzuki coupling of aryl triflates with organoboron compounds.76 Arylbor-onates may themselves be synthesized by the palladium-catalysed reactions of... 

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