With arenes

The condensation of tellurium tetrachloride with aromatic compounds was one of the first methods for the preparation of aryl tellurium trichlorides. Alkyl aryl ethers react easily with tellurium tetrachloride in refluxing chloroform or carbon tetrachloride (Vol. IX, p. 1153). The trichlorotelluro group enters in the / ara-position to the alkoxy group. Several additional monosubstituted benzenes and substituted phenols were found to condense with tellurium tetrachloride (Table 7, p. 306). 

4-Acetoxyphenyl Tellurium Trichloride A 250 ml flask is fitted with a reflux eondenser carrying a drying tube. To a refluxing solution of 27 g (0.1 mol) of tellurium tetrachloride in 75 ml of dry toluene are added 

6 g (0.1 mol) of 4-acetoxybenzene dissolved in SO ml of dry toluene. The mixture is heated under reflux until evolution of hydrogen chloride ceases (4 h). The mixture is then allowed to cool whereupon the product crystallizes. The crystals are filtered, washed with petroleum ether, and dried in a vacuum desiccator yield  

3-Chloro-4-hydroxyphenyl Tellurium Trichloride In a 100 ml flask under an atmosphere of dry nitrogen 5.0 g (18 mmol) of tellurium tetrachloride and 25.0 g (195 mmol) of 2-chlorophenol are heated at 75° until evolution of hydrogen chloride ceases. The precipitated product is filtered, and washed successively with carbon tetrachloride, benzene, and chloroform to remove unreacted starting material. The product is then dissolved in 50 ml of acetone and precipitated by addition of 50 ml of carbon tetrachloride yield 5.3 g (81%) m.p. 166°. 

Aromatic compounds without substituents that promote electrophilic attack also condense with tellurium tetrachloride although more drastic conditions than required for the reactions with alkoxybenzenes must be employed (Table 8, p. 307). 

When the reactions of telluiium tetrachloride with activated arenes (such as alkoxyben-zenes) are performed using a large excess of the organic substrate and/or under prolonged heating at high temperatures, diaryltellurium dichlorides are formed in high yields.  

Di-(p-methoxyphenyl)tellurium dichloride (typical procedure) Anisole (64.8 g, 0.6 mol) and TeCl4 (27.0 g, 0.1 mol) are heated at 160°C for 6 h. The mixture is allowed to crystallize under vacuum (30.6 g (90%)). The product is recrystallized from MeCN as colourless crystals (m.p. 181-182°C). 

In the presence of Lewis acids such as aluminium trichloride, diaryltellurium dichlorides are formed even with non-activated arenas. 

Diphenyltellurium dichloride (typical procedure) TeCl4 (27.0 g, 0.1 mol) and benzene (150 mL) are heated under reflux for 0.5 h. The solution is then cooled at 60°C and AICI3 (1.0 g) is added. Evolution of HCl ensues. The mixture is then refluxed for 12 h, cooled, filtered to remove the formed trichloride and inorganic impurities. After evaporation, the residue is recrystallized from MeCN (12.6 g (36%) m.p. 160-161°C). 

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The oxidative coupling of thiophene, furan[338] and pyrrole[339,340] is also possible. The following order of reactivity was observed in the coupling of substituted furans[338] R = H > Me > CHO > CO Me > CH(OAc)i > CO2H. The cross-coupling of furans and thiophenes with arene is possible, and 4-phenylfurfural (397) is the main product of the cross-coupling of furfural and benzene[341]. 

In the preceding chapter the special stability of benzene was described along with reac tions in which an aromatic ring was present as a substituent Now we 11 examine the aromatic ring as a functional group What kind of reactions are available to benzene and Its derivatives What sort of reagents react with arenes and what products are formed m those reactions ... 

A different reaction takes place when electrophiles react with arenes Substitution is observed instead of addition If we represent an arene by the general formula ArH where Ar stands for an aryl group the electrophihc portion of the reagent replaces one of the hydrogens on the ring... 

The —OH group of phenols makes it possible for them to participate m hydrogen bonding This contributes to the higher boiling points and greater water solubility of phenolic compounds compared with arenes and aryl halides... 

The 2-methyl group of 2-methyl-3T/-azepines, e.g. 11, is surprisingly reactive and undergoes rapid deuterium exchange and, in the presence of base, aldol condensation with areneal-dehydes to yield styryl derivatives, e.g. 12.76108... 

Table 2. 1,4-Diazocine Derivatives by the Condensation of 1,2-Dicarboxylic Acid Derivatives with Arene-1.2-diamines...

Beside these free radical reactions of sulfur dioxide, its electrophilic reactions generating sulfinates with organometallic compounds453,454 or sulfinic acids with arenes under Friedel-Crafts conditions455 are well known. To complete these three-component syntheses, the sulfinates prepared first are transformed to sulfones by reactions with appropriate electrophiles, discussed earlier in this chapter, i.e. equation 82. 

Mixed arene-2,5-dihydro-l,2,5-thiadiborole-iron complexes have been synthesized by a novel route thermally unstable bis(arene)iron sandwich complexes, prepared by cocondensation of iron atoms with arene, react in the temperature range of -100 to -60°C with free Et2C2B2Mc2S to form reactive intermediates that decom-... 

The reaction of rhodium vapor with arene affords arene-stabilized Rh microclusters, soluble in the excess of the... 

Me2CuLi to enones with sulfonamide hgands 94 MeLi to cyclohexenone with p-amino sulfide ligand 88-9 MeMgl to acychc enone with arene-thiolatocopperfl) complexes 90-1... 

Triethyl orthoformate or chloroform can react with arene nucleophiles to give triphenylmethanes with three identical aryl groups.5,52,67 In addition, dialkylarylamines, when treated with dialkoxycarbenium tetrafluoro-borates under thermodynamic conditions or with triethyl orthoformate/zinc chloride in ether under anhydrous conditions, give triarylmethanes.68 For example, 4-methoxycarbazole and triethyl orthoformate in the presence of acid catalyst give 44 in 66% yield69 (Scheme 7). In general, phenolic or... 

Scheme 1 Epoxide opening with arene radical anions under ET conditions...

In contrast with the role of cofactor B12 in methionine synthase (methyl group transfer to a thiol), functional Bi2 model complexes have provided a formidable challenge. Several oxime alkyl-cobalt (structural) B12 models when reacted with arene- and alkanethiolates lead only to... 

Co-condensation of transition metal atoms with arenes such as benzene and toluene is well known to yield bis-arene-metal compounds. However, in many cases the yields based on the metal atoms are less than 40%. Evidence that competing reactions such as carbon-hydrogen activation can occur is provided by the isolation of non-metal-containing products such as biaryl derivatives (2JL). ... 

A,A -di(/>-dimethylamino-benzyl) derivatives of di(imidazolidinylidene)gold(i) salts were polymerized into polyimides by condensation with arene-tetracarboxylic anhydrides. The products are tough, but flexible, and have high glass transition temperatures and high thermal stability. Yellow films of the materials are transparent above 365 nm.279... 

Labelling experiments provided the evidence that the Fe1- and Co1-mediated losses of H2 and 2H2 from tetralin are extremely specific. Both reactions follow a clear syn- 1,2-elimination involving C(i)/C(2) and C(3)/C(4), respectively. In the course of the multistep reaction the metal ions do not move from one side of the rr-surface to the other. The kinetic isotope effect associated with the loss of the first H2 molecule, k( 2)/k(Y)2) = 3.4 0.2, is larger than the KIE, WFLj/ATHD) = 1.5 0.2, for the elimination of the second H2 molecule. A mechanism of interaction of the metal ion with the hydrocarbon n-surface, ending with arene-M+ complex 246 formation in the final step of the reaction, outlined in equation 100, has been proposed241 to rationalize the tandem MS studies of the unimolecular single and double dehydrogenation by Fe+ and Co+ complexes of tetraline and its isotopomers 247-251. 

Dinuclear palladium complexes catalyze m-hydroarylation of alkynes with arenes.56 The reaction of 3-hexyne with benzene in the presence of a dinulear palladium complex Pd2R2(M-OH)(//-dpfam) [dpfam = j/V,Ar -bis[2-(diphenyl-phosphino)phenyl]formamidinate, R=/>-Tol] and tri(/z-butyl)borane at 100 °C for 4h affords ( )-3-phenyl-3-hexene quantitatively (Equation (53)). The hydroarylation of 3-hexyne with monosubstituted benzenes ( )-3-aryl-3-hexenes with a 2 1 ratio of the meta- and ra -isomers. This regioselectivity is different from that of the hydroarylation of diphenylacetylene catalyzed by Rh4(GO)12.57... 

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