Acetonitrile, aryl

Aryl tellurium trichlorides are detellurated upon treatment with iodine in acetonitrile. Aryl iodides are formed in low yields. Higher yields are obtained when the reactions are carried out in the presence of ammonium fluoride. Bromine is not very effective in this reaction1. 2-Chloroethenyl tellurium trichlorides are efficiently converted to dihaloethenes upon treatment with iodine or bromosuccinimide2. 

By the action of concentrated hydrochloric acid at about 40° upon aryl-acetonitriles hydrolysis is arrested at the arylacetamide stage (see Section IV, 160 for the preparation of phenylacetamide by this method) ... 

Abbreviations Aik, alkyl AN, acetonitrile Ar, aryl Bu, butyl cod, 1,5-cyclooctadiene Cp, cy-clopentadienyl Cp , pentamethylcyclopentadienyl Cy, cyclohexyl dppm, diphenylphosphinome-thane dpme, Ph2PC2H4PMe2 Et, ethyl fod, 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octane-dionate HOMO, highest occupied molecular orbital LUMO, lowest unoccupied molecular orbital Me, methyl MO, molecular orbital nbd, norbornadiene Nuc, nucleophile OTf, triflate Ph, phenyl Pr, propyl py, pyridine THE, tetrahydrofuran TMEDA V,V,M,M-tetramethylethylenediamine. 

Sjwyer and coworkers have developed an efficient alternative UUmann synthesis of diaryl ethers, diaryl thioethers, and diarylamines using the SnAt reaction. Phenol, thiophenol, or aniline reacts v/ith an appropriate aryl halide, In the presence of KF-aliunina and 18-crovm-6 In acetonitrile or DMSO to give the corresponding diaryl ether or diaryl thio ether as shovm In Eqs. 9.6 and 9.7. ... 

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. 

During the course of an elegant synthesis of the multifunctional FR-900482 molecule [( )-43, Scheme 9], the Danishefsky group accomplished the assembly of tetracycle 42 using an intramolecular Heck arylation as a key step.24 In the crucial C-C bond forming reaction, exposure of aryl iodide 41 to a catalytic amount of tetra-kis(triphenylphosphine)palladium(o) and triethylamine in acetonitrile at 80 °C effects the desired Heck arylation, affording 42 in an excellent yield of 93 %. The impressive success of this cyclization reaction is noteworthy in view of the potentially sensitive functionality contained within 41. 

Combination of nickel bromide (or nickel acetylacetonate) and A. A -dibutylnorephcdrinc catalyzed the enantioselective conjugate addition of dialkylzincs to a./Tunsaturated ketones to afford optically active //-substituted ketones in up to ca. 50% ee53. Use of the nickel(II) bipyridyl-chiral ligand complex in acetonitrile/toluenc as an in situ prepared catalyst system afforded the //-substituted ketones 2, from aryl-substituted enones 1, in up to 90% ee54. 

Another method of hydroxy-de-diazoniation with better yields was published by Satyamurthy et al. (1990). This method consists of the hydrolysis of l-aryl-3,3-di-ethyltriazenes in acetonitrile using a boiling mixture of the sulfonic acid resin BioRad AG 50W-X12 and water. For nine monosubstituted diethylaryl-triazenes, phenols were obtained in yields of 65-95% (Scheme 10-10). Other triazenes and the same sulfonic acid resin were also used for halo-de-diazoniations (see Sec. 10.6). 

Dassbjerg and Lund (1992) showed that treating arenediazonium or 3-pyridinedi-azonium fluoroborates with ferrous chloride in a 3 1 mixture of tetrachloromethane and acetonitrile (but not acetonitrile alone) yields the corresponding aryl chlorides or 3-chloropyridine respectively, in nearly quantitative yield. 

A number of approaches have been tried for modified halo-de-diazoniations using l-aryl-3,3-dialkyltriazenes, which form diazonium ions in an acid-catalyzed hydrolysis (see Sec. 13.4). Treatment of such triazenes with trimethylsilyl halides in acetonitrile at 60 °C resulted in the rapid evolution of nitrogen and in the formation of aryl halides (Ku and Barrio, 1981) without an electron transfer reagent or another catalyst. Yields with silyl bromide and with silyl iodide were 60-95%. The authors explain the reaction as shown in (Scheme 10-30). The formation of the intermediate is indicated by higher yields if electron-withdrawing substituents (X = CN, COCH3) are present. In the opinion of the present author, it is likely that the dissociation of this intermediate is not a concerted reaction, but that the dissociation of the A-aryl bond to form an aryl cation is followed by the addition of the halide. The reaction is therefore mechanistically not related to the homolytic halo-de-diazoniations. 

A suitable catalyst for carboxy-de-diazoniations was found by Matsuda s group in their work on arylations of alkenes. As in the case of alkene arylations (Sec. 10.9), they used Pd11 acetate (2 mole %) and carbon monoxide (9 atm) for reactions with benzenediazonium tetrafluoroborate and sodium acetate in acetonitrile as solvent at room temperature (Nagira et al., 1980 82-85% yield). Similar results were obtained... 

Arylthallium bis(trifluoroacetates) (see 12-21) can be converted to aryl nitriles by treatment with copper(I) cyanide in acetonitrile. Another procedure uses excess aqueous KCN followed by photolysis of the resulting complex ion ArTl(CN)3 in the presence of excess KCN. Alternatively, arylthallium acetates react with Cu(CN)2 or CuCN to give aryl nitriles. Yields from this procedure are variable, ranging from almost nothing to 90 or 100%. 

The use of iodotrimethylsilane for this purpose provides an effective alternative to known methods. Thus the reaction of primary and secondary methyl ethers with iodotrimethylsilane in chloroform or acetonitrile at 25—60° for 2—64 hours affords the corresponding trimethylsilyl ethers in high yield. The alcohols may be liberated from the trimethylsilyl ethers by methanolysis. The mechanism of the ether cleavage is presumed to involve initial formation of a trimethylsilyl oxonium ion which is converted to the silyl ether by nucleophilic attack of iodide at the methyl group. tert-Butyl, trityl, and benzyl ethers of primary and secondary alcohols are rapidly converted to trimethylsilyl ethers by the action of iodotrimethylsilane, probably via heterolysis of silyl oxonium ion intermediates. The cleavage of aryl methyl ethers to aryl trimethylsilyl ethers may also be effected more slowly by reaction with iodotrimethylsilane at 25—50° in chloroform or sulfolane for 12-125 hours, with iodotrimethylsilane at 100—110° in the absence of solvent, " and with iodotrimethylsilane generated in situ from iodine and trimcthylphenylsilane at 100°. ... 

In a recent study, poly(aryl ether) dendritic branches terminated with triethyleneglycol chains were attached to Cgg [66] dendrimer 32 represents the fourth generation. The photophysical properties of these fullerodendrimers have been systematically investigated in three solvents, namely toluene, dichloromethane, and acetonitrile. On increasing dendrimer generation, it has been found that in each solvent (i) the maximum of the fullerene fluorescence band is red-shifted... 

The anodic oxidation reaction of sulphoxides was not much studied, and just a few reports are available so far. The conversion into the corresponding sulphones of some phenyl alkyl and diaryl sulphoxides (oxidation potential for 86 + 2.07 V vs. SCE in acetonitrile/NaC104 electrolyte, Pt anode) has been reported. Similarly, diphenyl suiphoxide was long known to be transformed in a quantitative yield into the sulphone (Pt anode, solvent glacial acetic acid). Additional examples of the oxidation of a suiphoxide function attached to aryl groups are available . 

Good yields of chlorides have also been obtained for reaction of isolated diazonium tetrafluoroborates with FeCl2-FeCl3 mixtures.100 It is also possible to convert anilines to aryl halides by generating the diazonium ion in situ. Reaction of anilines with alkyl nitrites and Cu(II) halides in acetonitrile gives good yields of aryl chlorides and bromides.101... 

Hexfluorophosphate salts behave similarly.108 The diazonium tetrafluoroborates can be prepared either by precipitation from an aqueous solution by fluoroboric acid109 or by anhydrous diazotization in ether, THF, or acetonitrile using r-butyl nitrite and boron trifluoride.110 Somewhat milder reaction conditions can be achieved by reaction of aryl diazo sulfide adducts with pyridine-HF in the presence of AgF or AgNQ3. 

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