Iodine with arenes

The silver(I) complexes with the tetrakis(methylthio)tetrathiafulvalene ligand have been reported, the nitrate salt presents a 3D structure with an unprecedented 4.16-net porous inorganic layer of silver nitrate,1160 the triflate salt presents a two interwoven polymeric chain structure.1161 The latter behaves as a semiconductor when doped with iodine. With a similar ligand, 2,5-bis-(5,5,-bis(methylthio)-l,3,-dithiol-2 -ylidene)-l,3,4,6-tetrathiapentalene, a 3D supramolecular network is constructed via coordination bonds and S"-S contacts. The iodine-doped compound is highly conductive.1162 (Methylthio)methyl-substituted calix[4]arenes have been used as silver-selective chemically modified field effect transistors and as potential extractants for Ag1.1163,1164... 

Additional publications from Sanford et al. describe the full exploration of palladium-catalyzed chelate-directed chlorination, bromination, and iodination of arenes using N-halosuccinimides as the terminal oxidant <06T11483>. Moreover, an electrophilic fluorination of dihalopyridine-4-carboxaldehydes was reported by Shin et al. <06JFC755>. This was accomplished via transmetalation of the bromo derivative, followed by treatment with A-fluorobenzenesulfinimide as the source of electrophilic fluorine. 

Iodination of arenes.1 These two reagents generate nitryl iodide, which can iodinate arenes, particularly methylarenes, at 28°. The yield increases with the number of methyl substituents, being 90-95% with tri- and tetramethylbenzenes.1... 

Iodine, I2 Reacts with arenes in the presence of CuCl or H2O2 to yield iodoarenes (Section 16.2). 

Iodination of arenes2 Iodination of arenes can be effected by reaction with HgO HBF4 in the presence of iodine. The orientation conforms to that observed in electrophilic aromatic substitution except that ortho-attack is favored over para-attack in activated arenes. The method is particularly useful for meta-iodination of deactivated arenes (99% selectivity). 

Well-defined arene complexes of Group 4 metals in various oxidation states have been isolated. The air- and moisture-sensitive complexes Ti(r -arene)2 (56) have a sandwich structure similar to that of the related chromium compounds [176-178]. They have been used for deoxygenation of propylene oxide and coupling reaction of organic carbonyl compounds [179]. The first synthesis of 56 was cocondensation of metal vapor with arene matrix [176]. Two more convenient methods are reduction of TiCl4 with K[BEt3H] in arene solvent [180] and reaction of TiCl4(THF)2 with arene anions followed by treatment with iodine [170,176]. The latter method involves the formation of an anionic titanate complex, [Ti(ri -arene)2] (57), which can also be formed from KH and 56 [181]. 

Kitamura and Hossain have found that potassium peroxodisulfate can be used as an efficient oxidant for the preparation of (diacetoxyiodo)arenes and [bis(trifluoroacetoxy)iodo]arenes from iodoarenes [159,160]. A convenient modification of this approach employs the interaction of arenes with iodine and potassium peroxodisulfate in acetic acid (Scheme 2.16) [171]. The mechanism of this reaction probably includes the oxidative iodination of arenes, followed by oxidative diacetoxylation of Arl in situ leading to (diacetoxyiodo)-arenes 36. 

Iodine in combination with [bis(acyloxy)iodo]arenes is a classical reagent combination for the oxidative iodination of aromatic and heteroaromatic compounds [99], A typical iodination procedure involves the treatment of electron-rich arenes with the PhI(OAc)2-iodine system in a mixture of acetic acid and acetic anhydride in the presence of catalytic amounts of concentrated sulfuric acid at room temperature for 15 min [100,101]. A solvent-free, solid state oxidative halogenation of arenes using PhI(OAc)2 as the oxidant has been reported [102]. Alkanes can be directly iodinated by the reaction with the PhI(OAc)2-iodine system in the presence of f-butanol under photochemical or thermal conditions [103]. Several other iodine(in) oxidants, including recyclable hypervalent iodine reagents (Chapter 5), have been used as reagents for oxidative iodination of arenes [104-107]. For example, a mixture of iodine and [bis(trifluoroacetoxy)iodo]benzene in acetonitrile or methanol iodinates the aromatic ring of methoxy substituted alkyl aryl ketones to afford the products of electrophilic mono-iodination in 68-86% yield [107]. 

Several variants of polystyrene-supported [bis(acyloxy)iodo]arenes have been developed [11-21]. Poly[(diacetoxyiodo)styrene] (4) can be prepared in two steps from commercial polystyrene 1 with an average molecular weight ranging from 45 000 to 250 000 [11-13,19-21]. In the first step, polystyrene 1 is iodinated with iodine and iodine pentoxide in sulfuric acid to givepoly(iodostyrene) 3, which is subsequently converted into the diacetate 4 by treatment with peracetic acid (Scheme 5.3) [11, 13]. The loading capacity of the polymeric reagent 4 obtained by this procedure (Scheme 5.3) varies from 2.96 to 3.5 mmol g as measured by iodometry and elemental analysis [11-13]. 

The reactivity pattern of compounds 90 and 91 is similar to common hypervalent iodine reagents, as illustrated by their use for the oxidation of sulfides, oxidative iodination of arenes and a-tosyloxylation of ketones (Scheme 5.32) [89]. The products of all these reactions can be conveniently separated from the by-product, 3-iodobenzoic acid, by simple treatment with ion-exchange resin IRA-900 according to... 

This reaction has been modified by the addition of pyridine or a substoichiometric amount of iodine or arenes to the reaction solution and by treatment of the titanium powder with chlorosilaneJ ... 

Chlorination is carried out in a manner similar to bromination and follows a similar mechanism to give aryl chlorides. Fluorination and iodination of arenes are rarely performed. Fluorine is so reactive that its reaction with benzene is difficult to control. Iodination is very slow and has an unfavorable equilibrium constant. However, iodine, in the presence of a powerful oxidizing agent can be used for electrophilic aromatic iodination. In the following example, the oxidant peroxyacetic acid reacts with iodine to... 

Along with tin hydride-mediated arylations, electrochemical [61], photochemical [62] and iodine transfer methods [63] have each been successfully used for the generation of alkyl radicals in homolyhc aromahc subshtuhons. Moreover, nucleophilic a-oxyalkyl radicals, prepared from the corresponding aldehydes by treatment with either samarium diiodide [64] or stannyl radicals [65], reacted with arenes to afford the homolyhc subshtuhon products. In a series of reports, Zard highlighted the potenhal of xanthates as alkyl radical precursors in homolytic aromatic subshtuhons [66]. 

Scheme 6.17 H3 pervalent iodine-mediated CDC of thiophenes with arenes and heterocycles. TMSBr = hromotrimethylsilane and HFIP = hexafluoroisopropanol. ...

Sulfonic acids are prone to reduction with iodine [7553-56-2] in the presence of triphenylphosphine [603-35-0] to produce the corresponding iodides. This type of reduction is also facile with alkyl sulfonates (16). Aromatic sulfonic acids may also be reduced electrochemicaHy to give the parent arene. However, sulfonic acids, when reduced with iodine and phosphoms [7723-14-0] produce thiols (qv). Amination of sulfonates has also been reported, in which the carbon—sulfur bond is cleaved (17). Ortho-Hthiation of sulfonic acid lithium salts has proven to be a useful technique for organic syntheses, but has Httie commercial importance. Optically active sulfonates have been used in asymmetric syntheses to selectively O-alkylate alcohols and phenols, typically on a laboratory scale. Aromatic sulfonates are cleaved, ie, desulfonated, by uv radiation to give the parent aromatic compound and a coupling product of the aromatic compound, as shown, where Ar represents an aryl group (18). 

PART 1 HALOGENATED ARENES AND CARBOXYLATES WITH CHLORINE, BROMINE, OR IODINE SUBSTITUENTS... 

Fig. 2 Direct relationship of the charge-transfer absorption bands of various arene-iodine complexes (ordinate) with those of the corresponding aromatic complexes with different acceptors (abscissa) as indicated, T,... 

Dr. Thomas (to Dr. Hafemeister) You mentioned the possibihty of studying iodine in three different ways—either by decay to iodine or decay from iodine to either tellurium or xenon. Hence, you will end up either with tellurium as iodine or with xenon as an iodine complex. Since the electron s immediate environment of the nucleus will depend on its Z, aren t you likely to obtain different results depending on which way you do it ... 

To overcome problems associated with the removal of iodobenzene and its derivatives formed upon fluorination of arylalkenes and arylalkynes with (difluoroiodo)arenes, polymer-supported (difluoroiodo)arenes were proposed.139 With these agents, the separation procedures are reduced to filtration of the iodinated polymer. For this purpose popcorn polystyrene is io-dinated and then transformed into the difluoroiodide by treatment with xenon difluoride in the presence of hydrogen fluoride in dichloromelhane at 25 C. The amount of active fluorine bonded to iodine atoms on the polymer support is estimated by iodometric titration. The reactions with phenyl-substituted alkenes result in rearranged gew-difluorides. The procedure provides the same fluorination products as with (difluoroiodo)benzenc (see Section 4.13.) but in much higher yields, e.g. PhCF2CH2Ph (96%), PhCF2CH(Me)Ph (95%). PhCH2CF2H (86%), and l,l-difluoro-2-phenylcyclopentanc (91 %). 

The iodination of cross-linked polystyrene has been achieved using iodine under strongly acidic reaction conditions [55] or in the presence of thallium(III) acetate [61], but this reaction does not proceed as smoothly as the bromination. More electron-rich arenes, such as thiophenes [45,62-64], furans [46], purines [65], indoles [66], or phenols [67,68] are readily halogenated, even in the presence of oxidant-labile linkers (Figure 6.2). Polystyrene-bound thiophenes have also been iodinated by lithiation with LDA followed by treatment with iodine [64],... 

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