Aromatic compounds iodination

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). 

Charge-Transfer Compounds. Similat to iodine and chlorine, bromine can form charge-transfer complexes with organic molecules that can serve as Lewis bases. The frequency of the iatense uv charge-transfer adsorption band is dependent on the ionization potential of the donor solvent molecule. Electronic charge can be transferred from a TT-electron system as ia the case of aromatic compounds or from lone-pairs of electrons as ia ethers and amines. 

DIRECTED ALDOL CONDENSATIONS threo-4-HYDROXY-3-PHENYL-2-HEPTANONE, 54, 49 DIRECTED LITHIATION OF AROMATIC COMPOUNDS (2-DIMETHYL-AMINO- 5-METHYLPHENYL) DI-PHENYLCARBINOL, 53, 56 DIRECT IODINATION OF POLYALKYL-BENZENES IODODURENE, 51, 94 Disiamylborane, 53, 79 Disodium hydroxylaminedisulfo-nate, 52, 83... 

Most contrast agents elicit nephrotoxicity because they are primarily excreted by the kidneys. However, when administered in small doses, they constitute a rich source of GFR markers. The two major classes of contrast agents that are finding clinical utility as GFR markers are iodinated aromatic compounds and metal complexes. lodinated aromatics such as iohexol and iothalamate (Fig. 13) are commonly used as contrast agents for computed tomography (GT). They also have pharmacokinetics similar to inulin and hence are useful indicators of renal status [215]. The iodinated molecules used for GFR measurements consist of a triiodo-benzene core and hydrophilic groups to enhance solubility in aqueous medium. 

This case is related to the acid-catalyzed de-iodination of aromatic compounds which proceeds via its conjugate acid,... 

Cyanogen Iodide (ICN) has been used extensively for the cyanation of alkenes and aromatic compounds [12], iodination of aromatic compounds [13], formation of disulfide bonds in peptides [14], conversion of dithioacetals to cyanothioacetals [15], formation of trans-olefins from dialkylvinylboranes [16], lactonization of alkene esters [17], formation of guanidines [18], lactamization [19], formation of a-thioethter nitriles [20], iodocyanation of alkenes [21], conversion of alkynes to alkyl-iodo alkenes [22], cyanation/iodination of P-diketones [23], and formation of alkynyl iodides [24]. The products obtained from the reaction of ICN with MFA in refluxing chloroform were rrans-16-iodo-17-cyanomarcfortine A (14)... 

Aryl iodidesThe reagent iodinates aromatic compounds at 25° in reasonable yields (50-85%). 

A number of l-aryl-2-thienylethylenes have been photocyclized in the presence of an oxidizing agent (usually iodine) to polycyclic aromatic compounds. Representative examples are given in Table 1. The mechanism, as with the conversion of stilbene to phenanthrene, probably involves conversion of the trans-alkene to the c/s-form, cyclization to the dihydro isomer, and oxidation of the latter to the fully aromatic compound. The yield of the cyclized product seems to decrease when the ethylene is attached to the /3-position of the thiophene. 

Radioiodination involves the substitution of radioactive iodine atoms for reactive hydrogen sites in target molecules. The process usually involves the action of a strong oxidizing agent to transform iodide ions into a highly reactive electrophilic iodine II compound (typically I2 or a mixed halogen species such as IC1). Formation of this electrophilic species leads to the potential for rapid iodination of aromatic compounds... 

The halogenation of a wide variety of aromatic compounds proceeds readily in the presence of ferric chloride, aluminum chloride, and related Friedel-Crafts catalysts. Halogenating agents generally used are elemental chlorine, bromine, or iodine and interhalogen compounds (such as iodine monochloride, bromine monochloride, etc.). These reactions were reviewed554 and are outside the scope of the present discussion. 

The mechanism of this reaction shows that excitation of the substrate gave an n,n triplet state, but this excited state was unable to dissociate the carbon-iodine bond. This was demonstrated by showing that the n,n triplet state, when sensitized by chrysene, did not produce coupling products. Probably, the reaction occurred in an excited a,a triplet state mainly localized on the carbon-iodine bond, and the interaction between this triplet state and aromatic compounds led to homolytic cleavage of the C-I bond with the formation of both a 5-thienyl radical and a complex between the aromatic compound and the halogen atom. The formation of this complex was demonstrated by the presence of a short-lived transient with Amax = 510 nm, showing a second-order decay kinetics and a half-life of ca. 0.4 (is in laser flash photolysis. The thienyl radical thus formed... 

The purpose of present review is to summarize the application of different classes of iodine(III) compounds in carbon-carbon bond forming reactions. The first two sections of the review (Sects. 2 and 3) discuss the oxidative transformations induced by [bis(acyloxy)iodo] arenes, while Sects. 4 through 9 summarize the reactions of iodonium salts and ylides. A number of previous reviews and books on the chemistry of polyvalent iodine discuss the C-C bond forming reactions [1 -10]. Most notable is the 1990 review by Moriarty and Vaid devoted to carbon-carbon bond formation via hypervalent iodine oxidation [1]. In particular, this review covers earlier literature on cationic carbocyclizations, allyla-tion of aromatic compounds, coupling of /1-dicarbonyl compounds, and some other reactions of hypervalent iodine reagents. In the present review the emphasis is placed on the post 1990s literature. 

Aromatic compounds substituted by a heteroatom can be oxidized to corresponding quinone derivatives using hypervalent iodine reagents. Phenols can be oxidized either in the ortho [84] or in the para position [85] by using iodine(III) reagents. By this route, benzothiazoles of type 36, Scheme 17, are accessible and they have been tested as antitumor compounds [86,87]. 

Total Synthesis of Natural Products via Oxidation of Aromatic Compounds with Hypervalent Iodine Reagents... 

Benzylideneaminoguanidines (41) react with ethyl cyanoformimidate at room temperature to yield the intermediates (42) which cyclise to the dihydrotriazolotriazines (43) on brief reflux in methanol. These products are readily oxidised, e.g. by iodine, to the fully aromatic compounds [95M12],... 

The title reactions offer a possibility for exchanging the halogen atom in aryl halides (Hal = Cl, Br, I) first with a metal (MgHal, Li) and then with an electrophile. It is generally easier to introduce bromine than chlorine or iodine into aromatic compounds. Accordingly, functionalizations of aryl bromides are the preparatively most important examples of the title reaction. 

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