Iodonium salts heterocyclic

Palladium-catalyzed directed intramolecular activations of aryl C-H bonds have been reported, as in the phenyla-tion of heterocycle analogs. Palladacycles are proposed intermediates, acting as effective catalysts, and the mechanism is likely to proceed via oxidation of Pd(ll) to Pd(iv) by the iodonium salt, as for the Equation (57), which described the activation of benzylic i/-CH bonds (Equations (121)—(123).109... 

It was reported that Pd(0)-catalyzed coupling reactions of allenic alcohols, amines and acids with hypervalent iodonium salts afforded cyclized heterocyclic tetrahydrofurans, tetrahydropyrans, pyrrolidines, piperidines, or lactones under mild conditions <99SL324>. Intramolecular 1,5-hydrogen atom transfer radical cyclization reaction of pyrrolidine derivatives was examined. Reaction of 3,4-dialiyloxy-JV-(0-bromobenzyl)pyrtolidine gave hexahydro-... 

A number of 1-hydroxybenziodoxoles and related heterocycles, more efficiently through their triflates, upon reaction with RC = CSiMe3 afforded either alkynyl iodonium salts or the corresponding cyclic iodanes, depending on the conditions. Some of these compounds reacted with NaN3 and were converted into /J-azidoalkenyl derivatives as illustrated in Scheme 55 [127,167,168]. 

This chapter includes diaryl iodonium salts and some related heteroaromatic and heterocyclic analogues other categories are discussed separately in Chapter 9. Arylation is the dominating reaction of diaryl iodonium salts. From the applied point of view, they are useful in photopolymerizations and for the chemical amplification in imaging systems. Also, they show interesting biological activity [1,2]. 

Trimethylsilyl cyanide (0.54 ml, 4 mmol) was added to a stirred suspension of iodosyl triflate (0.58 g, 2 mmol) in dichloromethane (15 ml) at — 78°C under nitrogen. The mixture was allowed to warm to — 20°C and stirred at this temperature for 15 min until the formation of a clear solution. The solution was cooled to — 78°C and transferred to a cold stirred solution of the appropriate tributyltin heterocycle (4 mmol) in dichloromethane (15 ml). The mixture was brought to room temperature and crystallized by the addition of dry hexane (20-30 ml). The precipitated iodonium salt was filtered under nitrogen, washed with dry ether (30 ml) and dried in vacuo. Mono or bis hetaryl iodonium salts prepared by these and related methods also involved groups coming from selenophene [23], pyrazoles [24], benzothiophene [21], etc. 

Diaryliodonium salts, with few exceptions, are stable compounds towards heat, oxygen and humidity they are mildly light-sensitive and should be stored in the dark, without refrigeration. Generally, their reactivity is less pronounced than that of other hypervalent iodine compounds. Indeed, in several of their reactions relatively drastic conditions may be necessary, especially for the least reactive heterocyclic iodonium salts. The search for optimum conditions is often desirable even for well-established reactions, by applying new findings concerning the use of specific... 

The thermolysis of iodonium salts in which their counteranion is a halide may be performed in the molten state or in solution the products are an iodoarene and a haloarene. The reaction which is a nucleophilic aromatic substitution is, however, not preparatively useful an exception was 3-indolyl phenyliodonium trifluoroace-tate which on heating with various chlorides and bromides in DMSO afforded variable mixtures of 2- and 3-haloindoles. By contrast, the jV-methyl and N-benzyl analogues gave only 2-chloro derivatives [58], Sometimes useful products may be obtained from the thermolysis of dibenziodolium or other heterocyclic salts, as exemplified in the preparation of l-iodo-2-(2-iodophenyl)naphthalene [59] ... 

The arylation of nitrite and azide anions as well as some amines can be of synthetic interest in some instances for example, difuryl, dithienyl and diselenophyl iodonium salts were useful substrates for the preparation of the corresponding nitro heterocycles [61]. Diphenyliodonium 2-carboxylate transferred its carboxy-late-bearing ring with high specificity to several anilines in a reaction especially suitable for the preparation of weakly basic and sterically hindered A-arylanthranilic acids. 

The same salt from acetylene afforded similarly adducts with furan and 1,3-diphenyl i sobenzofuran. A number of alkynyl iodonium salts underwent also [2 + 3] cycloaddition with dipolarophiles such as a-diazocarbonyl compounds, nitrile oxides, etc., allowing the preparation of iodonium salts with an alkenyl or a heterocyclic moiety [7],... 

Syntheses of cyclic iodonium salts and other heterocycles from alkenylio-donium salts 00UK118. 

Reaction of trimethylsilylalkynes with 16 in dichloromethane in the presence of BF3 OEt2 at room temperature followed by heating in methanol at 60 °C results in the stable heterocyclic alkynyliodonium salts 17 [Eq. (9)] [31]. These species represent intramolecular iodonium salts where the counterion is a carboxylate. Unlike the acyclic alkynyl(phenyl)iodonium carbox-ylates 18, that are unstable to isolation and decompose to the corresponding alkynyl benzoates 19 [Eq. (10)] [32], the cyclic analogs 17 are readily isolable. 

To date, six single-crystal X-ray molecular structures of alkynyliodonium compounds have been reported four aIkynyl(phenyl)iodonium salts including the substituted cyanoethynyl salt, one heterocyclic and one dialkynyliodonium salt, all with oxyanions. Key structural data for these compounds are summarized in Table 3-1. 

Kang et al. showed that under the catalysis of Pd(PPh3)4 (5 mol%) the reactions of 4,5- or 5,6-allenyl alcohols/toluenesulfonamides and 4,5- or 5,6-allenoic acids with hypervalent iodonium salts led to the formation of five- or six-mem-bered-ring heterocyclic products (Schemes 22 and 23) [15, 16]. With AT-(3,4-pentadienyl)toluenesulfonamide, a mixture of four- and six-membered-ring products was also formed. 

When di-iodine reacts with heterocycles like thioamides or selonoamides new charge transfer complexes containing iodine are obtained [1-10], Various types of such complexes have been obtained thus far, including so called spoke or extended spoke structures (DS 1 or DS l -1 ) (D is the hgand donor) [1], Also iodine coordinated to two thioamides to form iodonium salts ([DS-I-DS] (Ij) )... 

Crivello and Lee have described the synthesis and characterization of a series of (4-alkoxyphenyl)phenyliodonium salts 7, which are excellent photo- and thermal-initiators for the cationic polymerization of vinyl and heterocyclic monomers [17]. Iodonium salts 7 are conveniently prepared by the reaction of alkoxyphenols 6 with [hydroxy(tosyloxy)iodo]benzene followed by anion exchange with sodium hexafluoroantimonate (Scheme 7.2). Products 7 have very good solubility and photoresponse characteristics, which make them especially attractive for use in UV curing applications. Compounds 7 with alkoxy chains of eight carbons and longer are essentially nontoxic, compared to diphenyliodonium hexafluoroantimonate, which has an oral LD50 of 40 mg kg (rats) [17]. 

N-Arylations of several other heterocycles have also been accomplished, including mono- and diarylation of imidazoles to form N-aryl imidazoles and imidazolium ions, respectively, which was extended to the synthesis of bis (N-heterocyclic) ligands [101, 102]. Pyridinium triazolinone ylides were obtained by a one-pot copper-catalyzed carboxygenation and chemoselective N-arylation of triazolopyridines with aryl(mesityl)iodonium salts (Scheme 6a) [103]. 

Besides iodonium ylides, alkynyliodonium salts are also useful in heterocyclic synthesis. These salts are obtained from the reaction of the alkynes with an appropriate organohypervalent iodine reagent (Scheme... 

A variety of five-membered nitrogen heterocycles can be prepared efficiently by inter- or intramolecular addition/cyclizations of sulfonamide anions with alkynyliodonium salts. The intermolecular variant employs the combination of the amides 172 or anilides 174 with propynyl(phenyl)iodonium triflate (Scheme 65) [131,132]. The yield of dihydropyrroles 173 in this cyclization is extremely sensitive to the nature of the protective group P the tosyl group in 172 proved... 

Many heterocycles in which the iodonium cationic centre is part of a ring are known even an iodiranium salt has been isolated from adamantylideneadamantane and... 

Likewise, interaction of terminal alkynes with 20 in refluxing acetonitrile in the presence of toluenesulfonic acid gives the intramolecular heterocyclic alkynyliodonium salts 21 [Eq. (11)] [33]. A wide range of the alkyl- and phenyl-substituted congeners 21 of these intramolecular analogs of the acyclic iodonium tosylates, 9, are obtained in 26-70% isolated yields. 

Various flve-membered heterocycles can be prepared by inter- or intramolecular addition/cyclizations of appropriate nucleophiles with alkynyliodonium salts via alkylidene carbene intermediates [856, 978, 979]. The intermolecular variant of this cyclization has been employed in the synthesis of 3-substituted-5,6-dihydroimidazo[2,l-( ]thiazoles [997], 2-substituted imidazo[l,2-a]pyrimidines [998] and 2-substituted-imidazo[l,2-fl]pyridines [999]. In a representative example, 2-substituted imidazo[l,2-fl]pyridines 744 were synthesized in good yield by cyclocondensation of 2-aminopyridine (742) with alkynyl(phenyl)iodonium tosylates 743 under mild conditions (Scheme 3.293) [999]. The mechanism of this cyclization involves... 

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