Aryl-A3-iodanes

The term iodane refers to hydrogen iodide (HI), a colorless non-flammable gas. According to IUPAC rules, compounds with nonstandard bonding number are shown by the lambda notation thus, H3I is called A3-iodane and H5I A5-iodane. The most common ArIL2 (L heteroatom ligands) with decet structure is named aryl-A3-iodane and ArIL4 with dodecet structure aryl-A5-iodane. 

When (ferf-butylethynyl)aryl-A3-iodanes were mixed with an excess of 2-hthiofuxan or 2-lithiothiophene and subsequently treated with p-TsOH, (2-fuxyl)- or (2-thienyl)aryl-A3-iodanes were obtained [38]. This carbon ligand exchange probably proceeds via selective elimination of the most stable alkynyl-lithium from the tetracoordinated iodate 20 [39]. 

Most important mode of reactions of hypervalent A3-iodanes is their reductive transformation to univalent iodide. This process is very facile and energetically favorable, and often proceeds without the assistance of the added reagent. The rate of this unimolecular process was measured by solvolysis of alkenyl(aryl)-A3-iodanes. 

Aryl-A3-iodane oxidation of amines to imines also involves a combination of ligand exchange and successive reductive -elimination. Oxidation of pyrrolidine with iodosylbenzene 18 affords quantitatively an equilibrium mixture of 1-pyrroline and its trimer [72]. When oxidation of piperidine with 18 (2 equiv) was carried out in water, 2-piperidone was produced [73]. In the latter reaction, a sequence of ligand exchange and reductive -elimination was repeated two times [Eq. (38)]. 

Aryl-A3-iodanes bearing an electron-deficient alkyl ligand such as aryl(sul-fonylmethyl)-A3-iodanes (Section 3.2.7) and aryl(perfluoroalkyl)-A3-iodanes are relatively stable. A series of (perfluoroalkyl)phenyl-A3-iodanes 96 were synthesized in good yields by treating bis(trifluoroacetoxy)-A3-iodanes with benzene in the presence of triflic acid [47]. The AModanes 96 transfer the perfluoroalkyl groups to a variety of nucleophiles with reductive elimination of iodobenzene. The nucleophiles involve Grignard reagents, alkyllithiums, enolate anions, alkenes, alkynes, trimethylsilyl enol ethers, arenes, phenols, and thiols. In these reactions, the AModane 96 serves as a source of the perfluoroalkyl cation and, in... 

Recent progress on the use of hypervalent iodine reagents for the construction of carbon-het-eroatom (N, O, P, S, Se, Te, X) bonds is reviewed. Reactions of aryl-A3-iodanes with organic substrates are considered first and are loosely organized by functional group, separate sections being devoted to carbon-azide and carbon-fluorine bond formation. Arylations and alkenyla-tions of nucleophilic species with diaryliodonium and alkenyl(aryl)iodonium salts, and a variety of transformations of alkynyl(aryl)iodonium salts with heteroatom nucleophiles are then detailed. Finally, the use of sulfonyliminoiodanes as aziridination and amidation reagents, and reactions of iodonium enolates formally derived from monoketones are summarized. 

Keywords. C-heteroatom bond formation, Aryl-A3-iodanes, Iodonium salts, Sulfonyliminoiodanes, Hypervalent iodine... 

Aryl-A3-iodanes 1 are electrophilic at iodine and undergo ligand exchange with a variety of nucleophilic species, including organic functional groups (Scheme 1). Such reactions may be regarded as nucleophilic substitutions at trivalent... 

The use of aryl-A3-iodanes for C-heteroatom bond formation at the a-carbon atoms of ketones and / -dicarbonyl compounds, and related transformations of silyl enol ethers and silyl ketene acetals, has been exhaustively summarized in recent reviews (Scheme 27) [5,8]. Reactions of this type are especially useful for the introduction of oxygen ligands (e. g., L2 = OH, OR, OCOR, 0S02R, OPO(OR)2), and have been extensively utilized for the synthesis of a-sulfonyl-oxy ketones and a-hydroxy dimethyl ketals. 

The use of hypervalent iodine reagents for heteroatom-heteroatom bond forming reactions is well established in the context of classical oxidation chemistry [1-11]. For example, oxidations of anilines to azobenzenes, thiols to disulfides, and sulfides to sulfoxides with aryl-A3-iodanes were documented decades ago [1-5]. During the last ten years, particular attention has also been given to oxidative transformations of compounds derived from heavier elements, including the interception of reaction intermediates or initially formed products with external nucleophiles. A second important development is the utilization of sulfonyliminoiodanes, ArI = NS02R, for heteroatom-nitrogen bond formation, especially for imidations of sulfur, selenium, phosphorus and arsenic com-... 

Oxidations of sulfides to sulfoxides can be effected with various aryl-A3-iodanes. For example, (dichloroiodo)benzene (1) in aqueous pyridine [12], [bis(ace-toxy)iodo]benzene (2, BAIB) in acetic anhydride (H2S04) [13], and [bis(trifluo-roacetoxy)iodo]benzene (3, BTIB) in chloroform [14] have all been utilized for this purpose (Scheme 1). 

In summary, recent investigations of reactions of aryl-A3-iodanes,ArIL1L2,with heteroatom substrates, derived from third-row elements and beyond, provide examples of P-O, S-O, Se-O, Se-P, Se-S, Te-O, Bi-O and Sb-0 bond formation. Sulfonylimino(aryl)iodanes, ArI = NS02R, are especially useful as imidation reagents, and have been utilized for the construction of P-N, S-N, Se-N, and As-N bonds. Diaryliodonium salts have been employed indirectly for formation of the Se-Se bond. 

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