Polyvalent iodine compounds

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. 

It is convenient to describe here certain polyvalent iodine compounds, formed by such substances as iodobenzene and p-iodotoluene. lodobenzeue in chloroform solution reacts readily with chlorine to form iodobenzene dlchlorlde (phenyl iododichloride) (I) ... 

The oxidation of acetylthiourea and phenylthiourea to afford the corresponding 1,2,4-thiadiazoles has been reported using [bis(acyloxy)iodo]arenes as the oxidants. The proposed mechanism involves the formation of a polyvalent iodine compound 74. After the elimination of iodobenzene, the 1,6-dip he nyl-dithioformamidine 75 is formed, which is set up to undergo a further oxidation to give the bis 3,5-diamino-l,2,4-thiadiazole 76 (Scheme 7) <2003T7521>. 

Bromine trifluoride has found use in the syntheses of polyvalent bromine,128 iodine,124 and sulfur130 compounds. 

Iodosobenzene bistrifluoroacetate is a versatile mild oxidant that has been used to oxidize a broad range of organic compounds, such as alkenes, alkynes, carbonyl compounds, and alcohols Its application in organic synthesis has been summarized m several recent reviews devoted to polyvalent iodine compounds [63, 64, 65]... 

Methods leading to polyvalent iodine compounds (Expts 6.31 to 6.36). 

Two polyvalent iodine compounds arising from o-iodobenzoic acid have been found to be useful synthetic reagents. Thus oxidation of the iodo acid (7) with potassium persulphate, followed by the addition of benzene and treatment with potassium iodide gives the iodonium iodide (8) which is converted into diphenyliodonium-2-carboxylate [DPIC (9)] with aqueous alkali (Expt 6.35).16... 

A. Varvoglis Polyvalent iodine compounds in organic synthesis [9]... 

E. B. Merkushev Organic compounds of polyvalent iodine. Derivatives of iodosobenzene [13]... 

Aryl-, as well as heteroaryliodonium salts, belong to the most common, stable, and well investigated class of polyvalent iodine compounds. The preparation and chemistry of aryliodonium salts was extensively covered in several reviews [5,7,9,10]. Diaryliodonium salts have found synthetic application as arylating reagents in reactions with various organic substrates. 

We hope and anticipate that this review will provide added stimulus for the further development of the chemistry of polyvalent iodine compounds. 

Iodine differs in many aspects from the other halogens. Because of the large atomic size and the relatively low ionization energy, it can easily form stable polycoordinate, multivalent compounds. Interest in polyvalent organic iodine compounds arises from several factors (a) the similarity of the chemical properties and reactivity of I(III) species to those of Hg(+2), Tl(+3), and Pb(+4), but without the toxic and environmental problems of these heavy metal congeners ... 

The most important structural features of polyvalent iodine compounds may be summarized as follows ... 

Full details for an improved method for preparation of these polyvalent iodine compounds are available.1 The method is similar to that used to prepare vinylio-donium tetrafluoroborates (13,151), and yields are 60-89%. 

Oxygenated polyvalent iodine compounds are also useful halogenating agents. oc-Iodoepoxides are prepared by reaction of iodosylbenzene diacetate (IBDA) with allyl alcohols (equation 116)832. Iodosylbenzene, activated by triflic acid, adds to acetylenes (equation 1 17)833. PhI(OAc)2 simultaneously iodinates and etherifies phenols (equation 118)834. 

Structures of vinyliodonium salts that have appeared in the literature since 1945 are shown in Table 8. For compounds that were reported earlier, the reader is directed to Willgerodt s monograph115 and to the compilation of polyvalent iodine compounds by Beringer and Gindler141. Table 8 includes a number of vinyliodonium ions whose stereoiso-meric configurations (i.e. is or Z) have been reported. Most of these assignments are based on NMR information and require some discussion. 

The intention is not to cover the vast halo-organic chemistry in this context, but only organic polyvalent halogen compounds that are actually limited to derivatives with iodine (I), iodine (III), and iodine (V), though evidence for the divalent L2T radical was obtained by the hemolytic cleavage of I-O bonds during thermolysis of tert-butyl-peroxyiodanes7 ... 

Polyvalent iodine compounds in the oxidation of heterocycles 02CRV2523. 

The only known alternative procedure for the preparation of alkynyl(phenyl)iodonium arylsulfonates, the latest member of the family of polyvalent Iodine compounds, involves the reaction of [hydroxy(tosyloxy)iodo]benzene. PhlOH-OTs, with terminal alkynes as first reported by Koser and elaborated by us. This procedure has a number of shortcomings. Formation of the desired alkynyliodonium salt is usually accompanied by a related vinyl species, R(TsO)C=CHIPh-OTs, that both decreases the yields and causes purification problems. Furthermore, when the alkyl substituent of the starting alkyne is small, such as CH3, n-Pr, n-Bu, etc., this procedure gives either no product or low yields at best. 

Use of polyvalent-iodine compounds in the synthesis of nitrogen-containing heterocycles 00MI30. 

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