Hypervalent iodine compounds applications

This chapter contains assorted hypervalent iodine compounds which have been sporadically used in reactions of synthetic interest. Although they cannot be considered presently as fully fledged reagents, comparable in scope to those appearing in previous chapters, it is possible that in the future they will be further developed. It is hoped that this separate presentation of minor reagents will serve as a source of inspiration for new useful applications. 

Wirth, T., Hirt, U. H. Hypervalent iodine compounds. Recent advances in synthetic applications. Synf/res/s 1999,1271-1287. 

A pyrrolone ring is formed from a methylene and a ring-carbon in a low-temperature cyclo-oxidation of the amide (104.2) which is promoted by [bis(tri-fluoroacetyloxy)iodo]benzene. The application of hypervalent iodine compounds to the formation of C—C bonds has been reviewed [3714]. A similar compound (104.3) is cyclized in lower yield by stirring it at 0 C with trifluoroacetic anhydride. 

Hypervalent iodine(III) compounds, such as [bis(trifluoroacetoxy)iodo]benzene, (diacetoxyiodo)benzene and [hydroxy(tosyloxy)iodo]benzene, are commonly used as reagents in various cationic cyclizations, rearrangements and fragmentations. Numerous examples of such reactions have been reported in the literature and summarized in the reviews dedicated to synthetic applications of hypervalent iodine compounds [4,7,10,11, 180, 191, 387]. 

Despite the demonstrated success of NBS and the hypervalent iodine compounds as modem HR reagents, the classical variant lead tetraacetate continues to find synthetic applications. A synthesis of the carbocyclic nucleoside (-)-aristeromycin features the conversion of amide 122 to Boc-protected amine 123. Similar tactics are used for syntheses of 6 - 3-... 

The focus of this chapter is to provide an overview of the reactivity of diaryliodonium salts, discuss common synthetic routes to them, and describe the recent developments in applications of these reagents after a brief historical perspective in each section. The chemistry of hypervalent iodine compounds has been summarized in a number of books and reviews [1-3], and the topics of diaryliodonium salts [4, 5], cyclic diaryliodonium salts [6], and iodonium salts [7] have been reviewed. Literature summaries of mechanistic aspects and selected transformations with diaryliodonium salts are referenced in the appropriate sections below. 

With the development of efficient synthetic routes to diaryliodonium salts, these hypervalent iodine compounds have become easily available and interesting alternatives to other arylation reagents. Their low toxicity, high stability, and high reactivity are attractive features which enable difficult transformations without the need for excess reagents or high temperatures. This chapter has summarized recent developments in metal-free and metal-catalyzed arylations of heteroatom nucleophiles and carbon-centered nucleophiles. The boundaries of the field have moved forward considerably in the last decade, and many more applications are foreseen based on the deepened mechanistic understanding of arylations under both metal-free and metal-catalyzed conditions. 

As mentioned above, the choice of an appropriate additive may be very crucial for trifluoromethylation reactions using hypervalent iodine compounds. Indeed, several different modes of activation of reagents 1 and 2 have been recognized. These empirical observations were supported further by kinetic and computational studies as well as by X-ray analysis of presumed intermediates isolated in crystalline form. Current knowledge shows that trifluoromethylation has mainly been achieved using (1) Br0nsted acids and (2) Lewis acidic metal complexes. A few reports have also shown the successful application of Lewis bases for activation. In several cases, the innate acidity of the nucleophile or the solvent can also be exploited. 

Instead of metal salts, peroxides and other more sophisticated oxidants were suggested in several publications and patent applications. Rather closely related to the preferred method for the manufacture of PEDOT PSS— the oxidative polymerization with peroxodisulfates—in situ polymerizahon by peroxidic compounds has been claimed by several patent applicahons. - Another patent application utilizes so-called hypervalent iodine compounds as oxidants. Examples for inorganic hypervalent iodine compounds are iodic acid, sodium iodate (iodine-V), and sodium periodate (iodine-VII). Typical organic hypervalent iodine compounds were of the iodine-III type, for instance, Koser s reagent = hydroxy-tosyloxy iodobenzene or bis(trifluoroacetoxy) iodobenzene (see Figure 8.4). 

The five-membered pentavalent iodine heterocycles represent a particularly important class of hypervalent iodine compounds. Cyclic iodine(V) compounds, such as IBX 212 and DMP 213, have found broad practical application as mild and selective reagents for the oxidation of alcohols and some other useful oxidative transformations. Several comprehensive reviews of the chemistry and synthetic applications of IBX and DMP have been published (2011JOC1185, 2006ARK26, 2010T7659, 2011AGE1524, 2001ACE2812). 

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. 

The formation of carbon-heteroatom bonds can be effected by reactions of hypervalent iodine reagents with a wide range of organic substrates and inorganic nucleophiles, and represents one of the most popular applications of organoiodine(III) compounds [1-10]. Except for C-I(III) bond forming reactions used for the synthesis of iodanes and iodonium salts, C-heteroatom bond formation is almost always accompanied by reduction of the hypervalent iodine reagents to iodine(I) compounds. 

Hypervalent Iodine Chemistry Preparation, Structure and Synthetic Applications of Polyvalent Iodine Compounds, First Edition. Viktor V. Zhdankin. 2014 John Wiley Sons, Ltd. Published 2014 by John Wiley Sons, Ltd. 

Hydroxybenziodoxole 104 can be readily converted into its acetoxy derivative, l-acetoxy-1,2-benziodoxole-3(l//)-one (88, 2X = O, Y = OAc), by heating 104 with acetic anhydride and the acetoxy derivative can be further converted into the alkoxy derivatives by treatment with an appropriate alcohol [280], The tetrabutylanmionium salt of hydroxybenziodoxole 104 has been prepared by the reaction of hydroxybenziodoxole with tetrabutylammonium fluoride in THF it is a mild oxidant that is useful for the preparation of epoxides from a,p-unsaturated carbonyl compounds [281], l-Hydroxy-l,2-benziodoxole-3(l//)-one and l-acetoxy-l,2-benziodoxole-3(l//)-one have found wide application as starting compounds for the synthesis of various benziodoxole-based hypervalent iodine reagents by ligand exchange on iodine [239]. 

Hypervalent iodine(III) compounds have found wide application for the oxidation of organic derivatives of nitrogen, sulfur, selenium, tellurium and other elements. Reactions of X -iodanes with organonitrogen compounds leading to the electron-deficient nitrenium intermediates and followed by cyclizations and rearrangements (e.g., Hofmann rearrangement) are discussed in Section 3.1.13. Several other examples of oxidations at a nitrogen center are shown below in Schemes 3.168-3.170. 

Hypervalent iodine reagents are commonly used for the oxidation of organosulfiir compounds. Applications of hypervalent iodine reagents for the preparation of sulfoxides, including enantioselective oxidations of organic sulfides, have been summarized in reviews [519,520]. 

Hypervalent iodine(V) reagents, such as IBX (2-iodoxybenzoic acid) and DMP, have found widespread synthetic application as stoichiometric oxidants for the facile and selective oxidation of primary alcohols and secondary alcohols to the respective carbonyl compounds and for other important oxidative transformations... 

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