Hypervalent iodine compounds oxidants

With many hypervalent iodine compounds oxidation reactions can be performed. This part highlights the most important transformations and is restricted to those transformations where a new oxygen atom is attached to the substrate. 

Varma and coworkers have explored the use of hypervalent iodine compounds on solid support for the first time and developed a facile oxidative procedure that rapidly converts alcohols to the corresponding carbonyl compounds using alumina-sup-ported IBD under solvent-free conditions and MW irradiation in almost quantitative yields [108]. The use of alumina as a support improved the yields markedly as compared to neat IBD (Scheme 6.33). 1,2-Benzenedimethanol, under these conditions, undergoes cyclization to afford l(3H)-isobenzofuranone. 

Diimide from hydrazine hydrate Diimide can be generated from hydrazine hydrate by oxidation with this hypervalent iodine compound in CH2C12. 

Other Hypervalent Iodine Compounds Used for Oxidation... 

The fluorine-containing hypervalent iodine compound 47, first described by Dess and Martin,5 finds occasional use in the oxidation of alcohols and is described in some substrates as superior than Dess-Martin periodinane.111... 

In recent years hypervalent iodine compounds have been extensively investigated yielding many results of practical synthetic importance. Iodi-nane reagents [e.g., iodoso or iodine(III)] have been prepared in a supported fashion by several groups, mainly as the bis-acetoxy-iodoso derivative28-30 or as the respective dihalogeno compounds.31 Iodoso reagents are employed in the oxidation of hydroquinones as well as phenols, and have been exploited in the formation of spiroketals from various tyrosines. 

Polymer-supported hypervalent iodine compounds in general are readily prepared and they have gained recently considerable popularity as reagents for clean oxidations. However, they are not newcomers since they have been known since 1961. A detailed procedure for the iodination of polystyrene and its conversion to poly[(diacetoxyiodo)styrene] appeared in 1972 [85]. However, this and other related methods were time consuming and despite encouraging results did not gain popularity. 

The first hypervalent iodine compound, (dichloroiodo)benzene 1, was prepared in 1886 by Willgerodt [9]. Since that time, several new reagents of iodine (III) and iodine (v) have been developed and are now frequently used in oxidative functionalizations. Scheme 1 shows a selection of the most frequently used... 

Disulfides, diselenides, and ditellurides can be oxidized by hypervalent iodine compounds quite easily. Depending on the reaction conditions disulfides can be oxidized to sulfinic esters [59] or thiosulfonic S-esters [60,61]. Diselenides can be transformed into selenosulfonates [62]. Arenetellurinic mixed anhydrides are mild oxidants and can be obtained by oxidation of the corresponding ditellurides as shown in Scheme 9 [63]. Recently it was shown that a thioacetal based linker for solid-phase synthesis can be cleaved oxidatively using [bis(trifluoro-acetoxy)iodo]benzene 4 [64]. 

The oxidation of phenols with hypervalent iodine compounds has been used frequently and nucleophilic additions can be performed as well as cyclization reactions using this technique. The resulting quinone derivatives show high reactivity and they have been used in a various subsequent reactions. Substituted phenols like 32 [78] or 34 [79] have been oxidized by hypervalent iodine reagents and, depending on the substitution pattern, cyclizations have taken place as shown in Scheme 16. Product 33 is unstable and undergoes subsequent... 

The Dess-Martin Periodinane (DMP), a hypervalent iodine compound, offers selective and very mild oxidation of alcohols to aldehydes or ketones. 

Chemical oxidation of silyl enolates has been performed with a variety of inorganic and organic oxidants such as ozone, copper(II) salts, Pb(OAc)4, Ag20, hypervalent iodine compounds such as iodosobenzene in methanol, (NH4)2[Ce(N03)6], xenon difluoride, tetranitromethane, halogens, nitronium-, diazonium- and triphenylmethyl salts, chloranil and ddq. 

Hypervalent iodine compounds, such as l-(difluoroiodo)-4-methylbcnzcnc or l-(difluoroiodo)-4-methoxybenzene, can serve as oxidant and simultaneously as the source of fluoride ions. They are used for fluorodesulfurization reactions under mild conditions.229 230 The reagents arc crystalline and soluble in organic solvents. 

The reaction of mono- and polycyclic 4-aIkylphenyl ethers using the hypervalent iodine compound, PhI(OCOCF3)2, in the presence of chloride and fluoride ions gives the corresponding 4-chloro- and 4-fluoro-cyclohexa-2,5-dienones . The corresponding oxidative reactions in the presence of the alcohols give 4-alkoxycyclohexadienones. These reactions may be used in the preparation of fluoro- and aUcoxy-substituted... 

Recently, some examples of synthetic reagents anchored onto ionic liquids have been reported. These new systems present the advantage of being readily separated from the reaction mixture by simple phase separation after the desired chemical transformation and can then be regenerated and reused. For example, IL-supported hypervalent iodine compounds have been used for the oxidation of alcohols to ketones (Scheme 4.7). 

Kim, D.Y, Mang, J.Y, and Oh, D.Y, Reaction of silyl enol ethers with phosphite using hypervalent iodine compound. A new synthesis of 2-aryl-2-oxoalkylphosphonates, Synth. Commun., 24, 629, 1994. Hohnquist, C.R., and Roskamp, E.J., Tin(II) chloride catalyzed addition of diazo sulfones, diazo phosphine oxides, and diazo phosphonates to aldehydes. Tetrahedron Lett., 33, 1131, 1992. 

Alkyl hypochlorites and hypobromites are relatively stable molecules alkyl hypoiodites can only be prepared in situ, usually by the reaction of alcohols with metal acetates or oxides and iodine or by the reaction of alcohols with a hypervalent iodine compound and iodine.1319 Alkyl hypochlorites and hypoiodites can be utilized in reactions that parallel those of the organic nitrites (Barton reaction Section 6.4.2). For example, the photochemistry of the steroidal hypoiodite 497, prepared by the reaction of the corresponding alcohol with iodine oxide (I2O) generated from mercury(II) oxide and molecular iodine in situ, affords a new five-membered ring via an O I bond fission, 1,5-hydrogen abstraction and substitution (Scheme 6.244).1353... 

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