Iodine reagents oxidative rearrangment

Generally, hypervalent iodine reagents are often better than traditional reagents of similar reactivity, with respect to efficiency and chemoselectivity - sometimes even stereoselectivity. Unusual reactivity is another interesting feature which has often resulted in unexpected transformation. Examples of such reactions may be found in the oxidation of nitrogen-containing compounds, the Hofmann rearrangement in acidic conditions, the acetalization of carbonyl compounds in alkali, the remote functionalization of steroids, etc. Some unique transformations were effected in the... 

As already mentioned, hypervalent iodine reagents are useful for the oxidatively assisted nucleophilic substitution of iodine in iodoalkanes (Section 5.4.2). In this way HTI was used for the preparation of some tosylates. A rearrangement occurred with neopentyl iodide, Me3CCH2I, which was converted into the ester Me2C(OTs)CH2Me (85%) [53]. The most successful application of such reactions for preparative purposes was the functionalization of some iodocubanes and iodohomocubanes, and especially the preparation of their triflates and mesylates from iodosylbenzene-trimethylsilyl triflate and [hydroxy(mesyloxy)iodo]benzene, respectively [54,55]. 

The oxidative rearrangement of cyclic alkenes and ketones often leads to ring expansion or ring contraction reactions. The reagents generally used for this purpose are hypervalent main group oxidants such as thallium(III), lead(lV), iodine(III) and selenium(IV), alAough palladium(II) has been used as well. 

Pirkuliev et al. examined the reaction of cyclobutene oxide 23 with a hypervalent iodine reagent and isolated a mixture of products consistent with the initial formation of cation 24 which can rearrange to give precursors to the other products (Scheme 12) <2002RJ01066>. 

Canesi and coworkers have developed several synthetically useful tandem rearrangements on the basis of hypervalent iodine-promoted phenolic oxidation [328-331]. An oxidative Prins-pinacol tandem process mediated by a hypervalent iodine reagent allows the stereoselective tfansformation of simple phenols 261 into highly elaborate spirocyclic dienone cores 262 containing several quaternary carbon centers (Scheme 3.108). 

An oxidative /pio-rearrangement mediated by a hypervalent iodine reagent that enables rapid generation of a functionalized dienone system 266 containing a quaternary carbon center has been developed (Scheme 3.110) [330]. The process occurs through transfer of an aryl group from a silyl segment present on the lateral chain of the phenol derivative 265. This transformation has been utilized in a total synthesis of an alkaloid sceletenone [330],... 

A very mild procedure for the Hofmann rearrangement of aromatic and aliphatic carboxamides 409 is based on the use of (tosylimino)phenyl-X. -iodane, PhINTs, as the oxidant (Scheme 3.165) [506]. Owing to the mild reaction conditions, this method is particularly useful for the Hofmann rearrangement of substituted benzamides 409 (R = aryl), which usually afford complex reaction mixtures with other hypervalent iodine oxidants. The mild reaction conditions and high selectivity in the reaction of carboxamides with PhINTs allow the isolation of the initially formed labile isocyanates 410, or their subsequent conversion into stable carbamates 411 by treatment with alcohols. Based on the previously reported mechanistic studies of the Hofmann rearrangement using other hypervalent iodine reagents [489,490,496], it is assumed that the reaction... 

All of the reactions described above use a readily available hypervalent iodine reagent. The Zhdankin group has also reported Hofmann-type rearrangements employing an iodine(ni) species generated in situ through reaction of iodobenzene and a co-oxidant. It is sometimes possible to employ a sub-stoichiometric amount of iodobenzene to catalyze the transformation. As an example, carbamates such as... 

The rearrangements described in parts 2-5 involve iodine(III) reagents which can be obtained commercially or prepared in situ in a catalytic fashion. However, some authors have described rearrangements promoted by an iodine(V) oxidant. For example, when reacted with IBX in the presence of Et4NBr, amides 136 undergo a Hofmann-type rearrangement to produce cyanides 137 (Scheme 39) [32]. 

Carbonyl oxidation with hypervalent iodine reagents involves the functionalization of the a-position of carbonyl compounds through the intermediacy of a hypervalent iodine enolate species. This electrophilic intermediate may be attacked by a variety of nucleophiles or undergo rearrangement or elimination [13]. Enantiomerically pure, a-substituted carbonyl compounds represent a family of derivatives important in nearly all fields of organic chemistry [14],... 

Hypervalent iodine is an important tool in synthetic and natural product chemistry. The use of iodine(III) and iodine(V) reagents to develop a variety of oxidative rearrangements... 

A review of oxidative rearrangements induced by iodine(III) and iodine(V) reagents has appeared.Enantioselective rearrangements of alkenes to a-arylated ketones have been promoted using lactic-acid-based iodine(lll) reagents (Scheme 108). ... 

Oxidation of carbonyl compounds with organo-hypervalent iodine reagents has been reviewed. The hypervalent iodine oxidation of several a-substituted 2,4-dihydroxyacetophenones (12) (Scheme 6) using phenyliodonium diacetate (PIDA) proceeds via rearrangement of an iodonium ylide (13) to afford novel o-iodophenoxy ethers (14). ... 

Keywords. Hypervalent iodine, Oxidation, Polymer-supported reagents, Rearrangement... 

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