Iodine-hydroxy iodobenzene

A similar approach was carried out reacting an enohzable ketone with amides in the presence of the hypervalent iodine(III) reagent (hydroxy(tosyl-oxy)iodobenzene, HDNIB) [48]. The reaction was carried out imder solvent-... 

While the silver and zinc salts were effective Lewis acids for these cyclizations, Kikugawa and coworkers reported that the alkoxynitrenium ions could be generated directly from hydroxamic esters (4) using hypervalent iodine oxidants such as hydroxy(tosyloxy) iodobenzene (HUB) and phenyliodine(lll)bis(trifluoroacetate) (PIFA) . Presumably, with such reagents the reactions proceed through A-(oxoiodobenzene) intermediates (54), which can themselves be regarded as anomeric hydroxamic esters and sources of alkoxynitrenium ions (55) (Scheme 11). 

A catalytic amount of acid is sufficient, on the other hand, for the halogenation of activated aromatics such as polyalkylbenzenes by all the three NXSs. NIS iodinates mesitylene in presence of the very mild acid hydroxy(tosyloxy)iodobenzene (Koser s reagent, HTIB)7 2. NBS performs much better in the presence of / -toluenesulfonic acid and NCS shows the highest yields when trifluoromethanesulfonic acid is used as catalyst743. This difference in reactivity leads to a novel method for preparation of a mixed halogenated mesitylene (equation 100). 

Ingenious application of remote oxidation has opened the way to a novel and potentially useful degradation of 5a-cholestan-3a-ol to 3a-hydroxy-5a-androstan-17-one ( androsterone ). The radical relay process, whereby photolysis of an iodoaryl ester with iodobenzene dichloride introduces a chlorine atom or unsaturation into the steroid nucleus, has been adapted by use of the 3a-(4 -iodobiphenyl-3-carboxylate) (301). The size of this ester grouping allows the iodine atom to come... 

Hydroxy (tosyloxy)iodobenzene [phenyl(hydroxyl)tosyloxy iodine, bydroxy(4-methyl-... 

At a lower oxidation level, orffto-hydroxy-acyl-arenes undergo base-catalysed aldol condensations with aromatic aldehydes to give chalcones, °° which can be cyclised to 2,3-dihydro-chromones via an intramolecular Michael process the dihydro-chromones can in turn be dehydrogenated to produce chromones by a variety of methods, for example by bromination then dehydrobromination or by oxidation with the trityl cation, iodine, dimethyldioxirane or iodobenzene diacetate. ° ... 

Silva and Lopes analyzed solutions of iodobenzene dicarboxylates in acetonitrile, acetic acid, aqueous methanol and anhydrous methanol by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS) [196]. The major species found in the solutions of PhI(OAc)2 in acetonitrile, acetic acid and aqueous methanol were [PhI(OAc)2Na]+, [PhI(OAc)2K]+, [Phl]+, [PhIOAc]+, [PhIOH]+, [PhI02Ac]+, [PhI02H]+ and the dimer [Ph2l202Ac]+. On the other hand, the anhydrous methanol solutions showed [PhIOMe]+ as the most abundant species. In contrast to the data obtained for PhI(OAc)2, the ESI-MS spectral data of PhI(02CCF3)2 in acetonitrile suggests that the main species in solutions is iodosylbenzene [196]. A similar ESI-MS and ESI-MS/MS study of solutions of [hydroxy(tosyloxy)iodo]benzene has been performed under different conditions and, based on these data, mechanisms were proposed for the disproportionation of the iodine(III) compounds into iodine(V) and iodine(I) species [197]. 

Organohypervalent iodine(in) compounds are particularly usefiil as the oxidants in the Hofmann-type degradation of aliphatic or aromatic carboxamides to the respective amines [483]. The most common reagents for Hofmann-type rearrangements include (diacetoxyiodo)benzene [484-488], [bis(trifluoroacetoxy)-iodo]benzene [489-494], [hydroxy(tosyloxy)]iodobenzene [495-499] and their recyclable analogs (Chapter 5). The catalytic version of the Hofmann rearrangement using aryl iodides and m-chloroperoxybenzoic acid as terminal oxidant has also been reported (Section 4.1). 

Togo and coworkers have found that alkyl aryl ketones and dialkyl ketones could be converted into the corresponding a-tosyloxyketones in generally low yields by the reaction with mCPBA and p-toluenesulfonic acid monohydrate in the presence of a catalytic amount of molecular iodine in a mixture of acetonitrile and 2,2,2-trifluoroethanol (method A, Scheme 4.5) [23]. The same conversion of ketones into the corresponding a-tosyloxyketones could be smoothly carried out by the reaction with mCPBA and TSOH H2O in the presence of catalytic amounts of iodine and fert-butylbenzene in a mixture of acetonitrile and 2,2,2-trifluoroethanol (method B). In these reactions, p-iodotoluene 8 (method A) and 4-fcrr-butyl-l-iodobenzene 9 (method B) are formed at first and are then converted into the corresponding [hydroxy(tosyloxy)iodo]arenes, ArI(OH)OTs,... 

The proposed mechanism for these catalytic oxidations includes two catalytic redox cycles (i) initial oxidation of iodobenzene with Oxone, producing hydroxy(phenyl)iodonium ion and hydrated iodosylbenzene and (ii) the oxidation of iron(III)-porphyrin to the oxoiron(IV)-porphyrin cation-radical complex by the intermediate iodine(III) species (Scheme 4.58) [93]. The oxoiron(IV)-porphyrin cation-radical complex acts as the actual oxygenating agent toward aromatic hydrocarbons. The presence of the [PhI(OH)]+ and PhI(OH)2 species in solutions containing Phi and Oxone has been confirmed by ESI mass spectrometry [93]. 

The reactivity pattern of recyclable hypervalent iodine reagents 65-67,69-71,73,74 and 76 is similar to the common iodobenzene-based reagents [34], For example, the recyclable (diacetoxyiodo)arenes 65,69,73 and 76 can be used instead of (diacetoxyiodo)benzene in the KBr or TEMPO-catalyzed oxidations of alcohols [74-78], while [hydroxy(tosyloxy)iodo]arenes 67, 71 and 74 are excellent reagents for tosyloxylation of ketones (Scheme 5.28) [76]. 

Oxidation at the a position of a keto group is achieved with the hypervalent iodine compound hydroxy(tosyloxy)iodobenzene (HTIB). The reagent is insoluble in the medium, and the sonochemical effect corresponds to a mechanical activation, even if in this case a chemical role cannot be excluded. With unsymmetrical ketones, the reaction is practically non-selective (Eq. 68). 

Oxidative desulfurization of acylthiosemicarbazides 97 and bisdiarylthioxneas 99 involving hydroxy(phenyl) iodonium ion was effectively applied by Telvekar et al. to deliver the corresponding 2-arylaminooxadiazoles 98 and 2-arylaminothiadiazoles 100 in good-to-excellent yields. This active iodine species, hydroxy(phenyl)iodonium ion was generated by the oxidation of iodobenzene using inexpensive and readily available Oxone as a co-oxidant at room temperature (Scheme 20) [36]. 

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). 

Papoutsis et al. and Malamidoli-Xenikaki and Spyroudis developed a method to transform 2-hydroxy-1,4-benzo-quinones, such as 132, into 2-cyclopentene-l,4-diones, like 124 112,113 rpjjg pjojocol is based on the thermolysis of a phenyl iodonium, such as 133, ° " which can be prepared treating a hydroxy quinine 132 with the commercially available hypervalent iodine reagent diacetoxy iodobenzene (PhI(OAc)2) (Scheme 18.29). 

Considerable interest has been expressed in the development of direct methods for the synthesis of a-hydroxy ketones using nontoxic hypervalent iodine reagents and which involve the foUowing methods reaction of a ketone with iodobenzene diacetate in the presence of potassium hydroxide in methanol and then hydrolysis of the dimethylacetals oxidation of the enol sUyl ether of acetophenone using the s) tem iodosobenzene/boron trifluoride efherate/water in methylene chloride at—40°C and reaction of ketones with [fcis(trifluoroacetoxy)]iodobenzene and trifluoroacetic acid in acetonitrile-water under acidic conditions. "... 

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