Hypervalent Iodine-Catalyzed Oxidations

The efficiency of this oxidation was also evaluated by comparison to other oxidations, such as the Dess-Martin, pyridinium dichromate and Swern oxidations. It was demonstrated that the hypervalent iodine(V)-catalyzed oxidation could be applied for almost all types of fluorinated alcohols and it was comparable to Dess-Martin oxidation, while pyridinium dichromate and Swern oxidations could not be employed for allylic and propargylic alcohols as well as the alcohols having an aliphatic side chain. Additionally, the hypervalent iodine-catalyzed oxidation could be applied for a larger scale reaction (Scheme 4.49) without any decrease in reaction efficiency [81]. 

Zhdankin and coauthors [92] showed that nitrile oxides 119 can be generated by hypervalent iodine-catalyzed oxidation of aldoximes 118 using oxone as a terminal oxidant (Scheme 29). These in situ generated nitrile oxides 119 reacted with several alkenes and alkynes to afford the corresponding isoxazolines 121 and isoxazoles 120 in moderate to good yields. 

Singh FV, Wirth T. Hypervalent iodine-catalyzed oxidative functionalizations including stereoselective reactions. Chem Asian J. 2014 9 950-971. 

Based on Ochiai s procedure for a-acetoxylation of ketones, Ishihara and coworkers have developed the hypervalent iodine-catalyzed oxylactonization of ketocarboxylic acids to ketolactones [18], Optimized reaction conditions consist of the treatment of a ketocarboxylic acid with iodobenzene (10 mol%), p-toluenesulfonic acid monohydrate (20 mol%) and mCPBA as a stoichiometric oxidant in nitromethane solution Scheme 4.3 shows as a representative example the cyclization of ketocarboxylic acid 4 to ketolactone 5. 

Based on the hypervalent iodine-catalyzed bromocarbocyclization of appropriate alkenoic precursors 21, Gulder and coworkers have developed an efficient synthetic approach to 3,3-disubstituted oxoindoles 22 (Scheme 4.10) [36], These cyclizations are catalyzed by 2-iodobenzamide 20 at room temperature using NBS as the source of electrophilic bromine. Alternatively, KBr can be used as the source of bromine in the presence of Oxone as a terminal oxidant. The synthetic utility of this cyclization has been demonstrated by the... 

Only a few examples of hypervalent iodine-catalyzed reactions leading to the formation of new C-C bonds have been reported. In seminal work, Kita and coworkers reported in the 2005 a single example of an intermolecular C-C bond formation reaction catalyzed by an iodoarene [2]. Specifically, the oxidative coupling of phenolic ether 70 using [bis(trifiuoroacetoxy)iodo]benzene as a catalyst and mCPBA as a terminal oxidant afforded product 71 in moderate yield (Scheme 4.35). 

Within his seminal work on catalytic oxidative spiro-cyclization reactions, Kita reported on hypervalent iodine catalyzed lactamization reactions [18, 19]. These reactions lead to de-aromatization throughout the process, but appear to provide valuable entries into C-N bond formation involving congested carbon frameworks. 

A. Yoshimura, K.R. Middleton, A.D. Todora, B.J. Kastem, S.R. Koski, A.V. Maskaev, V.V. Zhdankin, Hypervalent iodine catalyzed generation of nitrile oxides from oximes and their cycloaddition with alkenes or alk)mes, Org. Lett. 15 (2013) 4010-4013. 

The oxidation of chalcogen compounds by hypervalent iodine reagents is a known procedure. The oxidation of sulfides only leads to the formation of mixtures of sulfoxides and sulfones under drastic conditions. Usually only sulfoxides are formed and can be obtained in excellent yields [46-48]. Recent investigations showed that sulfide oxidation can be catalyzed by quaternary ammonium salts in micellar systems. Iodosobenzene 5 is catalytically activated by cetyltrimethylammonium bromide (CTAB) and the sulfoxides 24 can be obtained in high yields under very mild conditions, Scheme 6 [49]. Other micelle forming surfactants have also been employed, but CTAB showed the best results in this reaction. It is also possible to perform such oxidations to sulfoxides with (terf-butylperoxy)iodanes of type 13 [50]. 

Hypervalent iodine(lll) was shown to catalyze the direct cyanation of iV-tosylpyrroles and -indoles under mild conditions, without the need for any prefunctionalization <2007JOC109>. Phenyliodine(m) bis(trifluoroacetate)-induced oxidative regioselective coupling of pyrroles in the presence of bromotrimethylsilane gave a series of electron-rich bipyrroles <2007S2913>. 

TEMPO is a commercially available nitroxyl radical-containing reagent that catalyzes the oxidation of primary and secondary alcohols in conjunction with co-oxidants (oxygen, hypochlorite, bromite, hypervalent iodine, or peroxy acids).The catalyst is particularly useful for the oxidation of optically active a-alkoxy- or a-amino alcohols to the corresponding aldehydes without loss of enantiomeric purity. ... 

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. 

Similarly, chelation-assisted palladium-catalyzed oxidative functionalizations of C—H bonds with, for example, hypervalent iodine(III) reagents turned out to be particularly valuable. These protocols allowed for, inter alia, regioselective acetoxyla-tion or etherification of aromatic and aliphatic C— H bonds [17-19], and also halogenations of arenes (Scheme 9.3) [20, 21]. 

A similar oxidative protocol has been used for the oxidation of (fluoroalkyl)alkanols, Rf(CH2) CH20H, to the respective aldehydes [146], in the one-pot selective oxidation/olefination of primary alcohols using the PhI(OAc)2-TEMPO system and stabilized phosphorus ylides [147] and in the chemo-enzymatic oxidation-hydrocyanation of 7,8-unsaturated alcohols [148]. Other [bis(acyloxy)iodo]arenes can be used instead of PhI(OAc)2 in the TEMPO-catalyzed oxidations, in particular the recyclable monomeric and the polymer-supported hypervalent iodine reagents (Chapter 5). Further modifications of this method include the use of polymer-supported TEMPO [151], fluorous-tagged TEMPO [152,153], ion-supported TEMPO [154] and TEMPO immobilized on silica [148],... 

Hypervalent iodine oxidations of organic substrates can be effectively catalyzed by salts and complexes of gold [757-760]. For example, direct acetoxylation of electron-rich aromatic compounds 648 can be performed with (diacetoxyiodo)benzene in the presence of catalytic amounts of AuCb (Scheme 3.256) [757]. 

Several examples of cyclizations through intramolecular C-N bond formation catalyzed by hypervalent iodine species have been reported. Antonchick and coworkers developed an efficient organocatalytic method for the preparation of carbazoles through catalytic oxidative C-N bond formation [48]. The best yields of products were obtained in hexafluoro-2-propanol using 2,2 -diiodo-4,4, 6,6 -tetramethylbiphenyl (42) as the catalyst and peracetic acid as the oxidant, as illustrated by a representative example shown in Scheme 4.23. 

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