IBX-mediated oxidation

Shen L, Zhang J, Cao S, Yu JL, Liu NJ, Wu JJ, Qian XH (2008) One-pot synthesis of trifluoromethyl-containing pyrazoles via sequential Yb(PFO)(3)-catalyzed three-component reaction and IBX-mediated oxidation. Synlett 3058-3062... 

Cabarrocas G, Ventura M, Maestro M, Mahia J, Villalgordo JM (2001) Synthesis of novel optically pure quinolyl-P-amino alcohol derivatives from 2-amino thiophenol and chiral a-acetylenic ketones and their IBX-mediated oxidative cleavage to IV-Boc quinolyl carboxamides. Tetrahedron Asymmetry 12 1851-1863... 

The IBX-mediated oxidative Ugi-type multicomponent reaction of tetrahydroisoquinoUne with isocyanides and carboxylic acids affords the nitrogen- and carbon-functionalized tetrahydroisoquinolines 867 in good to excellent yields [1184]. Likewise, the three-component Passerini reaction of an alcohol, carboxylic acid and an isonitrile in the presence of IBX affords the corresponding a-acyloxy carboxamides 868 in generally high yields (Scheme 3.347) [1185]. 

In a convenient one-pot process, easily accessed propargyl vinyl ethers and aromatic amines are effectively converted into tetra- and pentasubstituted 5-methylpyrroles, which can fnrther be transformed into 5-formylpyrroles via 2-iodoxybenzoic acid (IBX)-mediated oxidation (Binder and Kirsch 2006). The cascade reaction proceeds through a silver(l)-catalyzed propargyl Claisen rearrangement, an amine condensation, and a gold(l)-catalyzed 5-exo-dig heterocyclization, as shown in Schane 11.4. 

T. Ngouansavanh, 1. Zhu, Angew. Chem. Int. Ed. 2007, 46, 5775-5778. IBX-mediated oxidative Ugi-type multicomponent reactions application to the N and Cl functionalization of tetrahydroisoquinoline. 

SCHEME 10.19 Postulated mechanism for IBX-mediated oxidation of aminonitrile. 

Gold-catalyzed cycloisomerizations of alkynyl ketones/aldehydes provide convenient access to 2-benzopyrylium salts, which are important intermediates for natural product syntheses. For example, the benzaldehyde derivative 151 was converted directly to the 2-benzopyrylium salt 152 in the presence of a catalytic amount of Au(OAc)3 in (CH2C1)2/TFA (Scheme 19.37) [62], IBX-mediated oxidation of 152 in the presence of n-Bi NI (as a phase-transfer catalyst) cleanly afforded the azaphilone 153 in 84% yield after reductive workup, which is a precursor of ( )-S-15183a (154). Similarly, AgNOs-promoted cyclization of the alkyne 155 furnished direct construction of the tricyclic 8/7-pyrano[2,3,4-rfe]chromen-8-one core of cassiarin A (158) (Scheme 19.38) [63]. 

Nicolaou et al. reported new mechanistic studies for an IBX-mediated dehydrogenation of carbonyl compounds, and suggested that the active species in this reaction is most likely a complex of IBX and DMSO. Extensive investigations demonstrated that IBX-7V-oxide complexes 10, especially the IBX-4-methoxypyridin-A -oxide complex (11), often exhibit superior reactivity so that of the parent oxidation reagent. ... 

An l-hydroxy-l,2-benziodoxol-3(17/)-one 1-oxide (IBX)-mediated process provides another efficient and stereoselective preparative route for the s)uithesis of amino sugars. For example, reaction of the D-glucal derivative 113 with p-methoxybenzene isocyanate in the presence of a catalytic amount of l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) followed by treatment with IBX furnishes the cyclic carbonate 115, through urethane 114. Subsequent removal of the p-methoxybenzyl (PMB) protecting group by CAN affords the protected amino sugar 116 (O Scheme 56) [94]. 

The IBX-mediated oxygenative dearomatization of phenols leading to cyclohexa-2,4- or -2,5-dienone systems is a particularly useful synthetic transformation [292]. Representative examples include the use of IBX in key oxidation steps in the total synthesis of the resveratrol-derived polyphenol natural products... 

A one-pot three-component synthesis of a-iminonitriles 866 via an IBX/tetrabutylammonium bromide-mediated oxidative Strecker reaction has been developed (Scheme 3.346) [1183]. This methodology was employed in a two-step synthesis of indolizidines via a microwave-assisted intramolecular cycloaddition of a-iminonitriles. 

Several modified catalysts for the iodine(V)-mediated oxidation of alcohols have been developed based on IBX derivatives and analogues (Figure 4.2). In particular, the fluorous IBX 91 works efficiently as a catalyst for the oxidation of various alcohols to the corresponding carbonyl compounds in good to high yields... 

Figure 4.2 IBX derivatives and analogues used as catalysts for the iodine(V)-mediated oxidation of alcohols.

P. Fontaine, A. Chiaroni, G. Masson, J. Zhu, Org. Lett. 2008, 10, 1509-1512. One-pot three-component synthesis of a-iminonitriles by IBX/TBAB-mediated oxidative Strecker reaction. 

Considering the kinetic data, the rate-determining step of the IBX-mediated cyclization of anilides 1 is the SET process (first step of the reaction). The variations of the measured oxidation potentials with the reaction rates are in good agreement with the initial SET proposed by the mechanism. 

Nicolaou and coworkers have reported an expeditious IBX (2-iodo3gr-benzoic acid, l-hydro q -l, 2-benziodoxol-3(l//)-one 1-oxide) mediated synthesis of Z-vancosamine " starting from vinyl iodide and protected aldehyde via an intramolecular Kishi-Nozaki coupling reaction. The coupling product, as a mixture of alcohols, was immediately oxidized with DMP (Dess-Martin periodinane). The oxidation was followed by a sodium borohydride/cerium chloride reduction to produce a protected alcohol intermediate. In the next step, the required alcohol was reacted... 

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