2-Iodoxybenzoic acid structure

The kinetics of oxidation of Dess-Martin periodinane (DMP) and its iodoxybenzoic acid (IBX) precursor have been compared to explain their often different selectivities.152 A fast pre-equilibrium produces transient iodic esters, whose axial alkoxy structure for IBX was determined by 1H NMR spectroscopy, which then disproportionate in a rate-limiting maimer to product. As a result, steric effects in alcohol oxidation reflect a balance between opposing effects on equilibrium constants and rate constants for disproportionation. With 1,2-diols DMP gives spirobicyclic... 

Esters of 2-iodoxybenzoic acid (IBX-esters) 489 have been prepared by the hypochlorite oxidation of the readily available 2-iodobenzoate esters 488 (Scheme 2.139) and isolated in the form of stable microcrystalline solids [657,658], This procedure has been used for the synthesis of IBX-esters 489 derived from various types of alcohols, such as primary, secondary and tertiary alcohols, adamantanols, optically active menthols and borneol. Single-crystal X-ray data on products 489 revealed a pseudo-benziodoxole stmcture in which the intramolecular L--0 secondary bonds partially replace the intermolecular I - O secondary bonds, disrupting the polymeric structure characteristic of Phl02 and other previously reported iodylarenes [658], This stmctural feature substantially increases the solubility of these compounds in comparison to other iodine(V) reagents and affects their oxidizing reactivity. 

Several research groups have used ionic liquids for the oxidation of alcohols with o-iodoxybenzoic acid (IBX) or Dess-Martin periodinane (DMP). Alcohols undergo smooth oxidation with IBX or with DMP in hydrophilic [bmim]BF4 (structure 36, Figure 6.2) and hydrophobic [bmimjPFe (structure 37) ionic liquids at room temperature under mild conditions to afford the corresponding carbonyl compounds in excellent yields with high selectivity [54]. Similar results were obtained for the oxidation of alcohols with IBX and DMP using ionic liquid [bmim]Cl (l-butyl-3-methyUmidazoliumchloride) [55,56]. IBX- and DMP-promoted oxidations are faster in ionic liquids compared to conventional solvents such as DMSO, DMF, ethyl acetate and water. Recovery of the by-product iodosobenzoic acid is especially simple in ionic liquids. The recovered ionic liquids can be recycled in subsequent reactions with consistent activity. 

Organoiodine(V) heterocycles are represented by several typical classes 78—86 shown in Figure 15. The most important representative of these compounds, 2-iodoxybenzoic acid (IBX, 78), was originally reported in 1893 (1893CB1727). The cycHc structure of IBX derivatives was confirmed by an X-ray crystallographic study in the work of A. R. Katritzky and coworkers (1990JCS(P2)1657). 

FIGURE 5 Structures of some representative I(V) reagents. AIBX, 5-trimethylammonio-l,3-dioxo-l,3-dihydro-benzo[d][l,2]iodoxo-l-ol anion IBX, 2-iodoxybenzoic acid NIPA, N-(2-iodylphenyl)acylamide. 

Methyl-2-iodoxybenzoate can be further converted to the diacetate 243 or a similar bis(trifluoroacetate) by treatment with acetic anhydride or trifluoroacetic anhydride, respectively (2005JOC6484). A single-crystal X-ray diffraction analysis of methyl-2-[(diacetoxy)(oxo)iodo]benzoate 243 revealed a pseudo-benziodoxole structure with three relatively weak intramolecular I 0 interactions. Esters of 2-iodoxyisophthalic acid (e.g., 244) were prepared by the oxidation of the respective iodoarenes with dimethyl-dioxirane. An X-ray structural analysis of diisopropyl 2-iodoxyisophthalate 244 has demonstrated strong intramolecular interaction with the... 

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