2-Iodoxybenzoic acid preparation

A few years later,3 it was shown that o-iodoxybenzoic acid (36)—itself a precursor in the preparation of Dess-Martin periodinane—is able to oxidize very effectively alcohols in DMSO solution. o-Iodoxybenzoic acid—normally referred to as IBX—exists mainly as a cyclic form 37, which crystallizes as a polymer with very low solubility in most solvents with the exception of DMSO. Although, IBX (36) was already known in 1893,4 this ultracentenial reagent found very little use till very recently, when awareness about its solubility in DMSO was raised. 

The o-iodoxybenzoic acid (37) (p. 181) commonly known as IBX was prepared for the first time more than a century ago by Hartman and Meyer by oxidation of o-iodobenzoic acid with KBrC>3.4 This compound was not explored in organic synthesis for a long time because it was wrongly supposed that its virtual lack of solubility in common organic solvents would preclude any synthetic usefulness. IBX came to the attention of the organic... 

Tetrahydroquinoline-2-methanoles 184 were obtained from the diaste-reomeric mixtures of cyclic hemiacetals 183 by treatment with aqueous solution of NaOH in THF (08T2321). C4b S) epimers of 183 (R = Me, Ph) furnished the entiomers of 184 (R = Me, Ph) in 84-90% yields. The oxidation of cyclic hemiacetals 183 with 2-iodoxybenzoic acid afforded 1-for-myltetrahydroquinoline-2-aldehydes 185. Enantiomers of 185 (R = Me, Ph, C=CPh) were prepared similarly. 

In contrast, periodinanes (i.e. iodoxo or iodine(V) reagents), preferably as the 1-hydroxy-(li-f)-benzo-l,2-iodoxol-3-one-l-oxide (2-iodoxybenzoic acid, IBX) [20, 21] or its acetylation product, the Dess-Martin reagent [22], have been widely used for oxidation of sensitive and complex alcohols. Periodinanes have not yet been prepared on a polymer support a silica-supported IBX has been reported recently [23]. 

Preparation of the ortho-qamont 162 from p-hydroxyacetophenone (160). This involved silylation of acetophenone, ketal protection, desilylation, and regiose-lective oxidation of phenol to o-quinone 162 using o-iodoxybenzoic acid (IBX) (Scheme 10a). 

Stable alkylperoxyiodinanes can be prepared from the corresponding cyclic iodoxybenzoic acids,... 

A popular oxidizing agent that effects rapid oxidation of primary or secondary alcohols to aldehydes or ketones is the Dess-Martin reagent. This is the hypervalent iodine(V) compound 46, prepared from 2-iodoxybenzoic acid 45 (IBX) (6.40). Both IBX and the Dess-Martin reagent are potentially explosive and should be handled with care. 

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. 

The chemistry of X -iodanes in general has been less developed than with the X -iodanes [1102]. Significant interest in these compounds originated in 1983, when Dess and Martin reported a simple two-step preparation of the triacetate 800 via the bromate oxidation of 2-iodobenzoic acid to 2-iodoxybenzoic acid (IBX, 799) followed by heating with acetic anhydride (Scheme 3.316) [1103]. The authors have also found that the... 

Amides of 2-iodoxybenzoic acid (IBX-amides) 246 can be prepared by the dioxirane oxidation of 2-iodobenzamides 245 (Scheme 56) in the form of stable, microcrystalline soHds moderately soluble in dichloromethane and chloroform (2003ACE2194). This procedure has been used for the synthesis of the amides 246 derived from various types of amino compounds, such as esters of a-amino acids, esters of P-amino adds, and (R)-l-phenylethylamine. A single-crystal X-ray analysis of the phenylalanine derivative [246, R = (S)-CH(CH2Ph)C02Me] shows a close intramolecular contact of 2.571 A between the pentavalent iodine center and the oxygen atom of... 

The Painter group developed another approach to tetramates (e.g., 320) that involved the reductive amination of y-oxobutenoates (e.g., 319) in the presence of primary amines (Scheme 81 2002S869). Unsaturated dicarbonyl 319 was prepared in three steps by the phosphine-catalyzed Michael addition of benzyl alcohol to butynoate 318, desilylation, and oxidation of the resulting primary alcohol with 2-iodoxybenzoic acid (IBX). Treatment of 319 with tert-butylamine followed by sodium borohydride gives the O-benzyl tetramate 320 via a reductive amination—lactamization. 

Related isoflavones have been prepared, using SPOS, by Harikrishnan and Showalter. Resin-bound salicyl aldehyde derivatives 336, immobilized via a traceless silyl linker unit, were prepared and treated with a Grignard reagent to introduce the first point of diversity. Subsequent re-oxidation with 2-iodoxybenzoic acid (IBX), and deprotection of the methoxymethyl (MOM) group provided ketone 338. Treatment of ketone 338 with amide acetals promoted an unusual cyclization, which concurrently installed R to give 339. Final traceless cleavage with CsF or TBAF releases isoflavones 340 (Scheme 3.59). 

Methyl 2-iodoxybenzoate can be further converted into the diacetate 490 or a similar bis(trifluoroacetate) derivative by treatment with acetic anhydride or trifluoroacetic anhydride, respectively [658]. Single-crystal X-ray diffraction of methyl 2-[(diacetoxy)iodosyl]benzoate 490 revealed a pseudo-benziodoxole stmcture with three relatively weak intramolecular l - O interactions. The esters of 2-iodoxyisophthalic acid (e.g., 491) have been prepared by oxidation of the respective iodoarenes with dimethyldioxirane. X-Ray stmctural analysis of diisopropyl 2-iodoxyisophthalate 491 showed intramolecular I - O interaction with the carbonyl oxygen of only one of the two ester groups, while NMR spectra in solution indicated equivalency of both ester groups [658]. 

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