Oxidations 2-iodoxybenzoic acid

In the o-iodoxybenzoic acid oxidation of aryl, allyl, and alkyl alcohols to the corresponding aldehydes, the preferential catalysis of reactions of the unsaturated alcohols by cucurbit[8]uril (69) has been related to the electron density and reactivity of an intermediate stabilized a-carbanion. ... 

The protected butane-1,2,3,4-tetraol 15, easily available in three steps from D-tartaric add diethyl ester, was the starting material for the synthesis of (+)-phomopsohde B (Scheme 2.4). Thus, IBX (2-iodoxybenzoic acid) oxidation of the primary alcohol followed by HWE olefination with a chiral phosphonate derived from L-lactic add (not depicted) gave a,fi-enone 16. Stereoselective reduction of the ketone carbonyl and acidic deavage of the acetal moiety furnished triol 17. Selective protection of the two secondary hydroxyl groups was achieved through triple silylation with subsequent selective desilylation of the primary OTBS group. 

Several organohypervalent iodine reagents have been used for the oxidation of alcohols and phenols such as iodoxybenzene, o-iodoxybenzoic acid (IBX), bis(trifluoroa-cetoxy)iodobenzene (BTI), and Dess-Martin periodinane etc. But the use of inexpensive iodobenzene diacetate (IBD) as an oxidant, however, has not been fully exploited. Most of these reactions are conducted in high boiling DMSO or toxic acetonitrile media that results in increased burden on the environment. 

IODOXYBENZOIC ACID (IBX)//i-Bu4NBr/CH2Cl2-H20 A MILD SYSTEM FOR SELECTIVE OXIDATION OF SECONDARY ALCOHOLS... 

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... 

Iodoxybenzene (PI1IO2) has been briefly explored in the oxidation of benzylic alcohols to benzaldehydes, giving best results with an acetic acid catalysis.120 The guanidinium salt of m-iodoxybenzoic acid is soluble in CH2C12 and able to carry out oxidative breakages of 1,2-diols.120... 

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... 

A variety of methods have been described to solve the task in solution.16 Common oxidative agents for this transformation include various heavy-metal reagents such as chromium-or ruthenium-based oxides, pyri-dine-S03, and dimethylsulfoxide (DMSO) in combination with acetic anhydride, carbodiimide, or oxalyl chloride for activation. One of the most prominent methods for the reliable conversion of sensitive compounds is the Dess-Martin reagent or its nonacetylated equivalent, 1-hydroxy-(17/)-benzo-l,2-iodoxol-3-one-l-oxide (2-iodoxybenzoic acid, IBX). 

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. 

Oxidation of 3-hydroxymethyl-2,3-dihydro-5H-pyrido[l,2,3-cfe][1,4] benzoxazin-5-ones with o-iodoxybenzoic acid in DMSO and with Dess-Martin periodinate in CH2CI2 afforded 3-formyl derivatives (08WOP2008/ 120003). Dehydrogenation of ethyl 10-[2-(ferf-butoxycarbonyl)-l,2,3,4,6,8a-hexahydropyrrolo[l,2-a]pyrazin-7-yl]-9-fluoro-3(S)-methyl-7-oxo-2,3-dihydro-7H-pyrido[l,2,3-de][l,4]oxazine-6-carboxylates in the presence of Pd/C with air in MeOH afforded 10-[2-(ferf-butoxycarbonyl)-l, 2,3,4-tetrahydropyrrolo[l,2-a]pyrazin-7-yl] derivatives, which then were deprotected (09BML4933). 

Oxidation of benzylic positions with o-iodoxybenzoic acid in DMSO proceeds via a similar mechanism involving the formation of benzyl radicals by SET [Eq. (89)] [164]. A variety of aromatic aldehydes were obtained in good yields with no over-oxidation to carboxylic acids. 

The tris trifluoroacetoxy analog of Dess-Martin reagent is formed from o-iodoxybenzoic acid and trifluoroacetic anhydride. Curiously, no reports about the reactivity of this interesting oxidant are available [65]. 

Several solid supports have been employed for the attachment of o-iodosobenzoic acid, including silica gel, titania and nylon [89]. Two polymer-supported o-iodoxybenzoic acid reagents have recently been reported. The first was obtained by attaching a carboxymethyloxy derivative of f-butyl o-iodo-benzoate to an aminopropylated silica gel and oxidation with oxone [90]. The second involved chloromethylated polystyrene which was coupled with methyl 5-hydroxy-2-iodobenzoate and eventually oxidized by Bu4NS05H/MeS03H [91]. Some of these polymeric reagents appear in Scheme 31. 

Recently it has been shown, that iodine(v) reagents can also be used for such transformations. An efficient regioselective method for the oxidation of phenols to ortho-quinones 40 can be achieved using 2-iodoxybenzoic acid (IBX) 7. With a subsequent reduction this proves to be a useful procedure for the synthesis of a variety of catechols 41, Scheme 20 [94]. 

The formation of the products 43 and 45 has also been studied from a mechanistic point of view. Labeling studies with H2180 revealed that two molecules of acetyl-2-iodoxybenzoic acid (formed by the reaction between Dess-Martin Peri-odinane 8 and water) are involved in para-quinone formation. It is suspected that the substituent in 2-position in 42 blocks another molecule of acetyl-2-iodoxybenzoic acid attacking the initially formed product leading to the formation of ortho-imidoquinones. Anilides substituted in the 3-position does lead to complex mixtures in the oxidation reaction. 

Recently it was found that iodine(v) compounds like 2-iodoxybenzoic acid (IBX) 7 can be used to affect selective oxidations at carbon atoms adjacent to aromatic systems. The mechanism of this transformation is believed to proceed via a SET (Single-Electron-Transfer) process. A postulated mechanism for the oxidation of benzylic positions is outlined in Scheme 32. This oxidation is quite general and proceeds efficiently in fluorobenzene/DMSO mixtures or in DMSO at 80 °C [ 135]. Starting from compounds 70, the corresponding aldehydes 71 can be obtained easily in good yields. 

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