Alcohols oxidation with hypervalent iodine reagents

Ionic solvents have been used to facilitate the Heck reaction (13-9), the oxidation of alcohols with hypervalent iodine reagents (19-3)," and the catalytic asymmetric dihydroxylation of olefins (15-48) using a recoverable and reusable osmium/... 

For a review on the oxidation of alcohols with hypervalent iodine reagents such as IBX and DMP, see H. Tohma, Y. Kita, Adv. Synth. Catal. 2004, 346, 111-124. 

Yadav JS, Reddy BVS, Basak AK, Narsaiah AV (2004) Recyclable 2nd generation ionic liquids as green solvents for the oxidation of alcohols with hypervalent iodine reagents. Tetrahedron 60 2131-2135... 

Common alcohol oxidation methods employ stoichiometric amounts of toxic and reactive oxidants like Cr03, hypervalent iodine reagents (Dess-Martin) and peracids that pose severe safety and environmental hazards in large-scale industrial reactions. Therefore, a variety of catalytic methods for the oxidation of alcohols to aldehydes, ketones or carboxylic acids have been developed employing hydrogen peroxide or alkyl hydroperoxides as stoichiometric oxygen sources in the presence of catalytic amounts of a metal catalyst. The commonly used catalysts for alcohol oxidation are different MoAV(VI), Mn(II), Cr(VI), Re(Vn), Fe(II) and Ru complexes . A selection of published known alcohol oxidations with different catalysts will be presented here. 

Hydroxybenziodoxole 104 can be readily converted into its acetoxy derivative, l-acetoxy-1,2-benziodoxole-3(l//)-one (88, 2X = O, Y = OAc), by heating 104 with acetic anhydride and the acetoxy derivative can be further converted into the alkoxy derivatives by treatment with an appropriate alcohol [280], The tetrabutylanmionium salt of hydroxybenziodoxole 104 has been prepared by the reaction of hydroxybenziodoxole with tetrabutylammonium fluoride in THF it is a mild oxidant that is useful for the preparation of epoxides from a,p-unsaturated carbonyl compounds [281], l-Hydroxy-l,2-benziodoxole-3(l//)-one and l-acetoxy-l,2-benziodoxole-3(l//)-one have found wide application as starting compounds for the synthesis of various benziodoxole-based hypervalent iodine reagents by ligand exchange on iodine [239]. 

A very mild procedure for the Hofmann rearrangement of aromatic and aliphatic carboxamides 409 is based on the use of (tosylimino)phenyl-X. -iodane, PhINTs, as the oxidant (Scheme 3.165) [506]. Owing to the mild reaction conditions, this method is particularly useful for the Hofmann rearrangement of substituted benzamides 409 (R = aryl), which usually afford complex reaction mixtures with other hypervalent iodine oxidants. The mild reaction conditions and high selectivity in the reaction of carboxamides with PhINTs allow the isolation of the initially formed labile isocyanates 410, or their subsequent conversion into stable carbamates 411 by treatment with alcohols. Based on the previously reported mechanistic studies of the Hofmann rearrangement using other hypervalent iodine reagents [489,490,496], it is assumed that the reaction... 

Oxidation by the Dess-Martin Reagent. Another reagent that has become important for laboratory synthesis is known as the Dess-Martin reagent,28 which is a hypervalent iodine(V) compound.29 The reagent is used in inert solvents such as chloroform or acetonitrile and gives rapid oxidation of primary and secondary alcohols. The by-product, o-iodosobenzoic acid, can be extracted with base and recycled. 

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. ... 

Selective oxidation of alcohols with ion-supported hypervalent iodine(III) reagent was investigated by Zhang et al. [19]. This reaction was carried out in [emim][BF ] using l-(4-diacetoxyiodobenzyl)-3-methylimidazolium tetrafluorob-orate [dibmim][BF ] as an oxidant in the presence of a low concentration of bromide ions under mild conditions. A variety of primary and secondary alcohols were oxidized to carbonyl compounds in moderate to excellent yields at room temperature, but secondary alcohols were oxidized over longer reaction times (Scheme 14.19). 

The search for mild oxidizing reagents that convert alcohols to aldehydes or ketones under neutral or near neutral conditions has produced a new type of reagent that contains a hypervalent iodine. Dess and Martin showed that 2-iodobenzoic acid (75) reacted with KBrOs in sulfuric acid to give a 93% yield of 76. Subsequent heating (100°C) with acetic anhydride and acetic acid produced 77 in 93% yield, the so-called Dess-Martin periodinane. This reagent converted alcohols to ketones or aldehydes, illustrated by the transformation of cyclohexanol to cyclohexanone in 90% yield, in dichloromethane at 25°C. In this particular... 

The oxidation of alcohols is not limited to chromium derivatives, DMSO derivatives, or hypervalent iodine compounds. There are several metal-based reagents that can be very effective, particularly with sensitive functionality. This section will examine several of the more important regents. 

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. 

In contrast with X, -iodanes (Section 3.2), hypervalent iodine(III) reagents are not effective oxidants of alcohols in the absence of catalysts. Kita and coworkers were the first to find that, in the presence of bromide salts, iodosylbenzene or (diacetoxyiodo)benzene can be used as an efficient reagent for selective oxidation of alcohols [136,137]. The iodosylbenzene-KBr system is applicable to the oxidation of various primary and secondary alcohols, even in the presence of sensitive functional groups such as ether, ester, sulfonamide and azido groups. Primary alcohols under these conditions afford carboxylic acids (Scheme 3.50), while the oxidation of various secondary alcohols under similar conditions affords the appropriate ketones in almost quantitative yield [136]. 

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