Preparation, structural characterization, and reactivity of 3-[bis(trifluoroacetoxy)iodo]benzoic acid and 3-[hydroxy(tosyloxy)iodo]benzoic acid, new recyclable iodine(III) reagents derived from 3-iodosylbenzoic acid, are described. The reduced form of these reagents, 3-iodobenzoic acid, can be easily recovered from the reaction mixtures using ion-exchange resin or basic aqueous workup followed by acidification with HCl.

A convenient procedure for the preparation of a-iodo ketones by oxidative iodination of ketones using iodine and m-iodosylbenzoic acid as a recyclable hypervalent iodine oxidant is reported. Various ketones and b-dicarbonyl compounds can be iodinated by this reagent system under mild conditions affording the respective a-iodo-substituted carbonyl compounds in excellent yields. The final products of iodination are conveniently separated from byproducts by simple treatment with anionic exchange resin Amberlite IRA 900 HCO 3 -and are isolated with good purity after evaporation of the solvent. The reduced form of the hypervalent iodine oxidant, m-iodobenzoic acid, can be recovered in 91-95% yield from the Amberlite resin by treatment with aqueous hydrochloric acid followed by extraction with ethyl acetate.Hypervalent iodine reagents have emerged as the reagent of choice for various synthetically useful oxidative transformations. 1 The most widely used reagents, (diacetoxyiodo)benzene, [hydroxy(tosyloxy)iodo]benzene, and iodosylbenzene, are based on the oxidized form of iodobenzene, and the reactions of these reagents with organic substrates lead to iodobenzene as the byproduct, which is difficult to recover and reuse because of its high volatility and solubility in organic solvents. Numerous research groups have tried to improve iodobenzene-based hypervalent iodine reagents by developing polymer-supported analogues, such as, poly(diacetoxyiodo)styrene. 2 Despite the utility of polymer-supported reagents, they still have several drawbacks. These reagents require multistep preparation, they have lower reactivity compared to the corresponding monomeric analogues, and, moreover, the repeated use of these polymers leads to significant degradation due to benzylic oxidation of the polystyrene chain.Recently, we have found that m-iodosylbenzoic acid 3a,b and its derivatives 3c,d are efficient oxidizing reagents whose reduced form, m-iodobenzoic acid, can be easily recovered from the reaction mixture by treatment with anionic exchange resin or by addition of NaHCO 3 . 3 In the present study, we wish to report the use of m-iodosylbenzoic acid as a convenient recyclable oxidant for the synthesis of a-iodo ketones, which are important building blocks in organic synthesis. 4 Previously reported methods for the preparation of a-iodo ketones commonly employ oxidative iodination of carbonyl compounds using such inconvenient and environmentally harmful reagents as selenium dioxide, 5a mercury(II) chloride, 5b or cerium(IV) ammonium nitrate. 5c We have found that m-iodosylbenzoic acid (1) (which actually has a polymeric structure) 6 is an excellent oxidizing reagent in the oxidative iodination of ketones 3 whose reduced form, m-iodobenzoic acid (2), can be removed at the end of the reaction by treatment with anionic exchange resin Amberlite IRA 900 HCO 3 -5 producing pure a-iodo ketones 4 (Scheme 1).Scheme 1 Oxidative iodination of ketones using m-iodosylbenzoic acid (1) The results for the iodination of various enolizable ketones a...