Tetra-n-butylammonium oxido-lambda(3)-iodane, prepared from 1-hydroxy-1,2-benziodoxol-3(1H)-one by reaction with tetra-n-butylammonium fluoride, directly undergoes oxygen atom transfer to alpha,beta-unsaturated carbonyl compounds, yielding epoxides.
Oxidation of sulfides with the crystalline (alkylperoxy)iodanes, 1-(tert-butylperoxy)-1,2-benziodoxol-3(1H)-ones 2a and 2b, in acetonitrile-water or in dichloromethane, affords sulfoxides in high yields. Measurement of the relative rates of oxidation for a series of ring-substituted thioanisoles 3b (p-MeO), 3c (p-Me), and 3d (p-Cl) in acetonitrile-water indicates that electron-releasing groups such as p-MeO and p-Me groups increase the rate of oxidation, and Hammett correlation of the relative rate factors with the substituent constants affords the reaction constants rho(+) = -2.23 (sigma(+), r = 0.98) for BF(3)-catalyzed oxidation and rho = -3.32 (sigma, r = 0.98) for uncatalyzed oxidation. The effects of a free-radical scavenger, galvinoxyl, were examined. A mechanism involving the intermediary formation of the sulfonium species 11 by nucleophilic attack of sulfide toward the iodine(III) atom of 2 is proposed for the oxidation in acetonitrile-water in the presence and the absence of BF(3). Et(2)O. On the other hand, the oxidation of sulfoxides in dichloromethane probably proceeds by a radical process, which involves the decomposition at room temperature of 2 via homolytic bond cleavage of the weak iodine(III)-peroxy bond, generating tert-butylperoxy radical and the [9-I-2] iodanyl radical 12.
The title iodane oxidizes benzyl and allyl ethers to the esters even at room temp. in the presence of alkali metal carbonates. Since this reaction is compatible with other protecting groups and because esters are readily hydrolyzed under basic conditions, this reaction offers a new method for the deprotection of benzyl and allyl ethers. Kinetic and mechanistic considerations reveal that the oxidation with the iodane occurs with activated C-H bonds generating α-oxy carbon-centered radicals, which can be detected by nitroxyl radical trapping.-(OCHIAI, M.; ITO, T.; TAKAHASHI, H.; NAKANISHI, A.; TOYONARI, M.; SUEDA, T.; GOTO, S.; SHIRO, M.; J.
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