Oxidation of Sulfides to Sulfoxides with Hypervalent (tert-Butylperoxy)iodanes

Abstract

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.

Radical scavengers: A practical solution to the reproducibility issue in the fluoridation of diaryliodonium salts

“…2) were selected based on their previously demonstrated ability in this role. These included 4-aminobenzoic acid [27], 2,6-di-tert-butyl-4-methylphenol (BHT) [28,29], 1,1-diphenylethylene [30], galvinoxyl [31][32][33], gentisic acid [ [34][35][36], hydroquinone [37][38][39], TEMPO [33,40], thiophenol [41], and DL-a-tocopherol [29].…”

Studies on deprotection of cysteine and selenocysteine side‐chain protecting groups

“…For these reactions, we synthesized test peptides of sequence VTGGC(Mob)A-OH and VTGGC(Acm)A-OH. We decided that we would include thioanisole in the cleavage cocktails as it might enhance deprotection as a sulfonium cation transfer catalyst [26,27]. The peptide derivatives were analyzed by HPLC and products were identified by MALDI-TOF MS. To our great surprise, the Acm group of cysteine could be removed by DTNP.…”

A Mild and Highly Efficient Oxidation of Sulfides to Sulfoxides with Periodic Acid Catalyzed by FeCl3

“…Diphenyl sulfide may exert a little steric hindrance for the oxidation as exhibited by the longer time of 10 minutes with 96% yield (entry 11). Such a rate retardation 4,8,[10][11][12]14,17 has already been clearly observed in the oxidation of diphenyl sulfide with longer reaction time (1-28 h) giving low yield (60-100%). However, the slow process can be nearly overcome when diphenyl sulfide is oxidized with present method.…”

“…The combined organic layers was dried (Na 2 SO 4 ) and evaporated to dryness. The products were purified by flash column chromatography on silica gel and identified by 1 H, 13 C NMR and GC-MS. All sulfoxides thus obtained were identified by comparing NMR data with the values reported in the literature 11,12,17,22 and those of the authentic samples.…”

“…In recent years, hypervalent iodine atoms [15][16][17][18][19] are employed to oxidize various organic substrates with or without catalyst. Very recently, oxidation of alcohols with H 5 IO 6 /2,2,6,6-tetramethylpiperidinyl-1-oxyl 20 has been found to yield the corresponding carbonyl compounds.…”