Oxidation Of Alkyl Aryl Sulfides Research Articles

Molybdenum-Catalyzed Enantioselective Sulfoxidation Controlled by a Nonclassical Hydrogen Bond between Coordinated Chiral Imidazolium-Based Dicarboxylate and Peroxido Ligands.

Chiral alkyl aryl sulfoxides were obtained by molybdenum-catalyzed oxidation of alkyl aryl sulfides with hydrogen peroxide as oxidant in mild conditions with high yields and moderate enantioselectivities. The asymmetry is generated by the use of imidazolium-based dicarboxylic compounds, HLR. The in-situ-generated catalyst, a mixture of aqueous [Mo(O)(O2)2(H2O)n] with HLR as chirality inductors, in the presence of [PPh4]Br, was identified as the anionic binuclear complex [PPh4]{[Mo(O)(O2)2(H2O)]2(μ-LR)}, according to spectroscopic data and Density Functional Theory (DFT) calculations. A nonclassical hydrogen bond between one C–H bond of the alkyl R group of coordinated (LR)− and one oxygen atom of the peroxido ligand was identified as the interaction responsible for the asymmetry in the process. Additionally, the step that governs the enantioselectivity was theoretically analyzed by locating the transition states of the oxido-transfer to PhMeS of model complexes [Mo(O)(O2)2(H2O)(κ1-O-LR)]− (R = H, iPr). The ∆∆G≠ is ca. 0 kcal∙mol−1 for R = H, racemic sulfoxide, meanwhile for chiral species the ∆∆G≠ of ca. 2 kcal∙mol−1 favors the formation of (R)-sulfoxide.

Amine templated open-framework vanadium(iii) phosphites with catalytic properties

Four novel amine templated open-framework vanadium(III) phosphites with the formula (C(5)N(2)H(14))(0.5)[V(H(2)O)(HPO(3))(2)], 1 (C(5)N(2)H(14) = 2-methylpiperazinium), and (L)(4-x)(H(3)O)(x)[V(9)(H(2)O)(6)(HPO(3))(14-y)(HPO(4))(y)(H(2)PO(3))(3-z)(H(2)PO(4))z]·nH(2)O (2, L = cyclopentylammonium, x = 0, y = 3.5, z = 3, n = 0; , L = cyclohexylammonium, x = 1, y = 0, z = 0.6, n = 2.33; , L = cycloheptylammonium, x = 1, y = 0, z = 0, n = 2.33) were synthesized employing solvothermal reactions and characterized by single-crystal X-ray diffraction, ICP-AES and elemental analyses, thermogravimetric and thermodiffractometric analyses, and IR and UV/vis spectroscopy. Single-crystal data indicate that 1 crystallizes in the triclinic system, space group P1, whereas 2, 3 and 4 crystallize in the hexagonal space group P6(3)/m. Compound 1 has a two-dimensional motif with anionic sheets of [V(H(2)O)(HPO(3))(2)](-) formula, whose charge is compensated by the 2-methylpiperazinium cations embedded between the layers. In contrast, 2, 3 and 4 present a pillar-layer network giving rise to a three-dimensional framework containing intersecting 16-ring channels with the primary amine templates and the crystallization water molecules enclosed in them. 1, 2, 3 and 4 behave as heterogeneous catalysts for the selective oxidation of alkyl aryl sulfides, with tert-butylhydroperoxide (TBHP) as the oxidizing agent, being active, selective and recyclable for several successive cycles of reaction.

The oxidation of alkylaryl sulfides and benzo[b]thiophenes by Escherichia coli cells expressing wild-type and engineered styrene monooxygenase from Pseudomonas putida CA-3

Nine different sulfur-containing compounds were biotransformed to the corresponding sulfoxides by Escherichia coli Bl21(DE3) cells expressing styrene monooxygenase (SMO) from Pseudomonas putida CA-3. Thioanisole was consumed at 83.3 μmoles min(-1) g cell dry weight(-1) resulting mainly in the formation of R-thioanisole sulfoxide with an enantiomeric excess (ee) value of 45 %. The rate of 2-methyl-, 2-chloro- and 2-bromo-thioanisole consumption was 2-fold lower than that of thioanisole. Surprisingly, the 2-methylthioanisole sulfoxide product had the opposite (S) configuration to that of the other 2-substituted thioanisole derivatives and had a higher ee value (84 %). The rate of oxidation of 4-substituted thioanisoles was higher than the corresponding 2-substituted substrates but the ee values of the products were consistently lower (10-23 %). The rate of benzo[b]thiophene and 2-methylbenzo[b]thiophene sulfoxidation was approximately 10-fold lower than that of thioanisole. The ee value of the benzo[b]thiophene sulfoxide could not be determined as the product racemized rapidly. E. coli cells expressing an engineered SMO (SMOeng R3-11) oxidised 2-substituted thioanisoles between 1.8- and 2.8-fold faster compared to cells expressing the wild-type enzyme. SMOeng R3-11 oxidised benzo[b]thiophene and 2-methylbenzo[b]thiophene 10.1 and 5.6 times faster that the wild-type enzyme. The stereospecificity of the reaction catalysed by SMOeng was unchanged from that of the wild type. Using the X-ray crystal structure of the P. putida S12 SMO, it was evident that the entrance of substrates into the SMO active site is limited by the binding pocket bottleneck formed by the side chains of Val-211 and Asn-46 carboxyamide group.

M(C6H16N3)2(VO3)4 as heterogeneous catalysts. Study of three new hybrid vanadates of cobalt(ii), nickel(ii) and copper(ii) with 1-(2-aminoethyl)piperazonium

Three new hybrid vanadates have been synthesized under hydrothermal conditions with the formula M(C(6)H(16)N(3))(2)(VO(3))(4), where M = Co(II), Ni(II) and Cu(II). The structural analyses show that the phases are isostructural and crystallize in the monoclinic space group P2(1)/c. These compounds show a two-dimensional crystal structure, with sheets composed of [VO(3)](n)(n-) chains and metal centres octahedrally coordinated, chelated by two 1-(2-aminoethyl)piperazonium ligands. The thermal study reveals that the copper containing phase is less stable than the cobalt and nickel containing ones. The IR spectra of the three phases are very similar, with little differences in the inorganic bond region of the copper containing phase. The UV-visible spectra show that the cobalt(II) and the nickel(II) are in slightly distorted octahedral environments. The catalytic tests show that the phases act as heterogeneous catalysts for the selective oxidation of alkyl aryl sulfides, with both H(2)O(2) and tert-butylhydroperoxide as oxidizing agents. The influence of the steric hindrance in the kinetic profile has been studied. The catalytic reactions induce the partial amorphization of the phases.

Homogeneous and heterogeneous catalytic oxidation of sulfides by H2O2 over zinc(ii) compounds

It has been recently shown that zinc compounds are effective catalysts for the oxidation of alkyl aryl sulfides to the corresponding sulfoxides in the presence of hydrogen peroxide. In this paper, we have investigated homogeneous and heterogeneous catalytic oxidation of sulfides by H(2)O(2) over Zn(NO(3))(2) x 6 H(2)O and the metal-organic porous material [Zn(2)(bdc)(L-lac)(dmf)] x DMF (where H(2)bdc = p-benzenedicarboxylic acid, H(2)lac = lactic acid), respectively. The experimental data can be explained by the proposed catalytic cycle which includes the activation of H(2)O(2) via coordination to Zn(II) ions followed by oxygen transfer step. In homogeneous conditions, the presence of a large amounts of H(2)O(2) results in the coordination of two molecules of hydrogen peroxide to Zn(II), so that sulfone is formed via transfer of two oxygen atoms from Zn(H(2)O)(4)(H(2)O(2))(2)(2+) active species. Contrary to the homogeneous system, the use of [Zn(2)(bdc)(L-lac)(dmf)] x DMF as catalyst does not lead to the formation of sulfone in the initial period of reaction. This is consistent with the proposed catalytic cycle of sulfoxidation as each Zn(II) center in the crystalline framework is able to activate only one H(2)O(2) molecule. Our investigations indicate that the sorption and activation of H(2)O(2) molecules by microporous framework [Zn(2)(bdc)(L-lac)(dmf)] occur faster than sulfide sorption and oxygen transfer.

Iron‐Catalyzed Oxidation of Thioethers by Iodosylarenes: Stereoselectivity and Reaction Mechanism

Catalytic properties of a series of iron(III)-salen (salen=N,N'-bis(salicylidene)ethylenediamine dianion) and related complexes in asymmetric sulfoxidation reactions, with iodosylarenes as terminal oxidants, have been explored. These catalysts have been found to efficiently catalyze oxidation of alkyl aryl sulfides to sulfoxides with high chemoselectivity (up to 100 %) and moderate-to-high enantioselectivity (up to 84 % with isopropylthiobenzene and iodosylmesitylene), the TON (TON=turnover number) approaching 500. The influence of the ligand (electronic and steric effects of the substituents), oxidant, and substrate structures on the oxidation stereoselectivity has been investigated systematically. The structure of the reactive intermediates (complexes of the type [Fe(III)(ArIO)(salen)] and the reaction mechanism have been revealed by both mechanistic studies with different iodosylarenes and direct in situ (1)H NMR observation of the formation of the reactive species and its reaction with the substrate.

Asymmetric oxidation of sulfides with H 2O 2 catalyzed by titanium complexes with aminoalcohol derived Schiff bases

Sulfoxidation catalysts generated in situ from titanium(IV) isopropoxide and enantiopure Schiff bases promote the enantioselective oxidation of alkyl aryl sulfides to the corresponding sulfoxides at low catalyst loadings (<1 mol%), 30% aqueous hydrogen peroxide being the terminal oxidant. Upon screening of several ligands derived from β-aminoalcohols and salicylaldehydes, a catalyst affording sulfoxides with over 90% chemoselectivity and up to 60% ee was found, and the kinetics of the catalytic reaction was analyzed by 1H NMR.

Effective asymmetric oxidation of enones and alkyl aryl sulfides

Asymmetric epoxidation of aliphatic enones can be achieved with good conversions and high levels of enantiomeric excess using a catalyst, formulated as 6, derived from dibutylmagnesium and a range of dialkyl tartrates, with tert-butylhydroperoxide as the oxidant. This process works best with the addition of small amounts of water and 4 Å molecular sieves, and can be scaled up to good effect. Optimisation of Bolm and Bienewald's vanadium-based method for asymmetric oxidation of alkyl aryl sulfides by aqueous hydrogen peroxide using Schiff bases derived from tert-leucinol as ligands, confirmed that the ligand 12 derived from 3,5-diiodosalicylaldehyde is the optimum choice.

Iron-catalyzed asymmetric sulfide oxidation with aqueous hydrogen peroxide.

An iron in the fire: Iron-based catalysts promote the asymmetric oxidation of alkyl aryl sulfides to the corresponding sulfoxides with up to 90 % ee (see scheme). Simple hydrogen peroxide (30 % in water) serves as the terminal oxidant.

Catalytic Asymmetric Oxidation of Alkyl Aryl Sulfides Mediated by a Series of Chiral N‐Alkyl‐1,2‐diphenylaminoethanol/Titanium/Water Complexes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Fluorous biphasic oxidation of sulfides catalysed by (salen)manganese(III) complexes

Abstract Quadridentate Schiff base ligands derived from 1,2-diamines and fluorous derivatives of salicylaldehyde were prepared and the corresponding manganese(III) complexes were tested as catalysts in the selective oxidation of alkyl aryl sulfides with PhIO. Complexes bearing two fluorinated ponytails were soluble in standard organic solvents and were used under classical homogeneous conditions, whereas heavily fluorinated complexes could be used in a CH3CN/perfluorooctane biphasic system. In both cases, sulfoxides were obtained as the main products, together with variable amounts of sulfones (≤10%), depending on the nature of the substrate and the catalyst. When reactions were carried out under fluorous biphasic (FB) conditions, the selectivity for sulfoxides was improved and the catalyst could be easily recovered by simple phase separation and reused up to four times. Despite their good chemoselectivity, catalytic efficiency and recyclability, chiral fluorous (salen)manganese(III) complexes showed low enantioselectivities in preliminary experiments run under fluorous biphasic conditions.

Catalytic Asymmetric Oxidation of Alkyl Aryl Sulfides Mediated by a Series of Chiral N-Alkyl-1,2-diphenylaminoethanol/Titanium/Water Complexes

A series of chiral N-alkyl-1,2-diphenylaminoethanol/titanium/water complexes were investigated as potential efficient catalyst for the enantioselective oxidation of alkyl aryl sulfides. The structure of the aminoethanols strongly influenced on the reactivity and enantioselectivity. Using (1S,2S)-N-methyl-1,2-diphenylaminoethanol (6) as ligand in oxidation of methyl phenyl sulfide, gave (S)-sulfoxide with moderate yield and ee.

Enantioselective Sulfide Oxidation with H2O2: A Solid Phase and Array Approach for the Optimisation of Chiral Schiff Base-Vanadium Catalysts

Two libraries of chiral Schiff base ligands were synthesised and screened in the vanadium-catalysed oxidation of alkyl aryl sulfides with hydrogen peroxide as terminal oxidant. The vanadium-chiral Schiff base complex 10, readily prepared from 3,5-diiodo-salicylaldehyde and (S)-tert-leucinol, was found to be highly enantioselective. Optically active sulfoxides could thus be obtained in good yields with up to 97% ee.

Fluorous Biphasic Catalytic Oxidation of Sulfides by Molecular Oxygen/2,2-Dimethylpropanal

The use of perfluoroalkyl-substituted cobalt complexes as catalysts for the oxidation of alkyl aryl sulfides with molecular oxygen/2,2-dimethypropanal has been studied in a fluorous organic biphasic system. The addition of very small amounts of a CoII−tetraarylporphyrin (Co-4) led to increased substrate conversions (67−100%). Sulfoxide was generally obtained as the main product, together with variable quantities of sulfone (0−100%), depending on the nature of the substrate. A perfluoroalkyl-substituted CoII−phthalocyanine (Co-6) proved to be less efficient with regard to substrate conversion (40−78%), but afforded sulfoxides selectively. Although the mechanism has not been investigated in detail, the reaction probably proceeds through a free-radical oxidative process, initiated by the CoII complexes. The attempts at recycling the catalysts through phase separation were partly ineffectual owing to their instability under the reaction conditions, which is more pronounced in the case of Co-6.

Titanium-Catalyzed, Asymmetric Sulfoxidation of Alkyl Aryl Sulfides with Optically Active Hydroperoxides

The Ti-catalyzed, asymmetric oxidation of alkyl aryl sulfides by enantiomerically pure hydroperoxides (ee >99%) has been examined. Enantioselectivities with ee values up to ca. 80% were achieved fo...

Enantioselective oxidation of sulfides to sulfoxides catalysed by bacterial cyclohexanone monooxygenases

This review article briefly introduces the applications of bacterial cyclohexanone monooxygenases to the enantioselective oxidations of organic sulfur compounds to sulfoxides. High enantioselectivities are observed in the sulfoxidation of alkyl aryl sulfides, disulfides, dialkyl sulfides, cyclic and acyclic 1,3-dithioacetals. The oxidation of alkyl aryl sulfides with flavin dependent microorganisms extends the synthetic interest of this class of enzymes.

The microperoxidase-11 catalyzed oxidation of sulfides is enantioselective

Microperoxidase-11 catalyzed oxidation of alkyl aryl sulfides by H 2O 2 preferentially give the (−)-(S)-sulfoxides (e.e. 16 – 25 %).

Studies on enzymatic oxidation of sulfides. Part II. Microbial oxidation of alkyl aryl sulfides to the corresponding optically active sulfoxides.

Studies on enzymatic oxidation of sulfides. Part II. Microbial oxidation of alkyl aryl sulfides to the corresponding optically active sulfoxides.

Mechanism of the oxidation of alkyl aryl sulfides by phenyliodoso diacetate

Mechanism of the oxidation of alkyl aryl sulfides by phenyliodoso diacetate

Substituent and steric effects in the oxidation of alkyl aryl sulfides by peroxydisulfate

The kinetics of oxidation of a number of alkyl aryl sulfides with potassium peroxydisulfate in aqueous ethanol have been investigated. The effect of substituents on the oxidation has been studied by employing a number of p- and m-substituted phenyl methyl sulfides: the reaction is accelerated by electron-releasing and retarded by electron-withdrawing substituents, indicating a rate-determining electrophilic attack by the peroxydisulfate ion at the reaction site, sulfur. A good correlation is found to exist between the rate constants and the Hammett σ+/σ− constants, the ρ+ value for the reaction being −0.56 with a correlation coefficient of 0.979. The activation parameters have also been determined.Studies with different alkyl phenyl sulfides clearly indicate that the reaction is quite sensitive to steric congestion around the reaction site. The results obtained in this study are compared with those found for the oxidation of the same set of sulfides with different oxidants.