Molybdenum-catalyzed asymmetric sulfoxidation with hydrogen peroxide and subsequent kinetic resolution, using an imidazolium-based dicarboxylate compound as chiral inductor

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

“…The optimization of the reaction conditions were performed with the ( S , S )-HL iPr compound, 1c , and methyl phenyl sulfide, and were previously communicated [ 42 ]. Chloroform was used as solvent (1 mL) with a 1:1:0.025:2 ratio of methyl phenyl sulfide:H 2 O 2 :Mo-complex:[PPh 4 ]Br.…”

“…A solution of MoO 3 (2.5% mmol) in aqueous hydrogen peroxide, namely [Mo(O)(O 2 ) 2 (H 2 O) n ] (see Materials and Methods), in conjunction with 1c and tetraphenylphosphonium bromide was employed to in-situ generate the catalyst. In these conditions, a 94% of conversion with high selectivity to sulfoxide (95%) and 40% ee to the ( R )-sulfoxide was obtained [ 42 ]. A number of additional imidazolium-based zwitterionic dicarboxylic acids were also tested as chiral inductors in the enantioselective oxidation of methyl phenyl sulfide ( Table 1 ).…”

“…Molybdenum-catalyzed enantioselective sulfoxidations have been investigated [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ] and, in general, the Mo catalysts provided results that are somewhat lower than those of other metals, as for example titanium [ 26 , 27 , 28 , 29 , 30 , 31 , 32 ] or vanadium [ 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ] complexes. However, we have recently demonstrated that the use of the imidazolium-based dicarboxylic compound ( S , S )-1-(1-carboxy-2-methylpropyl)-3-(1-carboxylate-2-methylpropyl)imidazolium (HL iPr in Scheme 1 ), as inductor of chirality, in combination with oxidoperoxidomolybdenum complexes, afforded a system capable to achieve by kinetic resolution a value of 83% ee in the sulfoxidation of alkyl aryl sulfides [ 42 ]. This system is easily accessible, simple, environmentally friendly, and compatible with a green oxidant as aqueous hydrogen peroxide.…”

“…In some cases, these advantages are not compatible with Ti or V catalysts. Following our recent research on Mo-catalyzed sulfoxidations [ 42 , 43 , 44 ], we report here the extension of our system [ 42 ] to other imidazolium-based dicarboxylic compounds, HL R , in order to improve its efficiency in the catalytic asymmetric oxidation of prochiral sulfides using aqueous hydrogen peroxide ( Scheme 1 ). Moreover, spectroscopic data and Density Functional Theory (DFT) calculations have allowed identification of the nature of the molybdenum catalytic species, {[Mo(O)(O 2 ) 2 (H 2 O)] 2 (μ-L R )} − , and the origin of the asymmetry in the sulfoxidation process.…”

Schiff base complex conjugates of bovine serum albumin as artificial metalloenzymes for eco-friendly enantioselective sulfoxidation

“…Asymmetric selective oxidation of suldes to sulfoxides is an important reaction that deserves much attention because enantiomerically pure sulfoxides are valuable compounds that have utility as powerful chiral auxiliaries, [1][2][3] ligands, 4,5 organocatalysts 6,7 in asymmetric organic synthesis, [8][9][10] and as active pharmaceutical ingredients. [11][12][13][14][15] Traditionally, catalysis has been divided into three subdisciplines: heterogeneous, homogeneous, and enzymatic catalysis. Although promising metal catalysts 16 have been developed and show encouraging practical potential, issues such as compound stability, efficacy, regio-and stereoselectivity, and environmental toxicity remain to be addressed.…”