Vanadium enantioselective sulfoxidation

F. van Rantwijk, and R. A. Sheldon, Enantioselective sulfoxidation mediated by vanadium-incorporated phytase a hydrolase acting as a peroxidase,... 

In 1995, Bolm et al. reported that the vanadium complexes of the triden-tate and amino-acid derived ligands 15 catalyze the enantioselective sulfoxidation of prochiral thioethers with dihydrogen peroxide as the terminal oxidant (Scheme 8) (24). The ligands are synthesized by a one-step condensation of the readily available salicylic aldehydes 16 with amino-acid derived amino alcohols, such as 17a. 

Enantioselective sulfoxidation has been also studied using polymeric aminoalcohol-derived Schiff bases. Polymers 354-357 have been prepared by copolymeristation of the corresponding monomer with either MMA and EGDMA or styrene and DVB (Scheme 150) [219], These four polymers were then stirred with VO(acac)2 for 4h at rt to lead to the vanadium complexes. For the enantioselective oxidation of thioanisole, although the yields were similar to those obtained with the homogeneous analogs, the enantioselectivity were lower. The best selectivity was obtained with the catalyst derived from 355. 

A vanadium-catalyzed enantioselective sulfoxidation using related Schiff-base ligands was later developed by the Jackson group. In this reaction, selective oxidation... 

The most practical method that is used in the industrial synthesis of esomeprazole involves titanium-catalyzed oxidation with an alkyl hydroperoxide, and a dialkyltartrate as chiral ligand, in an organic solvent such as dichloromethane. A variety of oxidoreductases are known to catalyze the enantioselective oxidation of prochiral sulfides, usually as whole-cell biotransformations in aqueous media, but no simple metal complexes have been shown to be effective in water and the development of practical systems employing aqueous hydrogen peroxide as the primary oxidant is still an important challenge. In this context it is worth mentioning the enantioselective sulfoxidation of prochiral sulfoxides catalyzed by the semisynthetic peroxidase, vanadium-phytase, in an aqueous medium. 

Zeng QL, Wang HQ, Wang TJ et al (2005) Vanadium-catalyzed enantioselective sulfoxidation and concomitant, highly efficient kinetic resolution provide high enantioselectivity and acceptable yields of sulfoxides. Adv Synth Catal 347 1933-1936... 

In addition, a recent report details a very efficient nonenzymatic method for the asymmetric oxidation of sulfides this employs an organo-vanadium species featuring the imine (38) (Scheme 25)[111]. A second, complementary strategy for the preparation of optically active sulfoxides involves the enantioselective oxidation of racemic sulfoxides. ... 

Bolm and Bienewald discovered in 1995 that some chiral vanadium (IV)-Schiff base complexes were efficient catalysts (1 mol %) for sulfoxidation [71a]. The catalyst 20 was prepared in situ by reacting VO(acac)2 with the Schiff base of a fJ-aminoalcohol (Scheme 6C.8). Reactions were conveniently performed in air at room temperature by slow addition of 1.1 mol equiv. of aqueous hydrogen peroxide (30%). Under these experimental conditions the reaction of methyl phenyl sulfide gave the corresponding sulfoxide in 94% yield and 70% ee. The best enantioselectivity was obtained in the formation of sulfoxide 21 (85% ee). Many structural analogues of catalyst 20 were screened for their efficacy, but none of... 

The Bolm protocol was recently used by Ellman et al. for the enantioselective oxidation of -butyl disulfide 22 [72], Excellent result was achieved in the formation of thiosulfinate 22 (91% ee, 93% yield) by using catalyst 20 (0.25 mol %) in a 0,5 mmol scale. In spite of extensive screening of chiral Schiff bases related to catalyst 20, better enantioselectivity was not realized. Chiral thiosulfinate 22 is a convenient starting material for the preparation of r-butyl sulfi-namides and t-butyl sulfoxides. Vetter and Berkessel modified the structure of the Schiff base moiety of catalyst 20 by replacing the aryl ring with a 1,l -binaphthyl system [73]. The corresponding vanadium catalyst realized 78% ee in the oxidation of thioanisol, which was better than that attained by the Bolm catalyst (59% ee). 

Kelly, R, Lawrence, S. and Maguhe, A. (2006). Asymmetric Synthesis of ArylBenzyl Sulfoxides by Vanadium-Catalysed Oxidation a Combination of Enantioselective Sulfide Oxidation and Kinetic Resolution in Sulfoxide Oxidation, Eur. J. Org. Chem., 19, pp. 4500-4509. 

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