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Chiral sulfoxides are important functional groups for various applications.1,2 For example, the biological activities of sulfoxide containing drugs such as omeprazole are strongly related to the chirality of the sulfoxide group; for this reason, esomeprazole, the enantiomerically pure form of omeprazole, was later developed. There are several chiral sulfoxide based drugs that have been introduced by the pharmaceutical industry including armodafinil, aprikalim, oxisurane, and ustiloxin. Chiral sulfoxides have also been utilized as chiral auxiliaries in asymmetric syntheses of chiral intermediates. Among the numerous sulfoxidation methods, the asymmetric oxidation of sulfides by hydrogen peroxide in the presence of a chiral catalyst is expected to be the most attractive method because of its high atom economy and the use of a "green oxidant", hydrogen peroxide.4 Our interest in the asymmetric oxidation of sulfides by hydrogen peroxide was also motivated by the desire to develop an efficient method to synthesize drugs such as esomeprazole.5 In this regard, reactions catalyzed by vanadium complexes of the Bolm type, 4a such as the tridentate chiral Schiff bases 2a and 2b (Scheme 1) were chosen since they have previously been used to prepare chiral sulfoxides with good enantioselectivities. 4gRecently, in an effort to improve catalytic activity, we designed new tridentate Schiff base ligands 5 and 6, which we hypothesized would show catalytic asymmetric sulfoxidation activity similar to ligand 2 (Scheme 2). The angles θ 5 and θ 6 of aldehyde 3, the starting material for ligand 5, were calculated by the MM2 program to be larger than θ 2 and θ 3 of salicylaldehyde, respectively, due to the fivemembered thiophene ring (Figure 1). However, the distance between O7 and O8 of 3, which is related to the bite angle of the metal-ligand complex 5, is similar to the distance between O8 and O9 of salicylaldehyde due to the small angle θ 4 of 3 compared with θ 1 . These data indicate that the

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