Camphor-Based Schiff Base Of 3-Endo-Aminoborneol (SBAB): Novel Ligand for Vanadium-Catalyzed Asymmetric Sulfoxidation and Subsequent Kinetic Resolution

Novel in situ formed vanadium Schiff base complexes, namely vanadyl Schiff base of 3-exo-aminoisoborneol (V(O)-SBAIB) and vanadyl Schiff base of 3-endo-aminoborneol (V(O)-SBAB), were demonstrated to catalyze an enantioselective sulfoxidation reaction. Among the twenty substitutionally and electronically different (1R)-camphor based Schiff base ligands, 6-bromo-2hydroxy-1-naphthaldehyde Schiff base of 3-endo-aminoborneol, 48 (SBAB-14), produced (S)-ethyl 2-naphthyl sulfoxide in excellent enantioselectivity (> 99%) with good yield (72%). In an optimized reaction condition, 1.5 mol% 48 (SBAB-14) catalyzed asymmetric sulfoxidation with concomitant kinetic resolution of various alkyl aryl sulfides and rendered corresponding sulfoxides with high ee (up to 97%) with moderate yield (up to 74%).