Highly enantioselective sulfoxidation with vanadium catalysts of Schiff bases derived from bromo- and iodo-functionalized hydroxynaphthaldehydes

• Published in: Journal of catalysis 2010-07, Vol.273 (2), p.177-181
• Main Authors: Wang, Ying, Wang, Mei, Wang, Yu, Wang, Xiuna, Wang, Lin, Sun, Licheng
• Format: Article
• Language: English
• Subjects: Asymmetric sulfoxidation; Catalysis; Catalysts; Chemistry; Chiral Schiff bases; Chiral sulfoxides; Exact sciences and technology; Fysikalisk kemi; General and physical chemistry; Kemi; NATURAL SCIENCES; NATURVETENSKAP; Oxidation; Physical chemistry; Sulfides; Sulfur content; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Vanadium
• ISSN: 0021-9517; 1090-2694; 1090-2694
• DOI: 10.1016/j.jcat.2010.05.013

Chiral Schiff bases with a bromo- and iodo-functionalized naphthyl backbone proved to be efficient ligands for the vanadium-catalyzed asymmetric oxidation of aryl methyl sulfides in dichloromethane and toluene with up to 99% ee and moderate-to-high isolated yields. Two series of chiral Schiff bases, 4a− e and 5a− e, prepared from the condensation of the mono-, di-, tribromohydroxynaphthaldehyde or monoiodohydroxynaphthaldehyde with chiral amino alcohols, were used in combination with VO(acac) 2 for the asymmetric oxidation of aryl methyl sulfides using H 2O 2 as terminal oxidant. Among these Schiff bases, dibromo-functionalized 4d and iodo-functionalized 5e gave high yields (91–93%) with good enantioselectivities (80–82% ee) for the oxidation of thioanisole in dichloromethane. The asymmetric oxidation of thioanisole in toluene using these Schiff bases gave methyl phenyl sulfoxide in satisfactory isolated yields (48–62%) with high enantioselectivities (91–94% ee), which were further improved by a modified procedure with the ee value up to 98% in 62% yield. The oxidations of other aryl methyl sulfides in toluene with dibromo- and iodo-functionalized Schiff bases 5d and 5e as ligands using the modified procedure afforded the corresponding sulfoxides in 55–67% isolated yields with 95–99% ee.