Title of Paper:Asymmetric oxidation of sulfides with H2O2 catalyzed by titanium complexes of Schiff bases bearing a dicumenyl salicylidenyl unit

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Date of Publication:2011-05-01

Journal:APPLIED ORGANOMETALLIC CHEMISTRY

Included Journals:SCIE、EI

Volume:25

Issue:5

Page Number:325-330

ISSN No.:0268-2605

Key Words:asymmetric catalysis; chiral sulfoxides; dicumenyl salicylaldehyde; Schiff bases; titanium

Abstract:The sterically hindered Schiff bases (L-3-L-5), prepared from 3,5-dicumenyl salicylaldehyde and chiral amino alcohols, were used in combination with Ti(OiPr)(4) for asymmetric oxidation of aryl methyl sulfides with H2O2 as terminal oxidant. Among the ligands L-3-L-5, L-4 with a tert-butyl group in the chiral carbon of the amino alcohol moiety gave the best result with 89% yield and 73% ee for the sulfoxidation of thioanisole under optimal conditions [with 1 mol% of Ti(OiPr)(4) in a molar ratio of 100 : 1 : 1.2 : 120 for sulfide : Ti(OiPr)(4) : ligand : H2O2 in CH2Cl2 at 0 degrees C for 3 h]. The reaction afforded good yield (84%) with a moderate enantioselectivity (62% ee) even with a lower catalyst loading from 1.0 to 0.5 mol%. The oxidations of methyl 4-bromophenyl sulfide and methyl 4-methoxyphenyl sulfide with H2O2 catalyzed by the Ti(OiPr)(4)-L-4 system gave 79-84% yieldsand54-59% ee of the corresponding sulfoxides in CH2Cl2 at 20 degrees C. The chiral induction capability of the cumenyl-modified sterically hindered Schiff bases for sulfoxidation was compared with the conventional Schiff bases bearing tert-butyl groups at the 3,5-positions of the salicylidenyl unit. Copyright (C) 2011 John Wiley & Sons, Ltd.