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Asymmetric oxidation of sulfides with H 2 O 2 catalyzed by titanium complexes of Schiff bases bearing a dicumenyl salicylidenyl unit
Author(s) -
Wang Ying,
Wang Mei,
Wang Lin,
Wang Yu,
Wang Xiuna,
Sun Licheng
Publication year - 2011
Publication title -
applied organometallic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.53
H-Index - 71
eISSN - 1099-0739
pISSN - 0268-2605
DOI - 10.1002/aoc.1762
Subject(s) - chemistry , thioanisole , steric effects , catalysis , sulfide , moiety , medicinal chemistry , aryl , schiff base , yield (engineering) , ligand (biochemistry) , salicylaldehyde , enantioselective synthesis , alcohol , polymer chemistry , organic chemistry , biochemistry , alkyl , materials science , receptor , metallurgy
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(O i Pr) 4 for asymmetric oxidation of aryl methyl sulfides with H 2 O 2 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(O i Pr) 4 in a molar ratio of 100:1:1.2:120 for sulfide:Ti(O i Pr) 4 :ligand:H 2 O 2 in CH 2 Cl 2 at 0 °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 H 2 O 2 catalyzed by the Ti(O i Pr) 4 –L 4 system gave 79–84% yields and 54–59% ee of the corresponding sulfoxides in CH 2 Cl 2 at 20 °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 © 2011 John Wiley & Sons, Ltd.