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

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.