Asymmetric oxidation of sulfides with H2O2 catalyzed by titanium complexes of Schiff bases bearing a dicumenyl salicylidenyl unit
2011 (English)In: Applied organometallic chemistry, ISSN 0268-2605, E-ISSN 1099-0739, Vol. 25, no 5, 325-330 p.Article in journal (Refereed) Published
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.
Place, publisher, year, edition, pages
2011. Vol. 25, no 5, 325-330 p.
asymmetric catalysis, chiral sulfoxides, dicumenyl salicylaldehyde, Schiff bases, titanium
IdentifiersURN: urn:nbn:se:kth:diva-33252DOI: 10.1002/aoc.1762ISI: 000289515300001ScopusID: 2-s2.0-79955012058OAI: oai:DiVA.org:kth-33252DiVA: diva2:414626
FunderKnut and Alice Wallenberg Foundation
QC 201105042011-05-042011-05-022011-05-04Bibliographically approved