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Enantioselective Oxidation of Thioethers to Sulfoxides by Means of a Structural Template with Chiral‐at‐Metal Ruthenium Complexes
Author(s) -
Li ZhengZheng,
Yao SuYang,
Ye BaoHui
Publication year - 2015
Publication title -
chempluschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.801
H-Index - 61
ISSN - 2192-6506
DOI - 10.1002/cplu.201402243
Subject(s) - sulfoxide , thioether , ruthenium , chirality (physics) , chemistry , pyridine , metal , stereochemistry , enantioselective synthesis , medicinal chemistry , crystallography , catalysis , organic chemistry , chiral symmetry breaking , physics , quantum mechanics , nambu–jona lasinio model , quark
Treatment of cis ‐[Ru(bpy) 2 Cl 2 ] ⋅ 2 H 2 O or Δ/Λ‐[Ru(bpy) 2 (py) 2 ] 2+ (bpy=2,2′‐bipyridine, py=pyridine) with the prochiral thioether ligands 2‐alkylthiobenzoic acid (HOSR) produces the corresponding thioether complexes rac ‐[Ru(bpy) 2 (OSR)](PF 6 ) (R=Me ( rac ‐ 1 ), i Pr ( rac ‐ 2 ), 2‐benzylthiobenzonate (Bn) ( rac ‐ 3 )) and Δ/Λ‐[Ru(bpy) 2 (OSR)](PF 6 ) (R=Me (Δ‐ 1 /Λ‐ 1 ), i Pr (Δ‐ 2 /Λ‐ 2 ), Bn (Δ‐ 3 /Λ‐ 3 )) with retention of the configurations at chiral metal centers. In situ oxidation of the thioether complexes by meta ‐chloroperoxybenzoic acid provides the corresponding sulfoxide complexes rac ‐[Ru(bpy) 2 (OSOR)](PF 6 ) (OSOR is 2‐alkylsulfinylbenzonate, R=Me ( rac ‐ 1 a ), i Pr ( rac ‐ 2 a ), Bn ( rac ‐ 3 a )), Δ‐[Ru(bpy) 2 {( R )‐OSOR}](PF 6 ) (R=Me (Δ‐ 1 a ), i Pr (Δ‐ 2 a ), Bn (Δ‐ 3 a )), and Λ‐[Ru(bpy) 2 {( S )‐OSOR}](PF 6 ) (R=Me (Λ‐ 1 a ), i Pr (Λ‐ 2 a ), Bn (Λ‐ 3 a )) in yields of 95 % with 98 % ee values. The absolute configurations at the metal centers and sulfur atoms were determined by means of X‐ray crystallography. The results indicate that the configurations of the metal centers are retained and have the function of controlling sulfoxide chirality during the oxidation process. The Δ metal‐centered configuration enantioselectively generates an R ‐configuration sulfoxide, and the Λ configuration enantioselectively forms an S ‐configuration sulfoxide in the course of the in situ oxidation reaction, thereby resulting in a predetermined chirality of the sulfoxide ligands. The predetermined chirality of sulfoxides ( S )‐HOSOR and ( R )‐HOSOR were obtained by the treatments of the corresponding sulfoxide complexes Δ‐[Ru(bpy) 2 {( R )‐OSOR}](PF 6 ) and Λ‐[Ru(bpy) 2 {( S )‐OSOR}](PF 6 ) with trifluoroacetic acid in yields of 90 % with 83.5–92.9 % ee values.