Chiral (Mercaptophenyl)oxazolines as Auxiliaries for Asymmetric Coordination Chemistry

Abstract

(4S)-2-(4-Isopropyl-4,5-dihydrooxazol-2-yl)-4-nitrobenzenethiol {(S)-TS} and its tert-butyl derivative {(S)-TS'} were developed as chiral auxiliaries for the asymmetric synthesis of polypyridyl ruthenium complexes. In their deprotonated form, these (mercaptophenyl)oxazolines were used as bidentate ligands and allowed the efficient transfer of chirality from the oxazoline moiety to the ruthenium stereocenter. After the induction of the absolute metal-centered configuration, the auxiliaries were labilized by converting the coordinated thiolate into a thioether ligand upon methylation with Meerwein salt, followed by the thermal replacement with 2,2'-bipyridine or 1,10-phenanthroline ligands under retention of configuration to afford octahedral polypyridyl ruthenium complexes with high enantiomeric excesses. These thiol-based auxiliaries complement our previously developed acid-labile chiral auxiliaries and thus expand the toolbox for the asymmetric synthesis of chiral ruthenium complexes.