Chiral Bis(8-Quinolyl)Ethane-Derived Diimine: Structure Elucidation and Catalytic Performance in Asymmetric Synthesis of (<i>S</i>)-Warfarin

C2-symmetric diimine generated in situ from (R,R)-HPEN and 8-formylquinoline was readily transformed to novel chiral diimine pre-III bearing 1(S),2(S)-bis(quinolin-8-yl) ethane and salicylic aldehyde fragments via stereoselective diaza-Cope rearrangement. The structure and absolute configuration of the product was established by the X-ray diffraction study of the corresponding Rh(III) complex. In the presence of pre-III, practically important enantioselective reactions of 4-hydroxycoumarin with α,β-enones afforded anticoagulant (S)-warfarin and its derivatives in aqueous THF in high yield (88–92%) with enantioselectivity 85–93% ee