Chiral pyridine imidazolines from C1-symmetric diamines: Synthesis, arene ruthenium complexes and application as asymmetric catalysis for Diels-Alder reactions

Condensation of mono N-substituted chiral ethylenediamines and pyridine-2-methoxyimidate gives new chiral pyridine imidazolines (1a-c). These react with RuCl₂(mes)]₂ (mes = 1,3,5-trimethyl benzene) in the presence of NaSbF₆ to give complexes RuCl(L)(mes)]SbF₆] (5a-c) which after treatment with AgSbF₆ are enantioselective catalysts for the Diels-Alder reaction of methacrolein and cyclopentadiene. The imidazoline catalysts are less selective than the corresponding oxazoline ones. Compounds 1a, 5b and 5c have been characterised by X-ray crystallography.