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.

Graphical abstractNew chiral pyridine imidazolines (L) have been synthesised and reacted with [RuCl2(mes)]2 (mes = 1,3,5-trimethyl benzene) to form [RuCl(L)(mes)][SbF6] (5a–c) which after treatment with AgSbF6 are enantioselective catalysts for the Diels-Alder reaction of acroleins and cyclopentadiene. The NR1 substituent affects the enantioselectivity.Figure optionsDownload full-size imageDownload as PowerPoint slide