Chiral Bis(imidazolidine)pyridine−Cu(OTf)2: Catalytic Asymmetric Endo-Selective [3 + 2] Cycloaddition of Imino Esters with Nitroalkenes

The novel C2-symmetric bis(imidazolidine)pyridine (PyBidine) ligand was easily synthesized in a single condensation of 2,6-pyridyl aldehyde and optically active (S,S)-diphenylethylenediamine. In the C2-symmetric PyBidine−Cu(OTf)2 complex, imidazolidine rings act as “chiral fences” to shield the first and third quadrants. Use of the PyBidine−Cu(OTf)2 complex as a catalyst enabled the highly endo-selective reaction of imino esters and nitroalkenes to give the adducts in up to 99% ee.