2,6-Bis[(2S,5S)-4,4-diphenyl-1-aza-3-oxabicyclo[3.3.0]octan-2-yl]pyridine

Experimental Procedure:
Bis(oxazolidine)pyridine ligand (B4228, 0.0165 mmol) and Cu(OAc)₂ (0.015 mmol) are added to a round flask containing a stir bar under Ar. CH₂Cl₂ (1 mL) is added to the flask and the mixture is stirred over 12 hours. To the resulting solution is added azomethine imine (0.15 mmol) at rt. After cooling to –40 °C, to the mixture is added ethyl propiolate (0.18 mmol). After stirring for 47 hours, the reaction mixture is purified by silica gel column chromatography (Et₂O/Hexane=2/1 to Et₂O) to afford the desired N,N-bicyclic pyrazolidinone derivative (99% yield, 94% ee).