Pyrrolidine, 1-(1,4-dioxaspiro[4.5]dec-7-en-8-yl)-

A 250-mL round-bottomed flflask equipped with a Dean–Stark trap and reflflux condenser was charged with the ketone (5.2 g, 33.3 mmol) and pyrrolidine (2.4 mL, 33.3 mmol) in anhydrous benzene (200 mL). The solution was reflfluxed for 8 h until no more H2O was collected in the Dean–Stark trap. The Dean–Stark trap was removed and replaced with a distillation head, and the benzene was removed by distillation. The product was distilled (0.2 torr, 105 ºC) to give the enamine (4.78 g, 69%) as a yellow viscous oil, which was used immediately to avoid decomposition.

Reference: Davis, K. M.; Carpenter, B. K. J. Org. Chem. 1996, 61, 4617–4622.