To a well-stirred bi-phasic mixture consisting of sodium carbonate (500 g, 4.72 mol) in water (3 liters) and trans-2,5-piperidine dicarboxylate dimethyl ester hydrochloride (280 g, 1.18 mol) in methylene chloride (4.5 liters), a solution of 2-phthalimido-ethyl triflate (417 g, 1.29 mol) in methylene chloride (3 liters) was added in a steady stream over a 3 hour period. The organic layer was separated, and the aqueous layer was extracted with fresh methylene chloride (3 liters). The combined organic extracts were washed with water (3 liters), then with brine (3 liters), dried with anhydrous magnesium sulfate and finally, concentrated in vacuo to a solid. The entire residue was triturated in refluxing ether (3 liters), with vigorous stirring, for 15 minutes. After cooling to ambient temperature, the solution was poured into hexanes (3 liters), and the resulting mixture was stirred for 18 hours. The resulting colorless solid was collected by filtration, and the filter cake was washed with hexanes (1 liter). In vacuo drying afforded 437.3 g (99.1% yield) of the title compound as a colorless solid. TLC Rf (ethyl acetate/methylene chloride=1:1 in volume; iodoplatinate spray): 0.5.
