A solution of 2,6-dioxo-3-benzyloxycarbonylamino-5-acetoxypiperidine (9 g, 28.2 mmol) and Pd/C (10%, 0.9 g) in acetic acid (90 mL) is shaken under hydrogen (50-60 psi) for 3 hours. The suspension is filtered through a pad of Celite and washed with acetic acid and the solvent is then removed in vacuo. The residue, triethylamine (2.9 g, 28 mmol), and methyl 2-bromomethyl-3-nitrobenzoate (7.7 g, 28.2 mmol) in dimethylformamide (100 mL) is heated at 80° C. for 18 hours. The solvent is removed in vacuo to give 3-(4-nitro-1-oxoisoindolin-2-yl)-2,6-dioxo-5-acetoxypiperidine which can be further purified by column chromatography.
