Phosgene → 3-Azaisatoic anhydride

A solution of ammonium 2-[[1-(4-pyridinyl)piperidin-4-ylmethyl]amino]pyridine-3-carboxylate (3.0 g, 9.12 mmol) in dioxane (45 mL) was treated with phosgene (1.9 M in toluene, 9.50 mL, 18.2 mmol), and the resulting mixture was heated at reflux. After 2 h, the mixture was concentrated yielding the corresponding aza-isatoic anhydride which was used without further purification. A solution of the crude anhydride (300 mg, 0.648 mmol) in tetrahydrofuran (2 mL) at 0° C. was treated with the magnesium salt of 2-amino-5-chloropyridine [2.60 mmol; freshly prepared by addition of methyl magnesium bromide (3.0 M in THF, 0.865 mL, 2.60 mmol) to 2-amino-5-chloropyridine (900 mg, 3.89 mmol) in THF (10 mL) at 0° C.]. After 17 h, the mixture was treated with a saturated aqueous solution of ammonium chloride and then partitioned between EtOAc and water. The aqueous layer was washed with EtOAc (3×) and the combined extracts were washed with water (1×), dried with sodium sulfate, and concentrated. The residue was purified by RPHPLC yielding 29 mg (9%) of the title compound as a hydrochloride salt.