To a cold (0° C.) suspension of methyl 8-(benzoyloxy)-5-oxo-5,6-dihydro[1,6]-naphthyridine-7-carboxylate (3.24 g, 10 mmol), 2-hydroxy-N,N-dimethylacetamide (1.13 g, 11 mmol), and triphenylphosphine (5.24 g, 20 mmol) in THF (100 mL), diethyl azodicarboxylate (3.1 mL, 19.6 mmol) was added over a period of 3 minutes. The resultant mixture was stirred at room temperature for two days. The product mixture was treated with 1 M aq HCl and extracted with methylene chloride. The organic extract was dried over anhydrous sodium sulfate, filtered and concentrated under vacuum. The residual oil was subject to column chromatography on silica gel eluting with 1-2% methanol in ethyl acetate. Collection and concentration of the appropriate fractions provided the slower eluting o-alkylated isomer as white solid.
