To a suspension of methyl 6-bromo-2-oxo-1,2,3,4-tetrahydro-1,8-naphthyridine-3-carboxylate (300 mg, 1.06 mmol), prepared as in J. Med. Chem. 2003, 46, 9, 1627-1635, in DMF (1 mL) and proprionitrile (3.5 mL) under Argon were added DIPEA (175 μL, 2.271 mmol), tert-butyl acrylate (615 mL, 4.24 mmol), tri(o-tolyl)phosphine (64 mg, 0.21 mmol) and palladium acetate (48 mg, 0.21 mmol). The mixture was stirred at 100° C. overnight. LCMS analysis showed that some unreacted starting material was remaining, so 24 mg of palladium acetate and 64 mg of tri(o-tolyl)phosphine were added. After 5 h at 100° C., the reaction was allowed to come back to room temperature, filtered through Celite pad and rinsed with methanol. The residue obtained after concentration was purified by flash chromatography (eluent: gradient DCM/EtOAc) to give the title compound as an orange solid (115 mg, 32%) contaminated with traces of tri(o-tolyl)phosphine oxide.
