6-Styryl-4H-pyrido[3,2-b][1,4]oxazin-3-one. To a solution of 6-bromo-4H-pyrido[3,2-b][1,4]oxazin-3-one (3.2 g, 14 mmol) in 1,4-dioxane (80 mL) was added trans-2-phenylvinylboronic acid (2.1 g, 14 mmol). After the reaction mixture was degassed with nitrogen, tetrakis(triphenylphosphine)palladium(0) (0.129 g, 0.112 mmol) and a solution of K2CO3 (3.7 g, 27 mmol) in H2O (10.7 mL) were added. The reaction was heated at reflux for 17 h, then cooled to RT, and diluted with EtOAc (300 mL). The organic layer was separated, washed with H2O (300 mL), brine (300 mL), dried (Na2SO4), and concentrated. The solid residue was purified on SiO2 (5-10% EtOAc/CHCl3) to provide 1.5 g (43%) of the title compound as a solid. MS (ESI): exact mass calculated for C15H12N2O2, 252.09; m/z found, 253.2 [M+H]+. 1H NMR (400 MHz, CDCl3): 7.53-7.00 (m, 9H), 4.66 (d, J=6.9, 2H).
