Reaction Steps
A solution of (E)-2-[[3-(3,4-dimethoxyphenyl)-1-oxo-2-propenyl]amino]benzoic acid (0.5 g, 1.5 mmol) in acetic anhydride (3 mL) was heated to reflux and stirred for 3 h. The reaction was cooled to rt and the resulting suspension was diluted with water. The suspension was stirred at rt for 1 h and the precipitate was collected by filtration, providing (E)-2-(3,4-dimethoxystyryl)-4H-benzo[d][1,3]oxazin-4-one (0.41 g, 88%) as a yellow crystalline solid; mp 175-179° C.; δH (500 MHz, DMSO-d6) 3.82 (s, 3H, OCH3), 3.85 (s, 3H, OCH3), 6.94 (d, J=16.0 Hz, 1H, CH═CHCO), 7.02 (d, J5′,6′=8.0 Hz, 1H, H5′), 7.35 (dd, J5′,6=8.0, J2′,6′=1.5 Hz, 1H, H6′), 7.47 (d, J2,6′=1.5 Hz, 1H, H2′), 7.58 (t, J3,4=J4,5=8.0 Hz, 1H, H4), 7.61 (d, J3,4=8.0 Hz, 1H, H3), 7.73 (d, J=16.0 Hz, 1H, CH═CHCO), 7.92 (t, J4,5=J5,6=8.0 Hz, 1H, H5), 8.12 (d, J5,6=8.0 Hz, 1H, H6); δC (125 MHz, DMSO-d6) 55.5, 55.6, 110.3, 111.6, 116.6, 122.9, 126.5, 127.4, 128.0, 128.0, 128.1, 136.8, 141.4, 146.8, 149.0, 150.9, 157.3, 158.8; HRMS (ESI) calculated for C18H15NO4 [M+H]+310.1074; found 310.1073; νmax 1020, 1254, 1515, 1634, 1755, 2835, 2940 cm−1.
