Preparation
3-Bromoisatoic anhydride is prepared from 7-bromo-3-carbaldehyde by stirring in a 4:1 mixture of CH3CN/H2O for 1 h at 40℃.
1 H NMR: δ11.08 (s, br., 1H), 8.02 (d, J = 7.8 Hz, 1H), 7.94 (d, J = 7.8 Hz, 1H), 7.19 (t, J = 7.8 Hz, 1H).
Synthesis
A suspension was formed by adding 2-amino-5-bromobenzoic acid (10.0 g, 46.3 mmol, 1.0 eq.) to a 500 mL single neck round bottom flask fitted with a soccer shaped PTFE stirring bar (16 mm x 37 mm) followed by tetrahydrofuran (230 mL, 0.2 M) and solid triphosgene (13.7 g, 46.3 mmol, 1.0 eq.). The reaction vessel was placed in a unit fitted with a metal heating jacket and a 24/40 Liebig condenser was fitted to the neck of the reaction flask. The suspension was stirred at 500 rpm and the temperature of the heating jacket was set at 70°C. After about 30 minutes, the suspension became homogeneous and subsequently precipitated a white solid. The non-homogeneous reaction mixture was allowed to stand for 12 hours and then cooled to room temperature (25°C). The slurry was poured into a 600 mL beaker containing 250 mL of deionized water and equipped with an overhead mechanical stirrer (PTFE 75 mm paddle). Under vigorous stirring, the mixture became homogeneous and subsequently precipitated as a pale white solid. The solids were collected by vacuum filtration through a Brinell funnel (7.6 cm diameter, lined with Whatman 1 filter paper, 70 mm) and purged with air for 5 min. The resulting solid was transferred to a 250 mL conical flask fitted with a cylindrical stir bar and 50 mL of methanol was added. The slurry was stirred for 10 minutes and then vacuum filtered again. The filter cake was dried under vacuum (0.1 mmHg, 25 °C) for 12 h to afford 8-bromo-1H-benzo[d][1,3]oxazine-2,4-dione (9b) as a white powder in 90% yield.
References
[1] Beilstein Journal of Organic Chemistry, 2018, vol. 14, p. 2529 - 2536
[2] Journal of Agricultural and Food Chemistry, 2015, vol. 63, # 31, p. 6883 - 6889
[3] Patent: WO2016/206101, 2016, A1. Location in patent: Page/Page column 58
