Lawesson's reagent → 2-(6-Bromo-3-thioxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)-propionic acid ethyl ester

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Reaction Steps

A solution of 2-(6-bromo-3-oxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)-propionic acid ethyl ester (32.5 g, 100 mmol) and Lawesson reagent (80.1 g, 200 mmol) in toluene (200 mL) was heated at 120° C. for 3 h then cooled at ambient temperature. The solvent was removed in vacuo to give the crude product, which was purified by chromatography on silica gel (eluting with 1% EtOAc in petroleum ether) to give 2-(6-bromo-3-thioxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)-propionic acid ethyl ester (28 g, 81.4 mmol, 82%) as a yellow liquid. 1H NMR (CDCl3, 400 MHz): δ 7.18 (dd, J=8.8 Hz, J=2.0 Hz, 1H), 7.01 (d, J=2.0 Hz, 1H), 6.91 (s, J=8.8 Hz, 1H), 6.54 (s, 1H), 4.90 (q, J=15.2 Hz, 2H), 4.22 (m, 2H), 1.68 (d, J=7.2 Hz, 3H), 1.16 (t, J=7.2 Hz, 3H).

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