Lawesson's reagent → 4-(4,4-Dimethyl-2-thioxo-1,4-dihydro-2H-benzo[d][1,3]oxazin-6-yl)-thiophene-2-carbonitrile

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A mixture of 4-(4,4-dimethyl-2-oxo-1,4-dihydro-2H-benzo[d][1,3]oxazin-6-yl)-thiophene-2-carbonitrile (0.23 g, 0.8 mmol) and Lawesson's reagent (0.38 g, 0.96 mmol) in anhydrous o-xylene was heated to reflux under nitrogen for 3 hours. The solvent was removed in vacuo and the residue was purified by a flash chromatography (silica gel, hexane:ethyl acetate/3:1) to afford the title compound as a yellow solid (85 mg, 35%): mp 242-243° C.; 1H-NMR (DMSO-d6) δ 12.22 (s, 1H, D2O exchangeable), 8.50 (d, 1H, J=1.2 Hz), 8.37 (d, 1H, J=1.0 Hz), 7.71 (m, 2H), 7.09 (d, 1H, J=8.0 Hz), 1.69 (s, 6H); MS (APCI) m/z 301 ([M+H]+, 100%); Anal. Calcd. For C15H12N2OS2: C, 59.97; H, 4.03; N, 9.33. Found: C, 59.67; H, 3.85; N, 9.14.

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