Lawesson's reagent → tert-Butyl (3R,6S)-6-(2,3-difluorophenyl)-2-thioxoazepan-3-ylcarbamate

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Lawesson's reagent [2,4-Bis(4-methoxyphenyl)-1,3-dithia-2,4-diphosphetane-2,4-disulfide] (2.90 g, 7.18 mmol) was added to a suspension of tert-butyl (3R,6S)-6-(2,3-difluorophenyl)-2-oxoazepan-3-ylcarbamate (4.79 g, 14.1 mmol) in toluene (250 mL) and the mixture was heated to 90° C. After 1 h, the reaction was allowed to cool to ambient temperature and concentrated. Purification by silica gel chromatography (100% dichloromethane→85% dichloromethane/ethyl acetate) gave a white solid. This solid was repurified by silica gel chromatography (20% ethyl acetate/hexanes→30% ethyl acetate/hexanes) to give the title compound (4.81 g). MS 357.0 (M+1). 1H NMR (500 MHz, CDCl3) δ 8.30 (s, 1H), 7.10-7.04 (m, 2H), 6.94-6.91 (m, 1H), 6.50 (d, J=6.1 Hz, 1H), 4.62 (dd, J=10.3, 3.7 Hz, 1H), 4.13-3.88 (m, 1H), 3.36 (dd, J=14.7, 7.1 Hz, 1H), 3.07 (t, J=11.2 Hz, 1H), 2.32-2.21 (m, 2H), 2.14-2.12 (m, 1H), 1.79-1.72 (m, 1H), 1.47 (s, 9H).

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