6,7-Dichloro-9-tosyl-2,3,4,9-tetrahydro-1H-carbazol-1-one (intermediate 1c) (420 mg, 1.02 mmol) dissolved in anhydrous THF (10 mL) and cooled to −78° C. was mixed with LiHMDS (1.13 mL, 1.1 mmol, 1M solution in THF). The reaction mixture was slowly warmed to 0° C., stirred for an additional 30 min. at 0° C., then cooled to −78° C. and N-fluoro benzene sulfonamide (0.31 g, 1.3 mmol) was added. The resulting mixture was slowly warmed to room temperature and stirred for 15 min., quenched with saturated NH4Cl and extracted with EtOAc (3×20 mL). The combined organic extracts were dried over Na2SO4, the solvent was removed under reduced pressure to give the crude compound which was purified by column chromatography [EtOAc-hexane (7:93) as eluant] to obtain the title compound (160 mg, 37%). 1H NMR (500 MHz, CDCl3, δ in ppm) 8.53 (s, 1H), 8.082 (d, J=8.0 Hz, 2H), 7.69 (s, 1H), 7.35 (d, J=8.5 Hz, 2H), 5.26-5.13 (m, 1H), 3.14-3.11 (m, 1H), 3.01-2.95 (m, 1H), 2.62-2.55 (m, 1H), 2.42 (s, 3H), 2.38-2.41 (m, 1H).
