A stirred suspension of 5-[(4-methoxyphenyl)sulfonyl]-6-methyl-5,6-dihydrophenanthridine (0.73 g, 2.0 mmol) was heated to 50° C. in glacial acetic acid 20 mL) and treated drop-wise over seven hours with excess bromine (1.92 g, 12 mmol). After cooling to room temperature, the reaction mixture was diluted with ethyl acetate and the precipitate filtered. The organic phase filtrate was washed sequentially with a saturated, aqueous sodium thiosulfate solution, a 1 N hydrochloric acid solution, and water. The organic phase was further washed sequentially with a 2.5 N aqueous sodium hydroxide solution until a basic extract was obtained, water, and a saturated aqueous sodium chloride solution. The organic phase was dried over anhydrous sodium sulfate, filtered through a short column of silica gel, and the solvent removed in vacuo to afford a crude yellow solid (0.75 g, 1.7 mmol, 85%). The crude solid was purified by preparative chromatography on a Biotage® 40 Mi column of pre-packed silica gel (90 g), eluting with a mixture of methyl tert-butyl ether-hexane (15:85) at a flow rate of 40 mL/min to afford, after evaporation of the solvent, a solid. Crystallization of the solid from a mixture of diethyl ether-hexane yielded the title compound (0.43 g, 0.97 mmol, 48%) as a homogeneous, colorless, crystalline solid, m.p. 192-194° C.;
