To a pre-cooled to 10 °C solution of 7 (250.0 g, 1.02 mol) in TFA (1250 mL) conc. H2SO4 (96%, 250 mL) was added in a dropwise manner with cautious stirring. The reaction mixture was stirred for additional 16 h at 25 °C and then concentrated under reduced pressure. The vessel with viscous residue was cooled in an ice-water bath and the latter was neutralized with ice-cold sat. aq K2CO3 to pH 9 (CAUTION! Slow addition is necessary! Violent reaction occurs!). The precipitated product was filtered, washed with water (7×1250 mL), and dried under a high vacuum (1 mmHg) to give pure 1. Yield 262.9 g, 1.00 mol, 98%.