A 6-L three-necked flask shielded from light was been loaded with freshly dried CH 2 Cl 2 (4 L), freshly distilled pyrrole (2.7 mL), and the greenish oil from the previous step diluted with 100 mL of dry CH 2 Cl 2 . The flask was been flushed with argon and BF 3 .Et 2 O (0.8 mL) was added dropwise into the heavily stirred reaction mixture. The solution was stirred under inert atmosphere in the dark for 90 min. The Ar flow was stopped and pyridinium chlorochromate (9 g) was added at once. The resulting slurry was stirred in the dark overnight. The solvent was evaporated under reduced pressure in a 2 L flask. Silica (~ 400 mL) was added into the last evaporation batch and the mixture was evaporated to dryness.