To a solution of 2,3-bis(trimethylsilyl)-benzo [b]biphenylene (4, 450 mg, 1.30 mmol) in dry CH2Cl2 (40 mL) cooled down to -78 °C, a solution of Br2 (200 mL, 3.90 mmol) in CH2Cl2 (78 mL) was added dropwise (3 hours, addition funnel with pressure equalizing arm). After being stirred at -78 °C for 20 min, the reaction mixture was quenched with aq. Na2S2O5 saturated solution (30 mL) and warmed up to room temperature. The organic layer was separated and concentrated in vacuo. The crude residue was subjected to sonication-assisted washing with hexane (2 x 5 mL) and CH2Cl2