Tris(1H-benzotriazol-1-yl)methane

[Experimental procedure]
BuLi (2.5 M in hexane, 4.4 mL, 11 mmol) is added dropwise at -78 °C to a solution of tris(1H-benzotriazol-1-yl)methane (3.67 g, 10 mmol) in dry THF (80 mL). The mixture is stirred at -78 °C for 2 h, and then the corresponding electrophile (11 mmol) in THF (10 mL) is added. The mixture is stirred at -78 °C for 5 h, and then at r.t. for 12 h. The reaction mixture is poured into sat. aq NH₄Cl (40 mL), and the aq layer is extracted with CHCl₃ (3x25 mL). The combined organic layers are washed with H₂O (25 mL), dried (MgSO₄), and the solvent is removed at reduced pressure to afford the crude adducts which are then recrystallized to give analytically pure products.
To a stirred solution of the trisbenzotriazolyl derivative (2 mmol) in THF (20 mL) is added conc. H₂SO₄ (95-98 %, 0.5 mL) and the solution is stirred at 50 °C for 48 h. Benzotriazole is filtered off and the filtrate is evaporated at reduced pressure to give an oil. H₂O (5 mL) is added and the mixture is extracted with Et₂O (3x10 mL). The combined extracts are washed with cold H₂O (2x5 mL), and dried (MgSO₄). Evaporation of the solvent gives the crude products which are then purified to afford the carboxylic acids.