1-[(Triisopropylsilyl)ethynyl]-1,2-benziodoxol-3(1H)-one

In a 10 mL round bottom-flask, 1-methyl-1H-indole (0.500 mmol,　65.6 mg) and 1-[(triisopropylsilyl)ethynyl]-1,2-benziodoxol-3(1H)-one (TIPS-EBX) (1.50 mmol, 643 mg) are dissolved in DCM (5 mL) under air, then water is added (0.10 mL). Lastly Pd(MeCN)₄(BF₄)₂ (2 mol%, 4.4 mg) is added with strong stirring. The flask is closed and the reaction mixture is stirred overnight (the reaction is generally completed after 4-6 h), when it became brownish. The solvent is evaporated under reduced pressure. EtOAc (25 mL) is added to the crude product, and the solution is washed with NaOH aq (0.1 M, 25 mL), conc. NaHCO₃ (2 x 25 mL) and brine (25 mL). The organic layer is dried over MgSO₄, filtered and the solvent is evaporated under reduced pressure. Purification by column chromatography gives the pure 1-methyl-2-[(triisopropylsilyl)ethynyl]-1H-indole as a pale yellow oil (66%, 102 mg).

Experimental procedure: TIPS-EBX (1.0 g, 2.4 mmol, 1.2 eq.) is added to a stirring solution of AuCl (4.6 mg, 0.020 mmol, 0.01 eq.) and indole (0.24 g, 2.0 mmol, 1.0 eq.) in Et₂O (40 mL) under air. The reaction is sealed and stirred at room temperature for 12-15 h. Et₂O (50 mL) is added, the organic layer is washed twice with NaOH aq (0.1 mol/L, 50 mL). The aqueous layers are combined and extracted with Et₂O (50 mL). The organic layers are combined, washed with saturated NaHCO₃ (50 mL), brine (50 mL), dried with MgSO₄ and concentrated under reduced pressure. Purification by flash chromatography (PET:Et₂O = 8:2) affords 1 (498 mg, 1.68 mmol, 84%) as brown solid.