Dimethylaminopyridine (100 mg) and acetic anhydride (1.12 ml) were added to a solution of N-(3,4-Dichlorobenzyl)-5-hydroxyindole-2-carboxylic acid in ethyl acetate (50 ml) and stirred at ambient temperature for 1 hour. Ethanol (10 ml) was added and the reaction was stirred for 30 min. Solvent partially evaporated and iso-hexane added to give a precipitate, which was filtered off and dried to give the product as a white solid (1.2 g). NMR: δ 2.25 (s, 3H), 5.85 (s, 2H), 6.9 (dd, 1H), 7.3-7.6 (m, 5H); m/z 376, 378 (M−H+)
