1-Ethyl-5-methyl-1H-pyrazole-4-carboxylic acid [3-(2-oxo-2,3-dihydro-1H-indole-6-carbonyl)-phenyl]-amide (0.235 g, 0.605 mmol) and ethyl formate (0.145 mL, 1.80 mmol) were dissolved in anhydrous ethanol (5 mL). The resulting solution was treated in dropwise fashion with a 21 wt % solution of sodium ethoxide in ethanol (1.13 mL, 3.02 mmol). This reaction mixture was heated at 78° C. for 0.5 h, producing a black oil. Subsequently, the reaction mixture was cooled to room temperature, and then the reaction pH was adjusted to pH 1 with dropwise addition of 1M HCl(aq) causing the formation of a brown precipitate. The suspension was filtered and the solids were washed with 0° C. EtOH to afford the pure 1-Ethyl-5-methyl-1H-pyrazole-4-carboxylic acid [3-(3-hydroxymethylene-2-oxo-2,3-dihydro-1H-indole-6-carbonyl)-phenyl]-amide (0.199 g, 0.478 mmol, 79%).
