General procedure for the synthesis of methyl 2-(hydroxymethyl)-1H-indole-5-carboxylate from methyl 2-(hydroxymethyl)-1H-indole-5-carboxylate: to a stirred solution of methyl 2-(hydroxymethyl)-1H-indole-5-carboxylate (4.7 g, 23.1 mmol) in 70 mL of chloroform was added MnO2 (12.5 g, 115.4 mmol) in batches. After 14 hours of reaction, the mixture was filtered through a diatomaceous earth plug and the filtrate was concentrated under reduced pressure to give methyl 2-formyl-1H-indole-5-carboxylate (4.0 g, 85% yield) as a brown oil. The product could be used in subsequent reactions without further purification. Thin layer chromatography (TLC) Rf = 0.21 (20% EtOAc/hexane). Elemental analysis (C11H11NO3) Calculated value: exact mass 203.06; measured value: 203.06. low resolution mass spectrometry (LRMS) APCI (M-1) m/z 202.
