Compound 27 (methyl 3-formylindole-6-carboxylate, 0.78 g, 3.84 mmol) was dissolved in anhydrous THF (30 mL) under argon protection and stirred at 0 °C. To this solution was added dropwise a THF solution of borane (1 M, 15.36 mL, 15.36 mmol). The reaction mixture was warmed up to 50 °C and stirred at this temperature for 1 hour. The reaction progress was monitored by thin layer chromatography (TLC). Upon completion of the reaction, the reaction mixture was quenched with saturated aqueous NaHCO3 solution. Subsequently, it was washed with NH4Cl solution (50 mL) and extracted with ethyl acetate (3 x 50 mL). The organic layers were combined, dried with anhydrous sodium sulfate, filtered and concentrated in vacuum to give the crude product. The crude product was purified by silica gel column chromatography with eluent 10% EtOAc/hexane to afford compound 28 (methyl 3-methyl-1H-indole-6-carboxylate, 0.36 g, 49.5% yield) as a brown solid.TLC conditions: 30% EtOAc/hexane (Rf: 0.6).1H-NMR (400 MHz, DMSO-d6): δ 11.15 (s, 1H), 8.00 (s, 1H), 7.62-7.55 (m, 2H), 7.37 (s, 1H), 3.84 (s, 3H), 3.27 (s, 3H). lcms observed value (m/z): 189.90 (M + 1).
