Synthesis
Step 1: Methyl indole-6-carboxylate (534 mg, 3.05 mmol) was dissolved in acetic acid (7.5 mL) and the solution was cooled to 0°C. Sodium cyanoborohydride (580 mg, 9.2 mmol, 3 equiv) was added to the solution in batches with stirring. The reaction mixture was stirred continuously for 40 minutes at 15 °C. Subsequently, sodium cyanoborohydride (193 mg, 3.05 mmol, 1 eq.) was added again and stirring was continued for 30 minutes at room temperature. After completion of the reaction, the solvent was removed by rotary evaporator. The residue was dissolved in dichloromethane and washed with 1N NaOH solution. The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated to afford methyl 2,3-dihydro-1H-indole-6-carboxylate as a pale yellow solid in a yield of 494 mg (77% yield). The product did not require further purification and could be used directly in the subsequent reaction.
References
[1] Patent: US2007/60567, 2007, A1. Location in patent: Page/Page column 25
[2] Patent: US2008/153805, 2008, A1. Location in patent: Page/Page column 12
[3] ChemMedChem, 2016, vol. 11, # 23, p. 2607 - 2620
[4] Patent: WO2018/52903, 2018, A1. Location in patent: Page/Page column 22; 43-44
[5] Patent: US2010/234340, 2010, A1. Location in patent: Page/Page column 20
