[Synthesis]
Step 1. Compound 34 (2.34 g, 9.44 mmol) was dissolved in 45 mL of ethanol and 5 mL of aqueous solution of KOH (85%, 1.87 g, 28.33 mmol) was added slowly and dropwise. The reaction mixture was stirred at room temperature overnight. Subsequently, KOH (85%, 1 g) was added additionally and the mixture was heated to 75 °C and maintained for 4 hours. Upon completion of the reaction, the reaction solution was acidified with 1 M HCl (2 x 25 mL) and extracted with ether (3 x 25 mL). The organic phases were combined and residual water and ethanol were removed under reduced pressure using acetonitrile as an azeotrope (about 4 times). Further concentration under reduced pressure afforded 1-pentyl-1H-indole-3-carboxylic acid (2.11 g, 92% yield). The product was characterized by 1H NMR (400 MHz, CDCl3): δ 8.27-8.20 (m, 1H), 7.93 (s, 1H), 7.42-7.37 (m, 1H), 7.33-7.28 (m, 2H), 4.17 (t, J = 7.2 Hz, 2H), 1.94-1.85 (m, 2H), 1.38-1.30 ( m, 4H), 0.90 (t, J = 6.9Hz, 3H). |