Methyl 6-chloro-5-[4-(1-hydroxycyclobutyl)phenyl]-1H-indole-3-carboxylate (131 g, 368 mmol), methanol (2.20 L), and an aqueous sodium hydroxide solution (90.2 g, 2.21 mol, dissolved in 740 mL of water) were added to a round bottom flask, and the reaction was stirred for 18 hours at 70 °C. Upon completion of the reaction, the mixture was cooled to room temperature, filtered through diatomaceous earth, and the filtrate was concentrated to approximately 30% of the original volume, at which time no precipitate formation was observed. After addition of water (700 mL), the clarified tan solution was washed with methyl tert-butyl ether (MTBE, 3 x 250 mL) and the organic layer was discarded. 38% hydrochloric acid (200 mL) was added dropwise to the stirred aqueous phase (total volume of about 1800 mL) to a pH of about 2-3 at 18-25°C, followed by a one-time addition of ethyl acetate (250 mL). Upon addition of ethyl acetate, solids began to precipitate. Heptane (250 mL) was slowly added to the stirred non-homogeneous mixture via an addition funnel at room temperature and stirring was continued for 4 hours. The solid was collected by filtration, washed sequentially with water and ethyl acetate-heptane mixture (1:1), dried by filtration at room temperature and dried under vacuum at 50 °C to give a light yellow solid. The solid was dissolved in tetrahydrofuran (630 mL) and stirred at 65 °C (internal temperature) for 4 h. Ethyl acetate (630 mL) was then slowly added through a dropping funnel and the resulting slurry was slowly cooled at room temperature overnight. The solid was filtered, washed with a tetrahydrofuran-ethyl acetate mixture (1:1) and dried under vacuum at 50 °C to give 107.0 g of product. The mother liquor was concentrated and the residue was washed with acetone, filtered and dried to give another 12.5 g of product. The resulting solid was dissolved in ethanol (800 mL) containing 0.3 mL of 1M NaOH aqueous solution, and water (800 mL) was slowly added through a dosing funnel at 55-60 °C, and a precipitate began to form after the addition of water. The suspension was stirred at 60 °C for 2 h, followed by stirring at 40 °C for 24 h, and finally for 40 h at room temperature. The solid was filtered, washed with an ethanol-water mixture (1:1) and dried under vacuum at 50 °C to afford 6-chloro-5-(4-(1-hydroxycyclobutyl)phenyl)-1H-indole-3-carboxylic acid as an off-white crystalline solid (72.4 g, 58% yield). The mother liquor was concentrated to about 30% of the original volume, precipitate was precipitated, filtered and dried in vacuum to give another batch of product (14.5 g, 12% yield). The total yield was 70%. Mass spectrum (ES-): m/z 340.3 ([M-H]-). 1H NMR (400 MHz, DMSO-d6) δ: 12.12 (s, 1H), 11.95 (br.s, 1H), 8.09 (d, 1H), 7.96 (s, 1H), 7.65 (s, 1H), 7.58 (d, 2H), 7.42 (d, 2H). 5.53 (s, 1H), 2.48-2.42 (m, 2H), 2.32 (m, 2H), 1.96 (tq, 1H), 1.62-1.79 (m, 1H).
![1H-Indole-3-carboxylic acid, 6-chloro-5-[4-(1-hydroxycyclobutyl)phenyl]-, methyl ester](/CAS/20210305/GIF/1467059-92-2.gif)
