Potassium Carbonate → Benzyl 4-[di(ethoxycarbonyl)methoxy]indole-1-carboxylate

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The indole 11 (10.69 g, 40 mmol) was added to a suspension of anhydrous potassium carbonate (8.29 g, 60 mmol) in acetone (400 mL) and the mixture was stirred at room temperature for 15 min. Diethyl bromomalonate (11.47 g, 48 mmol) was added and the mixture was heated under reflux for 17 h. The solid was filtered off and washed with acetone and the combined filtrates were evaporated. The residue was dissolved in diethyl ether (150 mL), washed with 0.5 M aq. sodium hydroxide and brine, dried and evaporated to a brown viscous oil (16.87 g). After trituration with diethyl ether, the precipitated white solid was filtered off and the filtrate was evaporated. The residue was flash chromatographed [ethyl acetate-hexanes (15:85)] to give more solid and the combined solids were recrystallised to give 12 as white crystals (13.83 g, 81%), mp 77-78° C. (from ethyl acetate-hexanes); 1H NMR (500 MHz) δ 7.86-7.92 (br d, 1H), 7.57 (d, J=3.7 Hz, 1H), 7.47-7.49 (m, 2H), 7.36-7.43 (m, 3H), 7.20 (t, J=8.1 Hz, 1H), 6.86 (d, J=3.9 Hz, 1H), 6.63 (d, J=8.1 Hz, 1H), 5.45 (s, 2H), 5.30 (s, 1H), 4.29-4.37 (m, 4H), 1.30 (t, J=7.1 Hz, 6H). Anal. Calcd for C23H23NO7: C, 64.93; H, 5.45; N, 3.29. Found: C, 65.06; H, 5.64; N, 3.21.

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