Trifluoroacetic acid → 3-(1-Cyclopentyl-octahydro-pyrrolo[3,2-b]pyrrol-3-yl)-6-fluoro-1H-indole

A solution containing 36 (2.0 g, 4.8 mmol) in DCM (20 mL) was cooled to 0° C. TFA (6 mL) was added and the pink reaction mixture was stirred at 0° C. After 1 h, the reaction mixture was warmed to ambient temperature then concentrated in vacuo. The residue was dissolved in EtOAc and the organic solution was washed successively with saturated aqueous NaHCO3 and brine, dried over anhydrous Na2SO4, filtered, and concentrated to afford 1.4 g of 37 which was used without further purification. 1H NMR (CDCl3, 300 MHz): δ8.50 (br s, 1H), 7.58 (dd, J=5.4, 8.4 Hz, 1H), 7.05-7.01 (m, 2H), 6.92-6.85 (m, 1H), 4.17-4.11 (m, 1H), 3.92 (app q, J=6.0 Hz, 1H), 3.74 (app q, J=6.6 Hz, 1H), 3.21-3.15 (m, 1H), 3.08-2.88 (m, 3H), 2.75-2.67 (m, 2H), 1.96-1.78 (m, 5H), 1.61 (m, 4H) ppm. Mass spectrum, m/z [314.2] (M+H)+.