Trifluoroacetic acid → {6-[4-(4-Trifluoromethoxy-phenyl)-piperazine-1-sulfonyl]-2,3-dihydroindol-1-yl}-acetic acid methyl ester

Triethylsilane (0.13 mL, 0.77 mmol) was added to a solution of {6-[4-(4-trifluoromethoxy-phenyl)-piperazine-1-sulfonyl]-indol-1-yl}-acetic acid methyl ester (82 mg, 0.16 mmol) and trifluoroacetic acid (4 mL) at rt. After 1 h, more triethylsilane (0.2 mL, 1.2 mmol) was added. After an additional 4 h, the reaction was poured into 1.2 M NaOH (50 mL) and extracted with CH2Cl2 (3×30 mL). The combined organic extracts were dried, filtered, concentrated and purified by silica gel chromatography (4:1→3:2; hexanes:ethyl acetate) to give {6-[4-(4-trifluoromethoxy-phenyl)-piperazine-1-sulfonyl]-2,3-dihydroindol-1-yl}-acetic acid methyl ester: MS (ESI): 500.1 (M+H). {6-[4-(4-Trifluoromethoxy-phenyl)-piperazine-1-sulfonyl]-2,3-dihydro-indol-1-yl}-acetic acid methyl ester was hydrolyzed following the procedure outlined in Example 1 Step 2 to give {6-[4-(4-trifluoromethoxy-phenyl)-piperazine-1-sulfonyl]-2,3-dihydro-indol-1-yl}-acetic acid: 1H NMR (400 MHz, DMSO-d6): δ 7.24 (d, 1H), 7.19 (d, 2H), 6.98 (d, 2H), 6.93 (d, 1H), 6.68 (s, 1H), 4.05 (s, 2H), 3.57 (t, 2H), 3.24-3.17 (m, 4H), 3.03 (t, 2H), 3.00-2.94 (m, 4H); MS (ESI): 486.1 (M+H).