[C:1]([O:5][C:6](=[O:20])[CH2:7][N:8]1[C:16]2[C:11](=[CH:12][C:13]([Cl:17])=[CH:14][CH:15]=2)[C:10]([CH:18]=[O:19])=[CH:9]1)([CH3:4])([CH3:3])[CH3:2].CC(=CC)C.[O-:26]Cl=O.[Na+].P([O-])(O)(O)=O.[Na+].Cl>C1COCC1.C(O)(C)(C)C.O>[C:1]([O:5][C:6]([CH2:7][N:8]1[C:16]2[C:11](=[CH:12][C:13]([Cl:17])=[CH:14][CH:15]=2)[C:10]([C:18]([OH:26])=[O:19])=[CH:9]1)=[O:20])([CH3:4])([CH3:2])[CH3:3]To a solution of (5-chloro-3-formyl-indol-1-yl)-acetic acid tert-butyl ester (902 mg, 2.92 mmol) in THF (12 mL) and tert-butanol (4.80 mL) were added successively 2-methyl-2-butene (9.27 mL, 88.0 mmol), a solution of NaClO2 (2.64 g, 29.2 mmol) and sodium dihydrogen phosphate (2.80 g, 23.3 mmol) in water (4.80 mL), followed by stirring at RT for 18 h. The reaction mixture was acidified with 0.1N HCl (pH 2 to 3) and extracted with EtOAc (3×). The combined organics were dried (Phase separator) and concentrated in vacuo. The residue was triturated with diethyl ether, the solid was filtered off, washed with diethyl ether and dried in vacuo to afford the title compound as a white solid. MS (LC/MS): 310 [M+H]+; tR (HPLC conditions b): 5.16 min.
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