[F:1][C:2]1[C:10]([C:11]([OH:13])=[O:12])=[CH:9][CH:8]=[C:7]2[C:3]=1[CH:4]=[CH:5][N:6]2[Si:14]([CH:21]([CH3:23])[CH3:22])([CH:18]([CH3:20])[CH3:19])[CH:15]([CH3:17])[CH3:16].[C:24](Cl)(=O)C(Cl)=O.CN(C=O)C.CCN(CC)CC>C(Cl)Cl.CO>[F:1][C:2]1[C:10]([C:11]([O:13][CH3:24])=[O:12])=[CH:9][CH:8]=[C:7]2[C:3]=1[CH:4]=[CH:5][N:6]2[Si:14]([CH:18]([CH3:20])[CH3:19])([CH:21]([CH3:23])[CH3:22])[CH:15]([CH3:16])[CH3:17]
To a solution of 4-fluoro-1-triisopropylsilanyl-1H-indole-5-carboxylic acid 70a (prepared using a procedure described in Eur. J. Org. Chem. 2006, 2956) (8.08 mmol, 2.71 g) in dry CH2Cl2 (20 mL) was added oxalyl chloride (9.69 mmol, 0.82 mL) followed by DMF (0.81 mmol, 0.063 mL). The reaction was stirred at rt for 30 min and then concentrated. The residue was dissolved in CH2Cl2 (20 mL) and cooled to 0° C. Et3N (40.4 mmol, 5.6 mL) was added, followed by slow addition of MeOH. The reaction mixture was stirred at 0° C. for 30 min and concentrated. The residue was partitioned between EtOAc and water. The organic layer was concentrated and purified by flash column chromatography (silica gel, 5% EtOAc/hexanes) to give compound 70b.
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