[N:1]1([C:20]([O:22][C:23]([CH3:26])([CH3:25])[CH3:24])=[O:21])[C:9]2[CH:8]=[CH:7][CH:6]=[C:5]([C:10]([O:12]CC3C=CC=CC=3)=[O:11])[C:4]=2[CH:3]=[CH:2]1.[H][H]>[Pd].CO.O>[C:23]([O:22][C:20]([N:1]1[C:9]2[CH:8]=[CH:7][CH:6]=[C:5]([C:10]([OH:12])=[O:11])[C:4]=2[CH:3]=[CH:2]1)=[O:21])([CH3:26])([CH3:24])[CH3:25]The mixture of 4-benzyl 1-tert-butyl 1H-indole-1,4-dicarboxylate (6.37 g) and 10% palladium on carbon (964 mg) in MeOH (95.6 mL) and water (3.2 mL) was hydrogenated at 3.5 atm of hydrogen for 3.5 hours. The resulting mixture was filtered through a bed of celite and the filtrate was evaporated in vacuo. The residue was dissolved in chloroform (100 mL) and the solution was dried over anhydrous MgSO4, filtered and evaporated in vacuo. The residue was triturated with cold MeOH (20 mL) to give 1-(tert-butoxycarbonyl)-1H-indole-4-carboxylic acid (2.90 g) as a colorless crystals. The above filtrate was evaporated in vacuo and the residue was triturated with solvent (n-hexane:EtOAc=5:1, 12 mL) to afford 1-(tert-butoxycarbonyl)-1H-indole-4-carboxylic acid (1.31 g) as colorless crystals.
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