To a solution of methyl 4-[(E)-2-(dimethylamino)vinyl]-3,5-dinitrobenzoate (D200) (10 g, 34 mmol, 1 eq.) in methanol (250 ml) was added 10% palladium charcoal (50% wet, 1.0 g, 5% w/w). The reaction mixture was stirred under hydrogen atmosphere for 7 hours. Upon completion of the reaction, the catalyst was removed by filtration through a diatomaceous earth pad and the filtrate was concentrated under reduced pressure. The residue was ground with ethyl acetate/isohexane mixed solvent to afford methyl 4-amino-1H-indole-6-carboxylate (D201) (5 g, 77% yield) as a dark pink solid. Mass spectrometry analysis showed [M+H]+ = 191.0 and retention time (RT) = 1.20 min.
