To solution containing (E)-3-(1-(tert-butoxycarbonyl)-1H-indol-3-yl)acrylic acid (150.0 mg, 0.52 mmol), N′-isopropyl-4-methylbenzohydrazide (150.0 mg, 0.78 mmol) and HATU (296.6 mg, 0.78 mmol) dissolved in DMF (3.0 ml), N,N-diisopropylethylamine (DIPEA)(0.14 ml, 0.78 mmol) was slowly drop-wise added and stirred at room temperature for 12 hr. The reaction mixture was diluted with EtOAc, washed with water and brine, dried with anhydrous MgSO4, filtered, and concentrated under reduced pressure. The residue was separated through silica gel chromatography (30% EtOAc) for refinement and dried so that white (E)-tert-butyl 3-(3-(1-isopropyl-2-(4-methylbenzoyl)hydrazinyl)-3-oxoprop-1-enyl)-1H-indole-1-carboxylate was obtained (141.0 mg, 58.8%).
