Ammonium Acetate → 3,4,5,6-Tetrahydro-3,10-diazabenzo[e]azulene-1-carboxylic acid ethyl ester

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A mixture of 4-oxo-1,4,5,6,7,8-hexahydrocyclohepta(b)pyrrole-3-carboxylic acid ethyl ester (7.0 g, 31.67 mmol), 3-amino-prop-2-enal (3.37 g, 47.5 mmol) and ammonium acetate (365 mg, 4.75 mmol) in triethylamine (7 mL) is heated at 110° C. for 4 h. It is cooled to room temperature and the solid residue is dissolved in 100 mL dichloromethane and 100 mL sat. NaHCO3 solution. Layers are separated and the aqueous phase is extracted with 4:1 DCM/2-propanol (4×100 mL). Combined organic layers are dried (Na2SO4) and evaporated. Flash Chromatography on silica gel, eluting with EtOAc:triethylamine (20:1), provides 3,4,5,6-tetrahydro-3,10-diaza-benzo[e]azulene-1-carboxylic acid ethyl ester (1.6 g, 20%) as off-white solid. 1H NMR (400 MHz, CD3OD) δ 1.247 (3H, t), 2.227 (2H, m), 2.631 (4H, m), 4.197 (2H, q), 7.170 (1H, m), 7.405 (1H, s), 7.686 (1H, d), 8.375 (1H, d). MS (ES+) 257 (M+1).

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