Reaction Steps
To a solution of 4-oxo-1,4,5,6,7,8-hexahydro-cyclohepta[b]pyrrole-3-carboxylic acid ethyl ester (4.80 g, 21.7 mmol) and Et3N (3.93 mL, 28.2 mmol) in CH2Cl2 (40 mL) at 0° C. is added Boc2O (5.68 g, 26.0 mmol) in one portion. The reaction mixture is allowed to stir at 0° C. for 10 min. and then at room temperature for 18 h. The reaction mixture is then diluted with half saturated aq NH4Cl (70 mL) and extracted with EtOAc. The organic layer is then washed with H2O (50 mL) and brine (50 mL). The aqueous washes are reextracted once with EtOAc, and the combined extracts are dried over Na2SO4 and concentrated. The crude material is purified by flash chromatography on silica gel. Elution with 4:1 hexanes-ethyl acetate followed by 3:1 hexanes-ethyl acetate afforded 7.00 g (quant) of 4-oxo-5,6,7,8-tetrahydro-4H-cyclohepta[b]pyrrole-1,3-dicarboxylic acid 1-tert-butyl ester 3-ethyl ester as a light yellow solid. 1H NMR (CDCl3, 300 MHz) δ 7.62 (s, 1H), 4.27 (q, J=7.2 Hz, 2H), 3.22 (m, 2H), 2.78 (m, 2H), 1.86 (m, 4H), 1.60 (s, 9H), 1.31 (t, J=7.2 Hz) Step 2: A mixture of 4-oxo-5,6,7,8-tetrahydro-4H-cyclohepta[b]pyrrole-1,3-dicarboxylic acid 1-tert-butyl ester 3-ethyl ester (1.13 g, 3.52 mmol) and tris(dimethylamino)methane (1.02 g, 7.04 mmol) is stirred at 60° C. in a sealed tube for 4.5 h. After cooling, the thick slurry is taken up in Et2O and filtered. The solid is washed with Et2O and dried, affording 847 mg (87%) of 5-dimethylaminomethylene-4-oxo-1,4,5,6,7,8-hexahydro-cyclohepta[b]pyrrole-3-carboxylic acid ethyl ester as a light yellow-orange solid. 1H NMR (CDCl3, 300 MHz) δ 9.93 (br s, 1H), 7.58 (s, 1H), 7.12 (d, J=2.7 Hz, 1H), 4.21 (q, J=7.2 Hz, 2H), 3.06 (s, 6H), 2.68 (m, 2H), 2.47 (m, 2H), 1.80 (m, 2H), 1.26 (t, J=7.2 Hz, 3H). Step 3: A mixture of 5-dimethylaminomethylene-4-oxo-1,4,5,6,7,8-hexahydro-cyclohepta[b]pyrrole-3-carboxylic acid ethyl ester (840 mg) and formamidine acetate (956 mg, 9.1 mmol) in EtOH (10 mL) is stirred at 120° C. for 4 h. After cooling, the reaction mixture is diluted with CH2Cl2 and washed with half saturated aq NaHCO3 (25 mL), H2O (25 mL), and brine (25 mL). The aqueous washes are reextracted once with CH2Cl2, and the combined extracts are dried over K2CO3 and concentrated. The crude material is purified by flash chromatography on silica gel. Elution with 30:1 CHCl3—MeOH followed by 20:1 CHCl3—MeOH and finally 15:1 CHCl3—MeOH afforded 606 mg (77%) of 3,4,5,6-tetrahydro-3,8,10-triaza-benzo[e]azulene-1-carboxylic acid ethyl ester as a light yellow solid. 1H NMR (CDCl3, 300 MHz) δ 9.30 (br s, 1H), 9.02 (s, 1H), 8.43 (s, 1H), 7.24 (d, J=2.7 Hz, 1H), 4.26 (q, J=7.2 Hz, 2H), 2.78 (t, J=7.2 Hz, 2H), 2.70 (m, 2H), 2.12 (m, 2H), 1.26 (t, J=7.2 Hz, 3H).
