Cl[CH2:2][CH2:3][CH2:4][N:5]1[C:9]2[CH:10]=[CH:11][C:12]([N+:14]([O-:16])=[O:15])=[CH:13][C:8]=2[O:7][C:6]1=[O:17].[O-:18][CH2:19][CH3:20].[K+].CCOCC.O>CN1CCCC1=O>[CH2:19]([O:18][C:6]([N:5]1[C:9]2[CH:10]=[CH:11][C:12]([N+:14]([O-:16])=[O:15])=[CH:13][C:8]=2[O:7][CH2:2][CH2:3][CH2:4]1)=[O:17])[CH3:20]
3-(3-Chloro-propyl)-6-nitro-3H-benzoxazol-2-one (5.08 g, 19.8 mmol) and Potassium Ethoxide (1.80 g, 21.4 mmol) in N-Methylpyrrolidinone (60 mL) was stirred at room temperature under an atmosphere of Nitrogen. At 24 h, an additional aliquot of Potassium Ethoxide (0.91 g, 11 mmol) was added. After stirring overnight, the solution was poured into ether (100 mL) and water (50 mL), separated and extracted 2×100 mL ether. The organic extracts were washed with water (2×50 mL) and brine (50 mL), dried and conc. in vacuo. The residue was powdered onto silica gel and chromatographed (ISCO, 0-30% EtOAc:Hex) to afford 3-Nitro-7,8-dihydro-6H-5-oxa-9-aza-benzocycloheptene-9-carboxylic acid ethyl ester as a yellow solid (2.657 g, 50%). 1H-NMR (CDCl3): 7.84 (m, 2H), 7.45 (s, 1H), 4.29 (m, 4H), 3.85 (m, 2H), 2.14 (m, 2H), 1.26 (m, 3H).
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