Reaction Steps
By adopting a similar procedure as described in “Mueller, W; Stauss, U.; Forschungsinst, W.; Bern, S. Helvetica Chimica Acta 1982, 65, 2118.” (S)-8-Nitro-2,3,3a,4-tetrahydro-1H-5-oxa-10b-aza-benzo[e]azulen-6-one was prepared as follows. A mixture of 2-fluoro-5-nitro-benzoic acid ethyl ester (1.16 g, 5.44 mmol), S-prolinol (638 mg, 6.31 mmol) and diisopropylethylamine (1.5 mL, 8.62 mmol) in dry NMP (20 mL) was stirred at 100° C. for 3 h. Solvent was removed and the mixture was partition between EtOAc and water. Organic layer was extracted two more times with EtOAc. Combined organic was washed successively with water (twice) and brine. After drying over magnesium sulfate, solvent was evaporated. The product, (S)-8-Nitro-2,3,3a,4-tetrahydro-1H-5-oxa-10b-aza-benzo[e]azulen-6-one was obtained as a solid (1.08 g, 80%). 12b) (S)-8-Nitro-2,3,3a,4-tetrahydro-1H-5-oxa-10b-aza-benzo[e]azulen-6-one (1 g, 4 mol) was taken in MeOH (50 mL) and was cooled to 0° C. Sodium borohydride (1 g, 26.43 mmol, 300 mg was added in portion in the first phase, 700 mg after 4 h at RT) was added and the cooling bath was removed. After stirring overnight at RT, the mixture was quenched with water. The mixture was treated with 1N Na2CO3 solution (100 mL) and dichloromethane (100 mL). The mixture was extracted from dichloromethane (twice). Combined organic was washed successively with water (twice) and brine. After drying over magnesium sulfate, solvent was evaporated. A gum was obtained which was taken in 50% H2SO4 (20 mL). The mixture was stirred at 120° C. for 45 minutes. The mixture was cooled to RT and was neutralized with NaHCO3 solution and was extracted from EtOAc. Combined organic was washed successively with water (twice) and brine. After drying over magnesium sulfate, solvent was evaporated. The crude product was purified by flash chromatography (hexane:EtOAc 3:1). The product (S)-8-Nitro-2,3,3a,4-tetrahydro-1H-5-oxa-10b-aza-benzo[e]azulen-6-one was obtained as an yellow solid (451 mg, 48% in two steps); 1H NMR (400 MHz, DMSO-d6) δ 8.02 (d, J=9.1 Hz, 1H), 8.00 (s, 1H), 6.75 (d, J=9.09 Hz, 1H0, 5.14 (d, J=14.14 Hz, 1H), 4.36 (d, J=13.89 Hz, 1H), 5.14 (d, J=14.14 Hz, 1H0, 4.36 (d, J=13.89 Hz, 1H), 4.07 (m, 1H0, 3.93 (m, 1H), 3.41 (m, 1H), 3.35-3.31 (2m, 2H), 2.17-1.89 (2m, 3H), 1.57 (m, 1H); MS (m/e) 235 (M+H).
