Reaction Steps
A solution of KNO3 (2.25 g, 22.3 mmol) in CH2SO4 (10 mL) was added dropwise to a stirred solution of 4-chromanone (225) (3.0 g, 20.2 mmol) in CH2SO4 (50 mL) at 0° C. and the mixture stirred at 0° C. for 2 h. The mixture was poured into ice/water (500 mL), stirred 30 min and the precipitate filtered. The solid was washed with water (3×10 mL) and dried. The solid was purified by chromatography, eluting with 20% EtOAc/pet. ether, to give (i) 8-nitro-2,3-dihydro-4H-chromen-4-one (226) (369 mg, 9%) as a white solid: mp (EtOAc/pet. ether) 120-121° C.; 1H NMR δ 8.17 (dd, J=7.8, 1.8 Hz, 1H, H-7), 8.10 (dd, J=8.0, 1.8 Hz, 1H, H-5), 7.12 (dd, J=8.0, 7.8 Hz, 1H, H-6), 4.73 (dd, J=6.5, 6.4 Hz, 2H, H-2), 2.95 (br t, J=6.5 Hz, 2H, H-3). Anal. calcd for C9H7NO4: C, 56.0; H, 3.7; N, 7.3. Found: C, 56.1; H, 3.7; N, 7.3%; and (ii) 6-nitro-2,3-dihydro-4H-chromen-4-one (227) (3.17 g, 81%) as a white solid: mp (EtOAc/pet. ether) 169-171° C.; 1H NMR δ 8.78 (d, J=2.8 Hz, 1H, H-5), 8.32 (dd, J=9.1, 2.8 Hz, 1H, H-7), 7.11 (d, J=9.1 Hz, 1H, H-8), 4.67 (dd, J=6.6, 6.4 Hz, 2H, H-2), 2.91 (dd, J=6.6, 6.4 Hz, 2H, H-3); 13C NMR δ 189.4, 165.7, 142.1, 130.3, 123.7, 120.8, 119.3, 67.6, 37.1. Anal. calcd for C9H7NO4: C, 56.0; H, 3.7; N, 7.3. Found: C, 56.1; H, 3.7; N, 7.4%.
