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HETEROCYCLES, Vol. 68, No. 6, 2006
carboxylate (6) (1.45 g, 4 mmol) in p-xylene (70 mL) was heated at 80 – 85 °C for 1 h. Thereafter, the
reaction temperature was brought to 110 – 115 °C for 1 h, during which time a steady evolution of
nitrogen gas took place. Finally, the temperature was raised slowly to 140 – 145 °C and maintained
thereat for 4 h. The solvent was then removed in vacuo, the residual solid product was soaked in hexane,
collected by suction filtration, and triturated with cold acetone (2 × 3 mL). Yield = 0.96 g (72 %); mp 192
– 193 °C (decomp). For analytical purposes, the title product was recrystallized from hot ethanol (or from
acetone) to afford yellow needles. Anal. Calcd for C15H12N3O5F (333.27): C, 54.06; H, 3.63; N, 12.61.
Found: C, 53.84; H, 3.58; N, 12.36; IR (KBr): ν 3097, 3063, 2994, 2925, 2846, 1729, 1635, 1608, 1587,
1542, 1461, 1426, 1384, 1365, 1342, 1316, 1304, 1270, 1236, 1195, 1171, 1128, 1045 cm-1; EI MS m / z
(%): 333 (19, M+), 288 (6), 275 (11), 261 (100), 252 (29), 245 (19), 232 (20), 226 (24), 200 (21), 172
(23), 146 (12), 133 (13), 125 (6), 120 (4); MS (TOF ES+): m/z 356 (M+Na)+; HRMS: calcd. for
1
C15H12N3O5FNa 356.0659, found 356.0653; H NMR (300 MHz, DMSO-d6): δ 1.25 (t, J = 7.1 Hz, 3H,
CH3CH2), 1.25 (m, 4H, H2-2′ / H2-3′, overlapped with / underneath the Me triplet), 4.04 (m, 1H, H-1′),
4.20 (q, J = 7.1 Hz, 2H, MeCH2O), 7.47, 7.48 (2d, 3JH-F = 10.5, 10.4 Hz, 1H, H-5), 8.46 (s, 1H, H-8); 13C
NMR (75 MHz, DMSO-d6): δ 10.4 (C-2′/ C-3′), 14.6 (CH3CH2), 40.2 (C-1′), 61.0 (MeCH2O), 107.9 (d,
2JC-F = 18.6 Hz, C-5), 108.6 (d, 2JC-F = 21.2 Hz, C-3a), 115.4 (C-7), 129.3 (d, 3JC-F = 4.2 Hz, C-5a), 131.0
(d, 4JC-F = 3.4 Hz, C-9a), 144.0 (d, 1JC-F = 258 Hz, C-4), 148.0 (C-8), 149.3 (C-9b), 164.1 (CO2Et), 170.3
(d, 4JC-F = 2.0 Hz, C-6).
9-Cyclopropyl-4-fluoro-6-oxo-6,9-dihydro[1,2,5]oxadiazolo[3,4-h]quinoline-7-carboxylic acid N(3)-
oxide (4)
A vigorously stirred suspension of 3 (1.0 g, 3 mmol) in 12 % aqueous HCl (50 mL) and ethanol (20 mL)
was heated at 65-70 °C. Progress of the ester hydrolysis was monitored by TLC and the reaction
completed within 16-18 h. Thereafter, the reaction mixture was cooled, the resulting heavy faint yellow
precipitate was collected, washed with cold water (2 × 20 mL), dried, and recrystallized from acetone.
Yield = 0.76 g (83 %), mp 239 – 240 °C (decomp). Anal. Calcd for C13H8N3O5F (305.22): C, 51.16; H,
2.64; N, 13.77. Found: C, 50.94; H, 2.61; N, 13.62; IR (KBr): ν 3435, 3228, 3120, 3081, 3007, 1723 (br),
1634, 1593, 1537, 1506, 1447, 1411, 1389, 1347, 1320, 1294, 1241, 1220, 1193, 1158, 1123, 1081, 1044,
1023 cm-1; EI MS m / z ( % ): 305 (17, M+), 289 (2), 261 (100), 245 (30), 232 (11), 200 (13), 172 (19),
146 (14), 133 (6), 125 (5), 120 (10); MS (TOF ES+): m/z 306 (M+H)+, HRMS calcd. for C13H9N3O5F
306.0526, found 306.0521; m/z 328 (M + Na)+, HRMS calcd. for C13H8N3O5FNa 328.0346, found
328.0340; 1H NMR (300 MHz, DMSO-d6): δ 1.29, 1.35 (2m, 4H, H2-2′ / H2-3′), 4.19 (m, 1H, H-1′), 7.65
(d, 3JH-F = 10 Hz, 1H, H-5), 8.78 (s, 1H, H-8), 14.72 (br s, 1H, CO2H); 13C NMR (75 MHz, DMSO-d6): δ
2
2
10.4 (C-2′/ C-3′). 41.6 (C-1′ ), 106.7 (d, JC-F = 19.1 Hz, C-5), 109.3 (d, JC-F = 21.3 Hz, C-3a), 112.6