6080 Li et al.
Asian J. Chem.
O
N
O
O
N
O
F
F
F
OH
OEt
H2O
F
CH3COOH, H2SO4
O O
O
O
H3C
CH3
B
O
O
2
F
F
1
O
N
H3C
O
H3C
H3C
O
O
HO
OH
H3C
O
B
O
O
B
O
OH
O
O
CH3
3
O
Boric acid
Acetic anhydride
Boron triacetate
Scheme-II: Procedure of preparing the title compound (3)
CCD area detector.All the reagents were of analytical reagent
grade.
Synthesis and characterization: The 1-cyclopropyl-6,7-
difluoro-8-methoxy-4-oxo-1,4-dihydro-3-quinoline carboxylic
acid-(O3,O4)-bis-(acetate-O)borate (3) was prepared according
to the following (Scheme-II).
s, 2-H), 8.01-8.38 (1H, dd, J = 8 Hz, 10 Hz, 5-H), 4.25-4.40
(1H, m, -NCH-), 3.98 (3H, s,-OCH3), 2.04 (6H, s, -OCOCH3),
1.14-1.46 (4H, m). 13C NMR (300 MHz, CDCl3): δ 190.18,
169.79, 153.55, 144.71, 139.54, 135.85, 134.63, 123.96,
107.42, 101.95, 70.29, 60.70, 41.88, 28.73, 9.87. MS(ESI)
m/z calc. for C18H17BF2NO6 392.14, found [M+H]+ 393.23,
[M-(CH3CO)2O, 100%]+ 296.26.
Preparation of compound 2: The mixture of acetic acid
(360 mL), water (240 mL) was stirred at room temperature
and H2SO4 (48 mL) was slowly dropwise added. After the
temperature was cooled to room temperature, the ethyl 1-
cyclopropyl-6,7-difluoro-8-methoxy-4-oxo-1,4-dihydroquin-
oline-3-carboxylate (1) (52 g, 0.16 mol) was added slowly
under stirring. The reaction mixture was refluxed for 2 h, then
cooled to room temperature and the resultant crystalline
compound was filtered and washed with water (500 mL) and
dried to afford the compound 1-cyclopropyl-6,7-difluoro-8-
methoxy-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (2)
(45.32 g). Yield: 95.92 %; white solid; m.p.188.4-190.2 ºC.
1H NMR (300 MHz, CDCl3) δ: 9.14 (1H, s, 2-H), 7.71-8.14(1H,
dd, J = 7.8 Hz, 9.9 Hz, 5-H), 4.15-4.53 (1H, m, -NCH-), 3.98
(3H, s, -OCH3), 1.12-1.48 (4H, m). 13C NMR (300 MHz,
CDCl3) δ: 175.67, 167.61, 150.62, 146.13, 139.54, 136.76,
130.50, 123.47, 109.35, 107.30, 60.52, 39.94, 10.66. MS (ESI)
m/z calc. for C14H11F2NO4 295.24, found [M+H]+ 296.23.
Synthesis of compound 3: Acetic anhydride (72.2 g,
0.7073 mol) was heated to 70 ºC and boric acid (12.5 g, 0.2021
mol) was slowly added at 70 ºC. Then the temperature was
raised to 110 ºC for 2 h, followed by cooling to about 50 ºC. 1-
Cyclopropyl-6,7-difluoro-8-methoxy-4-oxo-1,4-dihydroquinoline-
3-carboxylic acid (2) (40 g, 0.1354 mol) was added under
stirring. The reaction mixture temperature was raised to 90 ºC
and maintained for 3 h. After the completion of reaction the
reaction mixture was cooled to 0 ºC, water (500 mL) was
slowly added at 0 ºC and maintained for 1 h. The product was
filtered, washed with water (200 mL) and dried at 45-50 ºC in
fluid bed drier to get the compound 1-cyclopropyl-6,7-difluoro-
8-methoxy-4-oxo-1,4-dihydro-3-quinoline carboxylic acid-
(O3,O4)-bis-(acetate-O)borate 3 (54.6 g).Yield: 95.3 %; white
solid; m.p. 112-117. 1H NMR (300 MHz, CDCl3): 9.22 (1H,
Crystallography studies: The title compound (200 mg)
was dissolved in 10 mL a solvent mixture of MeOH and water
(3:1) and colourless transparent crystals suitable for X-ray
analysis grew over a period of two week when the solution
was exposed to air at room temperature. The crystal having
approximate dimensions of 0.15mm × 0.12 mm × 0.10 mm
was mounted on the top of a glass fiber in a random orientation.
The data were collected by a Bruker SMART 1000 CCD area
detector diffractometer equipped with a graphite-mono-
chromatized MoKα radiation radiation (λ = 0.71073 Å) by
using a φ-ω scan mode at 293 K. A total of 7790 reflections
were collected in the range of 1.43<θ<25.01º, of which 3457
were independent (Rint = 0.1239) and 2378 were observed with
I > 2σ(I).
The data collection and procession were performed with
program SMART and SHELXTL8. The structure was solved
by direct methods and refined by fullmatrix least-squares/
difference Fourier techniques with SHELXS-97 and SHELXL-
97 programs9. All non-hydrogen atoms were refined with
anisotropic displacement parameters. After that, all hydrogen
atoms were located theoretically and refined with riding model
position parameters and fixed isotropic thermal parameters.
The final R = 0.1083, wR = 0.3062 (w = 1/[σ2(Fo2) + (0.2P)2],
where P = (Fo2 + 2Fc2)/3), (∆/σ)max = 0.004, S = 1.104, (∆ρ)max
= 1.032 and (∆ρ)min = -0.470 e/Å-3.
RESULTS AND DISCUSSION
Crystal structure description: The title compound was
1
prepared according to Scheme-II. The H NMR, 13C NMR,
MS and m.p. for the product are in good agreement with the
title compound. In order to confirm the configuration of the
product, a single crystal of the title compound was cultured