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ISSN: 2056-9890

Ethyl 2-methyl-4-phenyl­pyrido[1,2-a]benzimidazole-3-carboxyl­ate

aSchool of Chemistry and Chemical Engineering, Taishan Medical College, Tai An, 271016, People's Republic of China
*Correspondence e-mail: xqcao@yahoo.cn

(Received 15 September 2011; accepted 28 September 2011; online 5 October 2011)

The title compound, C21H18N2O2, was synthesized using a novel tandem annulation reaction between (1H-benzimidazol-2-yl)(phen­yl)methanone and (E)-ethyl 4-bromo­but-2-enoate under mild conditions. The dihedral angles between the mean planes of the five-membered imidazole ring and the pyridine, benzene and phenyl rings are 0.45 (6), 1.69 (1) and 70.96 (8)°, respectively. In the crystal, mol­ecules are linked through inter­molecular C—H⋯N hydrogen bonds.

Related literature

For applications of nitro­gen-containing heterocyclic compounds in the agrochemical and pharmaceutical fields, see: Ge et al. (2009[Ge, Y. Q., Jia, J., Li, Y., Yin, L. & Wang, J. W. (2009). Heterocycles, 42, 197-206.]). For the synthesis of the title compound, see: Ge et al. (2011[Ge, Y. Q., jia, J., Yang, H., Tao, X. T. & Wang, J. W. (2011). Dyes Pigments, 88, 344-349.]). For the structure of 2,7,8-trimethyl-3-eth­oxy­carbonyl-4- phenyl­pyrido[1,2-a]benzimidazole, see: Ge et al.(2011[Ge, Y. Q., jia, J., Yang, H., Tao, X. T. & Wang, J. W. (2011). Dyes Pigments, 88, 344-349.]). Some pyrido[1,2-a]benzimidazole derivatives are of inter­est for their biological activity, such as anti­neoplastic activity and central GABA-A receptor modulators for the treatment of anxiety, see: Badawey & Kappe (1999[Badawey, E. S. A. M. & Kappe, T. (1999). Eur. J. Med. Chem. 34, 663-667.]).

[Scheme 1]

Experimental

Crystal data
  • C21H18N2O2

  • Mr = 330.37

  • Monoclinic, P 21 /c

  • a = 10.1176 (13) Å

  • b = 14.9136 (18) Å

  • c = 12.2648 (15) Å

  • β = 108.487 (2)°

  • V = 1755.1 (4) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 0.08 mm−1

  • T = 298 K

  • 0.26 × 0.22 × 0.19 mm

Data collection
  • Bruker SMART APEX CCD diffractometer

  • Absorption correction: multi-scan (SADABS; Sheldrick, 1996[Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany.]) Tmin = 0.979, Tmax = 0.985

  • 8867 measured reflections

  • 3093 independent reflections

  • 2515 reflections with I > 2σ(I)

  • Rint = 0.021

Refinement
  • R[F2 > 2σ(F2)] = 0.036

  • wR(F2) = 0.096

  • S = 1.06

  • 3093 reflections

  • 227 parameters

  • H-atom parameters constrained

  • Δρmax = 0.18 e Å−3

  • Δρmin = −0.16 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
C17—H17⋯N2i 0.93 2.31 3.2092 (18) 164
Symmetry code: (i) [x, -y+{\script{1\over 2}}, z-{\script{1\over 2}}].

Data collection: SMART (Bruker, 2005[Bruker (2005). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2005[Bruker (2005). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: XP in SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); software used to prepare material for publication: SHELXL97.

Supporting information


Comment top

Synthesis of nitrogen-containing heterocyclic compounds has been a subject of great interest due to the wide application in agrochemical and pharmaceutical fields (Ge et al.; 2011). Some pyrido[1,2-a]benzimidazole derivatives have been of interest for their biological activities, such as antineoplastic activity and central GABA-A receptor modulators for the treatment of anxiety (Badawey et al.; 1999). We report here the crystal structure of the title compound, (I) (Fig. 1)

Related literature top

For applications of nitrogen-containing heterocyclic compounds in the agrochemical and pharmaceutical fields, see: Ge et al. (2009). For the synthesis of the title compound, see: Ge et al. (2011). For the structure of 2,7,8-trimethyl-3-ethoxycarbonyl-4- phenylpyrido[1,2-a]benzimidazole, see: Ge et al.(2011). Some pyrido[1,2-a]benzimidazole derivatives are of interest for their biological activity, such as antineoplastic activity and central GABA-A receptor modulators for the treatment of anxiety, see: Badawey & Kappe (1999).

Experimental top

To a 50 ml round-bottomed flask were added (1H-benzo[d]imidazol-2-yl)(phenyl)methanone (1.00 mmol), (E)-ethyl 4-bromobut-2-enoate (2.00 mmol), potassium carbonate (0.28 g, 2.05 mmol) and dry DMF (10 ml). The mixture was stirred at room temperature for 6 h. The solvent was removed under reduced pressure and an product was isolated by column chromatography on silica gel (yield 74%). Crystals of (I) suitable for X-ray diffraction were obtained by allowing a refluxed solution of the product in ethyl acetate to cool slowly to room temperature (without temperature control) and allowing the solvent to evaporate for 3 d

Refinement top

All H atoms were placed in geometrically calculated positions and refined using a riding model with C—H = 0.97 Å (for CH2 groups) and 0.96 Å (for CH3 groups), their isotropic displacement parameters were set to 1.2 times (1.5 times for CH3 groups) the equivalent displacement parameter of their parent atoms.

Computing details top

Data collection: SMART (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I), showing displacement ellipsoids drawn at the 50% probability level.
Ethyl 2-methyl-4-phenylpyrido[1,2-a]benzimidazole-3-carboxylate top
Crystal data top
C21H18N2O2F(000) = 696
Mr = 330.37Dx = 1.250 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 4793 reflections
a = 10.1176 (13) Åθ = 2.2–28.2°
b = 14.9136 (18) ŵ = 0.08 mm1
c = 12.2648 (15) ÅT = 298 K
β = 108.487 (2)°BLOCK, yellow
V = 1755.1 (4) Å30.26 × 0.22 × 0.19 mm
Z = 4
Data collection top
Bruker SMART APEX CCD
diffractometer
3093 independent reflections
Radiation source: fine-focus sealed tube2515 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.021
ϕ and ω scansθmax = 25.0°, θmin = 2.1°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
h = 1212
Tmin = 0.979, Tmax = 0.985k = 1017
8867 measured reflectionsl = 1414
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.036H-atom parameters constrained
wR(F2) = 0.096 w = 1/[σ2(Fo2) + (0.0406P)2 + 0.4084P]
where P = (Fo2 + 2Fc2)/3
S = 1.06(Δ/σ)max < 0.001
3093 reflectionsΔρmax = 0.18 e Å3
227 parametersΔρmin = 0.16 e Å3
0 restraintsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0077 (13)
Crystal data top
C21H18N2O2V = 1755.1 (4) Å3
Mr = 330.37Z = 4
Monoclinic, P21/cMo Kα radiation
a = 10.1176 (13) ŵ = 0.08 mm1
b = 14.9136 (18) ÅT = 298 K
c = 12.2648 (15) Å0.26 × 0.22 × 0.19 mm
β = 108.487 (2)°
Data collection top
Bruker SMART APEX CCD
diffractometer
3093 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
2515 reflections with I > 2σ(I)
Tmin = 0.979, Tmax = 0.985Rint = 0.021
8867 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0360 restraints
wR(F2) = 0.096H-atom parameters constrained
S = 1.06Δρmax = 0.18 e Å3
3093 reflectionsΔρmin = 0.16 e Å3
227 parameters
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O10.10877 (12)0.07612 (10)0.79576 (12)0.0806 (4)
O20.26487 (10)0.01607 (7)0.91064 (10)0.0565 (3)
N10.57376 (11)0.22116 (7)0.87282 (9)0.0359 (3)
N20.60190 (12)0.26824 (8)1.05384 (9)0.0436 (3)
C10.68800 (13)0.27812 (9)0.90225 (11)0.0375 (3)
C20.70311 (14)0.30576 (9)1.01441 (11)0.0398 (3)
C30.81352 (16)0.36238 (11)1.07098 (13)0.0508 (4)
H30.82620.38171.14570.061*
C40.90241 (16)0.38855 (11)1.01303 (14)0.0545 (4)
H40.97670.42601.04960.065*
C50.88497 (16)0.36077 (11)0.90058 (14)0.0540 (4)
H50.94730.38040.86400.065*
C60.77758 (15)0.30500 (10)0.84297 (13)0.0468 (4)
H60.76540.28620.76810.056*
C70.52624 (13)0.21772 (9)0.96751 (11)0.0365 (3)
C80.40891 (14)0.16270 (9)0.95981 (11)0.0385 (3)
C90.35444 (14)0.15819 (10)1.05942 (12)0.0406 (3)
C100.42867 (17)0.11386 (11)1.15914 (13)0.0511 (4)
H100.51360.08721.16470.061*
C110.3766 (2)0.10917 (13)1.25066 (14)0.0637 (5)
H110.42610.07841.31700.076*
C120.2527 (2)0.14964 (13)1.24415 (16)0.0677 (5)
H120.21860.14661.30610.081*
C130.17917 (19)0.19447 (12)1.14640 (17)0.0634 (5)
H130.09560.22251.14220.076*
C140.22908 (16)0.19811 (11)1.05370 (14)0.0517 (4)
H140.17780.22770.98690.062*
C150.34899 (14)0.11679 (9)0.85925 (11)0.0389 (3)
C160.39968 (14)0.12299 (9)0.76289 (11)0.0400 (3)
C170.51144 (14)0.17530 (9)0.77255 (11)0.0398 (3)
H170.54640.18030.71120.048*
C180.33086 (17)0.07371 (12)0.65248 (12)0.0548 (4)
H18A0.38390.08230.60080.082*
H18B0.23820.09650.61790.082*
H18C0.32650.01090.66820.082*
C190.22564 (15)0.05809 (10)0.85009 (12)0.0443 (3)
C200.15708 (18)0.07492 (11)0.92566 (16)0.0598 (4)
H20A0.17690.13660.91090.072*
H20B0.06730.05870.87170.072*
C210.15356 (18)0.06592 (12)1.04557 (16)0.0656 (5)
H21A0.24370.08001.09850.098*
H21B0.08550.10641.05720.098*
H21C0.12920.00551.05830.098*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0426 (7)0.0950 (10)0.0882 (9)0.0126 (6)0.0019 (6)0.0330 (8)
O20.0439 (6)0.0466 (6)0.0797 (8)0.0035 (5)0.0206 (5)0.0096 (6)
N10.0368 (6)0.0431 (6)0.0287 (5)0.0039 (5)0.0119 (5)0.0010 (5)
N20.0455 (7)0.0532 (7)0.0345 (6)0.0091 (6)0.0160 (5)0.0049 (5)
C10.0355 (7)0.0412 (7)0.0352 (7)0.0016 (6)0.0105 (6)0.0041 (6)
C20.0404 (7)0.0438 (8)0.0347 (7)0.0027 (6)0.0111 (6)0.0021 (6)
C30.0526 (9)0.0554 (9)0.0407 (8)0.0105 (7)0.0093 (7)0.0024 (7)
C40.0449 (8)0.0561 (10)0.0555 (10)0.0134 (7)0.0062 (7)0.0057 (7)
C50.0443 (8)0.0637 (10)0.0559 (10)0.0092 (7)0.0187 (7)0.0121 (8)
C60.0468 (8)0.0558 (9)0.0408 (8)0.0046 (7)0.0182 (7)0.0061 (7)
C70.0375 (7)0.0438 (8)0.0295 (6)0.0014 (6)0.0125 (5)0.0014 (6)
C80.0372 (7)0.0455 (8)0.0336 (7)0.0006 (6)0.0126 (6)0.0031 (6)
C90.0414 (8)0.0452 (8)0.0386 (7)0.0096 (6)0.0176 (6)0.0036 (6)
C100.0502 (9)0.0640 (10)0.0421 (8)0.0040 (8)0.0187 (7)0.0028 (7)
C110.0735 (12)0.0798 (12)0.0428 (9)0.0143 (10)0.0257 (8)0.0046 (8)
C120.0809 (13)0.0801 (13)0.0603 (11)0.0246 (11)0.0483 (10)0.0144 (10)
C130.0583 (10)0.0676 (11)0.0788 (13)0.0100 (9)0.0425 (10)0.0138 (10)
C140.0472 (8)0.0547 (9)0.0572 (9)0.0036 (7)0.0224 (7)0.0012 (7)
C150.0365 (7)0.0430 (8)0.0362 (7)0.0008 (6)0.0100 (6)0.0037 (6)
C160.0421 (8)0.0440 (8)0.0320 (7)0.0008 (6)0.0090 (6)0.0008 (6)
C170.0445 (8)0.0480 (8)0.0278 (7)0.0012 (6)0.0129 (6)0.0000 (6)
C180.0591 (10)0.0625 (10)0.0397 (8)0.0102 (8)0.0113 (7)0.0080 (7)
C190.0394 (8)0.0531 (9)0.0398 (7)0.0045 (7)0.0115 (6)0.0019 (7)
C200.0554 (10)0.0456 (9)0.0834 (12)0.0115 (7)0.0291 (9)0.0012 (8)
C210.0583 (10)0.0596 (11)0.0838 (13)0.0024 (8)0.0294 (10)0.0088 (9)
Geometric parameters (Å, º) top
O1—C191.1894 (18)C10—C111.385 (2)
O2—C191.3211 (18)C10—H100.9300
O2—C201.4564 (18)C11—C121.371 (3)
N1—C171.3733 (16)C11—H110.9300
N1—C11.3868 (17)C12—C131.368 (3)
N1—C71.3917 (16)C12—H120.9300
N2—C71.3270 (17)C13—C141.384 (2)
N2—C21.3818 (17)C13—H130.9300
C1—C61.3887 (19)C14—H140.9300
C1—C21.3973 (19)C15—C161.4328 (19)
C2—C31.397 (2)C15—C191.4992 (19)
C3—C41.368 (2)C16—C171.3477 (19)
C3—H30.9300C16—C181.5036 (19)
C4—C51.397 (2)C17—H170.9300
C4—H40.9300C18—H18A0.9600
C5—C61.373 (2)C18—H18B0.9600
C5—H50.9300C18—H18C0.9600
C6—H60.9300C20—C211.488 (3)
C7—C81.4214 (19)C20—H20A0.9700
C8—C151.3722 (19)C20—H20B0.9700
C8—C91.4926 (19)C21—H21A0.9600
C9—C141.383 (2)C21—H21B0.9600
C9—C101.384 (2)C21—H21C0.9600
C19—O2—C20118.17 (12)C13—C12—H12120.0
C17—N1—C1130.26 (11)C11—C12—H12120.0
C17—N1—C7123.15 (11)C12—C13—C14120.04 (16)
C1—N1—C7106.58 (10)C12—C13—H13120.0
C7—N2—C2104.76 (11)C14—C13—H13120.0
N1—C1—C6131.99 (13)C9—C14—C13120.62 (16)
N1—C1—C2105.00 (11)C9—C14—H14119.7
C6—C1—C2122.99 (13)C13—C14—H14119.7
N2—C2—C3129.47 (13)C8—C15—C16122.51 (12)
N2—C2—C1111.30 (12)C8—C15—C19118.60 (12)
C3—C2—C1119.21 (13)C16—C15—C19118.88 (12)
C4—C3—C2117.93 (14)C17—C16—C15118.34 (12)
C4—C3—H3121.0C17—C16—C18119.87 (13)
C2—C3—H3121.0C15—C16—C18121.79 (13)
C3—C4—C5122.03 (15)C16—C17—N1120.08 (12)
C3—C4—H4119.0C16—C17—H17120.0
C5—C4—H4119.0N1—C17—H17120.0
C6—C5—C4121.30 (14)C16—C18—H18A109.5
C6—C5—H5119.4C16—C18—H18B109.5
C4—C5—H5119.4H18A—C18—H18B109.5
C5—C6—C1116.54 (14)C16—C18—H18C109.5
C5—C6—H6121.7H18A—C18—H18C109.5
C1—C6—H6121.7H18B—C18—H18C109.5
N2—C7—N1112.36 (11)O1—C19—O2124.91 (14)
N2—C7—C8129.73 (12)O1—C19—C15124.47 (14)
N1—C7—C8117.91 (11)O2—C19—C15110.62 (12)
C15—C8—C7117.99 (12)O2—C20—C21108.91 (14)
C15—C8—C9122.73 (12)O2—C20—H20A109.9
C7—C8—C9119.27 (12)C21—C20—H20A109.9
C14—C9—C10118.86 (14)O2—C20—H20B109.9
C14—C9—C8120.66 (13)C21—C20—H20B109.9
C10—C9—C8120.48 (13)H20A—C20—H20B108.3
C9—C10—C11120.09 (16)C20—C21—H21A109.5
C9—C10—H10120.0C20—C21—H21B109.5
C11—C10—H10120.0H21A—C21—H21B109.5
C12—C11—C10120.43 (17)C20—C21—H21C109.5
C12—C11—H11119.8H21A—C21—H21C109.5
C10—C11—H11119.8H21B—C21—H21C109.5
C13—C12—C11119.93 (15)
C17—N1—C1—C62.2 (2)C15—C8—C9—C10109.59 (17)
C7—N1—C1—C6178.59 (15)C7—C8—C9—C1071.49 (18)
C17—N1—C1—C2179.46 (13)C14—C9—C10—C110.7 (2)
C7—N1—C1—C20.20 (14)C8—C9—C10—C11179.29 (14)
C7—N2—C2—C3177.76 (15)C9—C10—C11—C121.2 (3)
C7—N2—C2—C10.44 (16)C10—C11—C12—C130.5 (3)
N1—C1—C2—N20.40 (15)C11—C12—C13—C140.7 (3)
C6—C1—C2—N2178.98 (13)C10—C9—C14—C130.5 (2)
N1—C1—C2—C3178.00 (13)C8—C9—C14—C13179.52 (14)
C6—C1—C2—C30.6 (2)C12—C13—C14—C91.2 (3)
N2—C2—C3—C4178.25 (15)C7—C8—C15—C160.4 (2)
C1—C2—C3—C40.2 (2)C9—C8—C15—C16178.50 (13)
C2—C3—C4—C50.3 (2)C7—C8—C15—C19179.67 (12)
C3—C4—C5—C60.5 (3)C9—C8—C15—C191.4 (2)
C4—C5—C6—C10.1 (2)C8—C15—C16—C170.7 (2)
N1—C1—C6—C5177.72 (14)C19—C15—C16—C17179.38 (13)
C2—C1—C6—C50.4 (2)C8—C15—C16—C18178.70 (14)
C2—N2—C7—N10.31 (15)C19—C15—C16—C181.2 (2)
C2—N2—C7—C8179.29 (14)C15—C16—C17—N10.1 (2)
C17—N1—C7—N2179.25 (12)C18—C16—C17—N1179.34 (13)
C1—N1—C7—N20.07 (15)C1—N1—C17—C16179.97 (13)
C17—N1—C7—C81.10 (19)C7—N1—C17—C160.8 (2)
C1—N1—C7—C8179.58 (12)C20—O2—C19—O18.9 (2)
N2—C7—C8—C15179.97 (14)C20—O2—C19—C15171.09 (13)
N1—C7—C8—C150.45 (19)C8—C15—C19—O1105.81 (18)
N2—C7—C8—C91.0 (2)C16—C15—C19—O174.1 (2)
N1—C7—C8—C9179.42 (12)C8—C15—C19—O274.15 (16)
C15—C8—C9—C1470.36 (19)C16—C15—C19—O2105.95 (15)
C7—C8—C9—C14108.56 (16)C19—O2—C20—C21106.00 (16)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C17—H17···N2i0.932.313.2092 (18)164
Symmetry code: (i) x, y+1/2, z1/2.

Experimental details

Crystal data
Chemical formulaC21H18N2O2
Mr330.37
Crystal system, space groupMonoclinic, P21/c
Temperature (K)298
a, b, c (Å)10.1176 (13), 14.9136 (18), 12.2648 (15)
β (°) 108.487 (2)
V3)1755.1 (4)
Z4
Radiation typeMo Kα
µ (mm1)0.08
Crystal size (mm)0.26 × 0.22 × 0.19
Data collection
DiffractometerBruker SMART APEX CCD
diffractometer
Absorption correctionMulti-scan
(SADABS; Sheldrick, 1996)
Tmin, Tmax0.979, 0.985
No. of measured, independent and
observed [I > 2σ(I)] reflections
8867, 3093, 2515
Rint0.021
(sin θ/λ)max1)0.596
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.036, 0.096, 1.06
No. of reflections3093
No. of parameters227
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.18, 0.16

Computer programs: SMART (Bruker, 2005), SAINT (Bruker, 2005), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), XP in SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C17—H17···N2i0.932.313.2092 (18)164
Symmetry code: (i) x, y+1/2, z1/2.
 

Acknowledgements

This study was supported by the Natural Science Foundation of Shandong Province (Y2007C135).

References

First citationBadawey, E. S. A. M. & Kappe, T. (1999). Eur. J. Med. Chem. 34, 663–667.  Web of Science PubMed CAS Google Scholar
First citationBruker (2005). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.  Google Scholar
First citationGe, Y. Q., Jia, J., Li, Y., Yin, L. & Wang, J. W. (2009). Heterocycles, 42, 197–206.  Google Scholar
First citationGe, Y. Q., jia, J., Yang, H., Tao, X. T. & Wang, J. W. (2011). Dyes Pigments, 88, 344-349.  Web of Science CSD CrossRef CAS Google Scholar
First citationSheldrick, G. M. (1996). SADABS. University of Göttingen, Germany.  Google Scholar
First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals Google Scholar

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