supplementary materials


fy2085 scheme

Acta Cryst. (2013). E69, o732    [ doi:10.1107/S1600536813009689 ]

1-(3-Chlorophenyl)-5-(2,4-dihydroxybenzoyl)pyridin-2(1H)-one

F. Ren, G. Li, Q. Zhang, J. Yao and X. Zhang

Abstract top

The chlorophenyl group of the title compound, C18H12ClNO4, is disordered over two orientations with occupancies of 0.331 (8) and 0.669 (8). An intramolecular hydrogen bond is formed between a hydroxy group and the acyclic carbonyl group. In the crystal, molecules are linked into chains along [110] by O-H...O and C-H...O hydrogen bonds, forming a ladder motif.

Comment top

The title compound was prepared during our ongoing research on anticancer compounds. It is one of a limited number of reported crystal structures of 2-pyridone derivatives. The structure was confirmed by X-ray crystallography as shown in Fig. 1. H-bonding interactions play a decisive role in the crystal packing arrangement (Fig. 2). Intermolecular C3—H3···O4 and O1—H1···O4 contacts form a supramolecular chain parallel with [110]. Pairs of these chains are linked via C15—H15···O1 interactions to form a ladder motif.

Related literature top

For similar structures, see: Ravinder et al. (2012); Sengupta et al. (2012). For the synthesis, see: Chen et al. (2011); Kim & Hong (2011). For the biological activity of similar structures, see: Kim et al. (2010).

Experimental top

A solution of 7-methoxy-chromen-4-one (0.015 mol) in methanol (150 ml) was added dropwise to a solution of piperidine (0.030 mol) and rufluxed for 3 h at 0°C to get a crude product. This was added dropwise to a solution of dichloromethane (150 ml) and I2 for an overnight reaction to give 3-iodo-7-methoxy-chromen-4-one with a 70% yield. Another 100 ml round-bottom flask fitted with mechanical stirrer was loaded with a mixture of 75 ml DMF and 5 ml water, then 3-iodo-7-methyloxy-4 H-chromone (3.0 g, 0.010 mol), methyl acrylate (1.2 g, 0.015 mol), Pd(Ph3P)2Cl2 (0.07 g, 0.1 mmol), CuI (0.19 g, 10 mmol), and K2CO3 (1.38 g, 0.01 mol) were added successively. The mixture was heated to 70°C and stirred for 4 h. Then the mixture was filtered. The filtrate was poured into 100 ml of ice-water and then extracted with EtOAc. The extract was washed with saturated NaCl solution, dried over anhydrous MgSO4, and concentrated to a volume of approximately 30 ml. The target compound 3-(7-methoxy-4-oxo-4H-chromen-3-yl)acrylic acid methyl ester was collected after the concentrated solution was cooled down to 4°C and maintained overnight (2.1 g, 76%). The solution of 3-(7-methoxy-4-oxo-4H-chromen-3-yl)acrylic acid methyl ester (1.04 g, 0.004 mol), 4-chlorophenylamine (0.41 g, 0.0044 mol), and triethylamine (3 drops) in MeOH (45 ml) was stirred under reflux for 8 h. After the mixture was cooled to room temperature and the solvent removed, the crude product was purified by chromatography over silica gel to give 1-(4-chlorophenyl)-5-(2-hydroxy-4-methoxy-benzoyl)-1H-pyridin-2-one with a yield of 72%. Then a solution of NaOH (0.004 mol) in water (5 ml) was added dropwise to a solution of 1-(4-chlorophenyl)-5-(2-hydroxy-4-methoxy-benzoyl)-1H-pyridin-2-one (0.003 mol) in ethanol (50 ml). Reaction at room temperature for 10 min gave the crude compound, which was recrystallized to obtain the title compound, 1-(4-chlorophenyl)-5-(2,4-dihydroxybenzoyl)-1H-pyridin-2-one. The recrystallized product was dissolved in EtOAc (1.5 ml) in an ampoule and PE (1.5 ml) was added dropwise. The ampoule was placed in refrigerator and single crystals were obtained by slow evaporation of the solvent (0.3 g, 35%; m.p. 391 K).

Refinement top

All hydrogen atoms bonded with carbon atoms were placed in calculated positions using a riding model, with d(C—H) = 0.93 Å and Uiso(H) = 1.2 Ueq(C). The orientations of the hydrogen atoms in the hydroxyl groups were determined using difference Fourier maps. The disordered chlorophenyl group was divided into two parts (33%:67%). A FLAT group restraint and seven ISOR instructions (for C13-18 and Cl1) were applied for the minor component of the disordered chlorophenyl group. O—H bond distances in the two hydroxyl groups were restrained by using DFIX to 0.96 (1) Å.

Computing details top

Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. Molecular structure with the numbering scheme adopted and ellipsoids drawn at the 30% probability level.
[Figure 2] Fig. 2. A view of the unit-cell contents of title compound. Hydrogen bonds are shown as dashed lines.
1-(3-Chlorophenyl)-5-(2,4-dihydroxybenzoyl)pyridin-2(1H)-one top
Crystal data top
C18H12ClNO4F(000) = 352
Mr = 341.74Dx = 1.435 Mg m3
Triclinic, P1Melting point: 391 K
a = 6.689 (3) ÅMo Kα radiation, λ = 0.71073 Å
b = 9.009 (4) ÅCell parameters from 841 reflections
c = 13.257 (6) Åθ = 2.3–26.8°
α = 87.193 (5)°µ = 0.26 mm1
β = 87.719 (5)°T = 293 K
γ = 82.674 (5)°Block, yellow
V = 791.0 (6) Å30.15 × 0.12 × 0.05 mm
Z = 2
Data collection top
Bruker SMART CCD
diffractometer
2726 independent reflections
Radiation source: fine-focus sealed tube1929 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.049
φ and ω scansθmax = 25.0°, θmin = 1.5°
Absorption correction: multi-scan
(SADABS; Bruker, 2002)
h = 57
Tmin = 0.962, Tmax = 0.987k = 910
3286 measured reflectionsl = 1415
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.078Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.233H atoms treated by a mixture of independent and constrained refinement
S = 1.00 w = 1/[σ2(Fo2) + (0.1737P)2]
where P = (Fo2 + 2Fc2)/3
2726 reflections(Δ/σ)max < 0.001
236 parametersΔρmax = 0.36 e Å3
48 restraintsΔρmin = 0.43 e Å3
Crystal data top
C18H12ClNO4γ = 82.674 (5)°
Mr = 341.74V = 791.0 (6) Å3
Triclinic, P1Z = 2
a = 6.689 (3) ÅMo Kα radiation
b = 9.009 (4) ŵ = 0.26 mm1
c = 13.257 (6) ÅT = 293 K
α = 87.193 (5)°0.15 × 0.12 × 0.05 mm
β = 87.719 (5)°
Data collection top
Bruker SMART CCD
diffractometer
2726 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2002)
1929 reflections with I > 2σ(I)
Tmin = 0.962, Tmax = 0.987Rint = 0.049
3286 measured reflectionsθmax = 25.0°
Refinement top
R[F2 > 2σ(F2)] = 0.078H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.233Δρmax = 0.36 e Å3
S = 1.00Δρmin = 0.43 e Å3
2726 reflectionsAbsolute structure: ?
236 parametersFlack parameter: ?
48 restraintsRogers parameter: ?
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*/UeqOcc. (<1)
C10.5151 (4)0.2487 (3)0.2138 (2)0.0538 (8)
H1A0.62950.30830.23680.065*
C20.3295 (4)0.3066 (3)0.2132 (2)0.0495 (7)
C30.1599 (4)0.2167 (3)0.1802 (2)0.0467 (7)
H30.03680.25450.18110.056*
C40.1723 (4)0.0708 (3)0.1460 (2)0.0437 (6)
C50.3569 (4)0.0092 (3)0.1467 (2)0.0445 (6)
C60.5255 (4)0.1048 (3)0.1803 (2)0.0504 (7)
H60.64950.06820.17960.060*
C70.3660 (4)0.1438 (3)0.1075 (2)0.0485 (7)
C80.5392 (4)0.2240 (3)0.1300 (2)0.0431 (6)
C90.6104 (4)0.3249 (3)0.0559 (2)0.0521 (7)
H90.55470.33470.00760.063*
C100.7578 (4)0.4071 (3)0.0762 (3)0.0608 (8)
H100.80620.46920.02530.073*
C110.8409 (4)0.4009 (3)0.1736 (2)0.0554 (8)
C120.6192 (4)0.2166 (3)0.2224 (2)0.0460 (7)
H120.57420.15140.27240.055*
C130.835 (4)0.298 (2)0.348 (2)0.0602 (8)0.331 (8)
C140.679 (4)0.326 (2)0.4232 (19)0.107 (3)0.331 (8)
H140.54650.35770.40650.128*0.331 (8)
C150.737 (4)0.302 (2)0.5263 (17)0.137 (4)0.331 (8)
H150.64060.32120.57810.164*0.331 (8)
C160.928 (4)0.254 (3)0.549 (2)0.109 (3)0.331 (8)
H160.96650.23860.61540.131*0.331 (8)
C171.065 (4)0.227 (3)0.471 (2)0.0914 (18)0.331 (8)
C181.027 (5)0.242 (3)0.364 (3)0.069 (2)0.331 (8)
H181.12320.21710.31320.083*0.331 (8)
Cl11.3150 (14)0.1781 (14)0.4928 (8)0.1598 (17)0.331 (8)
C13'0.8340 (19)0.2944 (10)0.3452 (10)0.0602 (8)0.669 (8)
C14'0.7299 (15)0.3857 (11)0.4146 (8)0.107 (3)0.669 (8)
H14'0.61240.44630.39660.128*0.669 (8)
C15'0.7991 (14)0.3875 (11)0.5106 (6)0.137 (4)0.669 (8)
H15'0.72860.44930.55760.164*0.669 (8)
C16'0.9725 (17)0.2980 (12)0.5372 (8)0.109 (3)0.669 (8)
H16'1.01940.29930.60220.131*0.669 (8)
C17'1.077 (2)0.2068 (13)0.4678 (10)0.0914 (18)0.669 (8)
C18'1.007 (2)0.2050 (12)0.3718 (11)0.069 (2)0.669 (8)
H18'1.07800.14320.32470.083*0.669 (8)
Cl1'1.2968 (6)0.0926 (8)0.5029 (3)0.1598 (17)0.669 (8)
N10.7644 (3)0.3024 (2)0.24405 (18)0.0477 (6)
O10.3277 (3)0.4514 (2)0.24453 (18)0.0642 (7)
O20.0021 (3)0.0106 (2)0.11379 (17)0.0591 (6)
O30.2307 (3)0.2123 (2)0.05679 (18)0.0686 (7)
O40.9690 (3)0.4788 (2)0.1992 (2)0.0816 (8)
H20.044 (5)0.096 (4)0.086 (3)0.077 (10)*
H10.214 (7)0.478 (5)0.227 (3)0.109 (15)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0483 (14)0.0462 (14)0.070 (2)0.0105 (11)0.0145 (13)0.0106 (13)
C20.0561 (16)0.0472 (14)0.0490 (18)0.0157 (12)0.0057 (12)0.0132 (11)
C30.0451 (14)0.0543 (15)0.0458 (17)0.0217 (11)0.0010 (11)0.0129 (11)
C40.0410 (13)0.0532 (14)0.0398 (16)0.0115 (11)0.0027 (10)0.0150 (11)
C50.0444 (14)0.0506 (14)0.0420 (16)0.0149 (11)0.0030 (10)0.0123 (11)
C60.0419 (13)0.0519 (15)0.061 (2)0.0145 (11)0.0059 (12)0.0161 (12)
C70.0430 (14)0.0538 (15)0.0516 (18)0.0132 (11)0.0041 (12)0.0112 (12)
C80.0462 (13)0.0413 (12)0.0442 (17)0.0117 (10)0.0031 (11)0.0079 (10)
C90.0550 (15)0.0587 (15)0.0453 (18)0.0167 (12)0.0046 (12)0.0019 (12)
C100.0614 (17)0.0601 (17)0.064 (2)0.0251 (14)0.0006 (14)0.0066 (14)
C110.0520 (15)0.0448 (14)0.073 (2)0.0189 (12)0.0066 (13)0.0067 (13)
C120.0526 (14)0.0428 (13)0.0454 (18)0.0160 (11)0.0004 (12)0.0056 (11)
C130.0676 (18)0.0643 (18)0.052 (2)0.0113 (14)0.0134 (14)0.0153 (14)
C140.121 (7)0.130 (8)0.061 (4)0.033 (6)0.024 (4)0.036 (5)
C150.172 (8)0.167 (10)0.062 (5)0.032 (8)0.024 (5)0.051 (6)
C160.118 (7)0.148 (8)0.065 (4)0.024 (5)0.029 (4)0.012 (5)
C170.079 (3)0.124 (4)0.072 (3)0.009 (3)0.026 (2)0.000 (3)
C180.066 (3)0.077 (7)0.065 (3)0.012 (4)0.009 (2)0.004 (4)
Cl10.1116 (14)0.220 (5)0.1318 (18)0.034 (3)0.0528 (12)0.048 (3)
C13'0.0676 (18)0.0643 (18)0.052 (2)0.0113 (14)0.0134 (14)0.0153 (14)
C14'0.121 (7)0.130 (8)0.061 (4)0.033 (6)0.024 (4)0.036 (5)
C15'0.172 (8)0.167 (10)0.062 (5)0.032 (8)0.024 (5)0.051 (6)
C16'0.118 (7)0.148 (8)0.065 (4)0.024 (5)0.029 (4)0.012 (5)
C17'0.079 (3)0.124 (4)0.072 (3)0.009 (3)0.026 (2)0.000 (3)
C18'0.066 (3)0.077 (7)0.065 (3)0.012 (4)0.009 (2)0.004 (4)
Cl1'0.1116 (14)0.220 (5)0.1318 (18)0.034 (3)0.0528 (12)0.048 (3)
N10.0537 (12)0.0454 (11)0.0477 (15)0.0153 (9)0.0103 (10)0.0097 (10)
O10.0658 (13)0.0476 (11)0.0836 (17)0.0193 (9)0.0186 (11)0.0013 (10)
O20.0421 (10)0.0625 (12)0.0751 (16)0.0144 (9)0.0131 (9)0.0011 (10)
O30.0598 (13)0.0624 (12)0.0871 (18)0.0197 (10)0.0250 (11)0.0100 (11)
O40.0729 (14)0.0669 (14)0.114 (2)0.0362 (11)0.0279 (13)0.0020 (13)
Geometric parameters (Å, º) top
C1—C61.359 (4)C13—C141.42 (3)
C1—C21.407 (4)C13—N11.47 (3)
C1—H1A0.9300C14—C151.43 (3)
C2—O11.350 (3)C14—H140.9300
C2—C31.380 (4)C15—C161.34 (3)
C3—C41.381 (4)C15—H150.9300
C3—H30.9300C16—C171.36 (3)
C4—O21.346 (3)C16—H160.9300
C4—C51.418 (3)C17—C181.45 (3)
C5—C61.402 (4)C17—Cl11.71 (3)
C5—C71.457 (4)C18—H180.9300
C6—H60.9300C13'—C18'1.373 (8)
C7—O31.232 (3)C13'—C14'1.373 (8)
C7—C81.489 (3)C13'—N11.432 (13)
C8—C121.352 (4)C14'—C15'1.373 (8)
C8—C91.415 (4)C14'—H14'0.9300
C9—C101.349 (4)C15'—C16'1.373 (8)
C9—H90.9300C15'—H15'0.9300
C10—C111.422 (4)C16'—C17'1.373 (8)
C10—H100.9300C16'—H16'0.9300
C11—O41.242 (3)C17'—C18'1.373 (8)
C11—N11.385 (4)C17'—Cl1'1.750 (14)
C12—N11.363 (3)C18'—H18'0.9300
C12—H120.9300O1—H10.87 (5)
C13—C181.34 (2)O2—H20.91 (4)
C6—C1—C2119.3 (3)C13—C14—H14121.6
C6—C1—H1A120.3C15—C14—H14121.6
C2—C1—H1A120.3C16—C15—C14120.6 (18)
O1—C2—C3122.9 (2)C16—C15—H15119.7
O1—C2—C1117.2 (3)C14—C15—H15119.7
C3—C2—C1119.9 (2)C15—C16—C17118.1 (16)
C2—C3—C4120.3 (2)C15—C16—H16120.9
C2—C3—H3119.8C17—C16—H16120.9
C4—C3—H3119.8C16—C17—C18127.1 (13)
O2—C4—C3117.5 (2)C16—C17—Cl1121.1 (18)
O2—C4—C5121.6 (2)C18—C17—Cl1111.6 (18)
C3—C4—C5120.9 (2)C13—C18—C17111.2 (12)
C6—C5—C4116.9 (2)C13—C18—H18124.4
C6—C5—C7123.5 (2)C17—C18—H18124.4
C4—C5—C7119.5 (2)C18'—C13'—C14'120.0
C1—C6—C5122.6 (2)C18'—C13'—N1121.4 (8)
C1—C6—H6118.7C14'—C13'—N1118.4 (7)
C5—C6—H6118.7C13'—C14'—C15'120.0
O3—C7—C5121.9 (2)C13'—C14'—H14'120.0
O3—C7—C8117.7 (2)C15'—C14'—H14'120.0
C5—C7—C8120.4 (2)C16'—C15'—C14'120.0
C12—C8—C9117.8 (2)C16'—C15'—H15'120.0
C12—C8—C7122.5 (2)C14'—C15'—H15'120.0
C9—C8—C7119.4 (3)C17'—C16'—C15'120.0
C10—C9—C8120.9 (3)C17'—C16'—H16'120.0
C10—C9—H9119.5C15'—C16'—H16'120.0
C8—C9—H9119.5C16'—C17'—C18'120.0
C9—C10—C11121.5 (3)C16'—C17'—Cl1'119.5 (8)
C9—C10—H10119.3C18'—C17'—Cl1'120.5 (8)
C11—C10—H10119.3C13'—C18'—C17'120.0
O4—C11—N1119.4 (3)C13'—C18'—H18'120.0
O4—C11—C10125.1 (3)C17'—C18'—H18'120.0
N1—C11—C10115.5 (2)C12—N1—C11122.8 (2)
C8—C12—N1121.5 (2)C12—N1—C13'118.3 (4)
C8—C12—H12119.3C11—N1—C13'118.9 (4)
N1—C12—H12119.3C12—N1—C13119.1 (9)
C18—C13—C14125.9 (12)C11—N1—C13118.0 (9)
C18—C13—N1118.1 (18)C2—O1—H1108 (3)
C14—C13—N1114.7 (18)C4—O2—H2104 (2)
C13—C14—C15116.8 (16)
C6—C1—C2—O1178.2 (3)C15—C16—C17—Cl1175 (2)
C6—C1—C2—C31.0 (4)C14—C13—C18—C175.7 (18)
O1—C2—C3—C4177.9 (2)N1—C13—C18—C17172.1 (17)
C1—C2—C3—C41.2 (4)C16—C17—C18—C134 (2)
C2—C3—C4—O2179.3 (2)Cl1—C17—C18—C13172.5 (17)
C2—C3—C4—C51.9 (4)C18'—C13'—C14'—C15'0.0
O2—C4—C5—C6179.0 (2)N1—C13'—C14'—C15'176.2 (8)
C3—C4—C5—C62.2 (4)C13'—C14'—C15'—C16'0.0
O2—C4—C5—C72.9 (4)C14'—C15'—C16'—C17'0.0
C3—C4—C5—C7178.4 (2)C15'—C16'—C17'—C18'0.0
C2—C1—C6—C51.4 (5)C15'—C16'—C17'—Cl1'179.7 (7)
C4—C5—C6—C12.0 (4)C14'—C13'—C18'—C17'0.0
C7—C5—C6—C1178.0 (3)N1—C13'—C18'—C17'176.0 (8)
C6—C5—C7—O3162.1 (3)C16'—C17'—C18'—C13'0.0
C4—C5—C7—O313.8 (4)Cl1'—C17'—C18'—C13'179.7 (7)
C6—C5—C7—C819.3 (4)C8—C12—N1—C110.6 (4)
C4—C5—C7—C8164.8 (2)C8—C12—N1—C13'176.6 (6)
O3—C7—C8—C12136.6 (3)C8—C12—N1—C13175.5 (12)
C5—C7—C8—C1242.0 (4)O4—C11—N1—C12178.0 (2)
O3—C7—C8—C936.4 (4)C10—C11—N1—C120.1 (4)
C5—C7—C8—C9145.0 (3)O4—C11—N1—C13'0.7 (6)
C12—C8—C9—C102.1 (4)C10—C11—N1—C13'177.3 (6)
C7—C8—C9—C10175.4 (2)O4—C11—N1—C131.8 (12)
C8—C9—C10—C112.9 (4)C10—C11—N1—C13176.2 (12)
C9—C10—C11—O4176.1 (3)C18'—C13'—N1—C1297.6 (6)
C9—C10—C11—N11.8 (4)C14'—C13'—N1—C1286.3 (6)
C9—C8—C12—N10.4 (4)C18'—C13'—N1—C1185.0 (6)
C7—C8—C12—N1173.4 (2)C14'—C13'—N1—C1191.0 (6)
C18—C13—C14—C154.8 (13)C18—C13—N1—C12114.9 (13)
N1—C13—C14—C15171.6 (15)C14—C13—N1—C1253.0 (14)
C13—C14—C15—C161.3 (16)C18—C13—N1—C1168.8 (15)
C14—C15—C16—C170 (3)C14—C13—N1—C11123.3 (10)
C15—C16—C17—C181 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O2—H2···O30.91 (4)1.75 (4)2.587 (3)152 (3)
O1—H1···O4i0.87 (5)1.79 (5)2.655 (3)175 (4)
C3—H3···O4i0.932.503.165 (3)129
C15—H15···O1ii0.932.713.37 (2)129
Symmetry codes: (i) x1, y1, z; (ii) x+1, y, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O2—H2···O30.91 (4)1.75 (4)2.587 (3)152 (3)
O1—H1···O4i0.87 (5)1.79 (5)2.655 (3)175 (4)
C3—H3···O4i0.932.503.165 (3)128.7
C15—H15···O1ii0.932.713.37 (2)129.2
Symmetry codes: (i) x1, y1, z; (ii) x+1, y, z+1.
Acknowledgements top

We are grateful to Attending Physician Tongqin Hao (The First Affiliated Hospital of Xinxiang Medical University, Henan, China) for the assistance with the antitumor assay.

references
References top

Bruker (2002). SMART, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.

Chen, H., Xie, F., Gong, J. & Hu, Y. (2011). J. Org. Chem. 70, 8495–8500.

Kim, D. & Hong, S. (2011). Org. Lett. 13, 4466–4469.

Kim, K. H., Kim, N. D. & Seong, B. L. (2010). Molecules, 15, 5878–5908.

Ravinder, M., Mahendar, B., Mattapally, S., Hamsini, K. V., Reddy, T. N., Rohit, C., Srinivas, K., Banerjee, S. K. & Rao, V. J. (2012). Bioorg. Med. Chem. Lett. 22, 6010–6015.

Sengupta, T., Gayen, K. S., Pandit, P. & Maiti, D. K. (2012). Chem. Eur. J. 18, 1905–1909.

Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.