supplementary materials


lh5613 scheme

Acta Cryst. (2013). E69, o924-o925    [ doi:10.1107/S1600536813012889 ]

3,4-Bis[1-(prop-2-ynyl)-1H-indol-3-yl]-1H-pyrrole-2,5-dione

M.-H. Huang, Y.-C. Gao, F.-L. Yang and Y.-J. Luo

Abstract top

In the title molecule, C26H17N3O2, both indole ring systems are essentially planar, with maximum deviations of 0.019 (2) and 0.033 (1) Å for the N atoms, and form dihedral angles of 34.40 (9) and 45.06 (8)° with the essentially planar pyrrole ring [maximum deviation = 0.020 (2) Å]. The dihedral angle between the two indole ring systems is 58.78 (6)°. In the crystal, molecules are connected by pairs of N-H...O hydrogen bonds, forming inversion dimers and generating R22(8) rings. Weak [pi]-[pi] stacking interactions, with a centroid-centroid distance of 3.983 (2) Å, are also observed.

Comment top

Bisindolylmaleimides are important in medicinal chemistry (Bulbule et al., 2008; Wang et al., 2012) and in the field of materials science (Chiu et al., 2003; Kaletas et al., 2005; Lin et al., 2010; Nakazono et al., 2007; Yeh et al., 2006). Bisindolylmaleimides have been isolated from natural products (Kamata et al., 2006). The synthesis of bisindolylmaleimides (Prateeptongkum et al., 2010) and an example of a related crystal structure (Huang et al., 2012) have been reported.

The molecular structure of the title compound is shown in Fig. 1. Both indole ring systems are essentially planar with maximum deviations of 0.019 (2)Å for N3 and 0.033 (1)Å for N2 and these ring systems form dihedral angles of 34.40 (9)Å [N3/C16-C23] and 45.06 (8)Å [N2/C5-C12] with the essentially planar pyrrole ring [N1/C1-C4] (maximum deviation 0.020 (2)Å for C1). The dihedral angle between the two indole ring systems is 58.78 (6)°. In the crystal, molecules are connected by pairs of N—H···O hydrogen bonds to form inversion dimers (Fig. 2) generating R22(8) rings (Bernstein et al., 1995). Weak ππ stacking interactions, with a Cg···Cg(2-x, 1-y, -z) distance of 3.983 (2)Å, are also observed [Cg is the centroid of the C18-C23 ring].

Related literature top

For the importance of bisindolylmaleimides in medicinal chemistry, see: Bulbule et al. (2008); Wang et al. (2012) and in materials science, see: Chiu et al. (2003); Kaletas et al. (2005); Lin et al. (2010); Nakazono et al. (2007); Yeh et al. (2006). For the isolation of bisindolylmaleimides from natural products, see: Kamata et al. (2006). For the synthesis of bisindolylmaleimides, see: Prateeptongkum et al. (2010). For a related crystal structure, see: Huang et al. (2012). For hydrogen-bond graph-set motifs, see: Bernstein et al. (1995).

Experimental top

The title compound was prepared by N-alkylation of 3, 4-di(1H-indol-3-yl)-1H-pyrrole-2,5-dione by propargyl bromide with the aid of NaH freshly distilled THF under N2 atmosphere. The reaction was initiated at 273K for 5 h. The reaction was quenched with sat. NH4Cl at 273K, extracted with EtOAc, dried over anhydrous Na2SO4 and concentrated in vacuo. The residue was purified by f.c.c.(silica gel, eluted with 14% EtOAc in Petroleum Ether) to give the title compound in a yield of 83%, which provided the sample suitable for X-ray analysis after natural evaporation of solvents.

Refinement top

All H atoms were palced in calculated positions with C—H = 0.95Å (aromatic and acetylene hydrogens), 0.99Å (methylene) and N—H = 0.88 Å. They were refined in a riding-model approximation with Uiso(H) = 1.2Ueq(C,N).

Computing details top

Data collection: SMART (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level.
[Figure 2] Fig. 2. A portion of the crystal packing viewed approximately along the a axis. The dashed lines indicate N—H···O hydrogen bonds.
3,4-Bis[1-(prop-2-ynyl)-1H-indol-3-yl]-1H-pyrrole-2,5-dione top
Crystal data top
C26H17N3O2V = 999.9 (3) Å3
Mr = 403.43Z = 2
Triclinic, P1F(000) = 420
Hall symbol: -P 1Dx = 1.340 Mg m3
a = 8.8015 (14) ÅMo Kα radiation, λ = 0.71073 Å
b = 11.2619 (14) Åθ = 1.5–51.8°
c = 11.838 (3) ŵ = 0.09 mm1
α = 62.860 (17)°T = 102 K
β = 73.625 (16)°Block, colorless
γ = 79.593 (12)°0.11 × 0.10 × 0.07 mm
Data collection top
Bruker SMART CCD
diffractometer
3920 independent reflections
Radiation source: fine-focus sealed tube3113 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.024
φ and ω scansθmax = 26.0°, θmin = 3.3°
Absorption correction: multi-scan
(SADABS; Bruker, 2002)
h = 109
Tmin = 0.991, Tmax = 0.994k = 1313
6379 measured reflectionsl = 1114
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)] = 0.049Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.114H-atom parameters constrained
S = 1.03 w = 1/[σ2(Fo2) + (0.0438P)2 + 0.3377P]
where P = (Fo2 + 2Fc2)/3
3920 reflections(Δ/σ)max < 0.001
280 parametersΔρmax = 0.37 e Å3
0 restraintsΔρmin = 0.23 e Å3
Crystal data top
C26H17N3O2γ = 79.593 (12)°
Mr = 403.43V = 999.9 (3) Å3
Triclinic, P1Z = 2
a = 8.8015 (14) ÅMo Kα radiation
b = 11.2619 (14) ŵ = 0.09 mm1
c = 11.838 (3) ÅT = 102 K
α = 62.860 (17)°0.11 × 0.10 × 0.07 mm
β = 73.625 (16)°
Data collection top
Bruker SMART CCD
diffractometer
3920 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2002)
3113 reflections with I > 2σ(I)
Tmin = 0.991, Tmax = 0.994Rint = 0.024
6379 measured reflectionsθmax = 26.0°
Refinement top
R[F2 > 2σ(F2)] = 0.049H-atom parameters constrained
wR(F2) = 0.114Δρmax = 0.37 e Å3
S = 1.03Δρmin = 0.23 e Å3
3920 reflectionsAbsolute structure: ?
280 parametersFlack parameter: ?
0 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*/Ueq
O20.33248 (15)0.75325 (12)0.29355 (12)0.0242 (3)
O10.11940 (15)0.34749 (12)0.48806 (13)0.0248 (3)
C120.7380 (2)0.27334 (17)0.39074 (16)0.0203 (4)
H120.72780.35310.40170.024*
C200.8983 (2)0.62081 (19)0.09736 (18)0.0259 (4)
H200.97900.68190.15020.031*
C190.7956 (2)0.62914 (17)0.01340 (17)0.0200 (4)
N20.48798 (18)0.09433 (14)0.33954 (14)0.0202 (3)
C180.6728 (2)0.54223 (17)0.09277 (17)0.0185 (4)
C230.6555 (2)0.44154 (18)0.05835 (18)0.0239 (4)
H230.57410.38070.10930.029*
N30.79109 (19)0.71857 (15)0.06452 (15)0.0253 (4)
C170.5904 (2)0.58517 (17)0.19368 (17)0.0205 (4)
C70.6120 (2)0.23464 (17)0.36673 (16)0.0180 (4)
C90.7717 (2)0.03492 (18)0.35768 (18)0.0245 (4)
H90.78340.04430.34560.029*
C140.5187 (2)0.04567 (18)0.15627 (19)0.0250 (4)
C160.6670 (2)0.69296 (18)0.17015 (19)0.0260 (4)
H160.63750.74270.22060.031*
C130.4647 (2)0.00393 (18)0.29867 (18)0.0247 (4)
H13A0.35080.02180.32550.030*
H13B0.52490.08890.34180.030*
C80.6308 (2)0.11411 (17)0.35377 (16)0.0194 (4)
C40.3246 (2)0.63429 (17)0.32913 (17)0.0201 (4)
C220.7586 (2)0.4323 (2)0.05068 (19)0.0287 (5)
H220.74750.36430.07370.034*
C110.8770 (2)0.19342 (19)0.39814 (17)0.0250 (4)
H110.96240.21790.41580.030*
C50.3823 (2)0.19972 (17)0.34038 (17)0.0201 (4)
H50.27630.20980.33120.024*
N10.19290 (18)0.56262 (14)0.41135 (15)0.0228 (4)
H10.10590.59570.44840.027*
C100.8942 (2)0.07670 (19)0.37999 (18)0.0271 (4)
H100.99230.02510.38310.033*
C20.3827 (2)0.41642 (17)0.35429 (17)0.0178 (4)
C150.5634 (3)0.09309 (19)0.0417 (2)0.0320 (5)
H150.59930.13130.05050.038*
C60.4527 (2)0.28858 (17)0.35655 (16)0.0181 (4)
C30.4463 (2)0.53771 (17)0.29249 (17)0.0189 (4)
C210.8777 (2)0.5207 (2)0.12664 (18)0.0291 (5)
H210.94660.51180.20060.035*
C250.9581 (2)0.83373 (18)0.1088 (2)0.0277 (5)
C10.2178 (2)0.43211 (17)0.42665 (17)0.0198 (4)
C240.8937 (3)0.8296 (2)0.0096 (2)0.0328 (5)
H24A0.83220.91480.03060.039*
H24B0.98220.82040.05980.039*
C261.0093 (3)0.83789 (19)0.1887 (2)0.0344 (5)
H261.05060.84130.25310.041*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O20.0229 (8)0.0190 (7)0.0286 (7)0.0038 (5)0.0003 (6)0.0108 (6)
O10.0188 (7)0.0217 (7)0.0301 (7)0.0056 (5)0.0049 (6)0.0124 (6)
C120.0228 (10)0.0222 (9)0.0144 (8)0.0046 (7)0.0031 (7)0.0062 (8)
C200.0177 (10)0.0301 (11)0.0183 (9)0.0005 (8)0.0007 (8)0.0027 (9)
C190.0159 (10)0.0201 (9)0.0194 (9)0.0026 (7)0.0061 (7)0.0046 (8)
N20.0214 (9)0.0190 (8)0.0198 (8)0.0028 (6)0.0025 (6)0.0088 (7)
C180.0136 (9)0.0201 (9)0.0162 (9)0.0001 (7)0.0044 (7)0.0029 (8)
C230.0204 (10)0.0291 (10)0.0203 (9)0.0001 (8)0.0058 (8)0.0088 (8)
N30.0210 (9)0.0246 (9)0.0238 (8)0.0074 (6)0.0013 (7)0.0065 (7)
C170.0157 (10)0.0184 (9)0.0221 (9)0.0007 (7)0.0010 (7)0.0064 (8)
C70.0184 (10)0.0197 (9)0.0114 (8)0.0020 (7)0.0003 (7)0.0043 (7)
C90.0269 (11)0.0213 (10)0.0193 (9)0.0018 (8)0.0027 (8)0.0063 (8)
C140.0304 (11)0.0198 (10)0.0279 (11)0.0038 (8)0.0065 (9)0.0120 (9)
C160.0244 (11)0.0236 (10)0.0263 (10)0.0048 (8)0.0023 (8)0.0110 (9)
C130.0310 (12)0.0204 (10)0.0247 (10)0.0053 (8)0.0044 (9)0.0110 (8)
C80.0213 (10)0.0196 (9)0.0138 (8)0.0031 (7)0.0021 (7)0.0045 (7)
C40.0183 (10)0.0212 (10)0.0195 (9)0.0049 (7)0.0012 (7)0.0082 (8)
C220.0279 (12)0.0329 (11)0.0241 (10)0.0027 (8)0.0087 (9)0.0112 (9)
C110.0198 (10)0.0327 (11)0.0170 (9)0.0050 (8)0.0048 (8)0.0043 (8)
C50.0166 (10)0.0211 (9)0.0187 (9)0.0035 (7)0.0005 (7)0.0070 (8)
N10.0174 (8)0.0203 (8)0.0274 (8)0.0028 (6)0.0058 (7)0.0133 (7)
C100.0211 (11)0.0293 (11)0.0211 (10)0.0048 (8)0.0042 (8)0.0052 (9)
C20.0149 (9)0.0219 (9)0.0171 (9)0.0024 (7)0.0017 (7)0.0093 (8)
C150.0466 (14)0.0262 (11)0.0252 (11)0.0083 (9)0.0066 (10)0.0114 (9)
C60.0178 (10)0.0188 (9)0.0147 (8)0.0031 (7)0.0013 (7)0.0069 (7)
C30.0172 (10)0.0205 (9)0.0185 (9)0.0009 (7)0.0015 (7)0.0094 (8)
C210.0249 (11)0.0393 (12)0.0197 (10)0.0076 (9)0.0048 (8)0.0135 (9)
C250.0206 (11)0.0220 (10)0.0340 (11)0.0060 (8)0.0004 (9)0.0088 (9)
C10.0190 (10)0.0199 (9)0.0201 (9)0.0036 (7)0.0004 (8)0.0099 (8)
C240.0291 (12)0.0299 (11)0.0305 (11)0.0137 (9)0.0008 (9)0.0055 (9)
C260.0323 (13)0.0262 (11)0.0406 (13)0.0017 (9)0.0068 (10)0.0118 (10)
Geometric parameters (Å, º) top
O2—C41.216 (2)C14—C151.180 (3)
O1—C11.224 (2)C14—C131.471 (3)
C12—C111.380 (3)C16—H160.9500
C12—C71.402 (2)C13—H13A0.9900
C12—H120.9500C13—H13B0.9900
C20—C211.375 (3)C4—N11.388 (2)
C20—C191.399 (3)C4—C31.506 (2)
C20—H200.9500C22—C211.388 (3)
C19—N31.382 (2)C22—H220.9500
C19—C181.407 (2)C11—C101.402 (3)
N2—C51.371 (2)C11—H110.9500
N2—C81.383 (2)C5—C61.374 (2)
N2—C131.459 (2)C5—H50.9500
C18—C231.412 (3)N1—C11.380 (2)
C18—C171.449 (3)N1—H10.8800
C23—C221.389 (3)C10—H100.9500
C23—H230.9500C2—C31.359 (2)
N3—C161.362 (2)C2—C61.451 (2)
N3—C241.462 (2)C2—C11.489 (2)
C17—C161.374 (2)C15—H150.9500
C17—C31.449 (2)C21—H210.9500
C7—C81.410 (2)C25—C261.178 (3)
C7—C61.439 (2)C25—C241.463 (3)
C9—C101.382 (3)C24—H24A0.9900
C9—C81.390 (3)C24—H24B0.9900
C9—H90.9500C26—H260.9500
C11—C12—C7118.76 (17)O2—C4—N1124.49 (17)
C11—C12—H12120.6O2—C4—C3128.73 (16)
C7—C12—H12120.6N1—C4—C3106.75 (14)
C21—C20—C19117.34 (18)C21—C22—C23121.13 (19)
C21—C20—H20121.3C21—C22—H22119.4
C19—C20—H20121.3C23—C22—H22119.4
N3—C19—C20129.06 (17)C12—C11—C10121.12 (18)
N3—C19—C18107.88 (16)C12—C11—H11119.4
C20—C19—C18123.06 (17)C10—C11—H11119.4
C5—N2—C8109.07 (14)N2—C5—C6109.78 (16)
C5—N2—C13124.26 (16)N2—C5—H5125.1
C8—N2—C13125.14 (15)C6—C5—H5125.1
C19—C18—C23117.57 (16)C1—N1—C4110.35 (15)
C19—C18—C17106.66 (15)C1—N1—H1124.8
C23—C18—C17135.75 (17)C4—N1—H1124.8
C22—C23—C18119.34 (18)C9—C10—C11121.56 (18)
C22—C23—H23120.3C9—C10—H10119.2
C18—C23—H23120.3C11—C10—H10119.2
C16—N3—C19108.84 (15)C3—C2—C6129.71 (17)
C16—N3—C24124.81 (16)C3—C2—C1108.11 (15)
C19—N3—C24126.19 (16)C6—C2—C1122.18 (15)
C16—C17—C18106.03 (16)C14—C15—H15180.0
C16—C17—C3124.76 (17)C5—C6—C7106.70 (15)
C18—C17—C3128.89 (16)C5—C6—C2126.26 (17)
C12—C7—C8118.80 (17)C7—C6—C2126.90 (15)
C12—C7—C6134.27 (16)C2—C3—C17131.66 (16)
C8—C7—C6106.86 (15)C2—C3—C4107.35 (15)
C10—C9—C8116.94 (17)C17—C3—C4120.44 (15)
C10—C9—H9121.5C20—C21—C22121.54 (19)
C8—C9—H9121.5C20—C21—H21119.2
C15—C14—C13175.8 (2)C22—C21—H21119.2
N3—C16—C17110.56 (17)C26—C25—C24179.5 (2)
N3—C16—H16124.7O1—C1—N1125.03 (17)
C17—C16—H16124.7O1—C1—C2127.66 (16)
N2—C13—C14110.29 (15)N1—C1—C2107.30 (14)
N2—C13—H13A109.6N3—C24—C25111.76 (16)
C14—C13—H13A109.6N3—C24—H24A109.3
N2—C13—H13B109.6C25—C24—H24A109.3
C14—C13—H13B109.6N3—C24—H24B109.3
H13A—C13—H13B108.1C25—C24—H24B109.3
N2—C8—C9129.68 (17)H24A—C24—H24B107.9
N2—C8—C7107.57 (16)C25—C26—H26180.0
C9—C8—C7122.74 (17)
C21—C20—C19—N3179.63 (18)C13—N2—C5—C6167.15 (15)
C21—C20—C19—C181.3 (3)O2—C4—N1—C1176.33 (18)
N3—C19—C18—C23179.89 (15)C3—C4—N1—C11.9 (2)
C20—C19—C18—C230.8 (3)C8—C9—C10—C110.1 (3)
N3—C19—C18—C171.25 (19)C12—C11—C10—C91.8 (3)
C20—C19—C18—C17178.03 (16)N2—C5—C6—C70.17 (19)
C19—C18—C23—C220.0 (3)N2—C5—C6—C2175.86 (16)
C17—C18—C23—C22178.43 (19)C12—C7—C6—C5175.92 (18)
C20—C19—N3—C16177.35 (18)C8—C7—C6—C50.94 (19)
C18—C19—N3—C161.9 (2)C12—C7—C6—C28.1 (3)
C20—C19—N3—C241.8 (3)C8—C7—C6—C2175.05 (16)
C18—C19—N3—C24177.39 (17)C3—C2—C6—C5134.3 (2)
C19—C18—C17—C160.2 (2)C1—C2—C6—C546.1 (3)
C23—C18—C17—C16178.7 (2)C3—C2—C6—C740.9 (3)
C19—C18—C17—C3173.55 (18)C1—C2—C6—C7138.68 (18)
C23—C18—C17—C35.0 (3)C6—C2—C3—C1711.6 (3)
C11—C12—C7—C81.3 (2)C1—C2—C3—C17168.76 (19)
C11—C12—C7—C6177.89 (18)C6—C2—C3—C4177.07 (17)
C19—N3—C16—C171.8 (2)C1—C2—C3—C42.5 (2)
C24—N3—C16—C17177.39 (17)C16—C17—C3—C2157.5 (2)
C18—C17—C16—N31.0 (2)C18—C17—C3—C229.8 (3)
C3—C17—C16—N3175.05 (17)C16—C17—C3—C432.1 (3)
C5—N2—C13—C1484.9 (2)C18—C17—C3—C4140.54 (18)
C8—N2—C13—C1479.4 (2)O2—C4—C3—C2178.66 (18)
C5—N2—C8—C9179.60 (18)N1—C4—C3—C20.5 (2)
C13—N2—C8—C913.3 (3)O2—C4—C3—C176.2 (3)
C5—N2—C8—C71.29 (19)N1—C4—C3—C17171.94 (16)
C13—N2—C8—C7167.59 (15)C19—C20—C21—C220.9 (3)
C10—C9—C8—N2176.65 (17)C23—C22—C21—C200.1 (3)
C10—C9—C8—C72.4 (3)C4—N1—C1—O1175.96 (18)
C12—C7—C8—N2176.07 (15)C4—N1—C1—C23.4 (2)
C6—C7—C8—N21.36 (19)C3—C2—C1—O1175.62 (18)
C12—C7—C8—C93.1 (3)C6—C2—C1—O14.7 (3)
C6—C7—C8—C9179.45 (16)C3—C2—C1—N13.8 (2)
C18—C23—C22—C210.3 (3)C6—C2—C1—N1175.90 (16)
C7—C12—C11—C101.1 (3)C16—N3—C24—C2552.3 (3)
C8—N2—C5—C60.7 (2)C19—N3—C24—C25132.89 (19)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O1i0.882.012.872 (2)165
Symmetry code: (i) x, y+1, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O1i0.882.012.872 (2)165.4
Symmetry code: (i) x, y+1, z+1.
Acknowledgements top

The authors wish to thank the Natural Science Foundation of China (No. 21202008) for generous support.

references
References top

Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. 34, 1555–1573.

Brandenburg, K. (2006). DIAMOND. Crystal Impact, Bonn, Germany.

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

Bruker (2007). SMART and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.

Bulbule, V. J., Rivas, K., Verlinde, C. L. M. J., Van Voorhis, W. C. & Gelb, M. H. (2008). J. Med. Chem. 51, 384–387.

Chiu, C.-W., Chow, T.-J., Chuen, C.-H., Lin, H.-M. & Tao, Y.-T. (2003). Chem. Mater. 15, 4527–4532.

Huang, L., Li, Y., Gao, D. & Du, Z. (2012). Acta Cryst. E68, o1328.

Kaletas, B. K., Kozhevnikov, V. N., Zimine, M., Williams, R. M., Koenig, B. & De Cola, L. (2005). Eur. J. Org. Chem. pp. 3443–3449.

Kamata, K., Suetsugu, T., Yamamoto, Y., Hayashi, M., Komiyama, K. & Ishibashi, M. (2006). J. Nat. Prod. 69, 1252–1254.

Lin, Z., Lin, Y.-D., Wu, C.-Y., Chow, P.-T., Sun, C.-H. & Chow, T. J. (2010). Macromolecules, 43, 5925–5931.

Nakazono, M., Nanbu, S., Uesaki, A., Kuwano, R., Kashiwabara, M. & Zaitsu, K. (2007). Org. Lett. 9, 3583–3586.

Prateeptongkum, S., Driller, K. M., Jackstell, R., Spannenberg, A. & Beller, M. (2010). Chem. Eur. J. 16, 9606–9615.

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

Spek, A. L. (2009). Acta Cryst. D65, 148–155.

Wang, K., Yan, Z., Wang, N. & Liu, Z. Z. (2012). Chin. Chem. Lett. 23, 462–465.

Yeh, T.-S., Chow, T. J., Tsai, S.-H., Chiu, C.-W. & Zhao, C.-X. (2006). Chem. Mater. 18, 832–839.