Dimethyl 6-bromo-2-methyl-1,2-di­hydro­quinoline-2,4-dicarboxyl­ate

Gültekin, Z.; Bolte, M.; Hökelek, T.

doi:10.1107/S1600536812005600

organic compounds

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ISSN: 2056-9890

Volume 68| Part 3| March 2012| Pages o710-o711

doi:10.1107/S1600536812005600

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Dimethyl 6-bromo-2-methyl-1,2-dihydroquinoline-2,4-dicarboxylate

Zeynep Gültekin,^a Michael Bolte ^b and Tuncer Hökelek ^c ^*

^aDepartment of Chemistry, Çankırı Karatekin University, TR-18100, Çankırı, Turkey, ^bInstitut für Anorganische Chemie, J. W. Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, D-60438 Frankfurt/Main, Germany, and ^cDepartment of Physics, Hacettepe University, 06800 Beytepe, Ankara, Turkey
^*Correspondence e-mail: merzifon@hacettepe.edu.tr

(Received 6 February 2012; accepted 8 February 2012; online 17 February 2012)

In the title compound, C₁₄H₁₄BrNO₄, the dihydropyridine ring adopts a screw-boat conformation. In the crystal, pairs of N—H⋯O hydrogen bonds link the molecules into inversion R₂²(10) dimers.

Related literature

For the synthesis of 1,2-dihydroquinolines, see: Hu et al. (2011 ); Yadav et al. (2007 , 2008 ); Waldmann et al. (2008 ); Zhang & Ji (2011 ). For the biological activity of dihydroquinolines, see: Craig & Pearson (1971 ); Muren & Weissman (1971 ); Hamann et al. (1998 ); He et al. (2003 ); LaMontagne et al. (1989 ). For related structures, see: Gültekin et al. (2010 , 2011a ,b , 2012 ). For hydrogen-bond motifs, see: Bernstein et al. (1995 ). For ring-puckering parameters, see: Cremer & Pople (1975 ).

Experimental

Crystal data

C₁₄H₁₄BrNO₄
M_r = 340.16
Triclinic, $[P \overline 1]$
a = 7.8273 (9) Å
b = 10.4827 (11) Å
c = 10.5029 (12) Å
α = 115.837 (9)°
β = 105.655 (9)°
γ = 96.889 (8)°
V = 718.25 (17) Å³
Z = 2
Mo Kα radiation
μ = 2.87 mm⁻¹
T = 173 K
0.33 × 0.32 × 0.22 mm

Data collection

Stoe IPDS II two-circle diffractometer
Absorption correction: multi-scan (MULABS; Spek, 2009 ; Blessing, 1995 ) T_min = 0.451, T_max = 0.571
7423 measured reflections
2692 independent reflections
2267 reflections with I > 2σ(I)
R_int = 0.045

Refinement

R[F² > 2σ(F²)] = 0.053
wR(F²) = 0.153
S = 1.21
2692 reflections
189 parameters
1 restraint
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.96 e Å⁻³
Δρ_min = −0.46 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1⋯O1ⁱ	0.90 (8)	2.12 (8)	3.013 (6)	176 (7)
Symmetry code: (i) -x+1, -y, -z.

Data collection: X-AREA (Stoe & Cie, 2001 ); cell refinement: X-AREA; data reduction: X-RED32 (Stoe & Cie, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ); software used to prepare material for publication: WinGX (Farrugia, 1999 ) and PLATON (Spek, 2009).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536812005600/xu5465sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536812005600/xu5465Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536812005600/xu5465Isup3.cml

checkCIF report

Comment top

1,2-Dihydroquinoline derivatives have been considerably important for the preparation of biologically important compounds (Craig & Pearson, 1971; Muren & Weissman, 1971). Many methods have been reported in the literature for the preparation of 1,2-dihydroquinolines (Yadav et al., 2007, 2008). The most convenient method is the condensation of aromatic amines with ketones using a catalytic amount of a Lewis acid or Brønsted acid (Hu et al., 2011; Waldmann et al., 2008; Zhang & Ji, 2011). Dihydroquinolines are also powerful intermediates for the preparation of quinolines and many quinolines display biological effects (Hamann et al., 1998; LaMontagne et al., 1989; He et al., 2003).

The structures of some 1,2-dihydroquinoline derivatives, C₁₆H₁₉NO₄ (Gültekin et al., 2010), C₁₄H₁₅NO₄ (Gültekin et al., 2011a), C₁₇H₂₁NO₇ (Gültekin et al., 2011b) and C₁₆H₁₇NO₅ (Gültekin et al., 2012) have also been determined.

In the title compound, (I), (Fig. 1), the ring A (C2–C4/C9/C10/N1) is not planar, but adopting a screw-boat confromation with puckering parameters (Cremer & Pople, 1975) Q_T = 0.339 (5)Å, ϕ = -162.6(1.5)° and θ = 129.2(1.1)°.

In the crystal structure, intermolecular N—H···O hydrogen bonds (Table 1) link the molecules into centrosymmetric R₂²(10) dimers (Bernstein et al., 1995) (Fig. 2).

Related literature top

For the synthesis of 1,2-dihydroquinolines, see: Hu et al. (2011); Yadav et al. (2007, 2008); Waldmann et al. (2008); Zhang & Ji (2011). For the biological activity of dihydroquinolines, see: Craig & Pearson (1971); Muren & Weissman (1971); Hamann et al. (1998); He et al. (2003); LaMontagne et al. (1989). For related structures, see: Gültekin et al. (2010, 2011a,b, 2012). For hydrogen-bond motifs, see: Bernstein et al. (1995). For ring-puckering parameters, see: Cremer & Pople (1975).

Experimental top

The title compound was synthesized by the literature method (Waldmann et al., 2008). p-bromo aniline (100 mg, 1 eq) was dissolved in acetonitrile (1.5 ml), and then Bi(OTf)₃ (5 mol%, 0.05 eq) and methyl pyruvate (2.2 eq) were added to the mixture. The mixture was heated by microwave irradiation for 7 h until the starting material was completely consumed as monitored by TLC. The resultant residue was directly purified by flash chromatography on silica (EtOAc:Cylohexane 1:2). Recrystallization over pentane and ethyl acetate (70:30) gave a yellow crystalline solid (yield: 81%), R_f 0.5 (2:1 Cyclohexane/EtOAc) m.p. 379–381 K.

Computing details top

Data collection: X-AREA (Stoe & Cie, 2001); cell refinement: X-AREA (Stoe & Cie, 2001); data reduction: X-AREA (Stoe & Cie, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999) and PLATON (Spek, 2009).

Figures top

	Fig. 1. The molecular structure of the title compound with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. A partial packing diagram. Hydrogen bonds are shown as dashed lines.

Dimethyl 6-bromo-2-methyl-1,2-dihydroquinoline-2,4-dicarboxylate top

Crystal data top

C₁₄H₁₄BrNO₄	Z = 2
M_r = 340.16	F(000) = 344
Triclinic, P1	D_x = 1.573 Mg m⁻³
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 7.8273 (9) Å	Cell parameters from 6851 reflections
b = 10.4827 (11) Å	θ = 3.5–25.9°
c = 10.5029 (12) Å	µ = 2.87 mm⁻¹
α = 115.837 (9)°	T = 173 K
β = 105.655 (9)°	Block, yellow
γ = 96.889 (8)°	0.33 × 0.32 × 0.22 mm
V = 718.25 (17) Å³

Data collection top

Stoe IPDS II two-circle diffractometer	2692 independent reflections
Radiation source: fine-focus sealed tube	2267 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.045
ω scans	θ_max = 25.6°, θ_min = 3.5°
Absorption correction: multi-scan (MULABS; Spek, 2009; Blessing, 1995)	h = −9→9
T_min = 0.451, T_max = 0.571	k = −12→12
7423 measured reflections	l = −12→12

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.053	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.153	w = 1/[σ²(F_o²) + (0.0648P)² + 1.4243P] where P = (F_o² + 2F_c²)/3
S = 1.21	(Δ/σ)_max < 0.001
2692 reflections	Δρ_max = 0.96 e Å⁻³
189 parameters	Δρ_min = −0.46 e Å⁻³
1 restraint	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.038 (5)

Crystal data top

C₁₄H₁₄BrNO₄	γ = 96.889 (8)°
M_r = 340.16	V = 718.25 (17) Å³
Triclinic, P1	Z = 2
a = 7.8273 (9) Å	Mo Kα radiation
b = 10.4827 (11) Å	µ = 2.87 mm⁻¹
c = 10.5029 (12) Å	T = 173 K
α = 115.837 (9)°	0.33 × 0.32 × 0.22 mm
β = 105.655 (9)°

Data collection top

Stoe IPDS II two-circle diffractometer	2692 independent reflections
Absorption correction: multi-scan (MULABS; Spek, 2009; Blessing, 1995)	2267 reflections with I > 2σ(I)
T_min = 0.451, T_max = 0.571	R_int = 0.045
7423 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.053	1 restraint
wR(F²) = 0.153	H atoms treated by a mixture of independent and constrained refinement
S = 1.21	Δρ_max = 0.96 e Å⁻³
2692 reflections	Δρ_min = −0.46 e Å⁻³
189 parameters

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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

	x	y	z	U_iso*/U_eq
Br1	0.98733 (9)	0.36331 (7)	0.80285 (6)	0.0521 (3)
O1	0.3080 (4)	0.0758 (4)	0.0556 (4)	0.0340 (8)
O2	0.2146 (4)	0.2722 (4)	0.0660 (4)	0.0309 (7)
O3	0.7138 (6)	0.6908 (4)	0.6183 (4)	0.0453 (9)
O4	0.6368 (5)	0.7295 (4)	0.4208 (4)	0.0400 (8)
N1	0.6748 (5)	0.2278 (4)	0.1501 (4)	0.0280 (8)
H1	0.678 (13)	0.138 (5)	0.085 (9)	0.11 (3)*
C2	0.5298 (6)	0.2890 (5)	0.1017 (5)	0.0262 (9)
C3	0.5671 (6)	0.4450 (5)	0.2227 (5)	0.0256 (9)
H3	0.5245	0.5116	0.1950	0.031*
C4	0.6599 (6)	0.4919 (5)	0.3699 (5)	0.0249 (9)
C5	0.8118 (6)	0.4208 (5)	0.5664 (5)	0.0308 (10)
H5	0.8093	0.5073	0.6451	0.037*
C6	0.8886 (6)	0.3213 (6)	0.5976 (5)	0.0326 (10)
C7	0.8965 (7)	0.1930 (6)	0.4853 (6)	0.0368 (11)
H7	0.9516	0.1288	0.5096	0.044*
C8	0.8212 (6)	0.1596 (5)	0.3345 (5)	0.0305 (10)
H8	0.8243	0.0720	0.2577	0.037*
C9	0.7412 (5)	0.2573 (5)	0.2986 (5)	0.0239 (9)
C10	0.7378 (6)	0.3919 (5)	0.4170 (5)	0.0237 (9)
C11	0.5237 (7)	0.2779 (6)	−0.0504 (5)	0.0374 (11)
H11A	0.5022	0.1767	−0.1236	0.056*
H11B	0.6393	0.3348	−0.0369	0.056*
H11C	0.4260	0.3153	−0.0856	0.056*
C12	0.3391 (6)	0.1982 (5)	0.0735 (5)	0.0250 (9)
C13	0.0293 (6)	0.1986 (6)	0.0410 (6)	0.0375 (11)
H13A	−0.0441	0.2672	0.0560	0.056*
H13B	0.0354	0.1623	0.1113	0.056*
H13C	−0.0256	0.1177	−0.0608	0.056*
C14	0.6766 (6)	0.6451 (5)	0.4849 (5)	0.0296 (10)
C15	0.6353 (10)	0.8756 (7)	0.5235 (8)	0.0572 (16)
H15A	0.6072	0.9287	0.4692	0.086*
H15B	0.7543	0.9266	0.6029	0.086*
H15C	0.5434	0.8686	0.5668	0.086*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Br1	0.0640 (4)	0.0637 (5)	0.0362 (3)	0.0183 (3)	0.0110 (3)	0.0345 (3)
O1	0.0334 (17)	0.0248 (17)	0.0434 (19)	0.0079 (14)	0.0182 (14)	0.0139 (15)
O2	0.0225 (15)	0.0373 (18)	0.0417 (18)	0.0120 (13)	0.0114 (13)	0.0257 (15)
O3	0.060 (2)	0.035 (2)	0.0338 (19)	0.0175 (18)	0.0171 (17)	0.0102 (16)
O4	0.054 (2)	0.0290 (18)	0.050 (2)	0.0216 (16)	0.0250 (18)	0.0240 (16)
N1	0.0270 (19)	0.032 (2)	0.0267 (18)	0.0135 (16)	0.0107 (15)	0.0142 (17)
C2	0.024 (2)	0.033 (2)	0.026 (2)	0.0108 (18)	0.0100 (17)	0.0169 (19)
C3	0.022 (2)	0.029 (2)	0.033 (2)	0.0087 (17)	0.0116 (17)	0.0196 (19)
C4	0.024 (2)	0.027 (2)	0.031 (2)	0.0083 (17)	0.0130 (17)	0.0186 (19)
C5	0.033 (2)	0.034 (3)	0.029 (2)	0.010 (2)	0.0124 (18)	0.018 (2)
C6	0.033 (2)	0.041 (3)	0.031 (2)	0.009 (2)	0.0105 (19)	0.025 (2)
C7	0.032 (2)	0.046 (3)	0.048 (3)	0.016 (2)	0.015 (2)	0.035 (3)
C8	0.029 (2)	0.030 (2)	0.036 (2)	0.0144 (19)	0.0129 (19)	0.016 (2)
C9	0.0187 (19)	0.030 (2)	0.029 (2)	0.0077 (17)	0.0115 (16)	0.0171 (18)
C10	0.023 (2)	0.025 (2)	0.028 (2)	0.0072 (17)	0.0108 (16)	0.0157 (18)
C11	0.037 (3)	0.050 (3)	0.032 (2)	0.014 (2)	0.015 (2)	0.024 (2)
C12	0.025 (2)	0.030 (2)	0.0205 (19)	0.0074 (18)	0.0099 (16)	0.0120 (17)
C13	0.022 (2)	0.047 (3)	0.050 (3)	0.007 (2)	0.011 (2)	0.030 (3)
C14	0.026 (2)	0.030 (2)	0.038 (3)	0.0093 (18)	0.0155 (19)	0.019 (2)
C15	0.073 (4)	0.034 (3)	0.079 (4)	0.031 (3)	0.040 (4)	0.029 (3)

Geometric parameters (Å, º) top

Br1—C6	1.905 (5)	C8—H8	0.9300
O2—C13	1.455 (5)	C9—C8	1.395 (6)
O4—C15	1.442 (7)	C10—C5	1.393 (6)
N1—C2	1.452 (6)	C10—C9	1.427 (6)
N1—C9	1.380 (6)	C11—H11A	0.9600
N1—H1	0.899 (10)	C11—H11B	0.9600
C2—C3	1.499 (6)	C11—H11C	0.9600
C2—C11	1.537 (6)	C12—O1	1.197 (6)
C2—C12	1.548 (6)	C12—O2	1.322 (5)
C3—C4	1.344 (6)	C13—H13A	0.9600
C3—H3	0.9300	C13—H13B	0.9600
C4—C10	1.469 (6)	C13—H13C	0.9600
C4—C14	1.493 (6)	C14—O3	1.200 (6)
C5—H5	0.9300	C14—O4	1.344 (6)
C6—C5	1.378 (7)	C15—H15A	0.9600
C7—C6	1.371 (8)	C15—H15B	0.9600
C7—H7	0.9300	C15—H15C	0.9600
C8—C7	1.393 (7)

C12—O2—C13	116.0 (4)	N1—C9—C10	120.0 (4)
C14—O4—C15	114.8 (4)	C8—C9—C10	119.7 (4)
C2—N1—H1	119 (6)	C5—C10—C4	125.1 (4)
C9—N1—C2	120.0 (4)	C5—C10—C9	118.7 (4)
C9—N1—H1	112 (6)	C9—C10—C4	116.2 (4)
N1—C2—C3	109.0 (3)	C2—C11—H11A	109.5
N1—C2—C11	108.4 (4)	C2—C11—H11B	109.5
N1—C2—C12	110.7 (4)	C2—C11—H11C	109.5
C3—C2—C11	112.4 (4)	H11A—C11—H11B	109.5
C3—C2—C12	109.3 (4)	H11A—C11—H11C	109.5
C11—C2—C12	107.0 (3)	H11B—C11—H11C	109.5
C2—C3—H3	118.8	O1—C12—O2	124.9 (4)
C4—C3—C2	122.3 (4)	O1—C12—C2	124.3 (4)
C4—C3—H3	118.8	O2—C12—C2	110.7 (4)
C3—C4—C10	120.3 (4)	O2—C13—H13A	109.5
C3—C4—C14	119.0 (4)	O2—C13—H13B	109.5
C10—C4—C14	120.7 (4)	O2—C13—H13C	109.5
C6—C5—C10	120.0 (4)	H13A—C13—H13B	109.5
C6—C5—H5	120.0	H13A—C13—H13C	109.5
C10—C5—H5	120.0	H13B—C13—H13C	109.5
C5—C6—Br1	119.1 (4)	O3—C14—O4	121.9 (5)
C7—C6—Br1	119.0 (4)	O3—C14—C4	126.2 (4)
C7—C6—C5	122.0 (4)	O4—C14—C4	111.8 (4)
C6—C7—C8	119.5 (4)	O4—C15—H15A	109.5
C6—C7—H7	120.2	O4—C15—H15B	109.5
C8—C7—H7	120.2	O4—C15—H15C	109.5
C7—C8—C9	120.1 (4)	H15A—C15—H15B	109.5
C7—C8—H8	120.0	H15A—C15—H15C	109.5
C9—C8—H8	120.0	H15B—C15—H15C	109.5
N1—C9—C8	120.1 (4)

C9—N1—C2—C3	40.9 (5)	C3—C4—C14—O4	−16.6 (6)
C9—N1—C2—C11	163.5 (4)	C10—C4—C14—O3	−17.1 (7)
C9—N1—C2—C12	−79.4 (5)	C10—C4—C14—O4	165.6 (4)
C2—N1—C9—C8	154.6 (4)	Br1—C6—C5—C10	−179.6 (3)
C2—N1—C9—C10	−29.0 (6)	C7—C6—C5—C10	0.5 (7)
N1—C2—C3—C4	−28.2 (6)	C8—C7—C6—Br1	178.6 (4)
C11—C2—C3—C4	−148.4 (4)	C8—C7—C6—C5	−1.5 (7)
C12—C2—C3—C4	92.9 (5)	C9—C8—C7—C6	1.0 (7)
N1—C2—C12—O1	−17.8 (6)	N1—C9—C8—C7	176.8 (4)
N1—C2—C12—O2	164.7 (3)	C10—C9—C8—C7	0.4 (7)
C3—C2—C12—O1	−137.9 (4)	C4—C10—C5—C6	−177.1 (4)
C3—C2—C12—O2	44.6 (4)	C9—C10—C5—C6	0.9 (6)
C11—C2—C12—O1	100.1 (5)	C4—C10—C9—N1	0.4 (6)
C11—C2—C12—O2	−77.4 (4)	C4—C10—C9—C8	176.9 (4)
C2—C3—C4—C10	3.3 (6)	C5—C10—C9—N1	−177.8 (4)
C2—C3—C4—C14	−174.5 (4)	C5—C10—C9—C8	−1.3 (6)
C3—C4—C10—C5	−169.9 (4)	O1—C12—O2—C13	3.0 (6)
C3—C4—C10—C9	12.0 (6)	C2—C12—O2—C13	−179.5 (4)
C14—C4—C10—C5	7.9 (7)	O3—C14—O4—C15	−2.4 (7)
C14—C4—C10—C9	−170.2 (4)	C4—C14—O4—C15	175.1 (4)
C3—C4—C14—O3	160.7 (5)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1ⁱ	0.90 (8)	2.12 (8)	3.013 (6)	176 (7)

Symmetry code: (i) −x+1, −y, −z.

Experimental details

Crystal data
Chemical formula	C₁₄H₁₄BrNO₄
M_r	340.16
Crystal system, space group	Triclinic, P1
Temperature (K)	173
a, b, c (Å)	7.8273 (9), 10.4827 (11), 10.5029 (12)
α, β, γ (°)	115.837 (9), 105.655 (9), 96.889 (8)
V (Å³)	718.25 (17)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	2.87
Crystal size (mm)	0.33 × 0.32 × 0.22

Data collection
Diffractometer	Stoe IPDS II two-circle diffractometer
Absorption correction	Multi-scan (MULABS; Spek, 2009; Blessing, 1995)
T_min, T_max	0.451, 0.571
No. of measured, independent and observed [I > 2σ(I)] reflections	7423, 2692, 2267
R_int	0.045
(sin θ/λ)_max (Å⁻¹)	0.608

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.053, 0.153, 1.21
No. of reflections	2692
No. of parameters	189
No. of restraints	1
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.96, −0.46

Computer programs: X-AREA (Stoe & Cie, 2001), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 1997), WinGX (Farrugia, 1999) and PLATON (Spek, 2009).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1ⁱ	0.90 (8)	2.12 (8)	3.013 (6)	176 (7)

Symmetry code: (i) −x+1, −y, −z.

Acknowledgements

The title compound was synthesized at RWTH Aachen University. The authors thank Professor Magnus Rueping of RWTH Aachen University, Germany, for helpful discussions.

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