Crystal structure of 22,24,25-trimethyl-8,11,14-trioxa-25-aza­tetra­cyclo­[19.3.1.02,7.015,20]penta­cosa-2,4,6,15(20),16,18-hexaen-23-one

Nguyen, V.T.; Truong, H.H.; Le, T.A.; Soldatenkov, A.T.; Thi, T.A.D.; Tran, T.T.V.; Esina, N.Y.; Khrustalev, V.N.

doi:10.1107/S2056989016020508

research communications

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 73| Part 2| February 2017| Pages 118-121

https://doi.org/10.1107/S2056989016020508

Open

access

Crystal structure of 22,24,25-trimethyl-8,11,14-trioxa-25-azatetracyclo[19.3.1.0^2,7.0^15,20]pentacosa-2,4,6,15(20),16,18-hexaen-23-one

Van Tuyen Nguyen,^a,^b ^* Hong Hieu Truong,^c Tuan Anh Le,^d Anatoly T. Soldatenkov,^e Tuyet Anh Dang Thi,^a Thi Thanh Van Tran,^d Natalia Ya. Esina ^f and Victor N. Khrustalev ^f,^g

^aInstitute of Chemistry, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Vietnam, ^bGraduate University of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Vietnam, ^cDepartment of Biotechnology, Vietnam–Russia Tropical Centre, 58 Nguyen Van Huyen, Hanoi, Vietnam, ^dFaculty of Chemistry, VNU University of Science, Vietnam National University, 19 Le Thanh Tong, Hoan Kiem, Hanoi, Vietnam, ^eOrganic Chemistry Department, Peoples' Friendship University of Russia, 6 Miklukho-Maklaya St., Moscow 117198, Russian Federation, ^fInorganic Chemistry Department, Peoples' Friendship University of Russia, 6 Miklukho-Maklay St., Moscow 117198, Russian Federation, and ^gX-Ray Structural Centre, A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 Vavilov St., B-334, Moscow 119991, Russian Federation
^*Correspondence e-mail: ngvtuyen@hotmail.com

Edited by D.-J. Xu, Zhejiang University (Yuquan Campus), China (Received 23 November 2016; accepted 25 December 2016; online 6 January 2017)

The title compound, C₂₄H₂₉NO₄, is the product of a Petrenko–Kritchenko condensation of 1,5-bis(2-formylphenoxy)-3-oxapentane, pentan-3-one and methylammonium acetate in ethanol. The molecule has mirror symmetry. The aza-14-crown-3 ether ring adopts a bowl conformation stabilized by a weak intramolecular C—H⋯O hydrogen bond. The conformation of the C—O—C—C—O—C—C—O—C polyether chain is t–g⁺–t–t–g⁻–t (t = trans, 180°; g = gauche, ±60°). The dihedral angle between the benzene rings fused to the aza-14-crown-4-ether moiety is 72.68 (4)°. The piperidinone ring adopts a chair conformation. The nitrogen atom has a trigonal–pyramidal geometry, the sum of the bond angles being 335.9°. In the crystal, the molecules are linked by weak C—H⋯O interactions, forming zigzag chains propagating along the [100] direction.

Keywords: crystal structure; macroheterocycles; crown ethers; stacking interactions.

CCDC reference: 1524447

1. Chemical context

Macroheterocycles containing both crown ether and azaheterocyclic moieties are prospective compounds not only as metal-ion receptors (Pedersen, 1988 ), but also as membrane ion-transporting vehicles (Gökel & Murillo, 1996 ), as active components of environmental chemistry (Bradshaw & Izatt, 1997 ), for the design of organic sensors (Costero et al., 2005 ), in nanosized on-off switches and other molecular electronic devices (Natali & Giordani, 2012 ). Moreover, they can possess antibacterial (An et al., 1998 ) and anticancer properties (Artiemenko et al., 2002 ; Le et al., 2014 , 2015 ), and other useful biological activity (Anh & Soldatenkov, 2016 ; Tran et al., 2016 ).

Recently, we have developed effective methods for the synthesis of azacrown ethers containing γ-piperidone (Levov et al., 2006 , 2008 ; Anh et al., 2008 , 2012a ,b ,c ; Hieu et al. (2011 , 2012a ,b ) or γ-arylpyridine (Anh & Soldatenkov, 2016; Tran et al., 2016) subunits. This chemistry allowed us to make systematic studies of the fine structural features of a novel series of azacrown macrocycles using X-ray diffraction. Such data should be of use for the subsequent design of more certain drug-like macroheterocyclic molecules bearing new would-be pharmacophore groups.

In attempts to apply this chemistry for obtaining azacrown ethers which contain a 1,3,5-trimethyl-substituted γ-piperidine moiety, we studied the condensation of diethylketone and 1,5-bis(2-formylphenoxy)-3-oxapentane in the presence of methylammonium acetate taken both as the nitrogen source and as the template in ethanol/acetic acid solution. The reaction proceeded smoothly to give the expected azacrown title molecule, (I), with 32% yield.

2. Structural commentary

The title compound (Fig. 1), the product of a Petrenko–Kritchenko condensation of 1,5-bis(2-formylphenoxy)-3-oxapentane, pentan-3-one and methylammonium acetate in ethanol, crystallizes in the orthorhombic space group Pnma and, in the crystal, occupies a special position on a mirror plane. The aza-14-crown-3 ether ring adopts a bowl conformation stabilized by the weak intramolecular C16—H16B⋯O11 hydrogen bond (Table 1, Fig. 1). The distances from the center of the macrocycle cavity (defined as the centroid of atoms O8/O11/O8A/N14) to the O8, O11 and N14 atoms are 2.265 (2), 1.880 (2) and 2.393 (2) Å, respectively [atoms with the suffix A are related by the symmetry operation x, $[{1\over 2}]$ − y, z.]. The conformation of the C7—O8—C9—C10—O11—C10A—C9A—O8A—C7A polyether chain is t–g⁺–t–t–g⁻–t (t = trans, 180°; g = gauche, ±60°). The dihedral angle between the planes of the benzene rings fused to the aza-14-crown-4-ether moiety is 72.68 (4)°. The piperidinone ring adopts a chair conformation. The nitrogen N14 atom has a trigonal–pyramidal geometry (sum of the bond angles is 335.9°).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C10—H10B⋯O12ⁱ	0.99	2.58	3.449 (2)	147
C16—H16B⋯O11	0.96	2.57	3.530 (3)	180
Symmetry code: (i) $[x-{\script{1\over 2}}, -y+{\script{1\over 2}}, -z-{\script{1\over 2}}]$ .

Figure 1
The molecular structure of (I)

. Displacement ellipsoids are shown at the 50% probability level. H atoms are presented as small spheres of arbitrary radius. The dashed line indicates the intramolecular C—H⋯O hydrogen bond. Atoms with the suffix A are related by the symmetry operation x, $[{1\over 2}]$ − y, z.

The molecule of (I) possesses four asymmetric centers at the C1, C13, C13A and C1A carbon atoms and can have potentially numerous diastereomers. The crystal of (I) is racemic and consists of enantiomeric pairs with the following relative configuration of the centers: rac-1R*,13S*,13AR*,1AS*.

3. Supramolecular features

In the crystal, molecules of (I) form zigzag chains along [100] via weak C—H⋯O interactions (Table 1, Figs. 2 and 3). π–π stacking is observed in the crystal, the distance between parallel benzene rings is 3.446 (3) Å and the shortest intermolecular C5⋯C7ⁱ distance is 3.495 (2) Å [symmetry code: (i) 1 − x, 1 − y, −z].

Figure 2
Crystal packing of (I)

along the b axis demonstrating the zigzag hydrogen-bonded chains along [100]. Dashed lines indicate the intra- and intermolecular C—H⋯O hydrogen bonds.

Figure 3
A portion of the crystal packing of (I)

indicating the intermolecular π–π stacking interactions. Dashed lines indicate the intra- and intermolecular C—H⋯O hydrogen bonds.

4. Synthesis and crystallization

Methylammonium acetate (3.85 g, 50 mmol) was added to a solution of 1,5-bis(2-formylphenoxy)-3-oxapentane (3.14 g, 10.0 mmol) and diethylketone (1.41 g, 10.0 mmol) in ethanol/acetic acid (40 mL/1 mL) mixture. The reaction mixture was stirred at 293 K for three days (monitored by TLC until the disappearance of the starting heterocyclic ketone spot). At the end of the reaction, the formed precipitate was filtered off, washed with ethanol and recrystallized from ethanol solution to give 2.1 g of crystals of (I) (yield 32% m.p. 485–487 K). IR (KBr), ν/cm⁻¹: 1702. ¹H NMR (CDCl₃, 400 MHz, 300 K): δ = 0.89 (d, 6H, CH₃, J = 6.7 Hz), 1.86 (c, 3H, NCH₃), 3.19 (d, 2H, H1, H21, J = 10.8 Hz), 3.76–4.16 (m, 10H, H_ether and H22, H24), 6.78–7.26 (m, 8H, H_arom). Analysis calculated for C₂₄H₂₉NO₄: C, 67.72; H, 7.31; N, 5.64. Found: C, 67.54; H, 7.42; N, 5.41.

5. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. All hydrogen atoms were placed in calculated positions with C—H = 0.95 Å (aryl-H), 0.96 Å (methyl-H), 0.98 Å (methylene-H) or 1.00 Å (methine-H) and refined using a riding model with fixed isotropic displacement parameters [U_iso(H) = 1.5U_eq(C) for the methyl groups and 1.2U_eq(C) for all other atoms].

Table 2
Experimental details

Crystal data
Chemical formula	C₂₄H₂₉NO₄
M_r	395.48
Crystal system, space group	Orthorhombic, Pnma
Temperature (K)	120
a, b, c (Å)	8.1468 (5), 20.3402 (11), 12.0155 (7)
V (Å³)	1991.1 (2)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.09
Crystal size (mm)	0.20 × 0.15 × 0.15

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2003 )
T_min, T_max	0.970, 0.980
No. of measured, independent and observed [I > 2σ(I)] reflections	25079, 3128, 2469
R_int	0.065
(sin θ/λ)_max (Å⁻¹)	0.715

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.056, 0.130, 1.02
No. of reflections	3128
No. of parameters	140
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.34, −0.23
Computer programs: APEX2 (Bruker, 2001 ) and SAINT (Bruker, 2005 ), SHELXT (Sheldrick, 2015a ), SHELXL2015 (Sheldrick, 2015b ) and SHELXTL (Sheldrick, 2008 ).

Supporting information

CCDC reference: 1524447

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S2056989016020508/xu5896sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989016020508/xu5896Isup2.hkl

checkCIF report

Computing details top

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2015 (Sheldrick, 2015b); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

22,24,25-Trimethyl-8,11,14-trioxa-25-azatetracyclo[19.3.1.0^2,7.0^15,20]pentacosa-2,4,6,15 (20),16,18-hexaen-23-one top

Crystal data top

C₂₄H₂₉NO₄	D_x = 1.319 Mg m⁻³
M_r = 395.48	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pnma	Cell parameters from 4090 reflections
a = 8.1468 (5) Å	θ = 3.0–29.2°
b = 20.3402 (11) Å	µ = 0.09 mm⁻¹
c = 12.0155 (7) Å	T = 120 K
V = 1991.1 (2) Å³	Prism, colourless
Z = 4	0.20 × 0.15 × 0.15 mm
F(000) = 848

Data collection top

Bruker APEXII CCD diffractometer	2469 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	R_int = 0.065
φ and ω scans	θ_max = 30.6°, θ_min = 2.0°
Absorption correction: multi-scan (SADABS; Bruker, 2003)	h = −11→11
T_min = 0.970, T_max = 0.980	k = −29→29
25079 measured reflections	l = −17→16
3128 independent reflections

Refinement top

Refinement on F²	Primary atom site location: difference Fourier map
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.056	Hydrogen site location: mixed
wR(F²) = 0.130	H-atom parameters constrained
S = 1.02	w = 1/[σ²(F_o²) + (0.046P)² + 1.66P] where P = (F_o² + 2F_c²)/3
3128 reflections	(Δ/σ)_max < 0.001
140 parameters	Δρ_max = 0.34 e Å⁻³
0 restraints	Δρ_min = −0.23 e Å⁻³

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
C1	0.58338 (18)	0.30912 (7)	−0.07447 (12)	0.0151 (3)
H1	0.4639	0.3029	−0.0903	0.018*
C2	0.60218 (18)	0.37109 (7)	−0.00494 (12)	0.0156 (3)
C3	0.75023 (19)	0.40480 (7)	0.00526 (13)	0.0190 (3)
H3	0.8432	0.3900	−0.0354	0.023*
C4	0.7652 (2)	0.45976 (7)	0.07366 (14)	0.0223 (3)
H4	0.8670	0.4822	0.0793	0.027*
C5	0.6301 (2)	0.48134 (7)	0.13342 (13)	0.0223 (3)
H5	0.6398	0.5188	0.1803	0.027*
C6	0.4808 (2)	0.44885 (7)	0.12557 (13)	0.0195 (3)
H6	0.3888	0.4637	0.1672	0.023*
C7	0.46690 (18)	0.39412 (7)	0.05590 (12)	0.0162 (3)
O8	0.32384 (13)	0.35995 (5)	0.04244 (9)	0.0194 (2)
C9	0.19912 (19)	0.36553 (8)	0.12588 (13)	0.0201 (3)
H9A	0.1387	0.4074	0.1172	0.024*
H9B	0.2488	0.3645	0.2011	0.024*
C10	0.08483 (19)	0.30816 (7)	0.11056 (13)	0.0197 (3)
H10A	−0.0119	0.3129	0.1597	0.024*
H10B	0.0462	0.3062	0.0325	0.024*
O11	0.17272 (19)	0.2500	0.13785 (13)	0.0192 (3)
C12	0.6367 (3)	0.2500	−0.24937 (18)	0.0157 (4)
O12	0.5743 (2)	0.2500	−0.34102 (13)	0.0219 (3)
C13	0.67442 (18)	0.31314 (7)	−0.18726 (12)	0.0160 (3)
H13	0.7951	0.3147	−0.1722	0.019*
N14	0.6428 (2)	0.2500	−0.01435 (14)	0.0148 (3)
C15	0.6282 (2)	0.37347 (7)	−0.25565 (13)	0.0192 (3)
H15A	0.6833	0.3715	−0.3281	0.029*
H15B	0.6626	0.4133	−0.2161	0.029*
H15C	0.5091	0.3744	−0.2667	0.029*
C16	0.6033 (3)	0.2500	0.10474 (17)	0.0186 (4)
H16A	0.6489	0.2885	0.1390	0.028*
H16B	0.4864	0.2500	0.1141	0.028*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0192 (7)	0.0111 (6)	0.0151 (6)	0.0006 (5)	0.0007 (5)	−0.0001 (5)
C2	0.0197 (7)	0.0118 (6)	0.0154 (6)	0.0002 (5)	−0.0012 (5)	0.0008 (5)
C3	0.0200 (7)	0.0152 (6)	0.0217 (7)	0.0009 (5)	−0.0016 (6)	0.0010 (5)
C4	0.0240 (8)	0.0169 (7)	0.0259 (8)	−0.0028 (6)	−0.0061 (6)	−0.0005 (6)
C5	0.0317 (8)	0.0133 (6)	0.0219 (7)	0.0005 (6)	−0.0075 (6)	−0.0042 (6)
C6	0.0248 (7)	0.0161 (7)	0.0177 (7)	0.0031 (6)	−0.0015 (6)	−0.0026 (5)
C7	0.0202 (7)	0.0124 (6)	0.0158 (7)	0.0003 (5)	−0.0018 (5)	0.0004 (5)
O8	0.0198 (5)	0.0201 (5)	0.0183 (5)	−0.0026 (4)	0.0035 (4)	−0.0054 (4)
C9	0.0208 (7)	0.0203 (7)	0.0193 (7)	0.0025 (6)	0.0038 (6)	−0.0033 (6)
C10	0.0176 (7)	0.0217 (7)	0.0199 (7)	0.0033 (6)	0.0015 (6)	−0.0008 (6)
O11	0.0177 (7)	0.0183 (7)	0.0216 (8)	0.000	−0.0020 (6)	0.000
C12	0.0152 (9)	0.0157 (9)	0.0162 (9)	0.000	0.0047 (7)	0.000
O12	0.0306 (9)	0.0190 (7)	0.0160 (7)	0.000	−0.0006 (6)	0.000
C13	0.0161 (6)	0.0149 (6)	0.0169 (7)	−0.0019 (5)	0.0014 (5)	−0.0001 (5)
N14	0.0193 (8)	0.0104 (7)	0.0147 (8)	0.000	−0.0017 (6)	0.000
C15	0.0245 (8)	0.0144 (6)	0.0187 (7)	−0.0008 (6)	−0.0002 (6)	0.0028 (5)
C16	0.0271 (11)	0.0154 (9)	0.0134 (9)	0.000	−0.0003 (8)	0.000

Geometric parameters (Å, º) top

C1—N14	1.4840 (17)	C9—H9B	0.9900
C1—C2	1.5197 (19)	C10—O11	1.4211 (17)
C1—C13	1.547 (2)	C10—H10A	0.9900
C1—H1	1.0000	C10—H10B	0.9900
C2—C3	1.393 (2)	O11—C10ⁱ	1.4211 (17)
C2—C7	1.403 (2)	C12—O12	1.213 (3)
C3—C4	1.393 (2)	C12—C13ⁱ	1.5168 (18)
C3—H3	0.9500	C12—C13	1.5168 (18)
C4—C5	1.385 (2)	C13—C15	1.524 (2)
C4—H4	0.9500	C13—H13	1.0000
C5—C6	1.388 (2)	N14—C16	1.467 (3)
C5—H5	0.9500	N14—C1ⁱ	1.4840 (17)
C6—C7	1.397 (2)	C15—H15A	0.9800
C6—H6	0.9500	C15—H15B	0.9800
C7—O8	1.3666 (18)	C15—H15C	0.9800
O8—C9	1.4319 (18)	C16—H16A	0.9595
C9—C10	1.504 (2)	C16—H16B	0.9593
C9—H9A	0.9900

N14—C1—C2	111.82 (12)	H9A—C9—H9B	108.6
N14—C1—C13	108.23 (12)	O11—C10—C9	107.80 (13)
C2—C1—C13	112.92 (12)	O11—C10—H10A	110.1
N14—C1—H1	107.9	C9—C10—H10A	110.1
C2—C1—H1	107.9	O11—C10—H10B	110.1
C13—C1—H1	107.9	C9—C10—H10B	110.1
C3—C2—C7	118.03 (13)	H10A—C10—H10B	108.5
C3—C2—C1	122.95 (13)	C10—O11—C10ⁱ	112.69 (16)
C7—C2—C1	118.96 (13)	O12—C12—C13ⁱ	122.11 (9)
C2—C3—C4	121.51 (15)	O12—C12—C13	122.11 (9)
C2—C3—H3	119.2	C13ⁱ—C12—C13	115.71 (18)
C4—C3—H3	119.2	C12—C13—C15	111.50 (13)
C5—C4—C3	119.40 (15)	C12—C13—C1	106.80 (12)
C5—C4—H4	120.3	C15—C13—C1	113.36 (12)
C3—C4—H4	120.3	C12—C13—H13	108.3
C4—C5—C6	120.68 (14)	C15—C13—H13	108.3
C4—C5—H5	119.7	C1—C13—H13	108.3
C6—C5—H5	119.7	C16—N14—C1ⁱ	113.80 (10)
C5—C6—C7	119.40 (14)	C16—N14—C1	113.80 (10)
C5—C6—H6	120.3	C1ⁱ—N14—C1	108.27 (15)
C7—C6—H6	120.3	C13—C15—H15A	109.5
O8—C7—C6	123.03 (14)	C13—C15—H15B	109.5
O8—C7—C2	116.00 (12)	H15A—C15—H15B	109.5
C6—C7—C2	120.97 (14)	C13—C15—H15C	109.5
C7—O8—C9	118.82 (11)	H15A—C15—H15C	109.5
O8—C9—C10	106.99 (12)	H15B—C15—H15C	109.5
O8—C9—H9A	110.3	N14—C16—H16A	109.5
C10—C9—H9A	110.3	N14—C16—H16B	109.4
O8—C9—H9B	110.3	H16A—C16—H16B	109.5
C10—C9—H9B	110.3

N14—C1—C2—C3	80.51 (18)	C2—C7—O8—C9	159.44 (13)
C13—C1—C2—C3	−41.84 (19)	C7—O8—C9—C10	−161.82 (12)
N14—C1—C2—C7	−96.59 (16)	O8—C9—C10—O11	67.31 (16)
C13—C1—C2—C7	141.06 (13)	C9—C10—O11—C10ⁱ	−171.15 (10)
C7—C2—C3—C4	0.1 (2)	O12—C12—C13—C15	−1.4 (2)
C1—C2—C3—C4	−177.05 (14)	C13ⁱ—C12—C13—C15	−178.58 (11)
C2—C3—C4—C5	0.3 (2)	O12—C12—C13—C1	122.9 (2)
C3—C4—C5—C6	−0.1 (2)	C13ⁱ—C12—C13—C1	−54.2 (2)
C4—C5—C6—C7	−0.5 (2)	N14—C1—C13—C12	58.80 (16)
C5—C6—C7—O8	−179.15 (14)	C2—C1—C13—C12	−176.87 (13)
C5—C6—C7—C2	0.9 (2)	N14—C1—C13—C15	−178.02 (12)
C3—C2—C7—O8	179.34 (13)	C2—C1—C13—C15	−53.68 (16)
C1—C2—C7—O8	−3.41 (19)	C2—C1—N14—C16	38.57 (19)
C3—C2—C7—C6	−0.7 (2)	C13—C1—N14—C16	163.56 (14)
C1—C2—C7—C6	176.59 (13)	C2—C1—N14—C1ⁱ	166.15 (9)
C6—C7—O8—C9	−20.6 (2)	C13—C1—N14—C1ⁱ	−68.85 (18)

Symmetry code: (i) x, −y+1/2, z.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C10—H10B···O12ⁱⁱ	0.99	2.58	3.449 (2)	147
C16—H16B···O11	0.96	2.57	3.530 (3)	180

Symmetry code: (ii) x−1/2, −y+1/2, −z−1/2.

Funding information

Funding for this research was provided by: National Foundation for Science and Technology Development (award No. 104.01-2014.39); Ministry of Education and Science of the Russian Federation (award No. 02.a03.21.0008 of June 24, 2016).

References

An, H., Wang, T., Mohan, V., Griffey, R. H. & Cook, P. D. (1998). Tetrahedron, 54, 3999–4012. Web of Science CrossRef CAS Google Scholar
Anh, L. T., Hieu, T. H., Soldatenkov, A. T., Kolyadina, N. M. & Khrustalev, V. N. (2012b). Acta Cryst. E68, o1588–o1589. CSD CrossRef IUCr Journals Google Scholar
Anh, L. T., Hieu, T. H., Soldatenkov, A. T., Kolyadina, N. M. & Khrustalev, V. N. (2012c). Acta Cryst. E68, o2165–o2166. CSD CrossRef IUCr Journals Google Scholar
Anh, L. T., Hieu, T. H., Soldatenkov, A. T., Soldatova, S. A. & Khrustalev, V. N. (2012a). Acta Cryst. E68, o1386–o1387. CSD CrossRef IUCr Journals Google Scholar
Anh, L. T., Levov, A. N., Soldatenkov, A. T., Gruzdev, R. D. & Hieu, T. H. (2008). Russ. J. Org. Chem. 44, 463–465. Google Scholar
Artiemenko, A. G., Kovdienko, N. A., Kuz'min, V. E., Kamalov, G. L., Lozitskaya, R. N., Fedchuk, A. S., Lozitsky, V. P., Dyachenko, N. S. & Nosach, L. N. (2002). Exp. Oncol. 24, 123–127. Google Scholar
Bradshaw, J. S. & Izatt, R. M. (1997). Acc. Chem. Res. 30, 338–345. CrossRef CAS Web of Science Google Scholar
Bruker (2001). SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Bruker (2003). SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Bruker (2005). APEX2. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Costero, A. M., Bañuls, M. J., Aurell, M. J., Ochando, L. E. & Doménech, A. J. (2005). Tetrahedron, 61, 10309–10320. Web of Science CSD CrossRef CAS Google Scholar
Gökel, G. W. & Murillo, O. (1996). Acc. Chem. Res. 29, 425–432. Google Scholar
Hieu, T. H., Anh, L. T., Soldatenkov, A. T., Golovtsov, N. I. & Soldatova, S. A. (2011). Chem. Heterocyc. Compd. 47, 1307–1308. Google Scholar
Hieu, T. H., Anh, L. T., Soldatenkov, A. T., Kolyadina, N. M. & Khrustalev, V. N. (2012a). Acta Cryst. E68, o2431–o2432. CSD CrossRef IUCr Journals Google Scholar
Hieu, T. H., Anh, L. T., Soldatenkov, A. T., Kurilkin, V. V. & Khrustalev, V. N. (2012b). Acta Cryst. E68, o2848–o2849. CSD CrossRef IUCr Journals Google Scholar
Le, A. T. & Soldatenkov, A. T. (2016). Chem. Heterocycl. Compd, 52, 152–154. Web of Science CrossRef CAS Google Scholar
Le, T. A., Truong, H. H., Nguyen, P. T. T., Pham, H. T., Kotsuba, V. E., Soldatenkov, A. T., Khrustalev, V. N. & Wodajo, A. T. (2014). Macroheterocycles, 7, 386–390. Web of Science CrossRef CAS Google Scholar
Le, A. T., Truong, H. H., Thi, T. P. N., Thi, N. D., To, H. T., Thi, H. P. & Soldatenkov, A. T. (2015). Mendeleev Commun. 25, 224–225. Web of Science CrossRef CAS Google Scholar
Levov, A. N., Anh, L. T., Komarova, A. I., Strokina, V. M., Soldatenkov, A. T. & Khrustalev, V. N. (2008). Russ. J. Org. Chem. 44, 457–462. Google Scholar
Levov, A. N., Strokina, V. M., Anh, L. T., Komarova, A. I., Soldatenkov, A. T. & Khrustalev, V. N. (2006). Mendeleev Commun. 16, 35–36. Web of Science CSD CrossRef Google Scholar
Natali, M. & Giordani, S. (2012). Chem. Soc. Rev. 41, 4010–4029. Web of Science CrossRef CAS PubMed Google Scholar
Pedersen, C. J. (1988). Angew. Chem. 100, 1053–1059. CrossRef CAS Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Sheldrick, G. M. (2015a). Acta Cryst. A71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2015b). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Tran, T. T. V., Anh, L. T., Nguyen, H. H., Truong, H. H. & Soldatenkov, A. T. (2016). Acta Cryst. E72, 663–666. Web of Science CSD CrossRef IUCr Journals Google Scholar

This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.