organic compounds
3-(3-Nitrophenyl)-1-[4-(prop-2-ynyloxy)phenyl]prop-2-en-1-one
aDepartment of Studies in Chemistry, University of Mysore, Manasagangotri, Mysore-570 006, India, bDepartment of Studies in Chemistry, Mangalore University, Mangalagangotri, Mangalore-574 199, India, cThomas Jefferson High School for Science and Technology, 6560 Braddock Rd, Alexandria VA 22312, USA, and dDepartment of Chemistry, Howard University, 525 College Street NW, Washington DC 20059, USA
*Correspondence e-mail: yathirajan@hotmail.com
The structure of the title compound, C18H13NO4, shows that the whole molecule is almost planar but with a dihedral angle between the two phenyl rings of 19.22 (5)°. The molecules are linked by C—H⋯O interactions, forming sheets in the (21) plane.
Keywords: crystal structure; nitrobenzene; alkyne; chalcone; phenyl ring.
CCDC reference: 2210152
Structure description
α-β unsaturated carbonyl system, which is present in open-chain form, and two aromatic rings are joined through three-carbon atoms (Kozlowski et al., 2007; Raghav & Garg, 2014). Studies depicting the biological activities of and their derivatives describe their immense significance as antidiabetic, anticancer, anti-inflammatory, antimicrobial, antioxidant, antiparasitic, psychoactive and neuroprotective agents, and their antioxidant and enzyme inhibitory activities (Lin et al., 2002; Bhat et al., 2005; Trivedi et al., 2007; Lahtchev et al., 2008; Aneja et al., 2018).
are among the leading bioactive with a therapeutic potential implicated to an array of bioactivities that have been investigated by a series of preclinical and clinical studies. They contain anChalcone as a privileged structure in medicinal chemistry has been reviewed by Zhuang et al. (2017). A comprehensive review of chalcone derivatives as antileishmanial agents has also been published (de Mello et al., 2018). The crystal structures of (2E)-1-(4-methylphenyl)-3-(4-nitrophenyl)prop-2-en-1-one (Butcher et al., 2007), (2E)-1-(3-bromophenyl)-3-(4,5-dimethoxy-2-nitrophenyl)prop-2-en-1-one (Jasinski et al., 2010), (2E)-3-(3-nitrophenyl)-1-[4-(piperidin-1-yl)phenyl]prop-2-en-1-one (Fun et al., 2012) and 4′-dimethylamino-3-nitrochalcone, 3-dimethylamino-3′-nitrochalcone and 3′-nitrochalcone (Hall et al., 2020) have been reported.
The present work describes the synthesis and ), which crystallizes in the triclinic P with one molecule in the It consists both a 3-nitrophenyl group and a (prop-2-yn-1-yloxy)benzene group linked to a central chalcone moiety. Even though the C—N bond length is 1.4706 (17) Å and thus single, the nitro group is almost coplanar with its phenyl ring [dihedral angle of 18.94 (6)°] as a result of the steric clash between O1 and H4 and between O2 and H2, respectively. The chalcone group is planar (average deviation from plane of 0.004 Å) and makes dihedral angles of 7.69 (8) and 10.96 (6)° with the 3-nitrophenyl ring and the phenyl ring of the (prop-2-yn-1-yloxy)benzene group, respectively. Lastly, the twist between the two phenyl rings which are linked by the chalcone is 19.22 (5)°.
of the title compound 3-(3-nitrophenyl)-1-[4-(prop-2-ynyloxy)phenyl]prop-2-en-1-one (Fig. 1The molecules are linked by C–H⋯O interactions (Table 1), which form sheets in the (21) plane as shown in Fig. 2. There are no π–π interactions between the phenyl rings.
Synthesis and crystallization
A well-stirred solution of 1-[4-(prop-2-ynyloxy)phenyl]ethanone (1 g, 1 mmol) in 20 ml of ethanol was added slowly to alcoholic potassium hydroxide (0.48 g, 1.5 mmol). To this solution, m-nitro benzaldehyde (1.03 g, 1.2 mmol) was added. The resulting mixture was stirred at room temperature for 30 min. Then, the separated solid from the reaction mixture was filtered, washed with cold water, dried and recrystallized from ethanol:dimethylformamide mixture (9:1). Golden yellow crystals (yield: 86%, m.p. 453–454 K). The reaction scheme is shown in Fig. 3. FT–IR: νmax, cm−1 (KBr): 2987 (C—H aliphatic), 2117 (C≡C str), 1650 (C=O), 1518 (asym NO2 stretch),1444 (sym NO2 stretch), 1252 (C—O stretch); 1H NMR (400 MHz, CDCl3, δ p.p.m.): 7.55 (d, 1H, J = 15.7 Hz, olefinic-β), 7.36 (d, 2H, J = 8.8 Hz, Ar—H), 7.28 (d, 2H, J = 8.6 Hz, Ar—H), 7.16 (d, 2H, J = 8.8 Hz, Ar—H), 7.09 (d, 2H, J = 8.3 Hz, Ar—H), 6.73 (d, 1H, J = 15.7 Hz, olefinic-α), 4.46 (s, 2H, O—CH2), 2.79 (s, 1H, acetylene proton).
Refinement
Crystal data, data collection and structure .
details for the title compound are summarized in Table 2Structural data
CCDC reference: 2210152
https://doi.org/10.1107/S2414314622009579/bt4126sup1.cif
contains datablock I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314622009579/bt4126Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2414314622009579/bt4126Isup3.cml
Data collection: APEX2 (Bruker, 2016); cell
SAINT (Bruker, 2016); data reduction: SAINT (Bruker, 2016); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).C18H13NO4 | Z = 2 |
Mr = 307.29 | F(000) = 320 |
Triclinic, P1 | Dx = 1.393 Mg m−3 |
a = 7.6534 (16) Å | Mo Kα radiation, λ = 0.71073 Å |
b = 8.6079 (15) Å | Cell parameters from 9976 reflections |
c = 11.369 (2) Å | θ = 2.7–32.9° |
α = 94.433 (7)° | µ = 0.10 mm−1 |
β = 97.953 (8)° | T = 100 K |
γ = 97.019 (7)° | Prism, yellow |
V = 732.8 (3) Å3 | 0.33 × 0.19 × 0.14 mm |
Bruker APEXII CCD diffractometer | 2700 reflections with I > 2σ(I) |
φ and ω scans | Rint = 0.089 |
Absorption correction: multi-scan (SADABS; Bruker, 2016) | θmax = 28.3°, θmin = 2.4° |
Tmin = 0.634, Tmax = 0.729 | h = −10→10 |
47166 measured reflections | k = −11→10 |
3638 independent reflections | l = −15→15 |
Refinement on F2 | Primary atom site location: dual |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.046 | Hydrogen site location: mixed |
wR(F2) = 0.137 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.08 | w = 1/[σ2(Fo2) + (0.0642P)2 + 0.1082P] where P = (Fo2 + 2Fc2)/3 |
3638 reflections | (Δ/σ)max < 0.001 |
212 parameters | Δρmax = 0.28 e Å−3 |
0 restraints | Δρmin = −0.21 e Å−3 |
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. The acetylenic H atom was freely refined. All remaining hydrogen atoms were placed geometrically and refined as riding atoms with their Uiso values 1.2 times that of their attached atoms. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.8224 (2) | −0.53179 (13) | 0.40582 (11) | 0.0732 (4) | |
O2 | 0.78869 (16) | −0.48667 (12) | 0.22192 (10) | 0.0557 (3) | |
O3 | 0.38666 (16) | 0.19330 (12) | 0.03294 (9) | 0.0557 (3) | |
O4 | 0.12863 (14) | 0.82184 (10) | 0.22678 (8) | 0.0419 (3) | |
N1 | 0.79204 (16) | −0.44535 (13) | 0.32710 (11) | 0.0436 (3) | |
C1 | 0.63484 (18) | −0.05300 (15) | 0.30785 (12) | 0.0358 (3) | |
C2 | 0.67213 (17) | −0.20372 (14) | 0.27518 (11) | 0.0342 (3) | |
H2A | 0.639784 | −0.249615 | 0.195197 | 0.041* | |
C3 | 0.75705 (18) | −0.28509 (15) | 0.36138 (12) | 0.0362 (3) | |
C4 | 0.8101 (2) | −0.22355 (17) | 0.47820 (12) | 0.0446 (3) | |
H4A | 0.868961 | −0.282414 | 0.535011 | 0.054* | |
C5 | 0.7751 (2) | −0.07331 (18) | 0.51018 (13) | 0.0518 (4) | |
H5A | 0.811026 | −0.027252 | 0.589874 | 0.062* | |
C6 | 0.6882 (2) | 0.00972 (17) | 0.42650 (13) | 0.0469 (4) | |
H6A | 0.663892 | 0.112233 | 0.450078 | 0.056* | |
C7 | 0.54529 (18) | 0.03375 (15) | 0.21647 (12) | 0.0378 (3) | |
H7A | 0.524932 | −0.013883 | 0.136707 | 0.045* | |
C8 | 0.49007 (19) | 0.17290 (15) | 0.23512 (12) | 0.0402 (3) | |
H8A | 0.505167 | 0.222444 | 0.314155 | 0.048* | |
C9 | 0.40553 (19) | 0.25253 (15) | 0.13558 (12) | 0.0386 (3) | |
C10 | 0.34071 (18) | 0.40617 (14) | 0.16303 (11) | 0.0345 (3) | |
C11 | 0.32576 (18) | 0.46816 (15) | 0.27815 (11) | 0.0366 (3) | |
H11A | 0.365827 | 0.414762 | 0.344742 | 0.044* | |
C12 | 0.25357 (19) | 0.60589 (15) | 0.29624 (11) | 0.0382 (3) | |
H12A | 0.242477 | 0.645757 | 0.374749 | 0.046* | |
C13 | 0.19719 (17) | 0.68610 (14) | 0.19960 (11) | 0.0343 (3) | |
C14 | 0.2132 (2) | 0.62771 (16) | 0.08447 (12) | 0.0418 (3) | |
H14A | 0.176033 | 0.682647 | 0.018101 | 0.050* | |
C15 | 0.2840 (2) | 0.48861 (16) | 0.06802 (12) | 0.0418 (3) | |
H15A | 0.293985 | 0.448410 | −0.010617 | 0.050* | |
C16 | 0.0652 (2) | 0.90385 (15) | 0.12751 (12) | 0.0412 (3) | |
H16A | −0.037244 | 0.838377 | 0.076985 | 0.049* | |
H16B | 0.160640 | 0.926181 | 0.078194 | 0.049* | |
C17 | 0.01114 (18) | 1.05106 (15) | 0.17380 (12) | 0.0397 (3) | |
C18 | −0.0334 (2) | 1.17155 (17) | 0.20482 (14) | 0.0466 (4) | |
H18A | −0.067 (2) | 1.266 (2) | 0.2248 (15) | 0.057 (5)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.1189 (11) | 0.0461 (6) | 0.0560 (7) | 0.0324 (7) | −0.0072 (7) | 0.0173 (5) |
O2 | 0.0791 (8) | 0.0448 (6) | 0.0449 (6) | 0.0280 (5) | 0.0012 (5) | −0.0014 (5) |
O3 | 0.0887 (9) | 0.0452 (6) | 0.0366 (6) | 0.0323 (6) | 0.0041 (5) | −0.0009 (4) |
O4 | 0.0605 (6) | 0.0339 (5) | 0.0339 (5) | 0.0210 (4) | 0.0040 (4) | 0.0022 (4) |
N1 | 0.0506 (7) | 0.0363 (6) | 0.0440 (7) | 0.0146 (5) | −0.0018 (5) | 0.0069 (5) |
C1 | 0.0395 (7) | 0.0333 (6) | 0.0357 (7) | 0.0103 (5) | 0.0049 (5) | 0.0040 (5) |
C2 | 0.0384 (7) | 0.0328 (6) | 0.0316 (6) | 0.0087 (5) | 0.0027 (5) | 0.0026 (5) |
C3 | 0.0397 (7) | 0.0333 (6) | 0.0372 (7) | 0.0102 (5) | 0.0052 (5) | 0.0063 (5) |
C4 | 0.0535 (8) | 0.0465 (8) | 0.0352 (7) | 0.0153 (6) | 0.0012 (6) | 0.0090 (6) |
C5 | 0.0691 (10) | 0.0530 (9) | 0.0320 (7) | 0.0183 (7) | −0.0018 (7) | −0.0026 (6) |
C6 | 0.0633 (9) | 0.0391 (7) | 0.0388 (7) | 0.0179 (7) | 0.0032 (6) | −0.0021 (6) |
C7 | 0.0457 (7) | 0.0333 (6) | 0.0353 (7) | 0.0121 (5) | 0.0040 (5) | 0.0016 (5) |
C8 | 0.0514 (8) | 0.0340 (7) | 0.0359 (7) | 0.0148 (6) | 0.0025 (6) | 0.0014 (5) |
C9 | 0.0484 (8) | 0.0324 (6) | 0.0366 (7) | 0.0130 (5) | 0.0061 (6) | 0.0021 (5) |
C10 | 0.0406 (7) | 0.0296 (6) | 0.0339 (6) | 0.0096 (5) | 0.0038 (5) | 0.0025 (5) |
C11 | 0.0472 (7) | 0.0324 (6) | 0.0317 (6) | 0.0115 (5) | 0.0037 (5) | 0.0066 (5) |
C12 | 0.0514 (8) | 0.0343 (6) | 0.0299 (6) | 0.0109 (6) | 0.0064 (5) | 0.0014 (5) |
C13 | 0.0396 (7) | 0.0281 (6) | 0.0352 (6) | 0.0090 (5) | 0.0033 (5) | 0.0007 (5) |
C14 | 0.0596 (9) | 0.0371 (7) | 0.0307 (6) | 0.0188 (6) | 0.0018 (6) | 0.0047 (5) |
C15 | 0.0603 (9) | 0.0365 (7) | 0.0305 (6) | 0.0177 (6) | 0.0044 (6) | 0.0011 (5) |
C16 | 0.0526 (8) | 0.0343 (7) | 0.0368 (7) | 0.0160 (6) | −0.0016 (6) | 0.0028 (5) |
C17 | 0.0429 (7) | 0.0361 (7) | 0.0408 (7) | 0.0107 (6) | 0.0019 (6) | 0.0062 (5) |
C18 | 0.0518 (9) | 0.0378 (7) | 0.0527 (9) | 0.0170 (6) | 0.0063 (7) | 0.0052 (6) |
O1—N1 | 1.2232 (15) | C8—C9 | 1.4815 (18) |
O2—N1 | 1.2168 (16) | C8—H8A | 0.9500 |
O3—C9 | 1.2189 (16) | C9—C10 | 1.4940 (17) |
O4—C13 | 1.3693 (14) | C10—C15 | 1.3866 (17) |
O4—C16 | 1.4362 (15) | C10—C11 | 1.3997 (18) |
N1—C3 | 1.4706 (17) | C11—C12 | 1.3809 (17) |
C1—C2 | 1.3957 (17) | C11—H11A | 0.9500 |
C1—C6 | 1.3996 (19) | C12—C13 | 1.3888 (17) |
C1—C7 | 1.4680 (18) | C12—H12A | 0.9500 |
C2—C3 | 1.3838 (17) | C13—C14 | 1.3924 (18) |
C2—H2A | 0.9500 | C14—C15 | 1.3835 (18) |
C3—C4 | 1.3780 (19) | C14—H14A | 0.9500 |
C4—C5 | 1.384 (2) | C15—H15A | 0.9500 |
C4—H4A | 0.9500 | C16—C17 | 1.4627 (18) |
C5—C6 | 1.380 (2) | C16—H16A | 0.9900 |
C5—H5A | 0.9500 | C16—H16B | 0.9900 |
C6—H6A | 0.9500 | C17—C18 | 1.1746 (19) |
C7—C8 | 1.3295 (17) | C18—H18A | 0.901 (18) |
C7—H7A | 0.9500 | ||
C13—O4—C16 | 116.23 (10) | O3—C9—C10 | 120.22 (12) |
O2—N1—O1 | 122.80 (12) | C8—C9—C10 | 118.90 (11) |
O2—N1—C3 | 118.79 (11) | C15—C10—C11 | 118.06 (11) |
O1—N1—C3 | 118.40 (12) | C15—C10—C9 | 117.85 (11) |
C2—C1—C6 | 118.12 (12) | C11—C10—C9 | 124.01 (11) |
C2—C1—C7 | 118.90 (11) | C12—C11—C10 | 120.89 (11) |
C6—C1—C7 | 122.97 (12) | C12—C11—H11A | 119.6 |
C3—C2—C1 | 118.80 (12) | C10—C11—H11A | 119.6 |
C3—C2—H2A | 120.6 | C11—C12—C13 | 119.98 (12) |
C1—C2—H2A | 120.6 | C11—C12—H12A | 120.0 |
C4—C3—C2 | 123.22 (12) | C13—C12—H12A | 120.0 |
C4—C3—N1 | 118.22 (11) | O4—C13—C12 | 115.58 (11) |
C2—C3—N1 | 118.56 (11) | O4—C13—C14 | 124.35 (11) |
C3—C4—C5 | 117.94 (12) | C12—C13—C14 | 120.07 (11) |
C3—C4—H4A | 121.0 | C15—C14—C13 | 119.11 (12) |
C5—C4—H4A | 121.0 | C15—C14—H14A | 120.4 |
C6—C5—C4 | 120.11 (13) | C13—C14—H14A | 120.4 |
C6—C5—H5A | 119.9 | C14—C15—C10 | 121.89 (12) |
C4—C5—H5A | 119.9 | C14—C15—H15A | 119.1 |
C5—C6—C1 | 121.80 (13) | C10—C15—H15A | 119.1 |
C5—C6—H6A | 119.1 | O4—C16—C17 | 108.45 (11) |
C1—C6—H6A | 119.1 | O4—C16—H16A | 110.0 |
C8—C7—C1 | 125.96 (12) | C17—C16—H16A | 110.0 |
C8—C7—H7A | 117.0 | O4—C16—H16B | 110.0 |
C1—C7—H7A | 117.0 | C17—C16—H16B | 110.0 |
C7—C8—C9 | 121.55 (12) | H16A—C16—H16B | 108.4 |
C7—C8—H8A | 119.2 | C18—C17—C16 | 176.40 (14) |
C9—C8—H8A | 119.2 | C17—C18—H18A | 177.0 (11) |
O3—C9—C8 | 120.87 (12) | ||
C6—C1—C2—C3 | 1.0 (2) | C7—C8—C9—C10 | 177.91 (13) |
C7—C1—C2—C3 | 179.80 (12) | O3—C9—C10—C15 | −9.4 (2) |
C1—C2—C3—C4 | −1.3 (2) | C8—C9—C10—C15 | 171.57 (13) |
C1—C2—C3—N1 | 178.51 (11) | O3—C9—C10—C11 | 167.42 (14) |
O2—N1—C3—C4 | −161.56 (14) | C8—C9—C10—C11 | −11.6 (2) |
O1—N1—C3—C4 | 18.8 (2) | C15—C10—C11—C12 | 1.2 (2) |
O2—N1—C3—C2 | 18.64 (19) | C9—C10—C11—C12 | −175.62 (13) |
O1—N1—C3—C2 | −160.96 (13) | C10—C11—C12—C13 | −1.0 (2) |
C2—C3—C4—C5 | 0.5 (2) | C16—O4—C13—C12 | −178.35 (11) |
N1—C3—C4—C5 | −179.33 (13) | C16—O4—C13—C14 | 2.0 (2) |
C3—C4—C5—C6 | 0.6 (2) | C11—C12—C13—O4 | −179.60 (12) |
C4—C5—C6—C1 | −0.7 (3) | C11—C12—C13—C14 | 0.1 (2) |
C2—C1—C6—C5 | −0.1 (2) | O4—C13—C14—C15 | −179.70 (13) |
C7—C1—C6—C5 | −178.78 (15) | C12—C13—C14—C15 | 0.7 (2) |
C2—C1—C7—C8 | 175.05 (13) | C13—C14—C15—C10 | −0.5 (2) |
C6—C1—C7—C8 | −6.3 (2) | C11—C10—C15—C14 | −0.4 (2) |
C1—C7—C8—C9 | 178.18 (13) | C9—C10—C15—C14 | 176.58 (13) |
C7—C8—C9—O3 | −1.1 (2) | C13—O4—C16—C17 | −175.40 (11) |
D—H···A | D—H | H···A | D···A | D—H···A |
C18—H18A···O2i | 0.901 (18) | 2.519 (18) | 3.3927 (18) | 163.6 (15) |
Symmetry code: (i) x−1, y+2, z. |
Acknowledgements
V is grateful to the DST–PURSE Project, Vignan Bhavana, UOM, for providing research facilities.
Funding information
HSY and BK are grateful to UGC, New Delhi, for the award of BSR Faculty Fellowship.
References
Aneja, B., Arif, R., Perwez, A., Napoleon, J. V., Hassan, P., Rizvi, M. M. A., Azam, A., Rahisuddin & Abid, M. (2018). ChemistrySelect, 2018, 3, 2638-2645. Google Scholar
Bhat, B. A., Dhar, K. L., Puri, S. C., Saxena, A. K., Shanmugavel, M. & Qazi, G. N. (2005). Bioorg. Med. Chem. Lett. 15, 3177–3180. Web of Science CrossRef PubMed CAS Google Scholar
Bruker (2016). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Butcher, R. J., Jasinski, J. P., Yathirajan, H. S., Veena, K. & Narayana, B. (2007). Acta Cryst. E63, o3680. Web of Science CSD CrossRef IUCr Journals Google Scholar
Fun, H.-K., Chia, T. S., Nayak, P. S., Narayana, B. & Sarojini, B. K. (2012). Acta Cryst. E68, o974. CSD CrossRef IUCr Journals Google Scholar
Hall, C. L., Hamilton, V., Potticary, J., Cremeens, M. E., Pridmore, N. E., Sparkes, H. A., D'ambruoso, G. D., Warren, S. D., Matsumoto, M. & Hall, S. R. (2020). Acta Cryst. E76, 1599–1604. Web of Science CSD CrossRef IUCr Journals Google Scholar
Jasinski, J. P., Butcher, R. J., Chidan Kumar, C. S., Yathirajan, H. S. & Mayekar, A. N. (2010). Acta Cryst. E66, o2936–o2937. Web of Science CSD CrossRef IUCr Journals Google Scholar
Kozlowski, D., Trouillas, P., Calliste, C., Marsal, P., Lazzaroni, R. & Duroux, J. L. (2007). J. Phys. Chem. A, 111, 1138–1145. Web of Science CrossRef PubMed CAS Google Scholar
Lahtchev, K. L., Batovska, D. I., Parushev, P., Ubiyvovk, V. M. & Sibirny, A. A. (2008). Eur. J. Med. Chem. 43, 2220–2228. Web of Science CrossRef PubMed CAS Google Scholar
Lin, Y.-M., Zhou, Y., Flavin, M. T., Zhou, L.-M., Nie, W. & Chen, F.-C. (2002). Bioorg. Med. Chem. 10, 2795–2802. Web of Science CrossRef PubMed CAS Google Scholar
Mello, M. V. P. de, Abrahim-Vieira, B. A., Domingos, T. F. S., de Jesus, J. B., de Sousa, A. C. C., Rodrigues, C. R. & Souza, A. M. T. (2018). Eur. J. Med. Chem. 150, 920–929. Web of Science PubMed Google Scholar
Raghav, N. & Garg, S. (2014). Eur. J. Pharm. Sci. 60, 55–63. Web of Science CrossRef CAS PubMed 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
Trivedi, J. C., Bariwal, J. B., Upadhyay, K. D., Naliapara, Y. T., Joshi, S. K., Pannecouque, C. C., De Clercq, E. & Shah, A. K. (2007). Tetrahedron Lett. 48, 8472–8474. Web of Science CrossRef CAS Google Scholar
Zhuang, C., Zhang, W., Sheng, C., Zhang, W., Xing, C. & Miao, Z. (2017). Chem. Rev. 117, 7762–7810. Web of Science CrossRef CAS PubMed 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.