INTRODUCTION

Conjugated nitroalkenes are known as highly active substrates in reactions of various types [1–4]. Among these compounds, representatives containing an additional electron acceptor group in the β-position to the nitro group are intensively studied in recent decades [5, 6]. Such practically significant products as the antibiotic orizoximycin [8] and some β-amino acids that used in synthesis of β-peptides [9, 10] were obtained on the basis of β-functionalized nitroalkenes—alkyl 3-nitroacrylates [7].

Geminal halonitroalkenes are even more attractive substrates, which are used in the synthesis of carboxylic [11‒15] and heterocyclic compounds [16, 17], including derivatives of a number of tetrahydrofuroquinoline [4], pyrrole [18, 19], isoxazole [20–22], pyrazole [23, 24], imidazole [25, 26], dihydrofuran [27], dihydrothiazole [28], and triazole [29].

Representatives of β-functionalized gem-halonitroalkenes—alkyl 3-bromo-3-nitroacrylates demonstrate broader synthetic capabilities, opening up simple ways to synthesize open-chain, carboxylic, and heterocyclic substances [30–33].

It should be noted that gem-halonitroalkenes have antifungal and antibacterial properties [34–36], inhibit activity against FBPase [37] and 1,3,8-trihydroxynaphthalene reductase [38]. In addition, they are used as substrates in the synthesis of substances inhibiting aminopeptidases [39], methyltransferases [39], and also as a potential agent for the treatment of acute myeloid leukemia [40].

The preparation of nitro- and halonitroalkenes is represented by the following main approaches: nitration of alkenes [41, 42] and gem-dihaloalkenes [23, 43], condensation of carbonyl compounds with nitro- [44] and halonitromethane [4, 45], dehydration of nitro alcohols [46], halogenation of nitroalkenes, and their subsequent dehydrohalogenation [47].

Nowdays there are two main approaches to the synthesis of 1-aryl-3-nitropropene-2-ones are known: the formation of arylvinyl ketone and the introduction of a nitro group into its molecule [48], and also condensation of aromatic α-ketoaldehyde with nitromethane and dehydration of the resulting nitro alcohols [6]. At the same time, both pathways are characterized by low yields (from 5 to 44%) of the target nitrovinyl ketones. Obtaining a single example of 1-aryl-3-bromo-3-nitropropene-2-ones involves halogenation of nitrovinyl ketone followed by dehydrohalogenation of dibromide [49]. It should be noted that the fine structure of the known nitro- and bromonitrovinyl ketones has not been studied in detail to date.

In this regard, the purpose of this work was to synthesize representatives of 1-aryl-3-nitro- and 3-bromo-3-nitroprop-2-en-1-ones, and also to study the features of their fine structure.

RESULTS AND DISCUSSION

Attempts to synthesize 1-aryl-3-nitroprop-2-en-1-ones under conditions of the procedure proposed by Nesmeyanov [48] showed its low reproducibility, especially at the stages of vinyl ketone framework formation and introduction of a nitro group into its molecule.

Using the approach applied by Choudhury [6] in single-reactor mode seemed impractical because of its low yields. However, carrying out this process stage by stage with isolating all intermediate products has significantly improved the final result.

Indeed, condensation of arylglyoxals 1a–1d with nitromethane leads to the production of 1-aryl-2-hydroxy-3-nitropropane-1-ones 2a–2d, isolated in crystalline form in 85–92% yields. Subsequent dehydration of hydroxynitropropanones 2a–2d under the action of a mixture of MsCl and Et3N (ratio 1-aryl-2-hydroxy-3-nitropropane-1-one : MsCl : Et3N = 1 : 3 : 3) at –18°C for 30 min results in formation of 1-aryl-3-nitropropane-2-en-1-ones 3a–3d in 60–88% yields (Scheme 1).

Scheme
scheme 1

1.

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Bromination of 1-aryl-3-nitropropane-2-en-1-ones 3a–3d with molecular bromine in anhydrous tetrachloromethane at room temperature leads to the formation of 1-aryl-2,3-dibromo-3-nitropropane-1-ones 4a–4d in 80–95% yields. Their subsequent dehydrobromination under the action of triethylamine in a tetrachloromethane solution at –10°C results in formation of 1-aryl-3-bromo-3-nitroprop-2-en-1-ones 5a–5d in 62–80% yields (Scheme 2).

Scheme
scheme 2

2.

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According to the data of 1H and 13C NMR spectroscopy, 1-aryl-3-nitroprop-2-en-1-ones 3a–3d and 1-aryl-3-bromo-3-nitroprop-2-en-1-ones 5a–5d are configurationally homogeneous. However, they can exist as E- or Z-isomers (C=C), as well as s-cis- or s-trans-conformers (C=O, C=C) (Scheme 3).

Scheme
scheme 3

3.

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The values of the J-coupling constant (3J = 13.2–13.3 Hz) of the C2H (δH 8.07–8.12 ppm) and C3H (δH 7.67–7.70 ppm) proton signals observed in the 1H NMR spectra of nitropropenones 3a–3d, respectively, pointing at the E-configuration of the C=C multiple bond in the molecules of these compounds and are consistent with the published data [50, 51].

In the 1Н NMR spectra of bromonitropropenones 5a–5d, the C2H proton signal observed at δ 8.44–8.49 ppm, which indicates the Z-configuration of the molecule in the same way as in the case of similar substances [52, 53].

In addition, the 1Н–1Н NOESY NMR experiment for nitropropenones 3b, 3c, and bromonitropropenones 5a and 5c showed the presence of the nuclear Overhauser effect (NOE) between C2H and Нo protons, which points to their close position in space and, and the s-cis-configuration of C=C and C=O bonds in the molecule respectively. (Scheme 4).

Scheme
scheme 4

4.

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An additional study of compounds 3 and 5 by 1H–15N HMBC experiment in СDCl3 showed that the nitrogen atom of the conjugated nitro group in case of nitropropenones 3a–3d is observed at (–9.3)– (–10.7) ppm, which is consistent with the published data for compounds containing a nitrovinyl fragment [54–57]. In the case of bromоnitropropenones 5a–5d, the nitrogen atom signal appears in the range (–16.3)–(–17.0), which is close to the range of signals for alkyl 3-bromo-3-nitroacrylates (–16.5, –17.1 ppm) [52].

The assumption made about the geometric configuration of nitro- and bromonitropropenones 3 and 5 is confirmed by the results of X-ray diffraction analysis (Table 1). Indeed, in the crystal of 1-(4-methylphenyl)-3-nitroprop-2-en-1-one 3b has an E-s-cis configuration, and 3-bromo-3-nitro-1-phenylprop-2-ene-1-one 5a – Z-s-cis configuration of the molecule (Fig. 1).

Table 1. Principal crystallographic parameters of compounds 3b and 5a based on X-ray diffraction data
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Fig. 1.
figure 1

Molecular structures of (a) (2E)-1-(4-methylphenyl)-3-nitropropyl-2-en-1-one 3b and (b) (2Z)-3-bromo-3-nitro-1-phenylprop-2-en-1-one 5a in the crystal.

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The molecule of nitropropenone 3b is planar within 0.122(1) Å, the O10 atom having the maximum deviation from the mean square plane. Apparently, this deviation is due to steric reasons: the O10 atom has short intramolecular contacts with the H3 and H9 atoms (2.41 and 2.50 Å, respectively). Nevertheless, a long chain of conjugations is realized in 3b molecule, which determines the planarity of the molecule (Fig. 1a). At the same time, the molecule of bromonitropropenone 5a is non-planar, the deviation of the bromine atom from the mean square plane of the molecule is 0.891(1) Å. Two planar fragments can be distinguished in the molecule – a benzene ring with a carbonyl group [torsion angle τ(О10–С1–С4–С9) 1.5(3)°)] and a fragment С2–С3–N12–O14 [τ = 3.5(3)°] including a nitro group and a bromine atom. These two fragments are unfolded relative to the bond С1–С2 [τ(О10–С1–С2–С3) 36.2(3)°] (Fig. 1b).

It should be noted that the lengths of the corresponding bonds in molecules 3b and 5a coincide within the experimental errors (Table 2), except for bond lengths involving C3 atoms. In molecule 5a, the С2=С3 double bond and the С3–N12 bond are slightly elongated compared to the same bonds in molecule 3b. Apparently, this difference, as well as the turn relative to the C1–C2 bond, are due to steric reasons—short intramolecular contacts of the bromine atom with oxygen atoms are observed in the 5a molecule with distances Br11···O10 3.153(4) and Br11···O13 2.895(4) Å and the sum of van derWaals radius 3.37 Å. With the planar structure of the 5a molecule, these distances would be even smaller. Thus, the different conformations of molecules 3b and 5a are due to steric reasons – a volumetric substituent at the C3 atom in 5a molecule.

Table 2. The main bond lengths (d) in molecules of (2E)-1-(4-methylphenyl)-3-nitropropyl-2-en-1-one 3b and (2Z)-3-bromo-3-nitro-1-phenylprop-2-en-1-one 5a
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In crystal 5a, there is a short intermolecular contact of the bromine atom with the carbonyl oxygen atom, Br11···O10, [1/2–x, 1/2+y, z] 2.962(3) Å, which is 0.41 Å less than the sum of van der Waals radius. Such a contact indicates a halogen bond in this crystal (Fig. 2). Short C–H···O type contacts corresponding to dispersion interactions are also observed in this crystal.

Fig. 2.
figure 2

Short contacts in the crystal of (2Z)-3-bromo-3-nitro-1-phenylprop-2-en-1-one 5a.

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Short C–H···O type contacts corresponding to dispersion interactions are also observed in 3b crystal. Stacking interactions of aromatic systems in crystals 3b and 5a are not observed.

CONCLUSIONS

Thus, a number of 1-aryl-3-nitroprop-2-en-1-ones and 1-aryl-3-bromo-3-nitroprop-2-en-1-ones were synthesized on the basis of the synthetic approaches “condensation–dehydration” and “halogenation-dehydrohalogenation.” Based on the data of the 1H–1H NOESY NMR spectroscopy and also X-ray diffraction analysis, the E-s-cis configuration of 1-aryl-3-nitroprop-2-en-1-ones and the Z-s-cis configuration of 1-aryl-3-bromine-3-nitroprop-2-en-1-ones were determined.

EXPERIMENTAL

The 1Н, 13С{1Н}, 1Н–1Н NOESY, 1H–13C HMQC and HMBC, and 1H–15N HMBC NMR spectra were recorded in CDCl3 on a Jeol ECX400A spectrometer with operating frequencies: 399.78 (1H), 100.53 (13С), and 40.52 (15N) MHz. Residual signals of the nondeuterated solvent (δH 7.25, δС 77.16 ppm) were used as a standard. The 15N chemical shifts were determined relative to CH3NO2. The vibrational spectra were recorded on a Shimadzu IRPrestige-21 Fourier spectrometer in CHCl3 solution (c = 20 mg/mL). The electronic absorption spectra were recorded on a Shimadzu UV 2401PC spectrophotometer in MeCN solution in quartz non-separable cuvettes (l = 1.01 mm). The elemental analysis was performed on the EuroVector EA3000 analyzer (CHN Dual).

2-Hydroxy-3-nitro-1-phenylpropane-1-one (2a). A suspension of 0.5 g (3.3 mmol) of 2-oxo-2-phenylacetaldehyde 1a and 0.74 g (7.26 mmol) Al2O3 in 12 mL of MeNO2 was stirred at room temperature for 1 h. The reaction mass was filtered, the filtrate was evaporated. The tarred residue was treated with isopropyl alcohol, the precipitate was filtered off. A white powder was obtained. Yield 0.55 g (85%), mp 65–67°C (i-PrOH). IR spectrum, ν, cm–1: 3447 (OH), 1690 (C=O), 1563 [νas(NO2)], 1376 [νs(NO2)]. 1H NMR spectrum, δ, ppm: 4.13 d (1H, OH, 3J 6.0 Hz), 4.57 d. d (1H, СH2NO2, 2J 13.4, 3J 7.1 Hz), 4.82 d. d (1H, СH2NO2, 2J 13.4, 3J 2.9 Hz), 5.60–5.70 m (1H, CH), 7.56 т (2H, Hm, 3J 7.7 Hz), 7.69 t (1H, Hp, 3J 7.4 Hz), 7.95 d (2H, Ho, 3J 7.4 Hz). 13C NMR spectrum, δC, ppm: 70.92 (C2), 78.79 (C3), 128.66 (Co), 129.49 (Cm), 132.75 (Cipso), 135.01 (Cp), 196.55 (C=O). 15N NMR spectrum, δN, ppm: –0.8 (NO2). Found, %: C 55.41; H 4.23; N 7.00. C9H9NO4. Calculated, %: C 55.39; H 4.20; N 7.02.

2-Hydroxy-1-(4-methylphenyl)-3-nitropropane-1-one (2b) was prepared similarly to compound 2a from 4.82 g (27 mmol) of 2-oxo-2-(4-methylphenyl)acetaldehyde 1b, 6.10 g (60 mmol) of Al2O3 and 100 mL of MeNO2. Yield 5.17 g (88%), white powder, mp 67–69°C (i-PrOH). IR spectrum, ν, cm–1: 3462 (OH), 1685 (C=O), 1562 [νas(NO2)], 1375 [νs(NO2)]. 1H NMR spectrum, δ, ppm: 2.44 s (3H, CH3), 4.14 br. s (1H, OH), 4.53 d. d (1H, СH2NO2,2J 13.3, 3J 7.4 Hz), 4.80 d. d (1H, СH2NO2, 2J 13.3, 3J 3.0 Hz), 5.63 d. d (1H, CH, 3J 7.4, 3J 3.0 Hz), 7.34 d (2H, Hm, 3J 8.2 Hz), 7.84 d (2H, Ho, 3J 8.2 Hz). 13C NMR spectrum, δC, ppm: 21.96 (CH3), 70.76 (C2), 79.02 (C3), 128.79 (Co), 130.10 (Cipso), 130.17 (Cm), 146.41 (Cp), 195.98 (C=O). Found, %: C 57.30; H 5.32; N 6.69. C10H11NO4. Calculated, %: C 57.41; H 5.30; N 6.70.

2-Hydroxy-1-(4-methoxyphenyl)-3-nitropropane-1-one (2b) was prepared similarly to compound 2a from 4.24 g (23 mmol) of 2-oxo-2-(4-methoxylphenyl)acetaldehyde 1b, 5.22 g (51 mmol) of Al2O3, and 100 mL of MeNO2. Yield 4.84 g (92%), white powder, mp 74–75°C (i-PrOH). IR spectrum, ν, cm–1: 3459 (OH), 1678 (C=O), 1562 [νas(NO2)], 1376 [νs(NO2)]. 1H NMR spectrum, δ, ppm: 3.90 s (3H, OCH3), 4.15 br. s (1H, OH), 4.50 d. d (1H, СH2NO2, 2J 13.2, 3J 7.9 Hz), 4.78 d. d (1H, СH2NO2, 2J 13.2, 3J 2.9 Hz), 5.64 d. d (1H, CH, 3J 7.9, 3J 2.9 Hz), 7.01 d (2H, Hm, 3J 8.9 Hz), 7.95 d (2H, Ho, 3J 8.9 Hz). 13C NMR spectrum, δC, ppm: 55.80 (OCH3), 70.52 (C2), 79.27 (C3), 114.75 (Cm), 125.31 (Cipso), 131.19 (Co), 165.08 (Cp), 194.46 (C=O). Found, %: C 53.30; H 4.90; N 6.24. C10H11NO5. Calculated, %: C 53.33; H 4.92; N 6.22.

1-(4-Bromophenyl)-2-hydroxy-3-nitropropane-1-one (2d) was prepared similarly to compound 2a from 3 g (38 mmol) of 2-oxo-2-(4-bromophenyl)acetaldehyde 1c, 3.31 g (33 mmol) of Al2O3, and 60 mL of MeNO2. Yield 2.85 g (90%), white powder, mp 63–65°C (i-PrOH). IR spectrum, ν, cm–1: 3473 (OH), 1691 (C=O), 1563[νas(NO2)], 1376 [νs(NO2)]. 1H NMR spectrum, δ, ppm: 4.03 br. s (1H, OH), 4.59 d. d (1H, СH2NO2, 2J 13.5, 3J 6.8 Hz), 4.80 d. d (1H, СH2NO2, 2J 13.5, 3J 3.1 Hz), 5.56 d. d (1H, CH, 3J 6.8, 3J 3.1 Hz), 7.70 d (2H, Hm, 3J 8.7 Hz), 7.82 d (2H, Ho, 3J 8.7 Hz). 13C NMR spectrum, δC, ppm: 70.93 (C2), 78.44 (C3), 130.08 (Cm), 130.39 (Cipso), 131.64 (Cp), 132.84 (Co), 195.69 (C=O). Found, %: C 39.40; H 2.92; N 5.10. C9H8BrNO4. Calculated, %: C 39.44; H 2.94; N 5.11.

(2E)-3-Nitro-1-phenylprop-2-en-1-one (3a). To a solution of 3.33 g (17 mmol) of 2-hydroxy-3-nitro-1-phenylpropane-1-one 2a and 3.95 mL (51 mmol) of mesyl chloride in dichloromethane, a solution of 7.07 mL (51 mmol) of triethylamine in dichloromethane was added dropwise at –18°C. The reaction mass was stirred for 30 min at –20°C and poured in a crushed ice. The product was extracted with chloroform (3×20 mL). The organic layer was dried over MgSO4. The solvent was evaporated, the crude residue was treated with isopropyl alcohol, and the precipitate was filtered off. Yield 2.5 g (83%), yellow powder, mp 92–94°C (i-PrOH) (mp 96–97°C[6]). IR spectrum, ν, cm–1: 1683 (C=O), 1539 [νas(NO2)], 1356 [νs(NO2)]. UV spectrum, λmax, nm (ε): 287 (5900), 236 (12200). 1H NMR spectrum, δ, ppm: 7.56 t (2H, Hm, 3J 7.7 Hz), 7.69 t (1H, Hp, 3J 7.4 Hz), 7.99–8.01 m (2H, Ho), 7.69 d (1H, H3, 3J 13.3 Hz), 8.12 d (1H, H2, 3J 13.3 Hz). 13C NMR spectrum, δC, ppm: 129.73 (C2), 148.26 (C3), 129.04 (Co), 129.33 (Cm), 134.97 (Cp), 135.97(Cipso), 187.11 (C=O). NMR spectrum 15N, δN, ppm: –9.6 (NO2).

(2E)-1-(4-Methylphenyl)-3-nitroprop-2-en-1-one (3b) was prepared similarly to compound 3a from 4.6 g (22 mmol) of 2-hydroxy-1-(4-methylphenyl)-3-nitropropane-1-one 2b, 5.1 mL (66 mmol) of mesyl chloride, and 9.15 mL (66 mmol) of triethylamine. Yield 3.7 g (88%), yellow powder, mp 90–92°C (i-PrOH), Rf = 0.35 (5% EtOAc in petroleum ether) [6]. IR spectrum, ν, cm–1: 1678 (C=O), 1539 [νas(NO2)], 1353 [νs(NO2)]. UV spectrum, λmax, nm (ε): 296 (7600), 236 (15100). 1H NMR spectrum, δ, ppm: 2.46 s (3H, CH3), 7.35 d (2H, Hm, 3JHH 8.3 Hz), 7.68 d (1H, H3, 3J 13.2 Hz), 7.90 d (2H, Ho, 3J 8.3 Hz), 8.11 d (1H, H2, 3J 13.2 Hz). 13C NMR spectrum, δC, ppm: 21.98 (CH3), 129.19 (Co), 129.91 (C2), 130.03 (Cm), 133.59 (Cipso), 146.37 (Cp), 148.04 (C3), 186.53 (C=O). NMR spectrum 15N, δN, ppm: –10.6 (NO2).

(2E)-1-(4-Methoxyphenyl)-3-nitroprop-2-en-1-one (3c) was prepared similarly to compound 3a from 2.78 g (12 mmol) of 2-hydroxy-1-(4-methoxyphenyl)-3-nitropropane-1-one 2b, 2.85 mL (37 mmol) of mesyl chloride, and 5.1 mL (37 mmol) of triethylamine. Yield 1.56 g (62%), yellow powder, mp 85–87°C (i-PrOH) (mp 76–78°C [6]). IR spectrum, ν, cm–1: 1674 (C=O), 1539 [νas(NO2)], 1354 [νs(NO2)]. UV spectrum, λmax, nm (ε): 327 (7400), 247 (13700). 1H NMR spectrum, δ, ppm: 3.91 s (3H, OCH3), 7.01 d (2H, Hm, 3J 9.0 Hz), 7.67 d (1H, Н3, 3J 13.2 Hz), 7.98 d (2H, Ho, 3J 9.0 Hz), 8.11 d (1H, Н2, 3J 13.2 Hz). 13C NMR spectrum, δC, ppm: 55.83 (OCH3), 114.60 (Cm), 129.13 (Cipso), 129.98 (C2), 131.61 (Co), 147.81 (C3), 165.13 (Cp), 185.09 (C=O). NMR spectrum 15N, δN, ppm: –9.3 (NO2).

(2E)-1-(4-Bromophenyl)-3-nitroprop-2-en-1-one (3d) was prepared similarly to compound 3a from 2.1 g (8.6 mmol) of 1-(4-bromophenyl)-2-hydroxy-3-nitropropane-1-one 2d, 2.0 mL (26 mmol) of mesyl chloride, and 3.56 mL (26 mmol) of triethylamine. Yield 1.17 g (60%), yellow powder, mp 116–118°C (i-PrOH). IR spectrum, ν, cm–1: 1679 (C=O), 1541 [νas(NO2)], 1352 [νs(NO2)]. UV spectrum, λmax, nm (ε): 289 (11100), 236 (18200). 1H NMR spectrum, δ, ppm: 7.70 d (1H, Н3, 3J 13.2 Hz), 7.71 d (2H, Hm, 3J 8.7 Hz), 7.86 d (2H, Ho, 3J 8.7 Hz), 8.07 d (1H, H2, 3J 13.2 Hz). 13C NMR spectrum, δC, ppm: 129.11 (C2), 130.38 (Co), 130.65 (Cipso), 132.75 (Cm), 134.65 (Cp), 148.58 (C3), 186.11 (C=O). NMR spectrum 15N, δN, ppm: –10.7 (NO2). Found, %: C 42.30; H 2.34; N 5.50. C9H6BrNO3. Calculated, %: C 42.22; H 2.36; N 5.47.

2,3-Dibromo-3-nitro-1-phenylpropane-1-one (4a). A solution of 0.5 g (2.82 mmol) of (2E)-3-nitro-1-phenylprop-2-en-1-one 3a and 0.36 mL (7.05 mmol) of molecular bromine in 20 mL of anhydrous CCl4 was kept at room temperature for 48 h. After removing the solvent, the crude residue was treated with isopropyl alcohol, and the precipitate was filtered off. Yield 0.95 g (95%), white powder, mp 55–57°C, Rf = 0.48 [49]. IR spectrum, ν, cm–1: 1690 (C=O), 1574 [νas(NO2)], 1354 [νs(NO2)]. Diastereomer a, 1H NMR spectrum, δ, ppm: 5.69 d (1H, Н2, 3J 9.7 Hz), 6.45 d (1H, Н3, 3J 9.7 Hz), 7.53 t (2H, Hm, 3J 7.7 Hz), 7.67 t (1H, Hp, 3J 7.4 Hz), 8.03 d (2H, Ho, 3J 7.4 Hz). 13C NMR spectrum, δC, ppm: 45.05 (C2), 77.60 (C3), 129.21 (Co), 129.40 (Cm), 132.61 (Cipso), 135.12 (Cp), 190.44 (C=O); diastereomer b, 1H NMR spectrum, δ, ppm: 5.83 d (1H, Н2, 3J 10.4 Hz), 6.43 d (1H, Н3, 3J 10.4 Hz), 7.56 t (2H, Hm, 3J 7.7 Hz), 7.70 t (1H, Hp, 3J 7.7 Hz), 8.00 d (2H, Ho, 3J 7.4 Hz). 13C NMR spectrum, δC, ppm: 41.80 (C2), 75.01 (C3), 129.21 (Co), 129.40 (Cm), 133.09 (Cipso), 135.26 (Cp), 188.33 (C=O). Found, %: C 32.10; H 2.11; N 4.15. C9H7Br2NO3. Calculated, %: C 32.08; H 2.09; N 4.16.

2,3-Dibromo-1-(4-methylphenyl)-3-nitropropane-1-one (4b) was prepared similarly to compound 4a from 1.6 g of (8.3 mmol) (2E)-1-(4-methylphenyl)-3-nitropropane-2-en-1-one 3b and 3.33 g (20.8 mmol) of molecular bromine. Yield 2.85 g (90%), white powder, mp 56–58°C. IR spectrum, ν, cm–1: 1684 (C=O), 1572 [νas(NO2)], 1353 [νs(NO2)]. Diastereomer a, 1H NMR spectrum, δ, ppm: 2.45 s (3H, CH3), 5.66 d (1H, Н2, 3J 9.8 Hz), 6.44 d (1H, Н3, 3J 9.8 Hz), 7.33 d (2H, Hm, 3J 8.4 Hz), 7.90 d (2H, Ho, 3J 8.4 Hz). 13C NMR spectrum, δC, ppm: 22.03 (CH3), 45.08 (C2), 77.71 (C3), 129.33 (Co), 130.08 (Cm), 130.64 (Cipso), 146.47 (Cp), 190.44 (C=O); diastereomer b, 1H NMR spectrum, δ, ppm: 2.46 s (3H, CH3), 5.80 (1H, Н2, 3J 10.4 Hz), 6.42 d (1H, Н3, 3J 10.4 Hz), 7.35 d (2H, Hm, 3JHH = 8.2 Hz), 7.92 (2H, Ho, 3J 8.2 Hz). 13C NMR spectrum, δC, ppm: 21.98 (CH3), 41.80 (C2), 75.14 (C3), 129.33 (Co), 129.91 (Cipso), 130.08 (Cm), 146.68 (Cp), 187.92 (C=O). Found, %: C 34.20; H 2.60; N 4.00. C10H9Br2NO3. Calculated, %: C 34.22; H 2.58; N 3.99.

2,3-Dibromo-1-(4-methoxyphenyl)-3-nitropropane-1-one (4c) was prepared similarly to compound 4a from 1.8 g (8.8 mmol) of (2E)-1-(4-methoxyphenyl)-3-nitropropane-2-en-1-one 3c and 3.54 g (22.1 mmol) of molecular bromine. Yield 2.6 g (80%), white powder, mp 58–60°C. IR spectrum, ν, cm–1: 1676 (C=O), 1574 [νas(NO2)], 1352 [νs(NO2)]. Diastereomer a, 1H NMR spectrum, δ, ppm: 3.90 s (3H, OCH3), 5.63 d (1H, Н2, 3J 9.7 Hz), 6.44 d (1H, Н3, 3J 9.7 Hz), 6.99 d (2H, Hm, 3J 9.1 Hz), 7.98 d (2H, Ho, 3J 9.1 Hz). 13C NMR spectrum, δC, ppm: 55.81 (OCH3), 45.04 (C2), 77.81 (C3), 114.49 (Cm), 125.45 (Cipso), 131.74 (Co), 165.12 (Cp), 188.83 (C=O); diastereomer b, 1H NMR spectrum, δ, ppm: 3.91 s (3H, OCH3), 5.77 d (1H, Н2, 3J 10.4 Hz), 6.41 d (1H, Н3, 3J 10.4 Hz), 7.01 d (2H, Hm, 3J 9.0 Hz), 8.00 d (2H, Ho, 3J 9.0 Hz). 13C NMR spectrum, δC, ppm: 55.85 (OCH3), 41.75 (C2), 75.29 (C3), 114.66 (Cm), 125.97 (Cipso), 131.74 (Co), 165.26 (Cp), 186.75 (C=O). Found, %: C 32.70; H 2.50; N 3.80. C10H9Br2NO4. Calculated, %: C 32.73; H 2.47; N 3.82.

2,3-Dibromo-1-(4-bromophenyl)-3-nitropropane-1-one (4d) was prepared similarly to compound 4a from 0.45 g of (1.75 mmol) (2E)-1-(4-bromophenyl)-3-nitropropane-2-en-1-one 3d and 0.7 g (4.37 mmol) of molecular bromine. Yield 0.63 g (85%), white powder, mp 103–105°C. IR spectrum, ν, cm–1: 1691 (C=O), 1576 [νas(NO2)], 1352 [νs(NO2)]. Diastereomer a, 1H NMR spectrum, δ, ppm: 5.61 d (1H, Н2, 3J 9.7 Hz), 6.43 d (1H, Н3, 3J 9.7 Hz), 7.68 d (2H, Hm, 3J 8.7 Hz), 7.86 d (2H, Ho, 3J 8.7 Hz). 13C NMR spectrum, δC, ppm: 44.89 (C2), 77.31 (C3), 130.08 (Ar), 130.36 (Co), 131.39 (Ar), 132.63 (Cm), 189.56 (C=O); diastereomer b, 1H NMR spectrum, δ, ppm: 5.75 d (1H, Н2, 3J 10.4 Hz), 6.40 d (1H, Н3, 3J 10.4 Hz), 7.71 d (2H, Hm, 3J 8.7 Hz), 7.88 d (2H, Ho, 3J 8.7 Hz). 13C NMR spectrum, δC, ppm: 41.68 (C2), 74.77 (C3), 130.52 (Co), 130.89 (CAr), 131.83 (CAr), 132.79 (Cm), 187.44 (C=O). Found, %: C 26.00; H 1.40; N 3.40. C9H6Br3NO3. Calculated, %: C 25.99; H 1.45; N 3.37.

(2Z)-3-Bromo-3-nitro-1-phenylprop-2-en-1-one (5a). To a solution of 2.85 g (8.47 mmol) of 2,3-dibromo-3-nitro-1-phenylpropane-1-one 4a in 30 mL of anhydrous CCl4, 1.17 mL (8.47 mmol) of triethylamine in 10 mL of anhydrous CCl4 was added dropwise at –10°C. The reaction mixture was stirred for 1 h at –10°C. The precipitate of triethylammonium bromide was filtered off. After evaporation of solvent, the crude residue was treated with isopropyl alcohol, and the precipitate was filtered out. Yield 1.73 g (80%), yellow powder, mp 30–32°C (i-PrOH) (mp 25–26°C [49]). IR spectrum, ν, cm–1: 1682 (C=O), 1598 (C=C), 1539 [νas(NO2)], 1356 [νs(NO2)]. UV spectrum, λmax, nm (ε): 265 (7600). 1H NMR spectrum, δ, ppm: 7.55 t (2H, Hm, 3J 7.7 Hz), 7.69 t (1H, Hp, 3J 7.4 Hz), 7.95 d (2H, Ho, 3J 7.4 Hz), 8.49 s (1Н, Н2). 13C NMR spectrum, δC, ppm: 129.18 (Co), 129.37 (Cm), 131.06 (C2), 135.00 (Cipso), 135.20 (Cp), 135.50 (C3), 187.82 (C=O). 15N NMR spectrum, δN, ppm: –16.3 (NO2). Found, %: C 42.20; H 2.38; N 5.50. C9H6BrNO3. Calculated, %: C 42.22; H 2.36; N 5.47.

(2Z)-3-Bromo-1-(4-methylphenyl)-3-nitroprop-2-en-1-one (5b) was prepared similarly to compound 5a from 2.6 g (7.38 mmol) of 2,3-dibromo-1-(4-methylphenyl)-3-nitropropane-1-one 4b and 1.2 mL (7.38 mmol) of triethylamine. Yield 1.25 g (63%), yellow powder, mp 79–81°C (i-PrOH). IR spectrum, ν, cm–1: 1678 (C=O), 1603 (C=C), 1539 [νas(NO2)], 1353 [νs(NO2)]. UV spectrum, λmax, nm (ε): 272 (10200). 1H NMR spectrum, δ, ppm: 2.45 s (3H, CH3), 7.34 d (2H, Hm, 3J 8.2 Hz), 7.84 d (2H, Ho, 3J 8.2 Hz), 8.47 s (1Н, H2). 13C NMR spectrum, δC, ppm: 22.04 (CH3), 129.34 (Co), 130.08 (Cm), 131.45 (C2), 132.54 (Cipso), 135.09 (C3), 146.65 (Cp), 187.41 (C=O). 15N NMR spectrum, δN, ppm: –16.5 (NO2). Found, %: C 44.50; H 3.00; N 5.15. C10H8BrNO3. Calculated, %: C 44.47; H 2.99; N 5.19.

(2Z)-3-Bromo-1-(4-methoxyphenyl)-3-nitroprop-2-en-1-one (5c) was prepared similarly to compound 5a from 1.99 g (5.42 mmol) of 2,3-dibromo-1-(4-methoxyphenyl)-3-nitropropane-1-one 4c and 0.75 mL (5.42 mmol) of triethylamine. Yield 1.55 (77%), yellow powder, mp 69–71°C (i-PrOH). IR spectrum, ν, cm–1: 1670 (C=O), 1597 (C=C), 1555 [νas(NO2)], 1322 [νs(NO2)]. UV spectrum, λmax, nm (ε): 288 (12100). 1H NMR spectrum, δ, ppm: 3.90 s (3H, OCH3), 7.00 d (2H, Hm, 3J 8.8 Hz), 7.92 d (2H, Ho, 3J 8.8 Hz), 8.44 s (1Н, Н2). 13C NMR spectrum, δC, ppm: 55.81 (OCH3), 114.65 (Cm), 128.00 (Cipso), 131.71 (C2), 131.75 (Co), 134.74 (C3), 165.28 (Cp), 186.18 (C=O). 15N NMR spectrum, δN, ppm: –16.6 (NO2). Found, %: C 42.00; H 2.85; N 4.85. C10H8BrNO4. Calculated, %: C 41.98; H 2.83; N 4.90.

(2Z)-3-Bromo-1-(4-bromophenyl)-3-nitroprop-2-en-1-one (5d) was prepared similarly to compound 5a from 0.24 g (0.58 mmol) of 2,3-dibromo-1-(4-bromophenyl)-3-nitropropane-1-one 4d and 0.08 mL (0.58 mmol) of triethylamine. Yield 0.12 g (62%), yellow powder, mp 51–53°C (i-PrOH). IR spectrum, ν, cm–1: 1682 (C=O), 1587 (C=C), 1558 [νas(NO2)], 1324 [νs(NO2)]. UV spectrum, λmax, nm (ε): 274 (10000). 1H NMR spectrum, δ, ppm: 7.69 d (2H, Hm, 3J 8.6 Hz), 7.81 d (2H, Ho, 3J 8.6 Hz), 8.44 s (1Н, Н2). 13C NMR spectrum, δC, ppm: 130.49 (Co), 130.82 (Cp), 130.32 (C2), 132.78 (Cm), 135.98 (C3), 133.77 (Cipso), 186.85 (C=O). 15N NMR spectrum, δN, ppm: –17.0 (NO2). Found, %: C 32.25; H 1.50; N 4.20. C9H5Br2NO3. Calculated, %: C 32.27; H 1.50; N 4.18.

X-ray diffraction study of single crystals of compounds 3b and 5a was carried out on a Bruker D8 QUEST diffractometer. The cell parameters and experimental data were obtained at 100 K (graphite monochromator, λMoKα = 0.71073 Å, ω and φ scanning in 0.5° steps). Data collection and indexing, determination and refinement of unit cell parameters were carried out using the APEX2 software package [58]. Absorption accounting was carried out according to the SADABS program [59]. The structure was interpreted by the direct method according to the SHELXT-2014/5 program [60] and clarified by the full-matrix F2 MNC according to the SHELXL-2018/3 program [61]. All calculations were performed using the WingX-2020.1 software package [62]. Nonhydrogen atoms were refined in the anisotropic approximation. The hydrogen atoms were placed in calculated positions and refined according to the rider model. The figures were performed in the Mercury 2020.3 program [63], the analysis of intermolecular contacts was performed according to the PLATON program [64]. The crystallographic data of the structure are deposited in the Cambridge Crystal Structure Data Bank. Statistics on the collection of X-ray diffraction data and refinement of the structure, and also the corresponding CCDC numbers are shown in Table 1.