Straightforward One-Pot Synthesis of New 4-Phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one Derivatives: X-ray Single Crystal Structure and Hirshfeld Analyses

Abstract

A straightforward one-pot route for the synthesis of a new 4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one is reported form the direct hydrazinolysis of triketo ester and hydrazine hydrate in ethanol. 4-Phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one was subjected to aza-Michael addition and N-alkylation on reaction with a set of alkylating agents in the presence of K₂CO₃. Hydrazinolysis of 4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one ester to hydrazide and conversion of hydrazide to thiosemicarbazide were successful. X-Ray single crystals analysis and ¹H, ¹³C NMR were used for unambiguous structure confirmation. The O…H, N…H, C…N and C…C in 2, and the N…H, C…N, C…C, C…O and H…H interactions in 6 are the most important in the molecular packing based on Hirshfled analysis. Moreover, the presence of short C…C and C…N contacts in both compounds revealed the presence of π–π stacking interactions.

1. Introduction

Polycyclic aromatic heterocycles are a class of chemicals include multi-ring aromatic compounds. In particular, fluoranthenes [1,2,3] are an example of four fused aromatic heterocycles which recentlyreceived a lot of attention, because this core structure has remarkable applications such as organic electronics [4]. Fluoranthene is a building block which was found in many natural products, for example, daldinone E (fungus Daldinia sp.) [5], and hortein (which is a fungus Hortaea werneckii associated with the sponge Aplysina aerophoba) [6]. In a different application of fluoranthenes which was discovered as fluorescent probe (FLUN-550) is a new class of live cell permeant, nontoxic, selective staining and intracellular lipid droplets quantifications based fluoranthenes [7].

Design and synthesis of new substituted of fluoranthenes have been gaining a lot of interest in the last decade. The synthetic roads for this interesting scaffold reported in the literatures though transition metal mediated [8,9,10,11,12,13,14,15,16,17,18,19] or Diels–Alder reactions [20,21,22,23].

Indeed, the palladium compound, Pd₂(dba)₃ (20 mol%) was employed as active catalyst for the reaction between 1,8-dichloronaphthalenes and arylboronic acid at elevated temperature (up to 175 °C) to afford the fluoranthenes derivatives [24]. Another approach that utilized the Pd-catalyst system was achieved for the synthesis of fluoranthenes which proceeded via three steps based on the inter- and intramolecular C-H arylation [25].

The Suzuki−Miyaura reaction also is considered one of the synthetic protocols for the synthesis of fluoranthenes derivatives initiating form 1,8-diiodonaphthalene in the presence of palladium catalysts [26]. Koutentis et al. also explored the chemistry of this interesting scaffold which synthesized the aza-analogues by the oxidative and non-oxidative cyclization approach [27]. Other approaches employed the silica sulphuric acid: a reusable solid catalyst for one pot synthesis of densely substituted pyrrole-fused isocoumarins under solvent-free conditions [28].

Recently, Boraei et al. have demonstrated a green and straightforward method for the synthesis of tatraazafluoranthenones starting from ninhydrin and ethyl acetoacetate (β-ketoesters) in water as a green solvent [29].

In this article, we are validating the application of our previous published method and used other β-ketoesters (ethyl benzoylacetate) and ninhydrin for the synthesis of new tatraazafluoranthenone analogues in straightforward, one-pot free catalyst route (Figure 1).

2. Materials and Methods

General Information

“Stuart Melting Point apparatus [SMP10], Bibby Scientific Ltd., (Wilmington, DE, USA) was used for measuring melting points in open capillaries and were uncorrected. Monitoring of reactions progress was done using TLC Merck aluminum-precoated silica gel plates (60 Å, F₂₅₄). Product spot visualization was achieved using UV light. NMR spectra were detected using Bruker spectrometer at 400 MHz for ¹H NMR and at 100 MHz for ¹³C NMR calibrated by (TMS, 0 ppm) as internal standard” (Supplementary Materials).

Synthesis of Ethyl 2-(2-hydroxy-1,3-dioxo-2,3-dihydro-1H-inden-2-yl)-3-oxo-3-phenylpropanoate (1)

This compound was synthesized and characterized according to the reported procedures [30,31].

Synthesis of 4-Phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one (2)

A mixture of triketo ester 1 [6.4 g, 18.2 mmol] and hydrazine hydrate [3.0 mL] was heated under refluxed in ethanol [10.0 mL] until ppt appeared (about 0.5–1 our). The reaction mixture cooled to room temperature and the formed solid was filtered, dried, and recrystallized from DMF/EtOH.

Yield (3.0 g, 55%), m.p. >300 °C. ¹H NMR (400 MHz, DMSO-d₆) δ 13.22 (s, 1H), 8.23 (d, J = 6.3 Hz, 1H), 7.99 (d, J = 8.0 Hz, 1H), 7.93 (d, J = 7.9 Hz, 2H), 7.69–7.68 (m, 2H), 7.55–7.54 (m, 3H); ¹³C NMR (100 MHz, DMSO-d₆) δ 158.1, 157.9, 157.1, 145.0, 137.3, 135.8, 135.7, 132.9, 131.7, 130.6, 130.4, 128.2, 127.6, 123.8, 123.1, 118.9; Elemental analysis (CHN) calculated for [C₁₈H₁₀N₄O]: C, 72.48, H, 3.38, N, 18.78, O, 5.36 found C, 72.61, H, 3.42, N, 18.65.

Michael Addition procedure

A mixture of Michael donor 2 (0.6 g, 2.0 mmol) and Michael acceptor-acrylonitrile (0.12 g, 2.2 mmol) was refluxed in ethanol (10.0 mL) containing Et₃N (0.31 mL, 2.2 mmol) for 6 h. The mixture was cooled, the solid was filtered, and recrystallized from ethanol.

3-(3-Oxo-4-phenyl-1,2,5,6-tetraazafluoranthen-2(3H)-yl)propanenitrile (3)

Yield (0.55 g, 77%), m.p. 229–230 °C. ¹H NMR (400 MHz, DMSO-d₆) δ 8.26 (s, 1H), 8.02 (s, 1H), 7.91 (s, 2H), 7.72 (s, 2H), 7.57 (s, 3H), 4.46 (s, 2H), 3.06 (s, 2H); ¹³C NMR (101 MHz, DMSO-d₆) δ 158.1, 157.2, 156.7, 144.7, 137.3, 135.5, 133.1, 132.2, 130.6, 130.4, 128.1, 127.2, 124.0, 123.4, 118.9, 118.2, 48.3, 16.9; Elemental analysis (CHN) calculated for [C₂₁H₁₃N₅O]: C, 71.79; H, 3.73; N, 19.93, O, 4.55 found C, 71.81; H, 3.83; N, 19.71.

Alkylation procedure

A mixture of tetraazafluoranthen-3(2H)-one 2 (0.6 g, 2.0 mmol) and K₂CO₃ (0.3 g, 2.2 mmol), in equal volumes of dry acetone/DMF (10 mL) was stirred for one hour, then alkyl halide (2.2 mmol) was added portion wise, and the reaction mixture was left on stirring overnight (the reaction is monitored by TLC and reflux is fixed if reaction did not complete). Then, the solvent was removed, water was added for complete precipitation and the formed solid was collected by filtration, dried, and recrystallized from EtOH or DMF/EtOH.

2-Allyl-4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one (4)

Yield (0.54 g, 79%), m.p. 190–191 °C. ¹H NMR (400 MHz, CDCl₃) δ 8.34–8.26 (m, 1H), 7.99–7.98 (m, 3H), 7.66–7.54 (m, 5H), 6.13–6.04 (m, 1H), 5.37 (d, J = 17.2 Hz, 1H), 5.30 (d, J = 10.2 Hz, 1H), 4.91 (d, J = 5.9 Hz, 2H); ¹³C NMR (101 MHz, CDCl₃) δ 158.1, 157.5, 156.3, 144.7, 137.3, 135.5, 134.8, 132.2, 131.8, 131.4, 130.5, 130.3, 128.0, 126.8, 124.00, 123.0, 119.1, 117.6, 55.6; Elemental Analysis calculated for [C₂₁H₁₄N₄O]: C, 74.54; H, 4.17; N, 16.56, O, 4.73 found C, 74.69; H, 4.30; N, 16.61.

2-Benzyl-4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one (5)

Yield (0.64 g, 83%), m.p. 224–225 °C. ¹H NMR (400 MHz, DMSO-d₆) δ 8.24 (s, 1H), 8.00 (s, 1H), 7.88 (s, 2H), 7.69 (s, 2H), 7.55 (s, 3H), 7.39 (s, 2H), 7.31 (d, J = 19.8 Hz, 3H), 5.41 (s, 2H); ¹³C NMR (101 MHz, DMSO-d₆) δ 158.2, 157.3, 156.8, 144.8, 137.4, 137.2, 135.7, 132.9, 132.0, 130.6, 130.3, 128.9, 128.1, 127.9, 127.3, 123.9, 123.3, 118.4, 56.0; Elemental Analysis calculated for [C₂₅H₁₆N₄O]: C, 77.30; H, 4.15; N, 14.42, O, 4.12 found C, 77.43; H, 4.21; N, 14.31.

2-Pentyl-4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one (6)

Yield (0.45 g, 61%), m.p. 116–117 °C. ¹H NMR (400 MHz, CDCl₃) δ 8.29–8.28 (m, 1H), 7.99–7.97 (m, 3H), 7.65–7.54 (m, 5H), 4.29 (t, J = 7.5 Hz, 2H), 1.95–1.74 (m, 2H), 1.41–1.40 (m, 4H), 0.93 (t, J = 6.0 Hz, 3H); ¹³C NMR (101 MHz, CDCl₃) δ 158.1, 157.5, 156.4, 144.2, 137.2, 135.7, 134.9, 132.2, 131.3, 130.4, 130.3, 128.0, 126.6, 124.0, 122.8, 117.5, 53.4, 28.9, 28.5, 22.4, 14.0; Elemental analysis (CHN) calculated for [C₂₃H₂₀N₄O]: C, 74.98; H, 5.47; N, 15.21, O, 4.34 found C, 75.11; H, 5.63; N, 15.30.

Ethyl 2-(3-oxo-4-phenyl-1,2,5,6-tetraazafluoranthen-2(3H)-yl)acetate (7)

Yield (0.63 g, 81%), m.p. 189–190 °C. ¹H NMR (400 MHz, CDCl₃) δ 8.31 (d, J = 7.1 Hz, 2H), 7.99–7.96 (m, 3H), 7.75–7.53 (m, 4H), 4.96 (s, 2H), 4.27 (q, J = 7.1 Hz, 2H), 1.26 (t, J = 7.1 Hz, 3H); ¹³C NMR (101 MHz, CDCl₃) δ 168.0, 158.1, 157.4, 156.8, 145.3, 137.5, 135.2, 134.7, 132.3, 131.8, 130.5, 130.3, 128.0, 127.3, 124.1, 123.2, 117.6, 62.0, 52.8, 14.2; Elemental Analysis calculated for [C₂₂H₁₆N₄O₃]: C, 68.74; H, 4.20; N, 14.58, O, 12.49 found C, 68.88; H, 4.14; N, 14.41.

Synthesis of 2-(3-Oxo-4-phenyl-1,2,5,6-tetraazafluoranthen-2(3H)-yl)acetohydrazide (8)

Tetraazafluoranthen-3(2H)-one ethyl ester 7 (0.77 g, 2.0 mmol) and hydrazine hydrate 80% (2.0 mL) was refluxed in ethanol (10 mL) for 2 hours, left to cool, the formed solid product was collected by filtration, dried, and recrystallized from EtOH.

Yield (0.67 g, 90%), m.p. 287–288 °C.¹H NMR (400 MHz, DMSO-d₆) δ 9.26 (s, 1H), 8.30–8.27 (m, 1H), 8.04–8.02 (m, 1H), 7.90–7.87 (m, 2H), 7.74–7.72 (m, 2H), 7.62–7.51 (m, 3H), 4.81 (s, 2H), 4.31 (s, 2H); ¹³C NMR (101 MHz, DMSO-d₆) δ 166.3, 158.2, 156.9, 144.8, 137.3, 135.5, 133.1, 132.2, 130.6, 130.5, 128.2, 127.5, 124.0, 123.4, 118.3, 55.0; Elemental Analysis calculated for [C₂₀H₁₄N₆O₂]: C, 64.86; H, 3.81; N, 22.69, O, 10.91 found C, 64.99; H, 3.93; N, 22.61.

Synthesis of 2-(2-(3-Oxo-4-Phenyl-1,2,5,6-tetraazafluoranthen-2(3H)-yl)acetyl)-N-phenylhydrazine-1-carbothioamide (9)

To the tetraazafluoranthene-hydrazide 8 (0.74 g, 2.0 mmol) in ethanol (10 mL), phenyl isothiocyanate (0.26 mL, 2.2 mmol) was added. The mixture was refluxed for 4 hours, then cooled. The solid product was collected by filtration, dried, and recrystallized from DMF/EtOH.

Yield (0.82 g, 82%), m.p. >300 ¹H NMR (400 MHz, DMSO-d₆) δ 10.40 (s, 1H), 9.82 (s, 1H), 9.36 (brs, 1H), 8.31–8.29 (m, 1H), 8.10–7.95 (m, 1H), 7.94–7.87 (m, 2H), 7.79–7.69 (m, 2H), 7.66–7.50 (m, 3H), 7.41–7.39 (m, 2H), 7.31 (t, J = 7.8 Hz, 2H), 7.19 (t, J = 7.7 Hz, 1H), 5.03 (s, 2H); ¹³C NMR (101 MHz, DMSO-d₆) δ 181.0, 166.9, 158.1, 157.2, 157.0, 144.8, 139.3, 137.2, 135.4, 133.1, 132.2, 130.6, 128.6, 128.2, 127.2, 125.6, 124.0, 123.4, 118.0, 55.6; Elemental Analysis calculated for [C₂₇H₁₉N₇O₂S]: C, 64.15; H, 3.79; N, 19.39; O, 6.33; S, 6.34 found C, 64.31; H, 3.71; N, 19.29; S, 6.37.

3. Results and Discussion

3.1. Chemistry

Hydrazinolysis of triketo ester 1 by hydrazine hydrate in ethanol under reflux for 0.5-1 h, fascinatingly, gave 4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one 2 in moderate yield (55%) (Scheme 1). The ¹H NMR displayed, in addition to the aromatic proton signals between δ 8.23 and 7.55 ppm, a signal at δ 13.22 ppm for NH. The ¹³C NMR showed all carbons between δ 158.1 and 118.9 ppm.

Aza-Michael addition was explored from the addition of 2 to acrylonitrile in ethanol and the presences of Et₃N to give the Michael adduct 3 in good yield (Scheme 2). The Michael adduct revealed two new signals at δ 4.46 and 3.06 ppm in ¹H NMR and their respective carbons appeared at δ 48.3 and 16.9 ppm in ¹³C NMR which strongly support aza-Michael addition, not oxa-Michael addition.

Alkylation of 4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one 2 with allyl bromide, benzyl bromide, amyl bromide, and ethyl chloroacetate was done in acetone/DMF and use of K₂CO₃ as proton capturer which led to N-alkylation and formation of aza-alkylated products 4–7 in good yields (Scheme 3). The allylated product 4 spectra demonstrated that the allyl group protons as: The sp² vinylic methine proton CH₂=CH- appeared as multiplet between 6.13 and 6.14 ppm, the vinylic sp² methylene protons H₂C=CH- were found as two doublet signals, one of them at 5.37 ppm with coupling constant value 17.2 Hz for the trans proton, and the other was deduced at 5.30 ppm with ³J value 10.2 Hz for the cis proton. The allylic sp³ methylene protons NCH₂ was established as doublet at 4.91 ppm. The allylic carbon atom NCH₂ was detected at δ 55.6 ppm. The benzylated compound 5 showed the benzyl methylene protons as singlet at 5.41 ppm and the corresponding benzylic methylene carbon at δ 56.0 ppm. The amylated tetraazafluoranthen-3(2H)-one 6 showed the amyl group protons at δ 4.29, 1.95–1.74, 1.41–1.40, and 0.93 ppm and the respective amyl carbons at δ 53.4, 28.5, 22.4, and 14.0 ppm. The esterified product 7 showed a singlet signal at 4.96 ppm for NCH₂, a quartet signal at δ 4.29 ppm for OCH₂, and a triplet signal at δ 1.26 ppm for CH₃. The ¹³C NMR displayed the carbonyl carbon of the ester group at δ 168.0 ppm, the OCH₂ at 62.0 ppm, NCH₂ at δ 52.8 ppm, and CH₃ at δ 14.2 ppm.

Reaction of 4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one ester 7 with hydrazine hydrate afforded the hydrazide 8 which was subjected to reaction with phenyl isothiocyanate in ethanol to afford the thiosemicarbazide 9 (Scheme 4). The 4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one hydrazide 8 displayed the hydrazide group protons at δ 9.26 and 4.31 ppm for NH and NH₂, respectively, in addition to the NCH₂ protons at δ 4.81 ppm. The ¹³C NMR showed the carbonyl carbon of the hydrazide group at δ 166.3 ppm and the NCH₂ methylene carbon at δ 55.0 ppm. The 4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one thiosemicarbazide 9 showed the three NH protons signals at δ 10.40, 9.82, and 9.36 ppm. The respective ¹³C NMR detected the thiocarbonyl carbon (C=S) at δ 181.0 ppm, the carbonyl carbon (C=O) at δ 166.9 ppm, and the NCH₂ methylene carbon at δ 55.6 ppm.

3.2. X-ray Discerption of Compounds 2 and 6

The X-ray structure of 2 is presented in Figure 2A. The structure of 2 crystallized in the orthorhombic crystal system and Pbca space group with lattice parameters: a = 12.82600(10) Å, b = 7.80290(10) Å andc = 26.6306(2) Å, and unit cell volume of 2665.19(4) Å3 and Z = 8 (Table 1). There are four fused ring systems which are almost coplanar. The phenyl ring attached to this fused system is twisted from its mean plan by 47.96°Selected geometric parameters of 2 are listed in Table 2.

The supramolecular structure of 2 is dominated by the N4-H4…N1 hydrogen bonding interactions leading to the hydrogen bonding polymer shown in the upper part of Figure 2. The hydrogen bond parameters are listed in Table 3. In addition, the hydrogen bonded chains are stacked to each other via significant amount of π–π contacts. The shortest π–πstacking interactions are listed in Table 4. Hence, the supramolecular structure of 2 could be described by 1D hydrogen bonding polymer along the b-direction (Figure 3; upper part) combined with π–π stacking interactions along the a-direction (Figure 3; lower part).

The X-ray structure of 6 is presented in Figure 2B. The structure of 6 crystallized in the less symmetric monoclinic crystal system and P2₁/c space group with lattice parameters: a = 5.26840(10) Å, b = 15.21900(10) Å, c = 22.7155(2)Å, α = γ = 90 while β = 93.6920(10) and unit cell volume of 1817.54(4) Å3 and Z = 4. Selected geometric parameters of 6 are listed in Table 2. In this case, the mean plane of the almost coplanar fused ring system and the phenyl ring attached to it are twisted from one another by 40.66°. The value of the twist angle is less than that in 2. The packing in 6 is dominated by π–π stacking interactions shown in Figure 4 and the shortest interactions between the stacked π-system are listed in Table 4.

3.3. Analysis of Molecular Packing

Each crystal has its characteristic Hirshfeld surfaces which shed the light on the important intermolecular interactions which play important role in the crystal stability. In Figure 5, the different mapped surfaces of compounds 2 and 6 are summarized. The d_norm indicated a number of red spots related to intermolecular contacts shorter than the vdWs radii sum of the interacting atoms. In compound 2, the most important contacts are the O…H, N…H, C…N and C…C interactions. On the other hand, the N…H, C…N, C…C, C…O and H…H interactions are the most important. Summary of these short contacts and the corresponding interaction distances are depicted in Table 5. The results revealed very well the presence of large number of C…C and C…N contacts in both compounds which confirm the presence of π–π stacking interactions. Generally, these contacts occurred at longer interaction distances in 2 compared to 6. In addition, the red/blue triangles in the shape index and large green area in curvedness are other evidences on the presence of π–π stacking interactions (region D in Figure 5).

On the other hand, analysis of the fingerprint plot gave a quantitative summary for all intermolecular contacts occurred in the crystal structure of compounds 2 and 6 (Figure 6).The decomposition of the fingerprint plot gave a quantitative summary for all contacts that occurred in the crystal structures of compounds 2 and 6 (Figure 7). It is clear that the most frequent contacts in both compounds are the H…H interactions. The percentages of H…H interactions are 53.6 and 32.4% in compounds 2 and 6, respectively. The shortest H…H contacts in 6 are H1…H1 with interaction distance of 2.108 Å. In 2, all H…H contacts are significantly long and are considered of less importance compared to compound 6. The second most frequent contacts are the C…H interactions which comprised 15.9 and 23.1% from the whole interactions occurred in the crystal of 2 and 6, respectively. In compound 2, the percentages of the important O…H, N…H, C…N and C…C interactions are 3.5%, 13.6%, 2.2%, and 8.3%, respectively. Both O…H and N…H contacts appeared as sharp spikes in the fingerprint plot (Figure 6). As a result, these interactions are considered strong and play an important role in the crystal stability of 2 and the π–π stacking interactions as well. The spikes of the N…H and O…H interactions in 6 are less sharp, indicating weaker interactions than those that occurred in 2. The percentages of the O…H, N…H, C…N and C…C interactions in 6 are 9.0, 15.8, 7.3, and 9.1%, respectively.

4. Conclusions

In conclusion, this manuscript introduced a direct one-pot method for obtaining 4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one from triketo ester to validate the application of our previous published method. Herein, another β-ketoester (ethyl benzoylacetate) was used for obtaining the triketo ester which used for the synthesis of tatraazafluoranthenone. On reaction with Michael acceptors like acrylonitrile, aza-Michael addition was produced. Alkylation of tetraazafluoranthen-3(2H)-one in the presence of K₂CO₃ led to N-alkylation, not O-alkylation, this evidence was deduced from the ¹³C NMR signal around 50.00 ppm for NCH₂. Hydrazinolysis of 4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one ester led to hydrazide formation which is converted to thiosemicarbazide by reaction with phenyl isothiocyanate. Different intermolecular interactions that occurred in the crystal structures of compound 2 and 6 were analyzed using Hirshfled calculations.

Author Contributions

Conceptualization, A.T.A.B., A.B. and A.A.M.S.; methodology, M.S. and A.A.M.S.; software, M.H. and S.M.S.; validation, M.S. and A.A.M.S.; formal analysis, A.T.A.B., S.M.S. and M.H.; investigation, A.T.A.B. and A.A.M.S.; resources, A.T.A.B.; data curation, A.T.A.B. and M.H.; writing—original draft preparation, A.T.A.B., A.B.; writing—review and editing, A.B.; visualization, A.M.A.-M.; supervision, A.B.; project administration, M.S. and A.M.A.-M.; funding acquisition, A.M.A.-M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Researchers Supporting Project (RSP2022R427), King Saud University, Riyadh, Saudi Arabia.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The authors would like to extend their sincere appreciation to the Researchers Supporting Project (RSP2022R427), King Saud University, Riyadh, Saudi Arabia.

Conflicts of Interest

The authors declare no conflict of interest.

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures, Schemes and Tables

Figure 1. Retro-synthesis of the fluoranthenes.

Scheme 1. Synthesis of 4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one 2.

Scheme 2. Aza-Michael addition of compound 2 to acrylonitrile.

Scheme 3. Aza-alkylation of 4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one2 with a set of alkylating agents.

Scheme 4. Hydrazinolysis of 4-phenyl-1,2,5,6-tetraazafluoranthen-3(2H)-one ester and thiosemicarbazide formation.

Figure 2. ORTEP of compounds 2 (A) and 6 (B).

Figure 3. Packing via N-H…N hydrogen bonds and π–π stacking (lower) in 2.

Figure 4. π–π stacking (lower) in 2.

Figure 5. Hirshfeld maps of compounds 2 and 6. The most important interactions are (A) O…H, (B) N…H, (C) C…N, (D) C…C, (E) C…O, and (F) H…H.

Figure 6. Decomposed fingerprint plots in compounds 2 and 6.

Figure 7. All intermolecular interactions in compounds 2 and 6.

Table 1

Crystal data of 2 and 6.

Identification Code	2	6
CCDC	2,129,954	2,129,955
empirical formula	C18H10N4O	C23H20N4O
Fw	298.30	368.43
temp (K)	120(2) K	120(2)
λ(Å)	1.54184 Å	1.54184
Cryst. Syst.	Orthorhombic	Monoclinic
space group	Pbca	P21/c
a (Å)	12.82600(10)	5.26840(10)
b (Å)	7.80290(10)	15.21900(10)
c (Å)	26.6306(2)	22.7155(2)
α, β, γ (deg)	α = β = γ = 90	α = γ = 90;β = 93.6920(10)
V (Å3)	2665.19(4)	1817.54(4)
Z	8	4
ρcalc (Mg/m3)	1.487	1.346
μ(Mo Kα) (mm−1)	0.787	0.677
No. reflns.	37,511	46,295
Unique reflns.	2802	3840
Completeness to θ = 67.684°	100%	100%
GOOF (F2)	1.057	1.052
Rint	0.0290	0.0377
R1a (I ≥ 2σ)	0.0328	0.0356
wR2b (I ≥ 2σ)	0.0958	0.0901

^aR₁ = Σ||F_o| − |F_c||/Σ|F_o|. ^b wR₂ = {Σ[w(F_o² − F_c²)²]/Σ[w(F_o²)²]}^1/2.

Table 2

Selected bond lengths [Å] and angles [°] for 2.

2
O(1)-C(10)	1.2109(12)
N(1)-C(9)	1.3153(13)
N(1)-N(2)	1.3726(12)
N(2)-C(12)	1.3361(13)
N(3)-C(7)	1.3034(14)
N(3)-N(4)	1.3660(12)
N(4)-C(10)	1.4089(12)
6
O(1)-C(18)	1.2207(13)
N(1)-C(7)	1.3415(13)
N(1)-N(2)	1.3709(12)
N(2)-C(8)	1.3168(13)
N(3)-N(4)	1.3716(12)
N(3)-C(18)	1.4137(13)
N(3)-C(19)	1.4696(12)

Table 3

Hydrogen bonds for 2 [Å and °].

D-H...A	d(D-H)	d(H...A)	d(D...A)	<(DHA)
N(4)-H(4)...N(1)#1	0.927(18)	1.992(18)	2.9135(12)	172.3(13)
Symmetry code: #1 x, y−1, z

Table 4

π–π stacking for 2 and 6 [Å and °].

Contacts	Length	Contacts	Length
2		6
C1…C7	3.387	N2…C5	3.195
C1…C8	3.378	C11…C8	3.344
C3…C10	3.334	C12…C15	3.303
C6…C9	3.337	C14…C18	3.301

Table 5

Short contacts in compounds 2 and 6.

Contact	Distance	Contact	Distance
2		6
N1…H1	1.911	N2…H13	2.446
N2…H14	2.584	C5…N2	3.195
O1…H17	2.405	C11…C8	3.344
C10…N2	3.227	C12…C15	3.303
C1…C7	3.387	C14…C18	3.301
C1…C8	3.378	C15…O1	3.158
C3…C10	3.334	H1…H1	2.108
C6…C9	3.337

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/cryst12020262/s1, X-ray structure determinations; Figure S1: ¹H NMR of 2; Figure S2: ¹³C NMR of 2; Figure S3: ¹H NMR of 3; Figure S4: ¹³C NMR of 3; Figure S5: ¹H NMR of 4; Figure S6: ¹³C NMR of 4; Figure S7: ¹H NMR of 5; Figure S8: ¹³C NMR of 5; Figure S9: ¹H NMR of 6; Figure S10: ¹³C NMR of 6; Figure S11: ¹H NMR of 7; Figure S12: ¹³C NMR of 7; Figure S13: ¹H NMR of 8; Figure S14: ¹³C NMR of 8; Figure S15: ¹H NMR of 9; Figure S16: ¹³C NMR of 9.

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