crystals Article Synthesis and X-ray Crystal Structure of New Substituted 3-40-Bipyrazole Derivatives. Hirshfeld Analysis, DFT and NBO Studies Ahmed T. A. Boraei 1,*, Matti Haukka 2 , Ahmed A. M. Sarhan 3, Saied M. Soliman 4 , Abdullah Mohammed Al-Majid 5 and Assem Barakat 5,* 1 Chemistry Department, Faculty of Science, Suez Canal University, Ismailia 41522, Egypt 2 Department of Chemistry, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland; matti.o.haukka@jyu.fi 3 Chemistry Department, Faculty of Science, Arish University, Al-Arish 45511, Egypt; [email protected] 4 Department of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426, Ibrahimia, Alexandria 21321, Egypt; [email protected] 5 Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia; [email protected] * Correspondence: [email protected] (A.T.A.B.); [email protected] (A.B.); Tel.: +966-11467-5901 (A.T.A.B.); Fax: +966-11467-5992 (A.B.) Abstract: A new compounds named 3-40-bipyrazoles 2 and 3 were synthesized in high chemical yield from a reaction of pyran-2,4-diketone 1 with aryl hydrazines under thermal conditions in MeOH. Compound 2 was unambiguously confirmed by single-crystal X-ray analysis. It crystalizes in a triclinic crystal system and space group P-1. Its crystal structure was found to be in good agreement Citation: Boraei, A.T.A.; Haukka, M.; with the spectral characterizations. With the aid of Hirshfeld calculations, the H ... H (54.8–55.3%) Sarhan, A.A.M.; Soliman, S.M.; and H ... C (28.3–29.2%) intermolecular contacts are the most dominant, while the O ... H (5.8–6.5%), Al-Majid, A.M.; Barakat, A. Synthesis N ... H (3.8–4.6%) and C ... C (3.0–4.9%) are less dominant. The compound has a polar nature and X-ray Crystal Structure of New with a net dipole moment of 6.388 Debye. The BD(2)C31-C32!BD*(2)N4-C34 (27.10 kcal/mol), Substituted 3-40-Bipyrazole ! ! Derivatives. Hirshfeld Analysis, DFT LP(1)N5 BD*(2)C31-C32 (36.90 kcal/mol), BD(1)C32-C34 BD*(1)C18-C31 (6.78 kcal/mol) and and NBO Studies. Crystals 2021, 11, LP(1)N4!BD*(1)N5-C31 (7.25 kcal/mol) are the strongest π!π*, n!π*, σ-σ* and n!σ* intramolec- 953. https://doi.org/10.3390/ ular charge transfer processes, respectively. cryst11080953 Keywords: pyran-2,4-dione; bipyrazole; Hirshfeld analysis; NBO; DFT Academic Editor: Paul R. Raithby Received: 10 July 2021 Accepted: 13 August 2021 1. Introduction Published: 15 August 2021 Pyranones are examples of ester-functional heterocyclic molecules which have been employed as a synthon for several targeted organic compounds [1]. These synthetic Publisher’s Note: MDPI stays neutral pyranones have been reported to have several applications related to medicine, including with regard to jurisdictional claims in HIV protease inhibitors [2], anticonvulsants [3], antitumor [4,5], antifungal [3], and anti- published maps and institutional affil- microbial [6] agents, and as plant-growth regulators [2,7]. On the other hand, some other iations. naturally occurring pyranones were reported to have interesting actions against bacteria, and also have cytotoxic effects (e.g., Marin natural product, Pectinatone) [8]. Another representative example works against inflammation and rheumatism (e.g., Bufalin) [9], and many others such as Pentylpyran-2-one [10] and Griseulin [11,12] exhibited antibiotic Copyright: © 2021 by the authors. and mosquitocidal effects, respectively. These substituted pyranones scaffold have been Licensee MDPI, Basel, Switzerland. studied extensively in the literature [13–15]. This article is an open access article Heterocycles comprising five-membered rings with two adjacent nitrogen atoms are distributed under the terms and called pyrazoles, and these pharmacophore-containing heterocycles have been shown to conditions of the Creative Commons have several therapeutic applications. They were reported to have interesting actions Attribution (CC BY) license (https:// against different diseases, including cancer, inflammation, and bacterial infection, and creativecommons.org/licenses/by/ 4.0/). can also be used as analgesic and antidepressant agents [16–18]. Pyrazolines are also Crystals 2021, 11, 953. https://doi.org/10.3390/cryst11080953 https://www.mdpi.com/journal/crystals Crystals 2021, 11, 953 2 of 13 widely distributed in nature in the cells of animals and plants, and also exist in alkaloids, pigments, and vitamins [19]. Many approaches have been reported for the synthesis of pyrazoline scaffolds [20–26]. One representative common approach is a reaction of carbonyl compounds with hydrazines under thermal conditions [27], in addition to other reported methods for the synthesis of pyrazolines scaffold, such as the metal catalyzed approach [28]. In this context and continuation of our research program [29,30] here, we are reporting a facile and direct straightforward approach for the synthesis of substituted 3-40-bipyrazoles in a catalyst free one-pot reaction, from pyran-2,4-dione and arylhydrazines. The structure of the newly synthesized 3-40-bipyrazoles was confirmed by using different spectral charac- terizations. The X-ray structure of the bipyrazole 2 was further confirmed by single-crystal X-ray structure. Additionally, DFT calculations were used to predict its electronic parame- ters and calculate the different intramolecular charge transfer processes which stabilize the structure of 2. 2. Materials and Methods 2.1. General Melting points were measured using a melting-point apparatus (SMP10) in open capillaries and are uncorrected. The progress of the reaction was observed by thin-layer chromatography (TLC), and detection was achieved by UV light. Nuclear magnetic res- 1 13 onance ( H- and C-NMR) spectra were determined in DMSO-d6 and were recorded on a Bruker AC 400 MHz spectrometer using tetramethylsilane as an internal standard. Chemical shifts are described in d (ppm) and coupling constants are given in Hz. Ele- mental analysis was performed on a Flash EA-1112 instrument. X-ray crystallographic analysis was collected on a Rigaku Oxford Diffraction Supernova diffractometer using Cu Kα radiation. The UV-Vis electronic spectra were recorded in EtOH using a T90+UV/VIS spectrometer. 2.2. Synthesis of 2 and 3 A methanolic solution of pyran-2,4-dione 1 (1.0 mmol) was mixed with phenylhy- drazine or 4-chlorophenylhydrazine HCl (2.2 mmol) in methanol (10 mL), then the mixture was refluxed for 4 h. The resulting solutions were cooled to room temperature. The formed precipitates were collected by filtration and dried. Purifications were performed by re- crystallization from EtOH in case of 2 and DCM/MeOH in case of 3. Only good quality single crystals were obtained for 2, which were found to be suitable for single-crystal X-ray diffraction analysis. 2.2.1. 2,20,5,50-Tetraphenyl-10,20-Dihydro-2H,30H-[3,40-Bipyrazol]-30-One (2) ◦ 1 Yield: 88%, m.p. 270–271 C. H-NMR (400 MHz, DMSO-d6) δ 12.01 (s, 1H), 7.99 (d, J = 7.6 Hz, 2H), 7.84 (d, J = 8.0 Hz, 2H), 7.53 (t, J = 7.6 Hz, 2H), 7.48 (t, J = 7.6 Hz, 13 2H),7.40–7.23 (m, 12H), 7.16 (s, 1H); C-NMR (101 MHz, DMSO-d6) δ 151.31, 140.28, 135.72, 133.33, 129.55, 129.30, 129.12, 128.79, 128.47, 127.57, 126.79, 126.59, 125.75, 124.21, 122.07, 108.40 (Figures S1 and S2 (Supplementary data)); CHN analysis for [C30H22N4O] C, 79.27; H, 4.88; N, 12.33; O, 3.52 found C, 79.38; H, 4.99; N, 12.21. UV-Vis (EtOH): 264 nm (Figure S7 (Supplementary data)). 2.2.2. 2,20-Bis(4-Chlorophenyl)-5,50-Diphenyl-10,20-Dihydro-2H,30H-[3,40- Bipyrazol]-30-One (3) ◦ 1 Yield: 61%, m.p. 227–228 C. H-NMR (400 MHz, DMSO-d6) δ 12.25 (s, 1H), 7.97 (d, J = 7.6 Hz, 2H), 7.89 (d, J = 8.8 Hz, 2H), 7.60 (d, J = 8.8 Hz, 2H), 7.48(t, J = 7.6 Hz, 2H), 13 7.41–7.27 (m, 10H), 7.16 (s, 1H); C-NMR (101 MHz, DMSO-d6) δ 151.68, 138.97, 135.66, 133.04, 131.88, 130.34, 129.54, 129.33, 129.16, 129.04, 128.91, 128.83, 128.65, 126.67, 126.36, 125.80, 125.65, 123.35, 108.53 (Figures S3 and S4 (Supplementary data)); CHN analysis for Crystals 2021, 11, 953 3 of 13 [C30H20Cl2N4O] C, 68.84; H, 3.85; Cl, 13.55; N, 10.70 found C, 68.99; H, 3.86; Cl, 13.67; N, 10.62. UV-Vis (EtOH): 269 nm and 320 nm (Sh); (Figure S7 (Supplementary data)). 2.3. Crystal Structure Determination The collecting experimental data for compound 2 are provided in the Supplementary Information. 2.4. Computational Study Protocols All software and protocols employed for Hirshfeld surface analysis and DFT calcula- tions are provided in the Supplementary Information. 3. Results and Discussion 3.1. Synthesis of 2 and 3 In our recent publication [29], we reported that the pyran-2,4-diketone 1 could react with different amines and also amino acid esters to afford b-enaminones in a region- selective conversion. Interestingly, when pyran-2,4-dione 1 was reacted with aromatic hydrazines (phenylhydrazine and 4-chlorophenylhydrazine HCl) in MeOH under reflux conditions, the 3,40-bipyrazol-30-ones 2 and 3 were obtained. We assumed that the reaction occurred under a set of chemical transformations, including keto-enol tautomerism, aryl hydrazone formation, ring opening–closure, then keto-enol tautomerism, followed by aryl hydrazone formation with the second molecule of aryl hydrazine, and finally, ring closure upon the dehydration process (Scheme1).