Synthesis and Characterization of Novel Heterocyclic Chalcones from 1-Phenyl-1H-pyrazol-3-ol

Abstract

An efficient synthetic route to construct diverse pyrazole-based chalcones from 1-phenyl-1H-pyrazol-3-ols bearing a formyl or acetyl group on the C4 position of pyrazole ring, employing a base-catalysed Claisen–Schmidt condensation reaction, is described. Isomeric chalcones were further reacted with N-hydroxy-4-toluenesulfonamide and regioselective formation of 3,5-disubstituted 1,2-oxazoles was established. The novel pyrazole-chalcones and 1,2-oxazoles were characterized by an in-depth analysis of NMR spectral data, which were obtained through a combination of standard and advanced NMR spectroscopy techniques.

1. Introduction

Chalcones (or 1,3-diaryl-2-propen-1-ones) are widely distributed in naturally occurring products produced by bacteria, fungi, and numerous plant species. Chalcones do not accumulate in natural sources and serve as intermediates for flavanoid biosynthesis [1,2,3]. Chalcone-rich sources are highly valued, as they possess beneficial biological properties [1]. For example, licochalcone A demonstrated antibacterial effects against B. subtilis, human pathogenic Mycobacteria and Legionella species [4,5] and inhibited the growth of both Leishmania major and Leshmania donovani promastigotes and amastigotes or P. falciparum strains [6,7]. Isobavachalcone showed antifungal effects against Candida albicans and Cryptococcus neoformans [8]. Moreover, xanthohumol demonstrated antiviral properties against bovine viral diarrhoea virus, HSV-1 (herpes simplex virus) and HSV-2, CMV (cytomegalovirus) [9], and coronaviruses [10] and showed anti-HIV-1 activity [11]. Xanthohumol caused a dose-dependent decrease in the growth of human breast cancer (MCF7) [12,13], colon cancer (HT-29) [14,15], ovarian cancer (A-2780) [16] and prostate cancer cells in vitro [17].

The structural simplicity and therapeutic potential have motivated the design and development of synthetic chalcones with enhanced activity and potency [18].

Chalcones are usually synthesized from aromatic aldehydes and aliphatic aldehydes or ketones via the Claisen–Schmidt condensation reaction in the presence of base or acid catalysts [19,20,21,22]. Other procedures were efficiently employed for the synthesis of chalcones, including the Pd-catalysed Suzuki cross-coupling reaction between the appropriate cinnamoyl chloride and phenylboronic acid or benzoyl chloride and phenylvinylboronic acid or Heck coupling reaction between aryl iodide and an unsaturated ketone [23,24,25]. The Wittig olefination reaction of triphenylbenzoylmethylene phosphoranes and benzaldehydes and the Julia–Kocienski olefination technique of heteroaryl-sulfonyl phenylethanones and benzaldehydes were also applied to give chalcones in efficient yields [26].

Molecular modeling studies of chalcones using DFT methods indicated that 1,3-diaryl-2-propen-1-ones have two isomers, the (E)-isomer being thermodynamically more stable than the (Z)-isomer [27]. The (E)-chalcone derivatives are synthesized far more easily than the (Z)-isomer, and there have been only a few reports concerning the synthesis of the (Z)-isomers [28,29]. However, Yoshizawa et al. reported the synthesis of (Z)-chalcones from 1,3-diaryl-2-propynyl silyl ethers by a catalytic reaction using potassium tert-butoxide under acid treatment, in high yields and stereoselectivity [29]. Rajakumar et al. induced the photochemical E- to Z- isomerization of chalcone derivatives [30].

Among the synthetic chalcone derivatives, heterocyclic chalcones are important for medicinal chemistry, as most biologically active chemical entities contain a heterocyclic scaffold [31,32]. For example, Pd(II) or Pt(II) complexes containing chalcone I displayed good anticancer and antimicrobial activities [33], while the structure of pyridine-chalcone derivative II was developed as a potential anti-tubulin agent, with antiproliferative activity against a panel of cancer cell lines (Figure 1) [34]. The anticancer activity was also reported for indolizinyl compound III, with the potential to induce the caspase-dependent apoptosis of human lymphoma cells [35] or quinoxalinyl derivative IV, which was active against MCF-7-cell lines [36], and thiophen-2-yl derivative V, which was active against colorectal carcinoma cells by causing apoptosis [37]. Chalcone VI showed remarkable inhibition potency against AChE and MAO-B enzymes and, therefore, can be further developed as a novel, phenothiazine-based, dual-targeting inhibitor for neurogenerative diseases [38], while compound VII acts as a tissue transglutaminase inhibitor [39]. Compound VIII and analogues were designed as promising anti-tubercular agents by combining in silico design, QSAR-driven virtual screening, synthesis, and experimental evaluation. The synthesized nitroaromatic chalcone derivatives were also active against Mycobacterium tuberculosis strains resistant to isoniazid or rifampicin [40]. In addition, indole-based chalcone IX was reported to act as a nonselective COX-1 and COX-2 inhibitor and showed anti-inflammatory and antioxidant activities in vivo [41]. Moreover, pyrazole-based chalcone derivatives X–XII were also synthesized and investigated. Compound X was evaluated for its anti-inflammatory activity, and compounds XI and XII showed potential activity as chemotherapeutic agents for the treatment of hepatocellular carcinoma (HCC), as they caused cell cycle arrest at the G2/M phase and induced apoptotic cell death [42,43].

Figure 1.

Selected examples of heterocyclic chalcone derivatives for some biological applications.

Among heterocycles, pyrazoles are considered privileged scaffolds in medicinal chemistry [32]. Pyrazole derivatives are known to exhibit anti-inflammatory, analgesic, anticancer, antimicrobial, anti-infective and other activities [44,45,46,47]. In recent publications, we have reported the synthesis and antimitotic activity of 2,4- or 2,6-disubstituted- and 2,4,6-trisubstituted-2H-pyrazolo[4,3-c]pyridines [48], the antiproliferative activity of 2,4,6,7-tetrasubstituted-2H-pyrazolo[4,3-c]pyridines [49], the photodynamic properties in the human skin melanoma cell line G361 of pyrazole-indole hybrids [50] and N-aryl-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridin-7-amines [51] and the anthelmintic activity of benzopyrano[2,3-c]pyrazol-4(2H)-ones [52].

In continuation of our interest in the efficient synthesis of pyrazole-containing polycyclic systems starting from easily accessible 3-hydroxy-1-phenyl-1H-pyrazole, we report herein the synthesis and structural elucidation of novel, diverse pyrazole-chalcone derivatives via the base-catalysed, Claisen–Schmidt condensation reaction of 4-formyl or 4-acetyl-1-phenyl-1H-pyrazol-3-ols and appropriate acetophenones or carbaldehydes.

2. Results and Discussion

The synthesis of various (E)-3-(3-alkoxy-1-phenyl-1H-pyrazol-4-yl)-1-phenylprop-2-en-1-ones 4a–k was carried out, as depicted in Scheme 1. It started with the easily accessible 1-phenyl-1H-pyrazol-3-ol 1, which was converted to 3-methoxy-, 3-propoxy-, 3-(2-methoxyethoxy)- and 3-benzyloxy-1-phenyl-1H-pyrazoles 2a–d and corresponding 4-carbaldehydes 3a–d via O-alkylation and Vilsmeier–Haack formylation procedures in a similar manner to what we described earlier [48,53,54,55,56]. The obtained compounds 3a–d were then subjected to a Claisen–Schmidt condensation reaction with variously 4′-substituted acetophenones in the presence of ethanolic sodium hydroxide. The heating reaction mixture at 55 °C for 30 min afforded chalcones 4a–k in fair to excellent yields (58–97%). A similar synthetic approach towards pyrazole-chalcones employing alcoholic NaOH-catalysed, Claisen–Schmidt condensation of 3-aryl-1H-pyrazole-4-carbaldehydes and acetophenones was also demonstrated by Aneja et al. in the course of pyrazolylpyrazolines [57] or by Baytas et al. for the preparation of 1,3-diarylpyrazoles [43].

Scheme 1.

Reagents and conditions: (i) NaH, DMF (abs.), 0 °C; alkylhalide, 70 °C, 1 h; (ii) POCl₃, DMF, −10 °C to 70 °C, 1 h; (iii) acetophenone, NaOH, EtOH, 55 °C, 30 min.

An in-depth analysis of NMR spectral data, which were obtained through a combination of standard and advanced NMR spectroscopy techniques, such as ¹H-¹³C HMBC, ¹H-¹³C HSQC, ¹H-¹³C H2BC, ¹H-¹⁵N HMBC, ¹H-¹⁵N LR-HSQMBC, ¹H-¹H TOCSY, ¹H-¹H COSY, ¹H-¹H NOESY and 1,1-ADEQUATE experiments, provided the key information in the establishment of structural assignments and predominant configuration, due to conformations in a solvent of novel pyrazole-chalcones. The synthesis and biological activity of the related compounds has been reported in previous works, but no data on conformational analysis supported by NMR experiments were given [58,59,60,61].

In the case of compound 4a, the key information for structure elucidation was obtained from the ¹H-¹³C HMBC, ¹H-¹³C H2BC, ¹H-¹³C HSQC and ¹H-¹⁵N LR-HSQMBC spectral data (Figure 2). For instance, the pyrazole 5-H proton (singlet, δ 7.96 ppm) was easily distinguished, as it exhibited not only long-range HSQMBC correlations with neighboring N-1 “pyrrole-like” (δ −183.7 ppm) and N-2 “pyridine-like” (δ −118.7 ppm) nitrogen atoms, but also HMBC correlations with the quaternary carbons C-3 (δ 163.3 ppm) and C-4 (δ 107.0 ppm), respectively. The ¹H-¹³C HSQC spectrum indicated that the aforementioned proton had a one-bond connectivity with carbon C-5 (δ 129.0 ppm), thus completing our assignment of the 1H-pyrazol-4-yl moiety. Moreover, these findings unambiguously confirmed the connectivity with the neighboring 1-phenylprop-2-en-1-one fragment via long-range HMBC correlations of the olefinic H_a proton and the aforementioned pyrazole ring carbons. The E-configuration at the C=C double bond unequivocally follows from the magnitude of the vicinal coupling between the olefinic protons H_a (δ 7.74 ppm) and H_b (δ 7.60 ppm), which exhibited an AB-spin system and appeared as two sets of doublets (³J_Ha,Hb = 15.5 Hz). As expected, the ¹H-¹³C HMBC spectrum revealed distinct, long-range correlations between these olefinic protons and the phenyl group 2″(6″)-H protons (δ 8.02–8.03 ppm), with the characteristic signal of a carbonyl carbon (δ 190.7 ppm). The ¹H-¹H NOESY spectrum of 4a further elucidated the connectivities based on through-space correlations. In this case, distinct NOEs were exhibited between the pyrazole ring proton 5-H and the olefinic proton H_a, while the phenyl group 2″(6″)-H protons displayed correlation with the olefinic proton H_b, thus allowing different structural fragments to be joined.

Figure 2.

Relevant ¹H-¹³C HMBC, ¹H-¹³C H2BC, ¹H-¹⁵N LR-HSQMBC and ¹H-¹H NOESY correlations and ¹H NMR (italics), ¹³C NMR and ¹⁵N NMR (bold) chemical shifts of compound 4a.

The obtained (E)-3-[3-(benzyloxy)-1-phenyl-1H-pyrazol-4-yl]-1-phenylprop-2-en-1-ones 4g–i were further treated with trifluoroacetic acid for debenzylation. (E)-3-(3-Hydroxy-1-phenyl-1H-pyrazol-4-yl)-1-phenylprop-2-en-1-ones 5a–c were obtained in fair to good yields (63–83%), as outlined in Scheme 2. As expected, the cleavage of the OCH₃ group (compound 5b) under the given conditions was not observed.

Scheme 2.

Reagents and conditions: (i) TFA, toluene, rt, 24 h.

Furthermore, we investigated the applicability of pyrazol-3-ol 1 as a starting material for the synthesis of (E)-1-(3-hydroxy-1-phenyl-1H-pyrazol-4-yl)-3-phenylprop-2-en-1-ones 8a–l (Scheme 3). Compound 1 was converted to pyrazol-3-yl acetate 6, which was further subjected to Fries rearrangement reaction conditions, as previously described [48,56]. The obtained 4-acyl-3-hydroxy-1-phenyl-1H-pyrazole 7 was reacted with various (het)aromatic carbaldehydes under the Claisen–Schmidt reaction conditions to form targeted chalcones 8a–l. Stirring the reaction mixture of pyrazole 7 and benzaldehyde in EtOH in the presence of NaOH at 55 °C [57] led to the formation of chalcone 8a with a 88% yield. The same reaction conditions were applied to synthesize a series of novel (2E)-1-(3-hydroxy-1-phenyl-1H-pyrazol-4-yl)-3-phenylprop-2-en-1-ones 8b–l. Most chalcones were obtained in fair to excellent yields (58–95%); when 4-(dimethylamino)benzaldehyde, pyridine-3-, pyridine-4- and thiophene-2-carbaldehydes were utilized for the condensation, lower yields of the appropriate products 8f,h,i, and k were obtained (25–48%).

Scheme 3.

Reagents and conditions: (i) Ac₂O, 100 °C, 0.5 h in accordance with ref. [56]; (ii) AlCl₃, CS₂, reflux, 3 h in accordance with ref. [56]; (iii) appropriate carbaldehyde, NaOH, EtOH, 55 °C, 3–5 h; (iv) NaH, DMF (abs.), 0 °C; alkylhalide, 70 °C, 1 h.

To obtain (E)-1-(3-alkoxy-1-phenyl-1H-pyrazol-4-yl)-3-(het)arylprop-2-en-1-ones 9a–i, appropriate pyrazol-3-ols 8 were further O-alkylated using appropriate methyl-, propyl- and 2-methoxyethylhalides to produce alkoxy derivatives 9a–i in fair to excellent yields (40–96%).

A representative 3-phenylprop-2-en-1-one 9a showed distinct, long-range correlations in the ¹H-¹³C HMBC, ¹H-¹³C H2BC and ¹H-¹⁵N HMBC spectra, which in combination with the data from the 1,1-ADEQUATE experiment, allowed us to provide unambiguous assignments of the ¹H, ¹³C and ¹⁵N NMR resonances (Figure 3). For example, the pyrazole 5-H proton (singlet, δ 8.42 ppm) exhibited not only long-range HMBC correlations throughout the 1H-pyrazol-4-yl moiety, but also a strong correlation with the most downfield ¹³C resonance, which confidently was assigned to a carbonyl carbon (δ 183.3 ppm). This finding, in combination with the data from the 1,1-ADEQUATE experiment, allowed the adjacent protonated carbon to be assigned to the signal at δ 124.3 ppm, which showed a sole correlation with the aforementioned carbonyl carbon. Moreover, the protonated carbon also shared a correlation with an adjacent olefinic carbon that resonated at δ 142.6 ppm. With this information, the ¹H-¹³C HSQC spectral data were applied to identify olefinic protons H_a (δ 7.63 ppm) and H_b (δ 7.82 ppm), which exhibited an AB-spin system and appeared as two sets of doublets (³J_Ha,Hb = 15.7 Hz). The ¹H-¹H NOESY spectrum of 9a exhibited NOEs between the phenyl group 2″(6″)-H protons and both olefinic protons H_a and H_b, while proton H_a also had an NOE with a pyrazole 5-H proton, which confirms their proximity in space.

Figure 3.

Relevant ¹H-¹³C HMBC, ¹H-¹³C H2BC, ¹H-¹⁵N HMBC, ¹H-¹H NOESY and 1,1-ADEQUATE correlations and ¹H NMR (italics), ¹³C NMR and ¹⁵N NMR (bold) chemical shifts of compound 9a.

To expand the structural diversity of the pyrazole-based, chalcone derivatives, we also employed Claisen–Schmidt reaction conditions for the synthesis of 1-(1-phenyl-1H-pyrazol-4-yl)-3-phenylprop-2-en-1-ones with pyridin-3-yl or pyridin-4-yl substituents on the third position of the pyrazole ring (Scheme 4). We have previously demonstrated that 1-(3-hydroxy-1-phenyl-1H-pyrazol-4-yl)ethan-1-one can be efficiently converted to various 1-(3-aryl-1-phenyl-1H-pyrazol-4-yl)ethan-1-ones via O-triflation and Pd-catalysed Suzuki, Sonogashira or Heck reaction sequences [56]. In this research, 4-acetyl-1-phenyl-1H-pyrazol-3-yl trifluoromethanesulfonate 10 was subjected to a Pd-catalysed, Suzuki cross-coupling reaction with pyridin-3-yl and pyridin-4-yl boronic acids. When the cross-coupling reaction of triflate 10 and pyridin-3-yl boronic acid was performed under conventional heating in the presence of Pd(PPh₃)₄ and K₃PO₄ in refluxing dioxane, the starting materials decomposed. Refluxing the reaction mixture of coupling partners in EtOH in the presence of Pd(OAc)₂ and Cs₂CO₃ led to the formation of product 11a with only a 20% yield. The best result of Suzuki cross-coupling was accomplished using Pd(PPh₃)₄ as a catalyst and Cs₂CO₃ as a base and by performing the reaction at 80 °C with a microwave irradiation potency of 150 W in EtOH. 1-[1-Phenyl-3-(pyridinyl)-1H-pyrazol-4-yl]ethan-1-ones 11a,b were obtained in 63–64% yields. The reaction was carried out in the presence of KBr, which is known to suppress triflate reduction by stabilizing the cationic (σ-aryl)-palladium transition state [62]. 4-Acetylpyrazoles 11a,b were further employed in the Claisen–Schmidt condensation reaction with different carbaldehydes. The reaction was performed under the above-described conditions in the presence of ethanolic NaOH at 55 °C. As a result, when 1-[1-phenyl-3-pyridinyl-1H-pyrazol-4-yl]ethan-1-ones 11a,b were reacted with benzaldehyde, 4-methyl- or 4-(trifluoromethoxy)benzaldehyde E- and Z-chalcones (12a–f and 13a–f, respectively) were obtained in fair to good total yields (51–70%). The NMR spectra of inseparable mixtures showed the presence of both isomers in different ratios, with a predominance of the E-isomer. In contrast, compounds 12g–j were obtained only as pure E-isomers. This latter observation can be explained by the strong electron-donor capacity of the 4-methyloxy group based on the resonance structure, which results in increased electron density of the enone moiety, while the electronegativity of the 4-trifluoromethyl group has a significance for decreased electron density of the enone moiety. It is known in most cases that the E-isomer is more stable from the perspective of thermodynamics, which makes it the predominant configuration among the chalcones [27].

Scheme 4.

Reagents and conditions: (i) Tf₂O, TEA, DCM, rt, 1 h in accordance with ref. [56]; (ii) pyridin-3- or pyridin-4-yl boronic acid, Pd(PPh₃)₄, Cs₂CO₃, KBr, EtOH, 80 °C, 150 W, 10 min; (iii) appropriate carbaldehyde, NaOH, EtOH, 55 °C, 10 min.

It is widely accepted that a large and constant difference in the magnitudes of the ³J_HH coupling constants of the olefinic protons in E-Z isomers can be used for structural elucidation, which in our case were larger by approximately 3 Hz for the predominant E-isomer (15.6–15.7 Hz), while the minor Z-isomer provided significantly lower coupling constant values (12.7–12.8 Hz). Moreover, the 1D selective NOESY experimental data clearly showed that upon irradiation of the olefinic protons of the minor Z-isomer, the expected NOEs between them were observed. In the case of the major E-isomer, the olefinic protons exhibited only appropriate correlations with neighboring aromatic protons, therefore, unambiguously confirming the correct configuration (Figures S1–S3).

As expected, the NMR spectral data of compound 12g revealed a distinct difference in chemical shifts in the 1H-pyrazol-4-yl moiety compared with the other series of pyrazolo-chalcones, due to the pyridin-3-yl substituent on the third position of the pyrazole ring (Figure 4). The key information for structure elucidation of the pyridin-3-yl moiety was obtained from the ¹H-¹H TOCSY spectrum. The results clearly showed a spin system of four protons, which were mostly downfield. Moreover, a comparison between the ¹H-¹H COSY spectra and the ¹H-¹H TOCSY spectra showed a complete absence of COSY cross-peaks between one of the protons, with the remainder from the aforementioned spin system. This finding strongly hinted at a neighboring quaternary carbon at site 3′′′, which was unambiguously assigned from 1,1-ADEQUATE spectral data, where the protonated pyridine carbons C-2′′′ (δ 149.0 ppm) and C-4′′′ (δ 135.9 ppm) showed a sole correlation with C-3′′′ at δ 127.5 ppm. The remainder of the protonated pyridine carbons were easily assigned from the appropriate correlations in the ¹H-¹³C H2BC spectrum. The 3-(pyridinyl)-1H-pyrazol-4-yl heterocyclic system contains three nitrogen atoms. The chemical shifts of the N-1 and N-2 atoms of compound 12g were δ −161.8 and δ −78.2 ppm, respectively. The pyridin-3-yl substituent nitrogen resonated at δ −70.6 ppm.

Figure 4.

Relevant ¹H-¹³C HMBC, ¹H-¹³C H2BC, ¹H-¹⁵N LR-HSQMBC, ¹H-¹H NOESY and 1,1-ADEQUATE correlations and ¹H NMR (italics), ¹³C NMR and ¹⁵N NMR (bold) chemical shifts of compound 12g.

Chalcones are versatile synthons for the synthesis of five- and six-membered nitrogen heterocycles, such as pyrazoles, pyrazolines, isoxazoles, isoxazolines, pyridines, pyrimidines, and others [63]. This was briefly demonstrated in this work by the treatment of compounds 4a and 9a with N-hydroxy-4-toluenesulfonamide (TsNHOH), in the presence of NaOH in EtOH/H₂O (9:1 v/v) [64,65,66] (Scheme 5). When a chalcone 4a was used as a substrate, a regioselective formation of 3-(1H-pyrazol-4-yl)-5-phenyl-1,2-oxazole 14 was observed in 56% yield, while 5-(1H-pyrazol-4-yl)-3-phenyl-1,2-oxazole 15 was formed in a lower yield (36%), using chalcone 9a as a starting material. The efforts to obtain pyrazole-isoxazoles from chalcones using more prevalent reaction conditions reported in the literature [67,68], i.e., treating compound 9a with hydroxylamine in the presence of NaOH in MeOH/H₂O (95/5 v/v), led to a mixture of 1,2-oxazoles 14 and 15 with a poor total yield of 23%. The formation of intermediate reaction products, such as isoxazolines or oximes, could be also identified by HPLC/MS data (HPLC data of crude reaction mixture are provided in Figure S194, followed by MS data in Figures S195–S198).

Scheme 5.

Conversion of chalcones 4a and 9a to 1,2-oxazoles 14 and 15.

The regioselective formation of pyrazole-isoxazoles 14 and 15 was confirmed by NMR studies (Figure 5). As expected, the ¹H, ¹³C and ¹⁵N NMR chemical shifts and the relevant correlations in the two-dimensional NMR spectra of these two isomeric 1,2-oxazoles were highly similar. The unambiguous formation of 1,2-oxazole (isoxazole) moiety was easily deduced from ¹H-¹⁵N HMBC spectral data, as it clearly showed a distinct long-range correlation between the isoxazole methine 4′-H proton and nitrogen N-2′, which resonated at δ −18.6 and −19.6 ppm for compounds 15 and 14, respectively, and this is in good agreement with the data reported in the literature [69]. The 2 Hz optimized ¹H-¹⁵N HMBC spectra hinted in favor of these structures. For instance, the conversion of chalcone 4a provided an 1,2-oxazole derivative, in which the pyrazole 5-H proton (singlet, δ 8.33 ppm) exhibited not only long-range HMBC correlations throughout the 1H-pyrazol-4-yl moiety, but also a weak correlation with the oxazole N-2′ nitrogen at δ −19.6 ppm was observed. Meanwhile, the 1,2-oxazole derivative obtained from chalcone 9a was assigned to structure 15, due to the correlation with the neighboring protons 2″(6″)-H (δ 7.88 ppm) from the phenyl moiety. The aforementioned protons from the pyrazole and phenyl moieties in the ¹H-¹³C HMBC spectrum showed three-bond connectivities with the appropriate isoxazole quaternary carbons C-3′ and C-5′, which allowed us to confirm the correct structure assignments afterwards via the analysis of J_CN couplings.

Figure 5.

Relevant ¹H-¹⁵C HMBC and ¹H-¹⁵C HMBC correlations and ¹H NMR (italics), ¹³C NMR and ¹⁵N NMR (bold) chemical shifts of compound 14, 15.

Then, in order to avoid any ambiguity in the structure assignment of regioisomeric 1,2-oxazoles, the ¹⁵N-labeled pyrazole-isoxazoles 16 and 17 were synthesized by analogy to 14 and 15. The treatment of chalcone 9a with ¹⁵N-hydroxylamine hydrochloride produced an inseparable mixture of regioisomers 16 and 17 in a ratio of about 8:1 (Scheme 6). The selective ¹⁵N-labeling in azaheterocycles is an important method for studying molecular structures, which significantly expands the possibilities of using standard NMR methods [70]. The ¹⁵N-labeled aromatic heterocyclic structures typically have well-resolved ¹H-¹⁵N (J_HN) and ¹³C-¹⁵N (J_CN) coupling constants, including additional splitting of the corresponding signals in the standard proton decoupled 1D ¹³C NMR and 1D ¹H NMR spectra [71,72].

Scheme 6.

Synthesis of ¹⁵N labeled 1,2-oxazoles 16 and 17.

In the case of ¹⁵N-labeled pyrazole-isoxazoles 16 and 17, the analysis of ¹H-¹⁵N (J_HN) coupling constants ³J_H4′-N2′ did not provide significant information regarding the correct structure confirmation, and were 1.23 Hz and 1.31 Hz for major and minor regioisomers, respectively. As expected, the unambiguous structure assignment of regioisomeric 1,2-oxazoles was achieved after a careful analysis of the ¹³C-¹⁵N (J_CN) coupling constants, which were obtained from a ¹³C NMR spectrum. The ¹³C-¹⁵N spin–spin interaction was observed for the signals of the major regioisomer C-3′ (¹J_C3′-N2′ = 2.89 Hz), C-4′ (²J_C4′-N2′ = 1.23 Hz) and C-5′ (²J_C5′-N2′ = 1.39 Hz) from the 1,2-oxazole moiety, as well as the ²J_CN and ³J_CN couplings from the adjacent phenyl ring. The minor regioisomer provided similar data, where the ¹J_CN coupling constants were higher than ²J_CN coupling constants, C-3′ (¹J_C3′-N2′ = 2.25 Hz), C-4′ (²J_C4′-N2′ = 1.11 Hz), and C-5′ (²J_C5′-N2′ = 1.52 Hz) in the 1,2-oxazole moiety, which is in good agreement with the data reported in the literature [73]. Moreover, the ²J_CN and ³J_CN couplings were observed for the signals from the pyrazole fragment. These ¹³C-¹⁵N spin–spin interactions with adjacent phenyl and pyrazole moieties were an additional criterion to confirm the final structures of the pyrazole-isoxazoles 16 and 17.

3. Materials and Methods

3.1. General Information

All starting materials were purchased from commercial suppliers and were used as received. Microwave reactions were conducted using a CEM Discover synthesis unit (CEM Corp., Matthews, NC, USA) and performed in glass vessels (capacity: 10 mL), sealed with a septum. The pressure was controlled by a load cell connected to the vessel. The temperature of the contents of the vessel was monitored using a calibrated infrared temperature controller, mounted under the reaction vessel. All experiments were performed with stirring. Flash column chromatography was performed on silica gel, 60 Å (230–400 µm, Merck). Thin-layer chromatography was carried out on silica gel plates (Merck Kieselgel 60 F254) and visualized by UV light (254 nm). The melting points were determined on a Büchi M-565 melting point apparatus (Büchi Labortechnik AG, Flawil, Switzerland) and were uncorrected. The IR spectra were recorded on a Bruker Vertex 70v FT-IR spectrometer (Bruker Optik GmbH, Ettlingen, Germany) using neat samples or on a Bruker Tensor 27 (Bruker Optik GmbH, Ettlingen, Germany) spectrometer using KBr pellets and were reported in frequency of absorption (cm⁻¹). Mass spectra were obtained on a Shimadzu LCMS-2020 (ESI⁺) spectrometer (Shimadzu Corporation, Kyoto, Japan). High-resolution mass spectra were measured on a Bruker MicrOTOF-Q III (ESI⁺) apparatus (Bruker Daltonik GmbH, Bremen, Germany). The ¹H, ¹³C and ¹⁵N NMR spectra were recorded in CDCl₃ or DMSO-d₆ solutions at 25 °C on a Bruker Avance III 700 (700 MHz for ¹H, 176 MHz for ¹³C, and 71 MHz for ¹⁵N) spectrometer (Bruker BioSpin AG, Fallanden, Switzerland), equipped with a 5 mm TCI ¹H-¹³C/¹⁵N/D z-gradient cryoprobe and a Bruker Avance III 400 (400 MHz for ¹H, 101 MHz for ¹³C, and 40 MHz for ¹⁵N) spectrometer (Bruker BioSpin AG), using a 5 mm directly detecting BBO probe. The chemical shifts (δ), expressed in ppm, were relative to tetramethylsilane (TMS). The ¹⁵N NMR spectra were referenced to neat, external nitromethane (coaxial capillary). Full and unambiguous assignment of the ¹H, ¹³C and ¹⁵N NMR resonances was achieved using a combination of standard NMR spectroscopic techniques [74], such as DEPT, COSY, TOCSY, NOESY, ROESY, gs-HSQC, gs-HMBC, H2BC, LR-HSQMBC and 1,1-ADEQUATE experiments [75]. The following abbreviations are used in reporting NMR data: Ph, phenyl; Pz, pyrazole; Pyr, pyridine; Naph, naphtalene; Quin, quinoline; Th, thiophene; Ox, 1,2-oxazole. ¹H-, ¹³C-, and ¹H-¹⁵N HMBC NMR spectra, and HRMS data of the new compounds are provided in the Supplementary Materials as Figures S4–S193.

3.2. Chemistry

3.2.1. General Procedure for the Synthesis of 2b,c

To a solution of 1-phenyl-1H-pyrazol-3-ol (1) (320 mg, 2 mmol) in abs. DMF (20 mL), cooled to 0 °C under an inert atmosphere, NaH (60% dispersion in mineral oil, 80 mg, 2 mmol) was added portion wise [76]. After stirring the mixture for 15 min, iodopropane (for 2b) or 1-chloro-2-methoxyethane (for 2c) (2.4 mmol) was added dropwise. The reaction mixture was stirred at 60 °C for 1 h, poured into water (20 mL) and extracted with ethyl acetate (3 × 20 mL). The organic layers were combined, washed with brine, dried over Na₂SO₄, and filtrated, and the solvent was evaporated. The residue was purified by column chromatography (SiO₂, eluent: ethyl acetate/n-hexane, 1:7, v/v) to produce pure 2b,c.

1-Phenyl-3-propoxy-1H-pyrazole (2b)

Colorless liquid; yield 64% (259 mg); R_f = 0.43 (EtOAc/Hex 1/2, v/v). IR (ν_max, cm⁻¹): 3048, 2965, 1601, 1464, 1366, 1177, 1049, 935. ¹H NMR (400 MHz, CDCl₃): δ_H ppm 1.06 (t, J = 7.4 Hz, 3H, CH₃), 1.80–1.89 (m, 2H, CH₃CH₂), 4.21 (t, J = 6.6 Hz, 2H, OCH₂), 5.89 (d, J = 2.4 Hz, 1H, 4-H), 7.17–7.21 (m, 1H, Ph 4-H), 7.38–7.42 (m, 2H, Ph 3,5-H), 7.60–7.62 (m, 2H, Ph 2,6-H), 7.73 (d, J = 2.3 Hz, 1H, 5-H). ¹³C NMR (101 MHz, CDCl₃): δ_C ppm 10.5 (CH₃), 22.6 (CH₂CH₃), 70.8 (OCH₂), 93.7 (C-4), 117.8 (Ph C-2,6), 125.2 (Ph C-4), 127.5 (C-5), 129.3 (Ph C-3,5), 140.3 (Ph C-1), 164.8 (C-3). HRMS (ESI⁺) for C₁₂H₁₅N₂O ([M + H]⁺) calcd 203.1179, found 203.1181.

3-(2-Methoxyethoxy)-1-phenyl-1H-pyrazole (2c)

Colorless liquid; yield 83% (362 mg); R_f = 0.43 (EtOAc/Hex 1/3, v/v). IR (ν_max, cm⁻¹): 752, 1051, 1352, 1482, 1506, 1543, 1660, 2815, 2881, 2931, 2982, 3048, 3070, 3127, 3146. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 3.45 (s, 3H, CH₃), 3.75–3.75 (m, 2H, CH₃OCH₂CH₂O), 4.42–4.45 (m, 2H, CH₃OCH₂CH₂O), 5.93 (d, J = 2.6 Hz, 1H, 4-H), 7.18–7.20 (m, 1H, Ph 4-H), 7.37–7.43 (m, 2H, Ph 3,5-H), 7.58–7.60 (m, 2H, Ph 2,6-H), 7.72 (d, J = 2.6 Hz, 1H, 5-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 59.2 (OCH₃), 68.2 (CH₃OCH₂CH₂O), 71.1 (CH₃OCH₂CH₂O), 94.2 (C-4), 117.9 (Ph C-2,6), 125.3 (Ph C-4), 127.8 (C-5), 129.4 (Ph C-3,5), 140.3 (Ph C-1), 164.3 (C-3). HRMS (ESI⁺) for C₁₂H₁₄N₂NaO₂ ([M + Na]⁺) calcd 241.0947, found 241.0948.

3.2.2. General Procedure for the Synthesis of 3b,c

Phosphoryl chloride (0.37 mL, 4 mmol) was added dropwise to DMF (0.31 mL, 4 mmol) at −10 °C. Then, 2b,c (1 mmol) was added to the Vilsmeier–Haack complex, and the reaction mixture was heated at 70 °C for 1 h. After the neutralization with 10% aq NaHCO₃, the precipitate was filtered off and recrystallized from DCM to produce pure 3b,c.

1-Phenyl-3-propoxy-1H-pyrazole-4-carbaldehyde (3b)

Colorless solid; yield 84% (193 mg); m.p. 90–91 °C; R_f = 0.38 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3103, 2960, 1735, 1669, 1559, 1370, 1206, 1007, 867, 754. ¹H NMR (400 MHz, CDCl₃): δ_H ppm 1.06 (t, J = 7.4 Hz, 3H, CH₃), 1.86–1.92 (m, 2H, CH₂CH₃), 4.36 (t, J = 6.7 Hz, 2H, OCH₂), 7.30–7.34 (m, 1H, Ph 4-H), 7.44–7.48 (m, 2H, Ph 3,5-H), 7.63–7.65 (m, 2H, Ph 2,6-H), 8.25 (s, 1H, 5-H), 9.87 (s, 1H, CHO). ¹³C NMR (101 MHz, CDCl₃): δ_C ppm 10.6 (CH₃), 22.5 (CH₂CH₃), 71.2 (OCH₂), 111.6 (C-4), 119.0 (Ph C-2,6), 127.4 (Ph C-4), 129.3 (C-5), 129.7 (Ph C-3,5), 139.2 (Ph C-1), 164.3 (C-3), 183.6 (CHO). HRMS (ESI⁺) for C₁₃H₁₄N₂NaO₂ ([M + Na]⁺) calcd 253.0947, found 253.0950.

3-(2-Methoxyethoxy)-1-phenyl-1H-pyrazole-4-carbaldehyde (3c)

Colorless solid; yield 90% (221 mg); m.p. 91–92 °C; R_f = 0.19 (EtOAc/Hex 1/3, v/v). IR (ν_max, cm⁻¹): 3121, 3099, 2975, 2812, 1752, 1669, 1500, 1225, 761.¹H NMR (400 MHz, CDCl₃): δ_H ppm 3.47 (s, 3H, CH₃), 3.83 (t, J = 3.8 Hz, 2H, CH₃OCH₂), 4.57 (t, J = 3.8 Hz, 2H, CH₃OCH₂CH₂), 7.31–7.35 (m, 1H, Ph 4-H), 7.45–7.48 (m, 2H, Ph 3,5-H), 7.63–7.65 (m, 2H, Ph 2,6-H), 8.26 (s, 1H, 5-H), 9.89 (s, 1H, CHO). ¹³C NMR (101 MHz, CDCl₃): δ_C ppm 59.4 (CH₃), 68.9 (CH₃OCH₂CH₂), 70.8 (CH₃OCH₂), 111.6 (C-4), 119.0 (Ph C-2,6), 127.4 (Ph C-4), 129.3 (C-5), 129.8 (Ph C-3,5), 139.2 (Ph C-1), 164.0 (C-3), 183.7 (CHO). HRMS (ESI⁺) for C₁₃H₁₄N₂NaO₃ ([M + Na]⁺) calcd 269.0897, found 269.0897.

3.2.3. General Procedure for the Synthesis of 4a–k

To a solution of appropriate 3-(alkyloxy)-1-phenyl-1H-pyrazole-4-carbaldehyde (3a–d) (1 mmol) in EtOH (96%, 5 mL), NaOH (0.2 g, 5 mmol) and appropriate acetophenone (1.1 mmol) were added. The reaction mixture was stirred at 55 °C for 30 min., cooled to room temperature, diluted with H₂O, and extracted with EtOAc (3 × 10 mL). The organic layers were combined, dried with sodium sulphate, filtrated off and concentrated. The obtained residue was purified by column chromatography (SiO₂, eluent: ethyl acetate/n-hexane, 1:6, v/v) to provide the desired product 4a–k.

(2E)-3-(3-Methoxy-1-phenyl-1H-pyrazol-4-yl)-1-phenylprop-2-en-1-one (4a)

Yellow solid; yield 61% (186 mg); m.p. 127–131 °C; R_f = 0.47 (EtOAc/Hex 1/4, v/v). IR (ν_max, KBr, cm⁻¹): 3142, 3111, 3040, 2951, 1660 (C=O), 1599, 1592, 1506, 1416, 1219, 1022, 973, 746, 681, 638. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 4.14 (s, 3H, OCH₃), 7.24–7.27 (m, 1H, NPh 4-H), 7.42–7.46 (m, 2H, NPh 3,5-H), 7.48–7.51 (m, 2H, CPh 3,5-H), 7.55–7.57 (m, 1H, CPh 4-H), 7.60 (d, J = 15.5 Hz, 1H, CHCHC(O)Ph), 7.62–7.64 (m, 2H, NPh 2,6-H), 7.74 (d, J = 15.5 Hz, 1H, CHCHC(O)Ph), 7.96 (s, 1H, Pz 5-H), 8.02–8.03 (m, 2H, CPh 2,6-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 56.6 (OCH₃), 107.0 (Pz C-4), 118.1 (NPh C-2,6), 120.5 (CHCHC(O)Ph), 126.2 (NPh C-4), 128.4 (CPh C-2,6), 128.5 (CPh C-3,5), 129.0 (Pz C-5), 129.5 (NPh C-3,5), 132.4 (CPh C-4), 133.7 (CHCHC(O)Ph), 138.6 (CPh C-1), 139.4 (NPh C-1), 163.3 (Pz C-3), 190.7 (C=O). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −183.7 (N-1), −118.7 (N-2). HRMS (ESI⁺) for C₁₉H₁₆N₂NaO₂ ([M + Na]⁺) calcd 327.1104, found 327.1101.

(2E)-1-(4-Methoxyphenyl)-3-(3-methoxy-1-phenyl-1H-pyrazol-4-yl)prop-2-en-1-one (4b)

Yellowish white solid; yield 73% (244 mg); m.p. 167–169 °C; R_f = 0.22 (EtOAc/Hex 1/6, v/v). IR (ν_max, KBr, cm⁻¹): 3137, 3098, 3072, 2948, 1656 (C=O), 1510, 1422, 1253, 1227, 1176, 1020, 974, 833, 754, 689, 603. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 3.88 (s, 3H, PhOCH₃), 4.15 (s, 3H, PzOCH₃), 6.97–6.99 (m, 2H, CPh 3,5-H), 7.25–7.27 (m, 1H, NPh 4-H), 7.43–7.45 (m, 2H, NPh 3,5-H), 7.61 (d, J = 15.5 Hz, 1H, CHCHC(O)Ph), 7.63–7.64 (m, 2H, NPh 2,6-H), 7.72 (d, J = 15.4 Hz, 1H, CHCHC(O)Ph), 7.96 (s, 1H, Pz 5-H), 8.04–8.05 (m, 2H, CPh 2,6-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 55.6 (PhOCH₃), 56.7 (PzOCH₃), 107.3 (Pz C-4), 113.8 (CPh C-3,5), 118.2 (NPh C-2,6), 120.5 (CHCHC(O)Ph), 126.2 (NPh C-4), 129.0 (Pz C-5), 129.6 (NPh C-3,5), 130.8 (CPh C-2,6), 131.6 (CPh C-1), 133.0 (CHCHC(O)Ph), 139.6 (NPh C-1), 163.3 (CPh C-4), 163.4 (Pz C-3), 189.1 (C=O). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −185.2 (N-1), −118.5 (N-2). HRMS (ESI⁺) for C₂₀H₁₈N₂NaO₃ ([M + Na]⁺) calcd 357.1210, found 357.1212.

(2E)-1-(4-Fluorophenyl)-3-(3-methoxy-1-phenyl-1H-pyrazol-4-yl)prop-2-en-1-one (4c)

Yellow solid; yield 60% (193 mg); m.p. 144–147 °C; R_f = 0.3 (EtOAc/Hex 1/6, v/v). IR (ν_max, KBr, cm⁻¹): 3138, 3106, 3061, 2950, 1660 (C=O), 1585, 1514, 1504, 1421, 1218, 1014, 973, 826, 750, 591. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 4.15 (s, 3H, CH₃), 7.15–7.18 (m, 2H, CPh 3,5-H), 7.26–7.28 (m, 1H, NPh 4-H), 7.44–7.46 (m, 2H, NPh 3,5-H), 7.57 (d, J = 15.4 Hz, 1H, CHCHC(O)Ph), 7.63–7.65 (m, 2H, NPh 2,6-H), 7.74 (d, J = 15.6 Hz, 1H, CHCHC(O)Ph), 7.97 (s, 1H, Pz 5-H), 8.04–8.07 (m, 2H, CPh 2,6-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 56.8 (CH₃), 107.1 (Pz C-4), 115.7 (d, ²J = 21.8 Hz, CPh C-3,5), 118.2 (NPh C-2,6), 120.1 (CHCHC(O)Ph), 126.4 (NPh C-4), 129.2 (Pz C-5), 129.6 (NPh C-3,5), 131.1 (d, ³J = 9.2 Hz, CPh C-2,6), 134.1 (CHCHC(O)Ph), 135.0 (d, ⁴J = 3.1 Hz, CPh C-1), 139.5 (NPh C-1), 163.5 (Pz C-3), 165.6 (d, ¹J = 253.6 Hz, CPh C-4), 189.1 (C=O). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −184.3 (N-1), −118.5 (N-2). HRMS (ESI⁺) for C₁₉H₁₅FN₂NaO₂ ([M + Na]⁺) calcd 345.1010, found 345.1007.

(2E)-1-(4-Chlorophenyl)-3-(3-methoxy-1-phenyl-1H-pyrazol-4-yl)prop-2-en-1-one (4d)

Yellow solid; yield 66% (224 mg); m.p. 179–182 °C; R_f = 0.37 (EtOAc/Hex 1/8, v/v). IR (ν_max, KBr, cm⁻¹): 3139, 3108, 3071, 2950, 1659 (C=O), 1592, 1514, 1505, 1421, 1219, 1013, 973, 823, 750, 685, 655. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 4.15 (s, 3H, CH₃), 7.26–7.29 (m, 1H, NPh 4-H), 7.44–7.48 (m, 4H, NPh 3,5-H, CPh 3,5-H), 7.55 (d, J = 15.4 Hz, 1H, CHCHC(O)Ph), 7.63–7.65 (m, 2H, NPh 2,6-H), 7.74 (d, J = 15.5 Hz, 1H, CHCHC(O)Ph), 7.96–7.97 (m, 3H, Pz 5-H, CPh 2,6-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 56.8 (CH₃), 107.1 (Pz C-4), 118.3 (NPh C-2,6), 120.1 (CHCHC(O)Ph), 126.4 (NPh C-4), 129.0 (CPh C-3,5), 129.3 (Pz C-5), 129.7 (NPh C-3,5), 130.0 (CPh C-2,6), 134.4 (CHCHC(O)Ph), 137.0 (CPh C-1), 138.9 (CPh C-4), 139.5 (NPh C-1), 163.5 (Pz C-3), 189.5 (C=O). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −183.9 (N-1), −119.0 (N-2). HRMS (ESI⁺) for C₁₉H₁₅ClN₂NaO₂ ([M + Na]⁺) calcd 361.0714, found 361.0716.

(2E)-1-Phenyl-3-(1-phenyl-3-propoxy-1H-pyrazol-4-yl)prop-2-en-1-one (4e)

Yellow solid; yield 58% (156 mg); m.p. 133–135 °C; R_f = 0.49 (EtOAc/Toluene 1/12, v/v). IR (ν_max, KBr, cm⁻¹): 3136, 3105, 3071, 2964, 1655 (C=O), 1588, 1574, 1502, 1417, 1215, 1021, 1010, 998, 748, 685, 643. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 1.16 (t, J = 7.5 Hz, 3H, CH₃), 1.93–1.98 (m, 2H, OCH₂CH₂CH₃), 4.42 (t, J = 6.5 Hz, 2H, OCH₂CH₂CH₃), 7.25–7.28 (m, 1H, NPh 4-H), 7.43–7.46 (m, 2H, NPh 3,5-H), 7.49–7.53 (m, 2H, CPh 3,5-H), 7.57–7.59 (m, 1H, CPh 4-H), 7.63–7.66 (m, 2H, NPh 2,6-H), 7.69 (d, J = 15.5 Hz, 1H, CHCHC(O)Ph), 7.78 (d, J = 15.5 Hz, 1H, CHCHC(O)Ph), 7.98 (s, 1H, Pz 5-H), 8.04–8.06 (m, 2H, CPh 2,6-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 10.7 (CH₃), 22.6 (OCH₂CH₂CH₃), 71.0 (OCH₂CH₂CH₃), 107.3 (Pz C-4), 118.1 (NPh C-2,6), 120.4 (CHCHC(O)Ph), 126.1 (NPh C-4), 128.4 (CPh C-2,6), 128.6 (CPh C-3,5), 128.8 (Pz C-5), 129.5 (NPh C-3,5), 132.5 (CPh C-4), 133.9 (CHCHC(O)Ph), 138.7 (CPh C-1), 139.5 (NPh C-1), 163.1 (Pz C-3), 190.6 (C=O). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −184.4 (N-1), −119.3 (N-2). HRMS (ESI⁺) for C₂₁H₂₀N₂NaO₂ ([M + Na]⁺) calcd 355.1417, found 355.1416.

(2E)-3-[3-(2-Methoxyethoxy)-1-phenyl-1H-pyrazol-4-yl]-1-phenylprop-2-en-1-one (4f)

Yellow solid; yield 62% (216 mg); m.p. 116–117 °C; R_f = 0.28 (EtOAc/Hex 1/6, v/v). IR (ν_max, KBr, cm⁻¹): 3138, 3101, 3063, 3040, 2931, 1655 (C=O), 1594, 1503, 1413, 1219, 1051, 976, 848, 743, 683, 640. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 3.52 (s 3H, CH₃), 3.87 (t, J = 4.6 Hz, 2H, OCH₂CH₂OCH₃), 4.59 (t, J = 4.6 Hz, 2H, OCH₂CH₂OCH₃), 7.25–7.27 (m, 1H, NPh 4-H), 7.43–7.45 (m, 2H, NPh 3,5-H), 7.48–7.50 (m, 2H, CPh 3,5-H), 7.55–7.57 (m, 1H, CPh 4-H), 7.61–7.63 (m, 2H, NPh 2,6-H), 7.71 (d, J = 14.6 Hz, 1H, CHCHC(O)Ph), 7.75 (d, J = 15.5 Hz, 1H, CHCHC(O)Ph), 7.97 (s, 1H, Pz 5-H), 8.03–8.05 (m, 2H, CPh 2,6-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 59.3 (CH₃), 68.7 (OCH₂CH₂OCH₃), 71.1 (OCH₂CH₂OCH₃), 107.4 (Pz C-4), 118.2 (NPh C-2,6), 120.8 (CHCHC(O)Ph), 126.3 (NPh C-4), 128.57 (CPh C-2,6), 128.63 (CPh C-3,5), 128.8 (Pz C-5), 129.6 (NPh C-3,5), 132.6 (CPh C-4), 133.6 (CHCHC(O)Ph), 138.7 (CPh C-1), 139.5 (NPh C-1), 162.8 (Pz C-3), 190.6 (C=O). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −184.2 (N-1), −118.3 (N-2). HRMS (ESI⁺) for C₂₁H₂₀N₂NaO₃ ([M + Na]⁺) calcd 371.1366, found 371.1364.

(2E)-3-[3-(Benzyloxy)-1-phenyl-1H-pyrazol-4-yl]-1-phenylprop-2-en-1-one (4g)

Yellow solid; yield 66% (253 mg); m.p. 168–169 °C; R_f = 0.36 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3063, 3029, 1654 (C=O), 1591, 1567, 1504, 1359, 1005, 970, 779, 680. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 5.50 (s, 2H, CH₂), 7.27–7.29 (m, 1H, NPh 4-H), 7.39–7.41 (m, 1H, CH₂Ph 4-H), 7.44–7.47 (m, 6H, CH₂Ph 3,5-H, C(O)Ph 3,5-H, NPh 3,5-H), 7.54–7.56 (m, 1H, C(O)Ph 4-H), 7.58–7.59 (m, 2H, CH₂Ph 2,6-H), 7.65–7.66 (m, 2H, NPh 2,6-H), 7.74 (d, J = 15.5 Hz, 1H, CHCHC(O)Ph), 7.77 (d, J = 15.4 Hz, 1H, CHCHC(O)Ph), 7.96–7.97 (m, 2H, C(O)Ph 2,6-H), 7.99 (s, 1H, Pz 5-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 71.2 (CH₂), 107.4 (Pz C-4), 118.3 (NPh C-2,6), 120.8 (CHCHC(O)Ph), 126.4 (NPh C-4), 128.0 (CH₂Ph C-2,6), 128.3 (CH₂Ph C-4), 128.5 (C(O)Ph C-2,6), 128.6 (C(O)Ph C-3,5), 128.7 (CH₂Ph C-3,5), 129.0 (Pz C-5), 129.7 (NPh C-3,5), 132.6 (C(O)Ph C-4), 133.5 (CHCHC(O)Ph), 136.9 (CH₂Ph C-1), 138.6 (C(O)Ph C-1), 139.5 (NPh C-1), 162.8 (Pz C-3), 190.4 (C=O). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −184.29 (Pz N-1), −117.99 (Pz N-2). HRMS (ESI⁺) for C₂₅H₂₀N₂NaO₂ ([M + Na]⁺) calcd 403.1417, found 403.1416.

(2E)-3-[3-(Benzyloxy)-1-phenyl-1H-pyrazol-4-yl]-1-(4-methoxyphenyl)prop-2-en-1-one (4h)

Yellow solid; yield 68% (279 mg); m.p. 164–165 °C; R_f = 0.34 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3064, 2928, 1652 (C=O), 1502, 1417, 1221, 1169, 1010, 972, 826, 700. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 3.88 (s, 3H, CH₃), 5.50 (s, 2H, CH₂), 6.92–6.93 (m, 2H, C(O)Ph 2,6-H), 7.27–7.28 (m, 1H, NPh 4-H), 7.39–7.41 (m, 1H, CH₂Ph 4-H), 7.44–7.47 (m, 4H, CH₂Ph 3,5-H, NPh 3,5-H), 7.58–7.60 (m, 2H, CH₂Ph 2,6-H), 7.64–7.66 (m, 2H, NPh 2,6-H), 7.74 (s, 2H, CHCHC(O)Ph), 7.96–7.97 (m, 2H, C(O)Ph 3,5-H), 7.98 (s, 1H, Pz 5-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 55.6 (CH₃), 71.2 (CH₂), 107.5 (Pz C-4), 113.8 (C(O)Ph C-2,6), 118.2 (NPh C-2,6), 120.7 (CHCHC(O)Ph), 126.3 (NPh C-4), 128.0 (CH₂Ph C-2,6), 128.3 (CH₂Ph C-4), 128.7 (CH₂Ph C-3,5), 128.9 (Pz C-5), 129.7 (NPh C-3,5), 130.8 (C(O)Ph C-3,5), 131.6 (C(O)Ph C-1), 132.7 (CHCHC(O)Ph), 137.0 (CH₂Ph C-1), 139.6 (NPh C-1), 162.7 (Pz C-3), 163.3 (C(O)Ph C-4), 188.8 (C=O). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −184.44 (Pz N-1), −117.93 (Pz N-2). HRMS (ESI⁺) for C₂₆H₂₂N₂NaO₃ ([M + Na]⁺) calcd 433.1523, found 433.1525.

(2E)-3-[3-(Benzyloxy)-1-phenyl-1H-pyrazol-4-yl]-1-(4-chlorophenyl)prop-2-en-1-one (4i)

Yellow solid; yield 97% (411 mg); m.p. 192–193 °C; R_f = 0.56 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3033, 2916, 1600 (C=O), 1501, 1409, 1365, 1215, 1003, 973, 823, 740. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 5.49 (s, 2H, CH₂), 7.28–7.30 (m, 1H, NPh 4-H), 7.40–7.42 (m, 3H, CH₂Ph 4-H, 4ClPh 2,6-H), 7.44–7.48 (m, 4H, CH₂Ph 3,5-H, NPh 3,5-H), 7.57–7.58 (m, 2H, CH₂Ph 2,6-H), 7.65–7.66 (m, 2H, NPh 2,6-H), 7.68 (d, J = 15.4 Hz, 1H, CHCHC(O)Ph), 7.77 (d, J = 15.4 Hz, 1H, CHCHC(O)Ph), 7.87–7.89 (m, 2H, 4ClPh 3,5-H), 7.99 (s, 1H, Pz 5-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 71.3 (CH₂), 107.3 (Pz C-4), 118.3 (NPh C-2,6), 120.1 (CHCHC(O)Ph), 126.5 (NPh C-4), 128.1 (CH₂Ph C-2,6), 128.4 (CH₂Ph C-4), 128.7 (4ClPh C-2,6), 128.9 (CH₂Ph C-3,5), 129.1 (Pz C-5), 129.7 (NPh C-3,5), 129.9 (4ClPh C-3,5), 134.1 (CHCHC(O)Ph), 136.9 (CH₂Ph C-1), 137.0 (4ClPh C-4), 139.0 (4ClPh C-1), 139.5 (NPh C-1), 162.8 (Pz C-3), 189.0 (C=O). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −183.94 (Pz N-1), −117.85 (Pz N-2). HRMS (ESI⁺) for C₂₅H₁₉ClN₂NaO₃ ([M + Na]⁺) calcd 437.1027, found 437.1028.

(2E)-3-[3-(Benzyloxy)-1-phenyl-1H-pyrazol-4-yl]-1-(4-fluorophenyl)prop-2-en-1-one (4j)

Yellow solid; yield 79% (318 mg); m.p. 145–146 °C; R_f = 0.54 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3033, 2944, 1654 (C=O), 1596, 1500, 1411, 1364, 1002, 973, 826, 685. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 5.49 (s, 2H, CH₂), 7.09–7.12 (m, 2H, 4FPh 3,5-H), 7.27–7.30 (m, 1H, NPh 4-H), 7.41–7.42 (m, 1H, CH₂Ph 4-H), 7.44–7.48 (m, 4H, CH₂Ph 3,5-H, NPh 3,5-H), 7.58–7.59 (m, 2H, CH₂Ph 2,6-H), 7.65–7.66 (m, 2H, NPh 2,6-H), 7.70 (d, J = 15.4 Hz, 1H, CHCHC(O)Ph), 7.76 (d, J = 15.4 Hz, 1H, CHCHC(O)Ph), 7.95–7.98 (m, 2H, 4FPh 2,6-H), 7.99 (s, 1H, Pz 5-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 71.3 (CH₂), 107.3 (Pz C-4), 115.7 (d, ²J = 21.7 Hz, 4FPh C-3,5), 118.3 (NPh C-2,6), 120.3 (CHCHC(O)Ph), 126.4 (NPh C-4), 128.1 (CH₂Ph C-2,6), 128.4 (CH₂Ph C-4), 128.7 (CH₂Ph C-3,5), 129.1 (Pz C-5), 129.7 (NPh C-3,5), 131.1 (d, ³J = 9.1 Hz, 4FPh C-2,6), 133.7 (CHCHC(O)Ph), 135.0 (d, ⁴J = 3.0 Hz, 4FPh C-1), 136.9 (CH₂Ph C-1), 139.5 (NPh C-1), 162.8 (Pz C-3), 164.2 (d, ¹J = 253.7 Hz, 4FPh C-4), 188.7 (C=O). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −184.26 (Pz N-1), −118.00 (Pz N-2). HRMS (ESI⁺) for C₂₅H₁₉FN₂NaO₃ ([M + Na]⁺) calcd 421.1323, found 421.1323.

(2E)-3-[3-(Benzyloxy)-1-phenyl-1H-pyrazol-4-yl]-1-[4-(dimethylamino)phenyl]prop-2-en-1-one (4k)

Yellow solid; yield 85% (376 mg); m.p. 179–180 °C; R_f = 0.15 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3102, 2918, 1564 (C=O), 1434, 1404, 1358, 1166, 1028, 977, 809, 742. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 3.06 (s, 6H, CH₃), 5.50 (s, 2H, CH₂), 6.64–6.66 (m, 2H, (CH₃)₂NPh 3,5-H), 7.24–7.26 (m, 1H, NNPh 4-H), 7.38–7.40 (m, 1H, CH₂Ph 4-H), 7.43–7.46 (m, 4H, CH₂Ph 3,5-H, NNPh 3,5-H), 7.60–7.61 (m, 2H, CH₂Ph 2,6-H), 7.64–7.65 (m, 2H, NNPh 2,6-H), 7.72 (d, J = 15.4 Hz, 1H, CHCHC(O)Ph), 7.78 (d, J = 15.4 Hz, 1H, CHCHC(O)Ph), 7.94–7.96 (m, 3H, (CH₃)₂NPh 2,6-H, Pz 5-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 40.2 (CH₃), 71.0 (CH₂), 107.7 (Pz C-4), 110.9 ((CH₃)₂NPh C-3,5), 118.1 (NNPh C-2,6), 121.1 (CHCHC(O)Ph), 126.1 (NNPh C-4), 126.4 ((CH₃)₂NPh C-1), 127.9 (CH₂Ph C-2,6), 128.1 (CH₂Ph C-4), 128.5 (Pz C-5), 128.6 (CH₂Ph C-3,5), 129.6 (NNPh C-4), 130.8 ((CH₃)₂NPh C-2,6), 131.2 (CHCHC(O)Ph), 137.1 (CH₂Ph C-1), 139.6 (NNPh C-1), 153.3 ((CH₃)₂NPh C-4), 162.6 (Pz C-3), 188.0 (C=O). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −325.44 (N(CH₃)₂), −185.23 (Pz N-1), −118.32 (Pz N-2). HRMS (ESI⁺) for C₂₇H₂₅N₃NaO₂ ([M + Na]⁺) calcd 446.1839, found 446.1842.

3.2.4. General Procedure for the Synthesis of 5a–c

To a solution of 4g–j (1 mmol) in toluene (3 mL), TFA (3mL) was added. The reaction mixture was stirred at room temperature for 24 h. Toluene and trifluoroacetic acid were evaporated. The residue was recrystalized from ACN to produce pure 5a–c.

(2E)-3-(3-Hydroxy-1-phenyl-1H-pyrazol-4-yl)-1-phenylprop-2-en-1-one (5a)

Yellow solid; yield 60% (208 mg); m.p. 257–258 °C; R_f = 0.2 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 2922, 2852, 1655 (C=O), 1593, 1573, 1504, 1416, 1020, 974, 751, 684. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 7.27–7.29 (m, 1H, NPh 4-H), 7.49–7.51 (m, 2H, NPh 3,5-H), 7.56–7.59 (m, 2H, CPh 3,5-H), 7.64–7.66 (m, 3H, CPh 4-H, CHCHC(O)Ph), 7.73–7.74 (m, 2H, NPh 2,6-H), 7.99–8.00 (m, 2H, CPh 2,6-H), 8.89 (s, 1H, Pz 5-H), 11.48 (s, 1H, OH). ¹³C NMR (176 MHz, DMSO DMSO-d₆): δ_C ppm 106.5 (Pz C-4), 117.3 (NPh C-2,6), 118.8 (CHCHC(O)Ph), 125.9 (NPh C-4), 128.0 (CPh C-2,6), 128.8 (CPh C-3,5), 129.5 (Pz C-5), 129.6 (NPh C-3,5), 132.7 (CPh C-4), 134.3 (CHCHC(O)Ph), 138.1 (CPh C-1), 139.0 (NPh C-1), 161.9 (Pz C-3), 189.0 (C=O). ¹⁵N NMR (71 MHz, DMSO-d₆): δ_N ppm −183.51 (Pz N-1). HRMS (ESI⁺) for C₁₈H₁₄N₂NaO₂ ([M + Na]⁺) calcd 313.0947, found 313.0948.

(2E)-3-(3-Hydroxy-1-phenyl-1H-pyrazol-4-yl)-1-(4-methoxyphenyl)prop-2-en-1-one (5b)

Yellow solid; yield 63% (202 mg); m.p. 250–251 °C; R_f = 0.13 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3097, 2935, 1655 (C=O), 1593, 1504, 1246, 1173, 1023, 972, 829, 753. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 3.86 (s, 3H, CH₃), 7.09–7.10 (m, 2H, CPh 2,6-H), 7.27–7.29 (m, 1H, NPh 4-H), 7.49–7.51 (m, 2H, NPh 3,5-H), 7.62 (d, J = 15.4 Hz, 1H, CHCHC(O)Ph), 7.67 (d, J = 15.4 Hz, 1H, CHCHC(O)Ph), 7.72–7.73 (m, 2H, NPh 2,6-H), 8.00–8.01 (m, 2H, CPh 3,5-H), 8.87 (s, 1H, Pz 5-H), 11.43 (s, 1H, OH). ¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 55.5 (CH₃), 106.6 (Pz C-4), 114.1 (CPh C-2,6), 117.3 (NPh C-2,6), 118.7 (CHCHC(O)Ph), 125.8 (NPh C-4), 129.3 (Pz C-5), 129.6 (CPh C-3,5), 130.3 (CPh C-3,5), 130.8 (CPh C-1), 133.2 (CHCHC(O)Ph), 139.1 (NPh C-1), 161.9 (Pz C-3), 162.9 (CPh C-4), 187.1 (C=O). ¹⁵N NMR (71 MHz, DMSO-d₆): δ_N ppm −183.85 (Pz N-1), −118.86 (Pz N-2). HRMS (ESI⁺) for C₁₉H₁₆N₂NaO₃ ([M + Na]⁺) calcd 343.1053, found 343.1054.

(2E)-1-(4-Chlorophenyl)-3-(3-hydroxy-1-phenyl-1H-pyrazol-4-yl)prop-2-en-1-one (5c)

Yellow solid; yield 83% (270 mg); m.p. 290–291 °C; R_f = 0.26 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3068, 2928, 1655 (C=O), 1509, 1416, 1217, 1093, 1040, 971, 827, 742. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 7.28–7.30 (m, 1H, NPh 4-H), 7.49–7.51 (m, 2H, NPh 3,5-H), 7.61–7.68 (m, 4H, CPh 3,5-H, CHCHC(O)Ph), 7.72–7.73 (m, 2H, NPh 2,6-H), 8.00–8.01 (m, 2H, CPh 2,6-H), 8.89 (s, 1H, Pz 5-H), 11.51 (s, 1H, OH). ¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 107.0 (Pz C-4), 117.8 (NPh C-2,6), 118.8 (CHCHC(O)Ph), 126.4 (NPh C-4), 129.4 (CPh C-3,5), 130.1 (NPh C-3,5), 130.1 (Pz C-5), 130.3 (CPh C-2,6), 135.2 (CHCHC(O)Ph), 137.2 (CPh C-4), 138.1 (CPh C-1), 139.4 (NPh C-1), 162.4 (Pz C-3), 188.2 (C=O). ¹⁵N NMR (71 MHz, DMSO-d₆): δ_N ppm −183.15 (Pz N-1), −118.69 (Pz N-2). HRMS (ESI⁺) for C₁₈H₁₃ClN₂NaO₂ ([M + Na]⁺) calcd 347.0558, found 347.0557.

3.2.5. General Procedure for the Synthesis of 8a–l

To a solution of 1-(3-hydroxy-1-phenyl-1H-pyrazol-4-yl)ethan-1-one (7) (2.02 g, 10 mmol) in EtOH (96%, 80 mL), NaOH (2 g, 50 mmol) and appropriate aldehyde (20 mmol) were added. The reaction mixture was stirred at 55 °C for 3–5 h, cooled to room temperature and neutralized to pH = 7 using 6N HCl. The precipitate was filtered off, washed with water and cold ether and recrystallized from ACN to produce pure 8a–l.

(2E)-1-(3-Hydroxy-1-phenyl-1H-pyrazol-4-yl)-3-phenylprop-2-en-1-one (8a)

The reaction mixture was stirred for 3 h. White solid; yield 88% (2.56 g); m.p. 222–223 °C; R_f=0.24 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3075, 3058, 3026, 1654 (C=O), 1584, 1511, 1448, 1217, 1062, 746, 735, 693, 678. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 7.32–7.34 (m, 1H, NPh 4-H), 7.44–7.45 (m, 1H, CPh 4-H), 7.46–7.48 (m, 2H, CPh 3,5-H), 7.51–7.53 (m, 2H, NPh 3,5-H), 7.69 (d, J = 15.7 Hz, 1H, C(O)CHCHPh), 7.75 (d, J = 15.6 Hz, 1H, C(O)CHCHPh), 7.76–7.78 (m, 2H, CPh 2,6-H), 7.84–7.85 (m, 2H, NPh 2,6-H), 9.16 (s, 1H, Pz- 5-H), 11.22 (s, 1H, OH). ¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 111.1 (Pz- C-4), 118.0 (NPh C-2,6), 124.3 (C(O)CHCH), 126.5 (NPh C-4), 128.4 (CPh C-2,6), 129.0 (CPh C-3,5), 129.6 (NPh C-3,5), 130.4 (CPh C-4), 131.7 (Pz C-5), 134.7 (CPh C-1), 138.8 (NPh C-1), 141.4 (C(O)CHCH), 162.0 (Pz C-3), 182.6 (C=O). ¹⁵N NMR (71 MHz, DMSO-d₆): δ_N ppm −181.9 (Pz N-1), −117.0 (Pz N-2). HRMS (ESI⁺) for C₁₈H₁₄N₂O₂ ([M + Na]⁺) calcd 313.0948, found 313.0947.

(2E)-3-(4-Fluorophenyl)-1-(3-hydroxy-1-phenyl-1H-pyrazol-4-yl)prop-2-en-1-one (8b)

The reaction mixture was stirred for 4.5 h. Orange solid; yield 70% (2.16 g); m.p. 239–240 °C; R_f = 0.46 (DCM/MeOH 100/1, v/v). IR (ν_max, cm⁻¹): 3360, 3111, 2978, 1646 (C=O), 1583, 1505, 1359, 1326, 821, 747, 673, 505. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 7.31–7.35 (m, 3H, NPh 4-H, CPh 3,5-H), 7.51–7.53 (m, 2H, NPh 3,5-H), 7.68 (s, 2H, C(O)CHCH), 7.83–7.86 (m, 4H, NPh 2,6-H, CPh 2,6-H), 9.14 (s, 1H, Pz 5-H), 11.20 (s, 1H, OH). ¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 111.1 (Pz C-4), 116.0 (d, ²J = 21.8 Hz, CPh C-3,5), 118.0 (NPh C-2,6), 124.2 (C(O)CHCH), 126.6 (NPh C-4), 129.6 (NPh C-3,5), 130.7 (d, ³J = 8.6 Hz, CPh C-2,6), 131.4 (d, ⁴J = 2.9 Hz, CPh C-1), 131.7 (Pz C-5), 138.8 (NPh C-1), 140.1 (C(O)CHCH), 161.9 (Pz C-3), 163.2 (d, ¹J = 248.6 Hz, CPh C-4), 182.5 (C=O). ¹⁵N NMR (71 MHz, DMSO-d₆): δ_N ppm −182.1 (Pz N-1), −119.5 (Pz N-2). HRMS (ESI⁺) for C₁₈H₁₄N₂O₂ ([M + H]⁺) calcd 331.0853, found 331.0853.

(2E)-3-(4-Chlorophenyl)-1-(3-hydroxy-1-phenyl-1H-pyrazol-4-yl)prop-2-en-1-one (8c)

The reaction mixture was stirred for 4 h. Yellow solid; yield 77% (2505 mg); m.p. 354–355 °C; R_f = 0.17 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3110, 3071, 1654 (C=O), 1586, 1511, 1456, 1325, 1218, 1094, 1062, 815, 745, 709, 681, 497. ¹H NMR (700 MHz, DMSO-d₆) δ_H ppm 7.33–7.35 (m, 1H, NPh 4-H), 7.51–7.55 (m, 4H, NPh 3,5-H, CPh 3,5-H), 7.66 (d, J = 15.7 Hz, 1H, C(O)CHCHPh), 7.73 (d, J = 15.7 Hz, 1H, C(O)CHCHPh), 7.80–7.81 (m, 2H, CPh 2,6-H), 7.83–7.84 (m, 2H, NPh 2,6-H), 9.15 (s, 1H, Pz- 5-H), 11.22 (s, 1H, OH). ¹³C NMR (176 MHz, DMSO-d₆) δ_C ppm 111.5 (Pz C-4), 118.5 (NPh C-2,6), 125.4 (C(O)CHCHPh), 127.1 (NPh C-4), 129.5 (CPh C-3,5), 130.0 (NPh C-3,5), 130.6 (CPh C-2,6), 132.3 (Pz 5-H), 134.2, 135.3, 139.3 (NPh C-1), 140.4 (C(O)CHCHPh), 162.3 (Pz C-3), 182.8 (C=O). ¹⁵N NMR (71 MHz, DMSO-d₆): δ_N ppm −181.7 (Pz N-1), −118.1 (Pz N-2). HRMS (ESI⁺) for C₁₈H₁₃ClN₂O₂ ([M + Na]⁺) calcd 347.0558, found 347.0558.

(2E)-1-(3-Hydroxy-1-phenyl-1H-pyrazol-4-yl)-3-(4-methoxyphenyl)prop-2-en-1-one (8d)

The reaction mixture was stirred for 3.5 h. Brown solid; yield 80% (2.57 g); m.p. 200–201 °C; R_f = 0.14 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3110, 3071, 1653 (C=O), 1586, 1509, 1457, 1219, 1172, 1049, 818, 769, 743, 679. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 3.82 (s, 3H, CH₃), 7.03–7.04 (m, 2H, CPh 3,5-H), 7.32–7.34 (m, 1H, NPh 4-H), 7.51–7.53 (m, 2H, NPh 3,5-H), 7.60 (d, J = 15.6 Hz, 1H, C(O)CHCH), 7.66 (d, J = 15.6 Hz, 1H, C(O)CHCH), 7.73–7.74 (m, 2H, CPh 2,6-H), 7.84–7.85 (m, 2H, NPh 2,6-H), 9.14 (s, 1H, Pz 5-H), 11.11 (s, 1H, OH). ¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 55.4 (CH₃), 111.0 (Pz C-4), 114.5 (CPh C-3,5), 118.0 (NPh C-2,6), 121.7 (C(O)CHCH), 126.5 (NPh C-4), 127.3 (CPh C-1), 129.6 (NPh C-3,5), 130.3 (CPh C-2,6), 131.5 (Pz C-5), 138.8 (NPh C-1), 141.4 (C(O)CHCH), 161.2 (Pz C-3), 161.9 (CPh C-4), 182.8 (C=O). ¹⁵N NMR (71 MHz, DMSO-d₆): δ_N ppm −182.2 (Pz N-1). HRMS (ESI⁺) for C₁₉H₁₆N₂O ([M + Na]⁺) calcd 343.1053, found 343.1053.

(2E)-1-(3-Hydroxy-1-phenyl-1H-pyrazol-4-yl)-3-[4-(trifluoromethoxy)phenyl]prop-2-en-1-one (8e)

The reaction mixture was stirred for 5 h. Yellow solid; yield 58% (2.21 g); m.p. 148–149 °C; R_f = 0.49 (DCM/MeOH 100/1, v/v). IR (ν_max, cm⁻¹): 3110, 3071, 1657 (C=O), 1599, 1583, 1525, 1506, 1214, 1146, 977, 925, 825, 745. ¹H NMR (400 MHz, DMSO-d₆): δ_H ppm 7.32–7.36 (m, 1H, NPh 4-H), 7.45–7.47 (m, 2H, CPh 2,6-H), 7.50–7.54 (m, 2H, NPh 3,5-H), 7.69 (d, J = 15.8 Hz, 1H, C(O)CHCH), 7.74 (d, J = 15.8 Hz, 1H, C(O)CHCH), 7.83–7.85 (m, 2H, CPh 3,5-H), 7.90–7.92 (m, 2H, NPh 2,6-H), 9.15 (s, 1H, Pz 5-H), 11.24 (s, 1H, OH). ¹³C NMR (101 MHz, DMSO-d₆): δ_C ppm 111.0 (Pz C-4), 118.1 (NPh C-2,6), 120.0 (q, ¹J = 256.8 Hz, OCF₃), 121.4, 125.4 (C(O)CHCHPh), 126.6, 129.6, 130.3, 131.8, 134.1 (Pz C-5), 138.8 (NPh C-1), 139.6 (C(O)CH), 149.4 (CPh C-4), 161.9 (Pz C-3), 182.4 (C=O). HRMS (ESI⁺) for C₁₉H₁₃F₃N₂O₃ ([M + Na]⁺) calcd 397.0770, found 397.0770.

(2E)-3-[4-(Dimethylamino)phenyl]-1-(3-hydroxy-1-phenyl-1H-pyrazol-4-yl)prop-2-en-1-one (8f)

The reaction mixture was stirred for 5 h. Dark red solid; yield 25% (835 mg); m.p. 203–204 °C; R_f = 0.09 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3111, 1635 (C=O), 1586, 1505, 1426, 1354, 1160, 1034, 808, 750, 687, 668. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 2.99 (s, 6H, CH₃), 6.75–6.76 (m, 2H, CPh 3,5-H), 7.31–7.33 (m, 1H, NPh 4-H), 7.47 (d, d, J = 15.5 Hz, 1H, C(O)CH), 7.50–7.52 (m, 2H, NPh 3,5-H), 7.59–7.61 (m, 2H, CPh 3,5-H), 7.63 (d, d, J = 15.5 Hz, 1H, C(O)CHCH), 7.83–7.84 (m, 2H, NPh 2,6-H), 9.10 (s, 1H, Pz 5-H), 11.02 (s, 1H, OH). ¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 39.7 (CH₃), 111.0 (Pz C-4), 111.8 (CPh 3,5-C), 118.0 (NPh C-2,6), 118.3 (C(O)CHCH), 121.9 (CPh C-1), 126.4 (NPh C-4), 129.6 (CPh C-2,6), 130.3 (NPh C-3,5), 131.0 (Pz C-5), 138.9 (NPh C-1), 142.7 (C(O)CHCH), 151.9 (CPh C-4), 162.1 (Pz C-3), 183.1 (C=O). HRMS (ESI⁺) for C₂₀H₁₉N₃O₂ ([M + Na]⁺) calcd 356.1369, found 356.1369.

(2E)-1-(3-Hydroxy-1-phenyl-1H-pyrazol-4-yl)-3-(naphthalen-2-yl)prop-2-en-1-one (8g)

The reaction mixture was stirred for 3.5 h. Orange solid; yield 94% (3.20 g); m.p. 257–258 °C; R_f = 0.43 (DCM/MeOH 100/1, v/v). IR (ν_max, cm⁻¹): 3117, 3056, 1650 (C=O), 1586, 1509, 460, 1322, 1216, 1062, 847, 806, 754, 732, 680. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 7.34–7.36 (m, 1H, NPh 4-H), 7.52–7.55 (m, 2H, NPh 3,5-H), 7.57–7.60 (m, 2H, Naph 4,8-H), 7.85–7.87 (m, 4H, NPh 2,6-H, C(O)CHCH), C(O)CHCH), 7.96–8.02 (m, 4H, Naph 3,5,6,7-H), 8.26 (s, 1H, Naph 1-H), 9.21 (s, 1H, Pz 5-H), 11.19 (s, 1H, OH). ¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 111.1 (Pz C-4), 118.1 (NPh C-2,6), 123.8 (Naph C-6), 124.5 (C(O)CHCH), 126.6 (NPh C-4), 126.9 (Naph C-4), 127.4 (Naph C-8), 127.8 (Naph C-3), 128.5 (Naph C-5), 128.6 (Naph C-7), 129.6 (NPh C-3,5), 130.4 (Naph C-1), 131.8 (Pz C-5), 132.3 (Naph C-4a), 133.0 (Naph C-2), 133.8 (Naph C-8a), 138.8 (NPh C-1), 141.4 (C(O)CHCH), 162.0 (Pz C-3), 182.6 (C=O). ¹⁵N NMR (71 MHz, DMSO-d₆): δ_N ppm −181.9 (Pz N-1). HRMS (ESI⁺) for C₂₂H₁₆N₂O₂ ([M + Na]⁺) calcd 363.1104, found 363.1104.

(2E)-1-(3-Hydroxy-1-phenyl-1H-pyrazol-4-yl)-3-(pyridin-4-yl)prop-2-en-1-one (8h)

The reaction mixture was stirred for 4 h. Yellow solid; yield 36% (1.05 g); m.p. 230–231 °C; R_f = 0.19 (DCM/MeOH 100/3, v/v). IR (ν_max, cm⁻¹): 3397, 3115, 3068, 1658 (C=O), 1585, 1509, 1453, 1318, 1216, 808, 748, 720, 675. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 7.33–7.36 (m, 1H, Ph 4-H), 7.52–7.54 (m, 2H, Ph 3,5-H), 7.62 (d, J = 15.8 Hz, 1H, C(O)CHCH), 7.73–7.74 (m, 2H, Pyr 3,5-H), 7.84–7.85 (m, 2H, Ph 2,6-H), 7.90 (d, J = 15.8 Hz, 1H, C(O)CHCH), 8.68–8.69 (m, 2H, Ph 2,6-H), 9.19 (s, 1H, Pz 5-H), 11.33 (s, 1H OH). ¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 111.0 (Pz C-4), 118.1 (Ph C-2,6), 122.3 (Pyr C-2,6), 126.7 (Ph C-4), 128.6 (C(O)CHCH), 129.6 (Ph C-3,5), 132.1 (Pz C-5), 138.4 (Pyr C-4), 138.7 (Ph C-1), 142.2 (C(O)CHCH), 150.2 (Pyr C-3,5), 161.9 (Pz C-3), 182.0 (C=O). ¹⁵N NMR (71 MHz, DMSO-d₆): δ_N ppm −181.8 (Pz N-1), −118.1 (Pz N-2), −63.9 (Pyr N). HRMS (ESI⁺) for C₁₇H₁₃N₃O₂ ([M + H]⁺) calcd 292.1081, found 292.1081.

(2E)-1-(3-Hydroxy-1-phenyl-1H-pyrazol-4-yl)-3-(pyridin-3-yl)prop-2-en-1-one (8i)

The reaction mixture was stirred for 3.5 h. Yellow solid; yield 48% (1.40 mg); m.p. 230–231 °C; R_f = 0.21 (DCM/MeOH 100/3, v/v). IR (ν_max, cm⁻¹): 3115, 3026, 1656 (C=O), 1583, 1510, 1455, 1320, 1216, 1061, 800, 748, 703, 678. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 7.33–7.35 (m, 1H, Ph 4-H), 7.50–7.54 (m, 3H, Ph 3,5-H, Pyr 5-H), 7.70 (d, J = 15.8 Hz, 1H, C(O)CH), 7.81–7.84 (m, 3H, Ph 2,6-H, C(O)CHCH), 8.19–8.21 (m, 1H, Pyr 4-H), 8.61 (dd, J = 4.7, 1.7 Hz, 1H, Pyr 6-H), 8.97 (d, J = 2.3 Hz, 1H, Pyr 2-H), 9.19 (s, 1H, Pz 5-H), 11.22 (s, 1H, OH).¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 111.0 (Pz C-4), 118.1 (Ph C-2,6), 124.0 (Pyr C-5), 126.1 (C(O)CH), 126.6 (Ph C-4), 129.6 (Ph C-3,5), 130.6 (Pyr C-3), 131.9 (Pz C-5), 134.8 (Pyr C-4), 137.9 (C(O)CHCH), 138.8 (Ph C-1), 149.8 (Pyr C-2), 150.7 (Pyr C-6), 161.9 (Pz C-3), 182.1 (C=O). ¹⁵N NMR (71 MHz, DMSO-d₆): δ_N ppm −182.1 (Pz N-1), −119.4 (Pz N-2), −65.0 (Pyr N). HRMS (ESI⁺) for C₁₇H₁₃N₃O₂ ([M + H]⁺) calcd 292.1080, found 292.1081.

(2E)-1-(3-Hydroxy-1-phenyl-1H-pyrazol-4-yl)-3-(quinolin-4-yl)prop-2-en-1-one (8j)

The reaction mixture was stirred for 4 h. Orange solid; yield 63% (2.15 mg); m.p. 240–241 °C; R_f = 0.24 (DCM/MeOH 100/3, v/v). IR (ν_max, cm⁻¹): 3111, 1654 (C=O), 1574, 1507, 1441, 1221, 1050, 746, 730, 684, 669. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 7.34–7.36 (m, 1H, NPh 4-H), 7.52–7.54 (m, 2H, NPh 3,5-H), 7.74–7.76 (m, 1H, Quin 6-H), 7.86–7.87 (m, 2H, NPh 2,6-H), 7.88–7.89 (m, 1H, Quin 7-H), 7.95–7.98 (m, 2H, C(O)CHCH, Quin 3-H), 8.12–8.13 (m, 1H, Quin 5-H), 8.35–8.36 (m, 1H, Quin 8-H), 8.39 (d, J = 14.0 Hz, 1H, C(O)CHCH), 9.04 (d, J = 4.5 Hz, 1H, Quin 2-H), 9.22 (s, 1H, Pz 5-H), 11.43 (s, 1H, OH). ¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 111.0 (Pz C-4), 118.1 (NPh C-2,6), 118.5 (Quin C-3), 123.8 (Quin C-8), 125.8 (Quin C-4), 126.7 (NPh C-4), 127.7 (Quin C-6), 129.1 (Quin C-5), 129.6 (NPh C-3,5), 130.2 (Quin C-7), 131.0 (C(O)CHCH), 132.2 (Pz C-4), 134.8 (C(O)CHCH), 138.7 (NPh C-1), 140.7 (Quin C-4a), 147.5 (Quin C-8a), 149.9 (Quin C-2), 161.9 (Pz C-3), 181.8 (C=O). ¹⁵N NMR (71 MHz, DMSO-d₆): δ_N ppm −181.1 (Pz N-1). HRMS (ESI⁺) for C₂₁H₁₅N₃O₂ ([M + H]⁺) calcd 342.1237, found 342.1237.

(2E)-1-(3-Hydroxy-1-phenyl-1H-pyrazol-4-yl)-3-(thiophen-2-yl)prop-2-en-1-one (8k)

The reaction mixture was stirred for 4 h. Yellow solid; yield 45% (1.33 mg); m.p. 196–197 °C; R_f = 0.54 (DCM/MeOH 100/3, v/v). IR (ν_max, cm⁻¹): 3104, 3067, 1647 (C=O), 1582, 1509, 1457, 1322, 1217, 1062, 967, 825, 699, 685. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 7.17–7.18 (m, 1H, Th 5-H), 7.31–7.34 (m, 1H, Ph 4-H), 7.46 (d, J = 15.4 Hz, 1H, C(O)CHCH), 7.50–7.52 (m, 2H, Ph 3,5-H), 7.58–7.59 (m, 1H, Th 3-H), 7.74–7.75 (m, 1H, Th 4-H), 7.84–7.88 (m, 3H, Ph 2,6-H, C(O)CHCH), 9.08 (s, 1H, Pz 5-H), 11.31 (s, 1H, OH). ¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 111.0 (Pz C-4), 118.1 (Ph C-2,6), 122.7 (C(O)CHCH), 126.5 (Ph C-4), 128.7 (Th C-5), 129.5 (Ph C-3,5), 129.8 (Th C-4), 131.6 (Pz C-5), 132.9 (Th C-3), 134.5 (C(O)CHCH), 138.8 (Ph C-1), 139.9 (Th C-2), 161.7 (Pz C-3), 182.2 (C=O). ¹⁵N NMR (71 MHz, DMSO-d₆): δ_N ppm −181.6 (Pz N-1), −118.4 (Pz N-2). HRMS (ESI⁺) for C₁₆H₁₂N₂O₂S ([M + Na]⁺) calcd 319.0512, found 319.0512.

(2E)-3-(Furan-3-yl)-1-(3-hydroxy-1-phenyl-1H-pyrazol-4-yl)prop-2-en-1-one (8l)

The reaction mixture was stirred for 5 h. White solid; yield 95% (2.67 mg); m.p. 195–196 °C; R_f = 0.62 (DCM/MeOH 100/3, v/v). IR (ν_max, cm⁻¹): 3111, 3071, 1653 (C=O), 1587, 1511, 1458, 1322, 1219, 1063, 1156, 727, 680. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 6.67–6.68 (m, 1H, Furanyl 5-H), 7.00 (m, 1H, Furanyl 4-H), 7.31–7.33 (m, 1H, Ph 4-H), 7.49–7.53 (m, 4H, Ph 3,5-H, C(O)CHCH), 7.85–7.86 (m, 2H, Ph 2,6-H), 7.89 (m, 1H, Furanyl 2-H), 9.04 (s, 1H, Pz 5-H), 11.35 (s, 1H, OH). ¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 111.1 (Pz C-4), 113.0 (Furanyl C-5), 116.8 (Furanyl C-4), 118.1 (Ph C-2,6), 121.1 (C(O)CHCH), 126.5 (Ph C-4), 128.1 (C(O)CHCH), 129.6 (Ph C-3,5), 131.5 (Pz C-5), 138.8 (Ph C-1), 145.9 (Furanyl C-2), 151.2 (Furanyl C-3), 161.6 (Pz C-3), 182.2 (C=O). ¹⁵N NMR (71 MHz, DMSO-d₆): δ_N −181.6 (Pz N-1). HRMS (ESI⁺) for C₁₆H₁₂N₂O₃ ([M + Na]⁺) calcd 303.0740, found 303.0740.

3.2.6. General Procedure for the Synthesis of 9a–i

To a solution of an appropriate compound 8 (1 mmol) in abs. DMF (3 mL), NaH (60% suspension in mineral oil, 0.04 g, 1 mmol) and an appropriate alkylhalide (1.1 mmol) were added [76]. The reaction mixture was stirred at room temperature for 1–2 h, diluted with KHSO₄ aq. (10 mL) and extracted with EtOAc (2 × 10 mL). The organic layers were combined, washed with H₂O (4 × 20 mL), dried with sodium sulphate, filtrated off and concentrated. The residue was purified by column chromatography (SiO₂, eliuent: hexane/ethyl acetate 9/1) to produce pure 9a–i.

(2E)-1-(3-Methoxy-1-phenyl-1H-pyrazol-4-yl)-3-phenylprop-2-en-1-one (9a)

The reaction mixture was stirred for 1 h. Yellow solid; yield 69% (210 mg); m.p. 163–164 °C; R_f = 0.78 (DCM/MeOH 100/3, v/v). IR (ν_max, cm⁻¹): 3118, 3089, 1652 (C=O), 1550, 1498, 1408, 1308, 1217, 756, 731, 685, 672. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 4.16 (s, 3H, CH₃), 7.30–7.32 (m, 1H, NPh 4-H), 7.39–7.43 (m, 3H, CPh 3,4,5-H), 7.45–7.48 (m, 2H, NPh 3,5-H), 7.63 (d, J = 15.7 Hz, 1H, C(O)CHCHPh), 7.64–7.66 (m, 2H, CPh 2,6-H), 7.68–7.69 (m, 2H, NPh 2,6-H), 7.82 (d, J = 15.7 Hz, 1H, C(O)CHCHPh), 8.42 (s, 1H, Pz 5-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 56.9 (CH₃), 112.3 (Pz C-4), 118.6 (NPh C-2,6), 124.3 (C(O)CHCHPh), 126.9 (NPh C-4), 128.5 (CPh C-2,6), 128.8 (CPh C-3,5), 129.5 (NPh C-3,5), 130.2 (CPh C-4), 131.3 (Pz C-5), 135.2 (CPh C-1), 139.2 (NPh C-1), 142.6 (C(O)CHCHPh), 162.5 (Pz C-3), 183.3 (C=O). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −181.4 (Pz N-1), −118.5 (Pz N-2). HRMS (ESI⁺) for C₁₉H₁₆N₂O₂ ([M + Na]⁺) calcd 327.1104, found 327.1104.

(2E)-3-(4-Fluorophenyl)-1-(3-methoxy-1-phenyl-1H-pyrazol-4-yl)prop-2-en-1-one (9b)

The reaction mixture was stirred for 2 h. Yellow solid; yield 43% (139 mg); m.p. 155–156 °C; R_f = 0.53 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3116, 3049, 1656 (C=O), 1560, 1500, 1408, 1327, 1221, 746, 706, 684, 641. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 4.04 (s, 3H, CH₃), 7.30–7.33 (m, 2H, CPh 3,5-H), 7.35–7.37 (m, 1H, NPh 4-H), 7.53–7.55 (m, 2H), 7.61 (d, J = 15.7 Hz, 1H, C(O)CHCHPh), 7.66 (d, J = 15.6 Hz, 1H, C(O)CHCHPh), 7.86–7.89 (m, 4H, NPh 2,6-H, CPh 2,6-H), 9.27 (s, 1H, Pz 5-H). ¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 54.9 (CH₃), 109.6 (Pz C-4), 114.3 (d, ²J= 21.7 Hz, CPh C-3,5), 116.5 (NPh C-2,6), 122.6 (C(O)CH), 125.1 (NPh C-4), 127.9 (NPh C-3,6), 129.1 (d, ³J= 8.5 Hz, CPh C-2,6), 129.7 (d, ⁴J = 3.1 Hz, CPh C-1), 131.4 (Pz C-5), 137.1 (NPh C-1), 138.5 (C(O)CHCH), 160.9 (Pz C-3), 161.6 (d, ¹J = 248.3 Hz, CPh C-4), 179.6 (C=O). HRMS (ESI⁺) for C₁₉H₁₅FN₂O₂ ([M + H]⁺) calcd 323.1190, found 323.1191.

(2E)-3-(4-Chlorophenyl)-1-(3-methoxy-1-phenyl-1H-pyrazol-4-yl)prop-2-en-1-one (9c)

The reaction mixture was stirred for 2 h. Yellow solid; yield 80% (272 mg); m.p. 173–174 °C; R_f = 0.69 (DCM/MeOH 100/1, v/v). IR (ν_max, cm⁻¹): 3122, 3069, 1659 (C=O), 1597, 1560, 1490, 1403, 1329, 1222, 813, 744, 683, 638 497. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 4.04 (s, 3H, CH₃), 7.34–7.36 (m, 1H, NPh 4-H), 7.52–7.55 (m, 4H, NPh 3,5-H, CPh 2,6-H), 7.63 (d, J = 15.6 Hz, 1H, C(O)CHCHPh), 7.66 (d, J = 15.7 Hz, 1H, C(O)CHCHPh), 7.82–7.83 (m, 2H, CPh 3,5-H), 7.88–7.89 (m, 2H, NPh 2,6-H), 9.27 (s, 1H, Pz 5-H). ¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 56.5 (CH₃), 111.2 (Pz C-4), 118.1 (NPh C-2,6), 125.1 (C(O)CHCHPh), 126.7 (NPh C-4), 129.0 (CPh C-2,6), 129.6 (NPh C-3,5), 130.2 (CPh C-3,5), 133.1(Pz C-5), 133.7 (CPh C-1), 134.8 (CPh C-4), 138.7 (NPh C-4), 140.0 (C(O)CHCHPh), 162.6 (Pz C-3), 181.2 (C=O). ¹⁵N NMR (71 MHz, DMSO-d₆): δ_N ppm −182.2 (Pz N-1), −119.1 (Pz N-2). HRMS (ESI⁺) for C₁₉H₁₅ClN₂O₂ ([M + Na]⁺) calcd 361.0714, found 361.0714.

(2E)-3-[4-(Dimethylamino)phenyl]-1-(3-methoxy-1-phenyl-1H-pyrazol-4-yl)prop-2-en-1-one (9d)

The reaction mixture was stirred for 1 h. Yellow solid; yield 43% (277 mg); m.p. 186–187 °C; R_f=0.15 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3111, 1634 (C=O), 1580, 1503, 1421, 1358, 1157, 1032, 810, 748, 688, 667. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 3.00 (s, 6H, N(CH₃)₂), 4.04 (s, 3H, OCH₃), 6.75–6.76 (m, 2H, CPh 3,5-H), 7.33–7.35 (m, 1H, NPh 4-H), 7.41 (d, J = 15.4 Hz 1H C(O)CHCHPh), 7.51–7.54 (m, 2H), 7.57–7.61 (m, 3H, CPh 2,6-H, C(O)CHCHPh), 7.88–7.90 (m, 2H, NPh 2,6-H), 9.16 (s, 1H, Pz 5-H). ¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 39.7 (N(CH₃)₂), 56.5 (OCH₃), 111.7 (Pz C-4), 111.8 (CPh 3,5-C), 118.0 (NPh C-2,6), 118.8 (C(O)CHCHPh), 122.0 (CPh C-1), 126.5 (NPh C-4), 129.5 (CPh C-2,6), 130.2 (NPh C-3,5), 132.4 (Pz C-5), 138.8 (NPh C-1), 142.5 (C(O)CHCHPh), 151.8 (CPh C-4), 162.3 (Pz C-3), 181.3 (C=O). HRMS (ESI⁺) for C₂₁H₂₁N₃NaO₂ ([M + Na]⁺) calcd 370.1526, found 370.1526.

(2E)-1-(3-Methoxy-1-phenyl-1H-pyrazol-4-yl)-3-(quinolin-4-yl)prop-2-en-1-one (9e)

The reaction mixture was stirred for 1 h. Yellow solid; yield 72% (256 mg); m.p. 182–183 °C, R_f = 0.6 (DCM/MeOH 100/3, v/v). IR (ν_max, cm⁻¹): 3120, 3091, 1654 (C=O), 1596, 1556, 1500, 1414, 1309, 1218, 834, 749, 726, 682. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 4.06 (s, 3H, CH₃), 7.35–7.38 (m, 1H, NPh 4-H), 7.53–7.56 (m, 2H, NPh 3,5-H), 7.71–7.73 (m, 1H, Quin 7-H), 7.83–7.85 (m, 1H, Quin 6-H), 7.87–7.91 (m, 3H, C(O)CHCH, NPh 2,6-H), 7.95–7.96 (m, 1H, Quin 4-H), 8.10–8.11 (m, 1H, Quin 5-H), 8.31–8.32 (m, 1H, Quin 8-H), 8.36 (d, J = 15.5 Hz, 1H, C(O)CHCH), 9.01 (m, 1H, Quin 2-H), 9.34 (s, 1H, Pz 5-H). ¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 56.6 (CH₃), 111.1 (Pz C-4), 118.2 (NPh C-2,6), 118.5 (Quin C-3), 123.6, 125.7, 126.9, 127.5, 129.6 (NPh C-3,5), 129.7, 129.8, 130.7, 133.4 (Pz C-5), 135.1 (C(O)CHCH), 138.7 (NPh C-1), 139.8 (Quin C-4a), 148.3 (Quin C-8a), 150.3 (Quin C-2), 162.7 (Pz C-3), 181.0 (C=O). HRMS (ESI⁺) for C₂₂H₁₇N₃O₂ ([M + H]⁺) calcd 356.1394, found 356.1394.

(2E)-1-(3-Methoxy-1-phenyl-1H-pyrazol-4-yl)-3-(thiophen-2-yl)prop-2-en-1-one (9f)

The reaction mixture was stirred for 1 h. Yellow solid; yield 60% (186 mg); m.p. 131–132 °C; R_f = 0.37 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3127, 3096, 1664 (C=O), 1560, 1502, 1410, 1399, 1225, 1014, 943, 750, 685, 669, 505. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 4.05 (s, 3H, CH₃), 7.18–7.19 (m, 1H, Th 5-H), 7.34–7.38 (m, 2H, Ph 4-H, C(O)CHCH), 7.51–7.54 (m, 2H, Ph 3,5-H), 7.60 (m, 1H, Th 3-H), 7.75–7.76 (m, 1H, Th 4-H), 7.84 (d, J = 15.3 Hz, 1H, C(O)CHCH), 7.88–7.91 (m, 2H, Ph 2,6-H), 9.21 (s, 1H, Pz 5-H). ¹³C NMR (176 MHz, DMSO-d₆): δ_H ppm 57.1 (CH₃), 111.6 (Pz C-4), 118.6 (Ph C-2,6), 123.3 (C(O)CHCH), 127.1 (Ph C-4), 129.1 (Th C-5), 130.0 (Ph C-3,5), 130.2 (Th C-4), 133.2 (Pz C-5), 133.3 (Th C-3), 135.0 (C(O)CHCH), 139.2 (Ph C-1), 140.3 (Th C-2), 162.8 (Pz C-3), 181.4 (C=O). ¹⁵N NMR (71 MHz, DMSO-d₆): δ_N ppm −181.9 (Pz N-1), −119.4 (Pz N-2). HRMS (ESI⁺) for C₁₇H₁₄N₂O₂S ([M + Na]⁺) calcd 333.0668, found 333.0668.

(2E)-3-(Furan-3-yl)-1-(3-methoxy-1-phenyl-1H-pyrazol-4-yl)prop-2-en-1-one (9g)

The reaction mixture was stirred for 1 h. Yellow solid; yield 77% (227 mg); m.p. 136–137 °C; R_f = 0.34 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3122, 3063, 1658 (C=O), 1558, 1501, 1461, 1404, 1220, 1014, 742, 681, 631, 595. ¹H NMR (700 MHz, DMSO-d₆): δ_H ppm 4.05 (s, 3H, CH₃), 6.67–6.68 (m, 1H, Furanyl 4-H), 7.01 (m, 1H, Furanyl 5-H), 7.33–7.35 (m, 1H, Ph 4-H), 7.40 (d, J = 14.0 Hz, 1H, C(O)CHCH), 7.48–7.53 (m, 3H, Ph 3,5-H, C(O)CHCH), 7.90–7.91 (m, 3H, Ph 2,6-H, Furanyl 2-H), 9.16 (s, 1H, Pz 5-H). ¹³C NMR (176 MHz, DMSO-d₆): δ_C ppm 56.6 (CH₃), 111.3 (Pz C-4), 113.0 (Furanyl C-4), 116.8 (Furanyl C-5), 118.1 (Ph C-2,6), 121.2 (C(O)CHCH), 126.7 (Ph C-4), 128.3 (C(O)CHCH), 129.5 (Ph C-3,5), 132.7 (Pz C-5), 138.7 (Ph C-1), 145.9 (Furanyl C-2), 151.1 (Furanyl C-3), 162.2 (Pz C-3), 181.1 (C=O). ¹⁵N NMR (71 MHz, DMSO-d₆): δ_N ppm −181.6 (Pz N-1), −119.0 (Pz N-2). HRMS (ESI⁺) for C₁₇H₁₄N₂O₃ ([M + Na]⁺) calcd 317.0897, found 317.0897.

(2E)-3-Phenyl-1-(1-phenyl-3-propoxy-1H-pyrazol-4-yl)prop-2-en-1-one (9h)

The reaction mixture was stirred for 1 h. Yellow solid; yield 96% (320 mg); m.p. 131–132 °C; R_f = 0.77 (DCM/MeOH 100/1, v/v). IR (ν_max, cm⁻¹): 3118, 3082, 1657 (C=O), 1597, 1561, 1491, 1447, 1349, 1330, 1222, 761, 746, 681, 638. ¹H NMR (400 MHz, DMSO-d₆): δ_H ppm 1.05 (t, J = 7.4 Hz, 3H, CH₃), 1.85 (sext, J = 7.1 Hz, 2H, CH₃CH₂CH₂), 4.33 (t, J = 6.5 Hz, 2H, CH₃CH₂CH₂), 7.32–7.36 (m, 1H, NPh 4-H), 7.44–7.54 (m, 5H, NPh 3,5-H, CPh 3,4,5-H), 7.64–7.72 (m, 2H, C(O)CHCHPh), 7.74–7.78 (m, 2H, CPh 2,6-H), 7.86–7.90 (m, 2H, NPh 2,6-H), 9.20 (s, 1H, Pz 5-H). ¹³C NMR (101 MHz, DMSO-d₆): δ_C ppm 10.4 (CH₃), 22.0 (CH₃CH₂CH₂), 70.6 (CH₃CH₂CH₂), 111.5 (Pz C-4), 118.1 (NPh C-2,6), 124.5 (C(O)CHCHPh), 126.7 (NPh C-4), 128.3 (CPh C-2,6), 129.0 (NPh C-3,5), 129.5 (CPh C-3,5), 130.4 (CPh C-4), 132.6 (Pz C-5), 134.7 (CPh C-1), 138.7 (NPh C-1), 141.3 (C(O)CHCHPh), 161.9 (Pz C-3), 181.5 (C=O). HRMS (ESI⁺) for C₂₁H₂₀N₂O₂ ([M + Na]⁺) calcd 355.1417, found 355.1417.

(2E)-1-[3-(2-Methoxyethoxy)-1-phenyl-1H-pyrazol-4-yl]-3-phenylprop-2-en-1-one (9i)

The reaction mixture was stirred for 1 h. Yellow solid; yield 50% (175 mg); m.p. 133–134 °C; R_f = 0.43 (DCM/MeOH 100/1, v/v). IR (ν_max, cm⁻¹): 3114, 3089, 1656 (C=O), 1596, 1556, 1493, 1468, 1371, 1220, 766, 750, 686, 677. ¹H NMR (400 MHz, DMSO-d₆): δ_H ppm 3.39 (s, 3H, CH₃), 3.78–3.80 (m, 2H, CH₃OCH₂CH₂), 4.49–4.51 (m, 2H, CH₃OCH₂CH₂), 7.33–7.37 (m, 1H, NPh 4-H), 7.46–7.55 (m, 5H, NPh 3,5-H, CPh 3,4,5-H), 7.66 (d, J = 15.6 Hz, 1H, C(O)CHCHPh), 7.75–7.79 (m, 3H, C(O)CHCHPh, CPh 2,6-H), 7.88–7.90 (m, 2H, NPh 2,6-H), 9.19 (s, 1H, Pz 5-H). ¹³C NMR (101 MHz, DMSO-d₆): δ_C ppm 58.3 (CH₃), 68.5 (CH₃OCH₂CH₂), 70.2 (CH₃OCH₂CH₂), 111.5 (Pz C-4), 118.2 (NPh C-2,6), 124.5 (C(O)CHCHPh), 126.7 (NPh C-4), 128.4 (CPh C-2,6), 129.0 (CPh C-3,5), 129.5 (NPh C-3,5), 130.4 (CPh C-4), 132.7 (Pz C-5), 134.7 (CPh C-1), 138.7 (NPh C-1), 141.3 (C(O)CHCHPh), 161.7 (Pz C-3), 181.5 (C=O). HRMS (ESI⁺) for C₂₁H₂₀N₂O₃ ([M + Na]⁺) calcd 371.1366, found 371.1366.

3.2.7. General Procedure for the Preparation of 3-pyridinyl- and 4-pyridinyl-1-phenyl-1H-pyrazol-4-ylethanones (11a,b)

To the solution of triflate 10 (320 mg, 1 mmol) in abs. EtOH (2.5 mL), 4-pyridinyl- or 3-pyridinylboronic acid (123 mg, 1 mmol), Cs₂CO₃ (652 mg, 2 mmol), KBr (36 mg, 0.3 mmol) and Pd(PPh₃)₄ (116 mg, 0.1 mmol) were added, and the reaction mixture was irradiated (150 W) at 80 °C temperature for 10 min. EtOH was evaporated, the mixture was diluted with water (10 mL) and extracted with ethyl acetate (3 × 10 mL). The organic layers were combined, washed with brine, dried over Na₂SO₄, filtrated off, and the solvent was evaporated. The residue was purified by flash column chromatography (SiO₂, eluent: ethyl acetate/n-hexane, 1:4, v/v) to provide the desired compounds 11a,b.

1-[1-Phenyl-3-(pyridin-3-yl)-1H-pyrazol-4-yl]ethan-1-one (11a)

White solid; yield 63% (166 mg); m.p. 121–122 °C; R_f = 0.36 (EtOAc, v/v). IR (ν_max, cm⁻¹): 3120, 3041, 1684 (C=O), 1599, 1521, 1448, 1362, 1260, 1241, 1221, 977, 940, 863, 751, 705, 683. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 2.50 (s, 3H, CH₃), 7.37–7.39 (m, 1H, Pyr 5-H), 7.39–7.42 (m, 1H, Ph 4-H), 7.51–7.54 (m, 2H, Ph 3,5-H), 7.78–7.79 (m, 2H, Ph 2,6-H), 8.18 (dt, J_4-H,5-H = 7.9 Hz, J = 2.0 Hz, 1H, Pyr 4-H), 8.48 (s, 1H, Pz 5-H), 8.65 (dd, J_5-H,6-H = 4.9 Hz, J = 1.7 Hz, 1H, Pyr 4-H), 9.03 (d, J = 2.3 Hz, 1H, Pyr 2-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 29.3 (CH₃), 119.8 (Ph C-2,6), 122.8 (Pz C-4), 122.9 (Pyr C-5), 128.1 (Ph C-4), 128.6 (Pyr C-3), 129.9 (Ph C-3,5), 132.2 (Pz C-5), 137.1 (Pyr C-4), 139.1 (NPh C-1), 149.9 (Pyr C-6), 150.2 (Pyr C-2), 150.7 (Pz C-3), 191.8 (C=O). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −162.6 (Pz N-1), −71.4 (Pyr N). HRMS (ESI⁺) for C₁₆H₁₃N₃O ([M + H]⁺) calcd 264.1131, found 264.1131.

1-[1-Phenyl-3-(pyridin-4-yl)-1H-pyrazol-4-yl]ethan-1-one (11b)

White solid; yield 64% (169 g); m.p. 120–122 °C; R_f = 0.16 (EtOAc/Hex 1/1, v/v). IR (ν_max, cm⁻¹): 3120, 3041, 1684 (C=O), 1599, 1521, 1448, 1362, 1260, 1241, 1221, 977, 940, 863, 751, 705, 683. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 2.51 (s, 3H, CH₃), 7.39–7.42 (m, 1H, Ph 4-H), 7.51–7.53 (m, 2H, Ph 3,5-H), 7.76–7.78 (m, 2H, Ph 2,6-H), 7.79–7.80 (m, 2H, Pyr 3,5-H), 8.47 (s, 1H, Pz 5-H), 8.69 (d, J_3,5-H,2,6-H = 6.2 Hz, 2H, Pyr 2,6-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 29.5 (CH₃), 119.9 (Ph C-2,6), 122.9 (Pz C-4), 123.9 (Pyr C-3,5), 128.3 (Ph C-4), 129.9 (Ph C-3,5), 132.5 (Pz C-5), 139.1 (Ph C-1), 140.2 (Pyr C-4), 149.9 (Pyr C-2,6), 150.9 (Pz C-3), 191.8 (C=O). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −162.2 (Pz N-1), −70.1 (Pyr N). HRMS (ESI⁺) for C₁₆H₁₄N₃O ([M + H]⁺) calcd 264.1131, found 264.1131.

3.2.8. General Procedure for the Synthesis of 12a–j

To a solution of an appropriate pyrazole ethanone (11a,b) (50 mg, 0.19 mmol) in EtOH (96%, 2 mL), NaOH (75 mg, 1.9 mmol) and appropriate benzaldehyde (0.47 mmol) were added. The reaction mixture was heated at 55 °C for 10 min. After the completion of the reaction as monitored by TLC, EtOH was evaporated, the mixture was diluted with water (10 mL) and extracted with ethyl acetate (3 × 10 mL). The organic layers were combined, washed with brine, dried over sodium sulphate, filtrated off, and the solvent was evaporated. The residue was purified by flash column chromatography (SiO₂, eluent: ethyl acetate/n-hexane, 1:2, v/v) to provide the desired compounds 12a–j.

(2E/Z)-3-Phenyl-1-[1-phenyl-3-(pyridin-3-yl)-1H-pyrazol-4-yl]prop-2-en-1-one (12a,13a)

A mixture of isomers was obtained in the ratio E-12a:Z-13a = 1:0.15. Yellow solid; yield 70% (55 mg); m.p. 169–170.8 °C; R_f = 0.67 (EtOAc/Hex 1/2, v/v). IR (ν_max, cm⁻¹): 3120, 3041, 1684 (C=O), 1599, 1521, 1448, 1362, 1260, 1241, 1221, 977, 940, 863, 751, 705, 683. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 6.45 (d, J = 12.7 Hz, 1H, C(O)CHCHPh of minor isomer), 6.91 (d, J =12.7 Hz, 1H, C(O)CHCHPh of minor isomer), 7.12 (d, J =15.6 Hz, 1H, C(O)CHCHPh of major isomer), 7.36–7.42 (m, 5H, NPh 4-H, CPh 3,4,5-H, Pyr 5-H), 7.49–7.50 (m, 2H, CPh 2,6-H), 7.52–7.55 (m, 2H, NPh 3,5-H), 7.64–7.66 (m, 2H, NPh 2,6-H of minor isomer), 7.76 (d, J = 15.6 Hz, 1H, C(O)CHCHPh of major isomer), 7.82–7.83 (m, 2H, NPh 2,6-H), 8.18 (dd, J_{Pyr 4-H,5-H} = 7.8 Hz, J_{Pyr 4-H,6-H} = 1.8 Hz, 1H, Pyr 4-H), 8.32 (s, 1H, Pz 5-H of minor isomer), 8.59 (s, 1H, Pz 5-H of major isomer), 8.65 (d, J = 4.8 Hz, 1H, Pyr 4-H of minor isomer), 8.68 (d, J_{Pyr 5-H,6-H} = 4.8 Hz, 1H, Pyr 6-H of major isomer), 9.04 (s, 1H, Pyr 2-H of minor isomer), 9.07 (s, 1H, Pyr 2-H of major isomer). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 119.8 (NPh C-2,6), 123.0 (Pyr C-5), 123.5 (Pz C-4), 124.4 (C(O)CH=CHPh), 128.1 (NPh C-4), 128.5 (CPh C-2,6), 128.7 (Pyr C-3), 129.1 (CPh C-3,5), 129.9 (NPh C-3,5), 130.8 (CPh C-4), 131.5 (Pz C-5), 134.7 (CPh C-1), 137.1 (Pyr C-4), 139.2 (NPh C-1), 144.2 (C(O)CH=CHPh), 149.9 (Pyr C-6), 150.2 (Pyr C-2), 150.9 (Pz C-3), 184.4 (CO). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −162.0 (Pz N-1), −71.4 (Pyr N). HRMS (ESI⁺) for C₂₃H₁₈N₃O ([M + H]⁺) calcd 352.1444, found 352.1444.

(2E/Z)-3-(4-Methylphenyl)-1-[1-phenyl-3-(pyridin-3-yl)-1H-pyrazol-4-yl]prop-2-en-1-one (12b,13b)

A mixture of isomers was obtained in the ratio E-12b:Z-13b = 1:0.17. Yellow crystals; yield 61% (42 mg); m.p. 150.2–151.3 °C; R_f=0.61 (EtOAc/Hex 1/2, v/v). IR (ν_max, cm⁻¹): 3120, 3041, 1684 (C=O), 1599, 1521, 1448, 1362, 1260, 1241, 1221, 1231, 977, 940, 863, 751, 705, 683. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 2.29 (s, 3H, CH₃ of minor isomer), 2.38 (s, 3H, CH₃ of major isomer), 6.40 (d, J =12.7 Hz, 1H, C(O)CHCHPh of minor isomer), 6.86 (d, J =12.7 Hz, 1H, C(O)CHCHPh of minor isomer), 7.07 (d, J =15.6 Hz, 1H, C(O)CHCHPh of major isomer), 7.19 (d, J = 7.8 Hz, 2H, CPh 3,5-H), 7.36–7.42 (m, 4H, NPh 4-H, CPh 2,6-H, Pyr 5-H), 7.47–7.49 (m, 2H, NPh 3,5-H of minor isomer), 7.51–7.54 (m, 2H, NPh 3,5-H of major isomer), 7.65–7.67 (m, 2H, NPh 2,6-H of minor isomer), 7.74 (d, J = 15.6 Hz, 1H, C(O)CHCHPh of major isomer), 7.81–7.83 (m, 2H, NPh 2,6-H), 8.17 (dt, J_{Pyr 4-H,5-H} = 7.9 Hz, J = 2.0 Hz, 1H, Pyr 4-H), 8.34 (s, 1H, Pz 5-H of minor isomer), 8.57 (s, 1H, Pz 5-H, of major isomer), 8.67 (dd, J_{Pyr 5-H,6-H} = 4.9 Hz, J = 1.7 Hz 1H, Pyr 4-H), 9.04 (d, J = 2.2 Hz, 1H, Pyr 2-H of minor isomer), 9.07 (d, J = 2.0 Hz, 1H, Pyr 2-H of major isomer). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 21.7 (CH₃), 119.8 (NPh C-2,6), 123.0 (Pyr C-5), 123.4 (Pz C-4), 123.6 (C(O)CHCHPh), 128.0 (NPh C-4), 128.6 (CPh C-2,6), 128.8 (Pyr C-3), 129.2 129.9 (CPh C-3,5, NPh C-3,5), 131.4 (Pz C-5), 131.9 (CPh C-1), 137.1 (Pyr C-4), 139.2 (NPh C-1), 141.4 (CPh C-4), 144.3 (C(O)CHCHPh), 149.9 (Pyr C-6), 150.2 (Pyr C-2), 150.8 (Pz C-3), 184.6 (C(O)CHCHPh). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −161.9 (Pz N-1), −70.8 (Pyr N). HRMS (ESI⁺) for C₂₄H₂₀N₃O ([M + H]⁺) calcd 366.1601, found 366.1601.

(2E/Z)-1-[1-Phenyl-3-(pyridin-3-yl)-1H-pyrazol-4-yl]-3-[4-(trifluoromethoxy)phenyl]prop-2-en-1-one (12c,13c)

A mixture of isomers was obtained in the ratio E-12c:Z-13c = 1:0.4. Yellow crystals; yield 55% (46 mg); m.p. 183–184 °C; R_f = 0.57 (EtOAc/Hex 1/2, v/v). IR (ν_max, cm⁻¹): 3120, 3041, 1684 (C=O), 1599, 1521, 1448, 1362, 1260, 1241, 1221, 1165, 977, 940, 863, 751, 705, 683. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 6.52 (d, J =12.8 Hz, 1H, C(O)CHCHPh of minor isomer), 6.84 (d, J =12.8 Hz, 1H, C(O)CHCHPh of minor isomer), 7.06 (d, J =15.6 Hz, 1H, C(O)CHCHPh of major isomer), 7.12–7.13 (m, 2H, CPh 3,5-H of minor isomer), 7.22–7.23 (m, 2H, CPh 3,5-H of major isomer), 7.37–7.43 (m, 2H, NPh 4-H, Pyr 5-H), 7.49–7.55 (m, 4H, CPh 2,6-H, NPh 3,5-H), 7.73 (d, J = 15.6 Hz, 1H, C(O)CHCHPh of major isomer), 7.81–7.83 (m, 2H, NPh 2,6-H), 8.17 (d, J_{Pyr 4-H,5-H} = 7.8 Hz, 1H, Pyr 4-H), 8.41 (s, 1H, Pz 5-H of minor isomer), 8.59 (s, 1H, Pz 5-H of major isomer), 8.66 (d, J_{Pyr 5-H,6-H} = 4.7 Hz, 1H, Pyr 6-H of major isomer), 8.69 (d, J_{Pyr 5-H,6-H} = 4.3 Hz, 1H, Pyr 6-H of minor isomer), 9.03 (s, 1H, Pyr 2-H of minor isomer), 9.06 (s, 1H, Pyr 2-H of major isomer). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 119.8 (NPh C-2,6), 121.3 (CPh C-3,5), 123.1 (Pyr C-5), 123.4 (Pz C-4), 125.1 (C(O)CHCHPh), 127.9 (NPh C-4 of minor isomer), 128.2 (NPh C-4 of major isomer), 128.7 (Pyr C-3), 129.9 (CPh C-2,6, NPh C-3,5), 130.5 (q, ¹J = 254.6 Hz, OCF₃), 131.6 (Pz C-5 of major isomer), 133.3 (CPh C-1 of major isomer), 133.6 (CPh C-1 of minor isomer), 137.0 (Pyr C-4 of minor isomer), 137.1 (Pyr C-4 of major isomer), 138.6 (NPh C-1 of minor isomer), 139.1 (NPh C-1 of major isomer), 142.3 (C(O)CHCHPh), 150.0 (Pyr C-6), 150.2 (Pyr C-2), 150.7 (Pz C-3), 150.9 (CPh C-4), 184.0 (C(O)CHCHPh of major isomer), 186.8 (C(O)CHCHPh of minor isomer). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −161.6 (Pz N-1), −70.9 (Pyr N). HRMS (ESI⁺) for C₂₄H₁₇N₃O₂F₃ ([M + H]⁺) calcd 436.1267, found 436.1267.

(2E/Z)-3-Phenyl-1-[1-phenyl-3-(pyridin-4-yl)-1H-pyrazol-4-yl]prop-2-en-1-one (12d,13d)

A mixture of isomers was obtained in the ratio E-12d:Z-13d = 1:0.18. White crystals; yield 58% (39 mg); m.p. 162.8–165 °C; R_f = 0.29 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3120, 3041, 1684 (C=O), 1599, 1521, 1448, 1362, 1260, 1241, 1221, 977, 940, 863, 751, 705, 683. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 6.47 (d, J =12.7 Hz, 1H, C(O)CHCHPh of minor isomer), 6.93 (d, J =12.7 Hz, 1H, C(O)CHCHPh of minor isomer), 7.12 (d, J =15.7 Hz, 1H, C(O)CHCHPh of major isomer), 7.38–7.42 (m, 4H, NPh 4-H, CPh 3,4,5-H), 7.48–7.51 (m, 2H, CPh 2,6-H), 7.52–7.54 (m, 2H, NPh 3,5-H), 7.63–7.64 (m, 2H, NPh 2,6-H of minor isomer), 7.76 (d, J = 15.7 Hz, 1H, C(O)CHCHPh of major isomer), 7.79–7.83 (m, 4H, Pyr 3,5-H, NPh 2,6-H), 8.31 (s, 1H, Pz 5-H of minor isomer), 8.56 (s, 1H, Pz 5-H of major isomer), 8.68–8.71 (m, 2H, Pyr 2,6-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 119.8 (NPh C-2,6), 123.6 (Pz C-4), 123.8 (Pyr C-3,5), 124.5 (C(O)CHCHPh), 128.2 (NPh C-4), 128.6 (CPh C-2,6), 129.1 (CPh C-3,5), 129.9 (NPh C-3,5), 130.9 (CPh C-4), 131.7 (Pz C-5), 134.5 (CPh C-1), 139.1 (NPh C-1), 140.3 (Pyr C-4), 144.4 (C(O)CHCHPh), 149.9 (Pyr C-2,6), 151.1 (Pz C-3), 184.6 (C(O)CHCHPh). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −161.5 (Pz N-1), −70.6 (Pyr N). HRMS (ESI⁺) for C₂₃H₁₈N₃O ([M + H]⁺) calcd 352.1444, found 352.1444.

(2E/Z)-3-(4-Methylphenyl)-1-[1-phenyl-3-(pyridine-4-yl)-1H-pyrazol-4-yl]prop-2-en-1-one (12e,13e)

A mixture of isomers was obtained in the ratio E-12e:Z-13e = 1:0.13. Yellow crystals; yield 58% (40 mg); m.p. 176–177 °C; R_f=0.35 (EtOAc/Hex 1/2, v/v). IR (ν_max, cm⁻¹): 3120, 3041, 1684 (C=O), 1599, 1521, 1448, 1362, 1260, 1241, 1221, 977, 940, 863, 751, 705, 683. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 2.29 (s, 3H, CH₃ of minor isomer), 2.38 (s, 3H, CH₃ of major isomer), 6.42 (d, J =12.7 Hz, 1H, C(O)CHCHPh of minor isomer), 6.89 (d, J =12.7 Hz, 1H, C(O)CH=CHPh of minor isomer), 7.07 (d, J =15.6 Hz, 1H, C(O)CHCHPh of major isomer), 7.19 (d, J = 7.8 Hz, 2H, CPh 3,5-H), 7.38–7.42 (m, 3H, NPh 4-H, CPh 2,6-H), 7.47–7.50 (m, 2H, NPh 3,5-H of minor isomer), 7.52–7.54 (m, 2H, NPh 3,5-H of major isomers), 7.64–7.66 (m, 2H, NPh 2,6-H of minor isomer), 7.74 (d, J = 15.6 Hz, 1H, C(O)CHCHPh of major isomer), 7.79–7.83 (m, 4H, Pyr 3,5-H, NPh 2,6-H), 8.32 (s, 1H, Pz 5-H of minor isomer), 8.55 (s, 1H, Pz 5-H of major isomer), 8.70 (d, ³J = 5.3 Hz, 1H, Pyr 2,6-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 21.7 (CH₃), 119.9 (NPh C-2,6), 123.6 (C(O)CHCHPh), 123.7 (Pz C-4), 123.8 (Pyr C-3,5), 128.1 (NPh C-4), 128.6 (CPh C-2,6), 128.8 (Pyr C-1), 129.9 (CPh C-3,5, NPh C-3,5), 131.6 (Pz C-5), 131.8 (CPh C-1), 139.1 (NPh C-1), 141.5 (CPh C-4), 144.6 (C(O)CHCHPh), 149.9 (Pyr C-2,6), 151.0 (Pz C-3), 184.8 (C(O)CHCHPh). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −161.7 (Pz N-1), −70.2 (Pyr N). HRMS (ESI⁺) for C₂₄H₂₀N₃O ([M + H]⁺) calcd 366.1601, found 366.1601.

(2E/Z)-1-[1-Phenyl-3-(pyridine-4-yl)-1H-pyrazol-4-yl]-3-[4-(trifluoromethoxy)phenyl]prop-2-en-1-one (12f,13f)

A mixture of isomers was obtained in ratio E-12f:Z-13f = 1:0.24. Yellow crystals; yield 51% (42 mg); m.p. 168–170 °C; R_f = 0.42 (EtOAc/Hex 1/2, v/v). IR (ν_max, cm⁻¹): 3120, 3041, 1684 (C=O), 1599, 1521, 1448, 1362, 1260, 1241, 1221, 1165, 977, 940, 863, 751, 705, 683. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 6.54 (d, J =12.8 Hz, 1H, C(O)CHCHPh of minor isomer), 6.87 (d, J =12.8 Hz, 1H, C(O)CHCHPh of minor isomer), 7.07 (d, J =15.6 Hz, 1H, C(O)CHCHPh of major isomer), 7.12–7.13 (m, 2H, CPh 3,5-H of minor isomer), 7.20–7.24 (m, 2H, CPh 3,5-H of major isomer), 7.40–7.43 (m, 1H, NPh 4-H), 7.49–7.56 (m, 4H, CPh 2,6-H, NPh 3,5-H), 7.68–7.69 (m, 2H, NPh 2,6-H of minor isomer), 7.73 (d, J = 15.7 Hz, 1H, C(O)CHCHPh of major isomer), 7.79–7.82 (m, 4H, NPh 2,6-H, Pyr 3,5-H), 8.57 (s, 1H, Pz 5-H), 8.67–8.77 (m, 2H, Pyr 2,6-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 119.8 (NPh C-2,6 of minor isomer), 119.9 (NPh C-2,6 of major isomer), 120.7 (CPh C-3,5 of minor isomer), 121.4 (CPh C-3,5 of major isomers), 123.5 (Pyr C-3,5), 123.9 (Pz C-4), 125.2 (C(O)CH=CHPh), 127.9 (NPh C-4 of minor isomer), 128.3 (NPh C-4 of major isomer), 128.4 (Pyr C-4), 129.9 (NPh C-3,5 of major isomer), 130.0 (CPh C-2,6), 130.7 (q, ¹J = 266.6 Hz, OCF₃), 131.7 (Pz C-5), 133.1 (CPh C-1), 138.9 (NPh C-1 of minor isomer), 139.1 (NPh C-1 of major isomer), 140.3 (Pyr C-4 of major isomer), 140.7 (Pyr C-4 of minor isomer), 142.5 (C(O)CHCHPh), 149.8 (Pyr C-2,6 of minor isomer), 149.9 (Pyr C-2,6 of major isomer), 150.8 (CPh C-4 of major isomer), 151.0 (CPh C-4 of minor isomer), 151.0 (Pz C-3 of minor isomer), 151.1 (Pz C-3 of major isomer), 184.1 (C(O)CHCHPh). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −161.2 (Pz N-1). HRMS (ESI⁺) for C₂₄H₁₇N₃O₂F₃ ([M + H]⁺) calcd 436.1267, found 436.1267.

(2E)-3-(4-Chlorophenyl)-1-[1-phenyl-3-(pyridin-3-yl)-1H-pyrazol-4-yl]prop-2-en-1-one (12g)

White crystals; yield 67% (49 mg); m.p. 169.7–172.3 °C; R_f = 0.50 (EtOAc/Hex 1/2, v/v). IR (ν_max, cm⁻¹): 3120, 3041, 1684 (C=O), 1599, 1521, 1448, 1362, 1260, 1241, 1221, 987, 977, 940, 863, 751, 705, 683. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 6.99 (d, J = 15.6 Hz, 1H, C(O)CHCHPh), 7.26 (d, J = 8.5 Hz, 2H, CPh 3,5-H), 7.28–7.33 (m, 4H, NPh 4-H, CPh 2,6-H, Pyr 5-H), 7.42–7.45 (m, 2H, NPh 3,5-H), 7.60 (d, J = 15.6 Hz, 1H, C(O)CHCHPh), 7.72–7.74 (m, 2H, NPh 2,6-H), 8.08 (dt, J_{Pyr 4-H,5-H} = 7.9 Hz, J = 2.0 Hz, 1H, Pyr 4-H), 8.51 (s, 1H, Pz 5-H), 8.58 (dd, J_{Pyr 5-H,6-H} = 4.9 Hz, J = 1.6 Hz, 1H, Pyr 6-H), 8.98 (d, J = 2.2 Hz, 1H, Pyr 2-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 118.6 (NPh C-2,6), 121.9 (Pyr C-5), 122.2 (Pz C-4), 123.6 (C(O)CHCHPh), 126.9 (NPh C-4), 127.5 (Pyr C-3), 128.2 (CPh C-3,5), 128.5 (CPh C-2,6), 128.7 (NPh C-3,5), 130.4 (Pz C-5), 132.0 (CPh C-1), 135.5 (CPh C-4), 135.9 (Pyr C-4), 138.0 (NPh C-1), 141.4 (C(O)CHCHPh), 148.8 (Pyr C-6), 149.0 (Pyr C-2), 149.7 (Pz C-3), 182.8 (C(O)CHCHPh). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −161.8 (Pz N-1), −78.2 (Pz N-1), −70.6 (Pyr N). HRMS (ESI⁺) for C₂₃H₁₇N₃OCl ([M + H]⁺) calcd 386.1055, found 386.1055.

(2E)-3-(4-Methoxyphenyl)-1-[1-phenyl-3-(pyridin-3-yl)-1H-pyrazol-4-yl]prop-2-en-1-one (12h)

Yellow crystals; yield 54% (39 mg); m.p. 157–159 °C; R_f = 0.51 (EtOAc/Hex 1/2, v/v). IR (ν_max, cm⁻¹): 3120, 3041, 1659 (C=O), 1599, 1521, 1448, 1362, 1260, 1241, 1221, 977, 940, 863, 751, 705, 683. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 3.84 (s, 3H, OCH₃), 6.89 (d, J = 8.6 Hz, 2H, CPh 3,5-H), 6.99 (d, J = 15.6 Hz, 1H, C(O)CHCHPh), 7.37–7.41 (m, 2H, NPh 4-H, Pyr 5-H), 7.43–7.45 (m, 2H, CPh 2,6-H), 7.51–7.54 (m, 2H, NPh 3,5-H), 7.72 (d, J = 15.6 Hz, 1H, C(O)CH=CHPh), 7.81–7.83 (m, 2H, NPh 2,6-H), 8.17 (d, J_{Pyr 4-H,5-H} = 7.9 Hz, 1H, Pyr 4-H), 8.56 (s, 1H, Pz 5-H), 8.67 (d, J_{Pyr 5-H,6-H} = 4.2 Hz, 1H, Pyr 6-H), 9.07 (s, 1H, Pyr 2-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 55.6 (OCH₃), 114.6 (CPh C-3,5), 119.8 (NPh C-2,6), 122.1 (C(O)CHCHPh), 123.0 (Pyr C-5), 123.7 (Pz C-4), 127.4 (CPh C-1), 128.0 (NPh C-4), 128.8 (Pyr C-3), 129.9 (NPh C-3,5), 130.3 (CPh C-2,6), 131.3 (Pz C-5), 137.1 (Pyr C-4), 139.2 (NPh C-1), 144.1 (C(O)CHCHPh), 149.8 (Pyr C-6), 150.2 (Pyr C-2), 150.8 (Pz C-3), 161.9 (CPh C-4), 184.6 (C(O)CHCHPh). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −162.2 (Pz N-1), −70.9 (Pyr N). HRMS (ESI⁺) for C₂₄H₂₀N₃O₂ ([M + H]⁺) calcd 382.1550, found 382.1550.

(2E)-3-(4-Chlorophenyl)-1-[1-phenyl-3-(pyridin-4-yl)-1H-pyrazol-4-yl]prop-2-en-1-one (12i)

White crystals; yield 55% (40 mg); m.p. 205–207 °C; R_f = 0.41 (EtOAc/Hex 1/2, v/v). IR (ν_max, cm⁻¹): 3120, 3041, 1684 (C=O), 1599, 1521, 1448, 1362, 1260, 1241, 1221, 987, 977, 940, 863, 751, 705, 683. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 7.07 (d, J = 15.6 Hz, 1H, C(O)CHCHPh), 7.34–7.37 (m, 2H, CPh 3,5-H), 7.40–7.43 (m, 3H, NPh 4-H, CPh 2,6-H), 7.52–7.55 (m, 2H, NPh 3,5-H), 7.71 (d, J = 15.6 Hz, 1H, C(O)CHCHPh), 7.77–7.79 (m, 2H, Pyr 3,5-H), 7.80–7.81 (m, 2H, NPh 2,6-H), 8.56 (s, 1H, Pz 5-H), 8.69–8.72 (m, 2H, Pyr 2,6-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 119.9 (NPh C-2,6), 123.5 (Pz C-4), 123.8 (Pyr C-3,5), 124.9 (C(O)CHCHPh), 128.2 (NPh C-4), 129.5 (CPh C-3,5), 129.7 (CPh C-2,6), 129.9 (NPh C-3,5), 131.7 (Pz C-5), 133.0 (CPh C-1), 136.8 (CPh C-4), 139.1 (NPh C-1), 140.3 (Pyr C-4), 142.9 (C(O)CHCHPh), 150.0 (Pyr C-2,6), 151.1 (Pz C-3), 184.2 (C(O)CHCHPh). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −161.3 (Pz N-1), −70.3 (Pyr N). HRMS (ESI⁺) for C₂₃H₁₇N₃OCl ([M + H]⁺) calcd 386.1055, found 386.1055.

(2E)-3-(4-Methoxyphenyl)-1-[1-phenyl-3-(pyridin-4-yl)-1H-pyrazol-4-yl]prop-2-en-1-one (12j)

Yellow crystals; yield 50% (36 mg); m.p. 167–169 °C; R_f = 0.36 (EtOAc/Hex 1/2, v/v). IR (ν_max, cm⁻¹): 3120, 3041, 1659 (C=O), 1599, 1521, 1448, 1362, 1260, 1241, 1221, 977, 940, 863, 751, 705, 683. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 3.84 (s, 3H, OCH₃), 6.89–6.90 (m, 2H, CPh 3,5-H), 6.98 (d, J = 15.6 Hz, 1H, C(O)CHCHPh), 7.39–7.41 (m, 1H, NPh 4-H), 7.44–7.46 (m, 2H, CPh 2,6-H), 7.51–7.54 (m, 2H, NPh 3,5-H), 7.73 (d, J = 15.6 Hz, 1H, C(O)CHCHPh), 7.78–7.81 (m, 4H, NPh 2,6-H, Pyr 3,5-H), 8.54 (s, 1H, Pz 5-H), 8.69–8.70 (m, 2H, Pyr 2,6-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 55.6 (OCH₃), 114.6 (CPh C-3,5), 119.8 (NPh C-2,6), 122.3 (C(O)CHCHPh), 123.78 (Pyr C-3,5), 123.83 (Pz C-4), 127.2 (CPh C-1), 128.1 (NPh C-4), 129.9 (NPh C-3,5), 130.4 (CPh C-2,6), 131.5 (Pz C-5), 139.2 (NPh C-1), 140.4 (Pyr C-4), 144.3 (C(O)CHCHPh), 149.9 (Pyr C-2,6), 150.9 (Pz C-3), 162.0 (CPh C-4), 184.7 (C(O)CHCHPh). ¹⁵N NMR (71 MHz, CDCl3): δ_N ppm −161.8 (Pz N-1), −70.4 (Pyr N). HRMS (ESI⁺) for C₂₄H₂₀N₃O₂ ([M + H]⁺) calcd 382.1550, found 382.1550.

3.2.9. General Procedure for the Preparation of 3-(3-methoxy-1-phenyl-1H-pyrazol-4-yl)-5-phenyl-1,2-oxazole (14) and 5-(3-methoxy-1-phenyl-1H-pyrazol-4-yl)-3-phenyl-1,2-oxazole (15)

To a solution of N-hydroxy-4-toluenesulfonamide (1.56g, 8.35 mmol) in EtOH/H₂O (9:1 v/v, (25 mL)), NaOH (0.4 g, 10 mmol) was added. A solution of appropriate chalcone 4a or 9a (0.3 g, 1 mmol) in EtOH (3 mL) was added to a mixture. The reaction mixture was stirred at 40 °C for 48 h; the progress of the reaction was monitored by TLC. An additional amount of NaOH (0.4 g, 10 mmol) was added and the reaction mixture was stirred at 55 °C for another 24 h. Upon completion, the reaction mixture was diluted with EtOAc (30 mL). Then, the mixture was washed with water (3 × 30 mL) and brine (30 mL). The organic layers were dried over sodium sulphate, filtrated and concentrated. The residue was purified by column chromatografy (SiO₂, eliuent: hexane/ethyl acetate, 3/1, v/v) to produce pure 14 or 15.

3-(3-Methoxy-1-phenyl-1H-pyrazol-4-yl)-5-phenyl-1,2-oxazole (14)

Yellow solids; yield 56% (178 mg); m.p. 132–133 °C; R_f = 0.66 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3098, 2953, 1595, 1525, 1420, 1249, 1220, 1173, 950, 830, 752, 683. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 4.16 (s, 3H, CH₃), 6.93 (s, 1H, 4-H), 7.27–7.28 (m, 1H, NPh 4-H), 7.43–7.50 (m, 5H, NPh 3,5-H, CPh 3,5-H, CPh 4-H), 7.68–7.69 (m, 2H, NPh 2,6-H), 7.85–7.86 (m, 2H, CPh 2,6-H), 8.33 (s, 1H, Pz 5-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 56.6 (CH₃), 98.4 (Ox C-4), 98.8 (Pz C-4), 118.1 (NPh C-2,6), 125.9 (CPh C-2,6), 126.03 (Pz C-5), 126.06 (NPh C-4), 127.6 (CPh C-1), 128.9 (NPh C-3,5), 129.5 (CPh C-3,5), 130.1 (CPh C-4), 139.7 (NPh C-1), 155.4 (Ox C-3), 162.3 (Pz C-3), 169.6 (Ox C-5). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −184.8 (Pz N-1), −120.0 (Pz N-2), −19.6 (Ox N). HRMS (ESI⁺) for C₁₉H₁₅N₃NaO₂ ([M + Na]⁺) calcd 340.1056, found 340.1061.

5-(3-Methoxy-1-phenyl-1H-pyrazol-4-yl)-3-phenyl-1,2-oxazole (15)

Yellow solids; yield 37% (117 mg); m.p. 162–163 °C; R_f = 0.63 (EtOAc/Hex 1/4, v/v). IR (ν_max, cm⁻¹): 3138, 2916, 1592, 1528, 1506, 1393, 1359, 1220, 948, 899, 752, 685. ¹H NMR (700 MHz, CDCl₃): δ_H ppm 4.16 (s, 3H, CH₃), 6.77 (s, 1H, 4-H), 7.27–7.29 (m, 1H, NPh 4-H), 7.45–7.49 (m, 5H, NPh 3,5-H, CPh 3,5-H, CPh 4-H), 7.67–7.69 (m, 2H, NPh 2,6-H), 7.88–7.89 (m, 2H, CPh 2,6-H), 8.24 (s, 1H, Pz 5-H). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 56.7 (CH₃), 97.5 (Ox C-4), 99.0 (Pz C-4), 118.2 (NPh C-2,6), 125.6 (Pz C-5), 126.3 (NPh C-4), 126.9 (CPh C-2,6), 128.9 (CPh C-3,5), 129.3 (CPh C-1), 129.6 (NPh C-3,5), 129.9 (CPh C-4), 139.5 (NPh C-1), 161.1 (Pz C-3), 162.8 (Ox C-3), 162.9 (Ox C-5). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −184.4 (Pz N-1), −119.7 (Pz N-2), −18.6 (Ox N). HRMS (ESI⁺) for C₁₉H₁₅N₃NaO₂ ([M + Na]⁺) calcd 340.1056, found 340.1059.

3.2.10. Procedure for the Preparation of Mixture of 3-(3-methoxy-1-phenyl-1H-pyrazol-4-yl)-5-phenyl-¹⁵N-1,2-oxazole (16) and 5-(3-methoxy-1-phenyl-1H-pyrazol-4-yl)-3-phenyl-¹⁵N-1,2-oxazole (17)

To a solution of ¹⁵N hydroxylamine hydrochloride (139 mg, 2 mmol) and potassium hydroxide (160 mg, 4 mmol) in EtOH (96%, 15 mL), chalcone 9a was added (304 mg, 1 mmol). The reaction mixture was stirred at 80 °C for 3 h, poured into water (30 mL) and extracted with EtOAc (3 × 50 mL). The organic layers were washed with brine (30 mL) and dried over sodium sulphate, filtrated and concentrated. The residue was purified by column chromatografy (SiO₂, eliuent: hexane/ethyl acetate, 3/1, v/v) to produce an inseparable mixture of compounds 16 and 17 with a 23% yield. The inseparable mixture of regioisomers 16 (major) and 17 (minor) was obtained in a ratio of about 8:1.

Yellow solid; yield 23% (73 mg mixture); ¹H NMR (700 MHz, CDCl₃): δ_H ppm 4.15 (s, 3H, CH₃ of minor regioisomer), 4.16 (s, 3H, CH₃ of major regioisomer), 6.77 (d, J = 1.23 Hz, 1H, Ox 4-H of major regioisomer), 6.93 (d, J = 1.31 Hz, 1H, Ox 4-H of minor regioisomer), 7.27–7.29 (m, 1H, NPh 4-H of both regioisomers), 7.45–7.49 (m, 5H, NPh 3,5-H, CPh 3,5-H, CPh 4-H of both regioisomers), 7.67–7.69 (m, 2H, NPh 2,6-H of both regioisomers), 7.84–7.86 (m, 1H, NPh 2,6-H of minor regioisomer), 7.87–7.89 (m, 2H, CPh 2,6-H of major regioisomer), 8.24 (s, 1H, Pz 5-H of major regioisomer), 8.33 (s, 1H, Pz 5-H of minor regioisomer). ¹³C NMR (176 MHz, CDCl₃): δ_C ppm 56.62 (CH₃ of minor regioisomer), 56.73 (CH₃ of major regioisomer), 97.51 (d, ²J_C,N = 1.23 Hz, Ox C-4 of major regioisomer), 98.45 (d, ²J_C,N = 1.11 Hz, Ox C-4 of minor regioisomer), 98.82 (d, ²J_C,N = 8.40 Hz, Pz C-4 of minor regioisomer), 98.96 (d, ³J_C,N = 0.66 Hz, Pz C-4 of major regioisomer), 118.12 (NPh C-2,6 of minor regioisomer), 118.20 (NPh C-2,6 of major regioisomer), 125.53 (Pz C-5 of major regioisomer), 125.88 (CPh C-2,6 of minor regioisomer), 126.03 (d, ³J_C,N = 1.47 Hz, Pz C-5), 126.06 (NPh C-4 of minor regioisomer), 126.27 (NPh C-4 of major regioisomer), 126.91 (d, ³J_C,N = 2.28 Hz, CPh C-2,6 of major regioisomer), 127.59 (CPh C-1 of minor regioisomer), 128.85 (CPh C-3,5 of major regioisomer), 128.94 (NPh C-3,5 of minor regioisomer), 129.28 (d, ²J_C,N = 7.11 Hz, CPh C-1 of major regioisomer), 129.50 (CPh C-3,5 of minor regioisomer), 129.54 (NPh C-3,5 of major regioisomer), 129.89 (CPh C-4 of major regioisomer), 130.06 (CPh C-4 of minor regioisomer), 139.51 (NPh C-1 of major regioisomer), 139.68 (NPh C-1 of minor regioisomer), 155.35 (d, ¹J_C,N = 2.25 Hz, Ox C-3 of minor regioisomer), 161.09 (Pz C-3 of major regioisomer), 162.27 (d, ³J_C,N = 1.92 Hz, Pz C-3 of minor regioisomer), 162.77 (d, ¹J_C,N = 2.89 Hz, Ox C-3 of major regioisomer), 162.84 (d, ²J_C,N = 1.39 Hz, Ox C-5 of major regioisomer), 169.61 (d, ²J_C,N = 1.52 Hz, Ox C-5 of minor regioisomer). ¹⁵N NMR (71 MHz, CDCl₃): δ_N ppm −184.8 (Pz N-1 of minor regioisomer), −184.5 (Pz N-1 of major regioisomer), −119.9 (Pz N-2 of minor regioisomer), −119.7 (Pz N-2 of major regioisomer), −19.5 (Ox N of minor regioisomer), −18.6 (Ox N of major regioisomer). HRMS (ESI⁺) for C₁₉H₁₅¹⁵NN₂NaO₂ ([M + Na]⁺) calcd 340.1056, found 340.1061.

4. Conclusions

In conclusion, we have synthesized novel diverse pyrazole-chalcone derivatives, starting with easily accessible 3-hydroxy-1-phenyl-1H-pyrazole via the Claisen–Schmidt condensation reaction of intermediate 4-acetyl or formyl-1-phenyl-1H-pyrazoles. The condensation of 4-formyl-1-phenyl-1H-pyrazoles with various acetophenones, as well as the reaction of 4-acetyl-3-hydroxy-1-phenyl-1H-pyrazoles with different carbaldehydes, produced appropriate (E)-chalcones. The reaction of 4-acetyl-3-pyridinyl-phenyl-1H-pyrazoles with acetophenones caused the formation of mixtures of compounds with predominant (E)-chalcones and less stable (Z)-chalcones in different ratios. Extensive NMR spectroscopic studies have been undertaken using standard and advanced methods to unambiguously determine the structure and configuration of novel, pyrazole-chalcone regioisomeric 3(5)-(1H-pyrazol-4-yl)-5(3)-phenyl-1,2-oxazole derivatives.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/molecules27123752/s1, Figure S1: 1H-1H NOESY NMR spectrum (E-12a, Z-13a), Figures S2 and S3: One-dimensional selective gradient NOESY spectra (E-12a, Z-13a); Figures S4–S193: ¹H, ¹³C NMR and ¹H-¹⁵N HMBC spectra of compounds 4–17. Figures S194–S198: HPLC and MS data of of crude reaction mixture of compounds 14,15.

Author Contributions

Conceptualization, A.Š.; methodology, E.A. (Eglė Arbačiauskienė); validation, A.U., G.F., E.A. (Emilija Ambrazaitytė), V.M. and E.P.; formal analysis, A.B. and E.A. (Eglė Arbačiauskienė); investigation, A.U., G.F., E.A. (Emilija Ambrazaitytė) and V.M.; data curation, V.M.; writing—original draft preparation, A.Š., A.B., E.A. (Eglė Arbačiauskienė) and V.M.; writing—review and editing, S.K. and R.L.; visualization A.B., A.Š. and E.A. (Eglė Arbačiauskienė); resources, E.A. (Eglė Arbačiauskienė) and A.Š.; supervision, A.Š. and E.A. (Eglė Arbačiauskienė). All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data that support the findings of this study are available upon request.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Sample Availability

Not available.

Funding Statement

This research was funded by the Research Council of Lithuania (No. S-MIP-20-60) and by the Doctoral Fund of Kaunas University of Technology No. A-410, approved 26 June 2019.