In recent years, green chemistry using environmentally benign reagents and conditions has become one of the most fascinating developments in the synthesis of widely used organic compounds. This review describes the theory and importance of ultrasound as an efficient tool in the synthesis of heterocyclic compounds.

Ammonium chloride as a very inexpensive and readily available reagent efficiently catalyzes one-pot four-component condensation of dimedone with aromatic aldehyde, malononitrile or ethyl cyanoacetate, and sulfonamide derivatives in ethanol at 70°C under ultrasonic irradiation to afford the corresponding 2-amino-4-aryl-1,4,5,6,7,8-hexahydroquinolines bearing a sulfonamide moiety in high yields. In comparison to conventional methods, high yields, easy work-up, and short reaction time are advantages of this sonochemical procedure. The effects of the catalyst, solvent, and temperature are assessed.

Background

Thiazolidinone, has been employed in the preparation of different important drugs required for treatment of inflammations, bacterial infections, and hypertension. Mannich bases have been shown to exhibit diverse biological activities, such as antibacterial, and antifungal activities. Spiroheterocycles including thiazolidine moiety have antimicrobial activity.

Results

In this study, a novel, rapid, and efficient protocol is developed for the synthesis of various 2-arylidine-1-thia-4-azaspiro[4.5]decan-3-ones using sodium dodecylbenzene sulfonate (DBSNa) as an inexpensive and readily available reagent in acetic acid at room temperature. High yields, easy work-up, and short reaction times are advantages of this procedure. The synthesized arylidines were undergone Mannich reaction with formaldehyde and secondary amines in absolute ethanol at room temperature to afford the corresponding N-Mannich bases. All prepared Mannich bases were evaluated for their antimicrobial activity.

Conclusions

Good activity was noted for Mannich bases from 2-arylidine-1-thia-4-azaspiro[4.5]decan-3-ones, with some members recorded higher antimicrobial activity.

A series of novel substituted 6′-(4-chlorophenyl)-3,4′-bipyridine-3′-carbonitriles with incorporated pyrazole and/or triazole moieties have been synthesized using 2-(6′-(4-chlorophenyl)-3′-cyano-3,4′-bipyridin-2′-yloxy)acetohydrazide (3) as starting material. Also, the key intermediate 3 reacted with aromatic aldehydes and tosyl chloride to give the corresponding Schiff bases and tosyl hydrazide derivatives, respectively. The antimicrobial of these newly synthesized compounds was evaluated against Bacillus subtilis as Gram-positive bacteria and Trichoderma viride as a fungus; some of these compounds such as 5, 6, 7, 8, 10, 12, and 14 showed excellent activities as antimicrobial agents. Moreover, the cytotoxic activity of the most active compounds was assessed in vitro against human tumor liver cancer cell line (HEPG2); compounds 8, 10, 13a, and 14 showed potent activities relative to Doxorubicin which was used as a reference standard drug in this study.

Indole-tethered chromene derivatives were synthesised in a one-pot multicomponent reaction using N-alkyl-1H-indole-3-carbaldehydes, 5,5-dimethylcyclohexane-1,3-dione, and malononitrile, catalysed by DBU at 60–65 °C in a short reaction time. The benefits of the methodology include non-toxicity, an uncomplicated set-up procedure, a faster reaction time, and high yields. Moreover, the anticancer properties of the synthesised compounds were tested against selected cancer cell lines. The derivatives 4c and 4d displayed very good cytotoxic activity, with IC₅₀ values ranging from 7.9 to 9.1 µM. Molecular docking revealed the potent derivatives have good binding affinity towards tubulin protein, better than the control, and the molecular dynamic simulations further demonstrated the stability of ligand-receptor interactions. Moreover, the derivatives followed all the drug-likeness filters.

Three novel tetra substituted p‑tert-butylthiacalix[4]arene derivatives (3, 4, and 5) with five coordinating carbonyl groups at the lower rims were synthesized. Accordingly, diethyl tetra-t‑butyl‑trihydroxy-tetrathia-tetrabenzenacyclooctaphanyl)oxy)malonate react with ethyl bromoacetate, phenacyl bromide and 2‑chloro-N-(p-tolyl)acetamide, to produce new p‑tert-butylthiacalix[4]arenes in of 60, 90, and 80% yields, respectively. The molecular structures of the products were verified using FT-IR, ¹H NMR, and ¹³C NMR spectroscopy. Metal ions such as Na⁺, K⁺, Cs⁺, Hg²⁺, Cd²⁺, Pb²⁺, Ni²⁺, Co²⁺, Cu²⁺, and Ag⁺ are easily chelated by the new thiacalixarene derivatives using liquid-liquid extraction technique. These compounds surprisingly show high efficiency in liquid-liquid extraction of alkali, heavy, and transition metal ions. Uptake efficiencies of 71.00% (for Co(II)), 46.00% (for Cu(II), and 15.00% (for Hg(II)) were attained by thiacalixarene 3, 4, and 5. These derivatives were subjected to DFT-based computational analysis with the aim of increasing the efficiency with which thiacalixarene (as a nucleophilic) interacts with the metal ion (3, 4, and 5 in the role of electrophile).

This paper reports on a study of the photophysical properties, density functional theory (DFT) calculations, infrared (IR), ultraviolet (UV) and nuclear magnetic resonance (NMR) spectroscopic techniques of a series of aurone compounds. The photophysical properties were investigated using UV absorption and fluorescence spectroscopy in a dimethyl sulfoxide (DMSO) solution. Furthermore, the fluorescence quantum yields of the target compounds (1–24) were also investigated. Remarkably, these compounds revealed high quantum yields (Φ = 0.001–0.729) as compared to the already existing aurones in literature. The DFT calculations were performed to elucidate the electronic structure, energy levels and draw a comparison between experimental and theoretical findings. The simulated properties such as molecular frontier orbitals, the density of states, reactivity descriptors (GCRD), electrostatic potential distribution, transition density matrix, electron localization function (ELF) and localized orbital locator (LOL) have been calculated using DFT. The DFT calculations provided insight into the electronic structure and energy levels of the aurone compounds, while the IR and UV spectroscopy results shed light on their functional groups and electronic transitions, respectively. The results of this study contribute to a better understanding of the photophysical properties of aurone compounds and suggest their potential use in technological applications.

Imidazopyridazines are fused heterocycles, like purines, with a pyridazine ring replacing the pyrimidine ring in purines. Imidazopyridazines have been primarily studied for their kinase inhibition activity in the development of new anticancer and antimalarial agents. In addition to this, they have also been investigated for their anticonvulsant, antiallergic, antihistamine, antiviral, and antitubercular properties. Herein, we review the background and development of different imidazopyridazines as potential pharmacological agents. Moreover, the scope of this relatively less charted heterocyclic scaffold is also highlighted.

An unprecedented and efficient three-component 1,3-dipolar cycloaddition reaction using (E)-2-(benzo[d]thiazol-2-yl)-3-(aryl)acrylonitriles 4a–g and an in situ generated azomethine ylide 3 from isatin and N-methylglycine is described. The reaction exhibits exclusive regioselectivity, resulting in the formation of 3′-(benzo[d]thiazol-2-yl)-1′-methyl-2-oxo-4′-(aryl)spiro[indoline-3,2′-pyrrolidine]-3′-carbonitriles regioisomers through exo/endo approaches. The diastereoselectivity of the reaction is highly dependent on the substitution pattern of the phenyl ring in dipolarophiles 4a–g, leading to the formation of exo-/endo-cycloadducts in varying ratios. To understand the stereoselectivity, the transition state structures were optimized using the TS guess geometry with the QST3-based method. The reaction mechanism and regioselectivity were elucidated by evaluating global and local electrophilicity and nucleophilicity descriptors at the B3LYP/cc-pVTZ level of theory, along with considerations based on the HSAB principle. The analysis of global electron density transfer (GEDT) showed that the reactions are polar and electron density fluxes from azomethine ylide 3 toward dipolarophile 4a–g. It was found from the molecular electrostatic potential map (MESP) that at the more favorable transition state, approach of reactants locates the oppositely charged regions over each other resulting in attractive forces between the two fragments. The computational results are consistent with the experimental observations, confirming that the reactions proceed through an asynchronous one-step mechanism.