Sustainable Synthetic Approach for (Pyrazol-4-ylidene)pyridines By Metal Catalyst-Free Aerobic C(sp2)-C(sp3) Coupling Reactions between 1-Amino-2-imino-pyridines and 1-Aryl-5-pyrazolones

Green Protocol for the Novel Synthesis of Thiochromeno[4,3-b]pyridine and Chromeno[4,3-b]pyridine Derivatives Utilizing a High-Pressure System

A suitable and effective Q-tube-assisted strategy for the synthesis of novel, unrivalled thiochromeno[4,3-b]pyridine and chromeno[4,3-b]pyridine derivatives has been sophisticated, which includes ammonium acetate-mediated cyclocondensation reactions between 3-oxo-2-arylhydrazonopropanals and heterobenzocyclic ketones such as thiochroman-4-one and chroman-4-one, respectively. The high-pressure Q-tube reactor was shown to be superior to conventional heating. Furthermore, this Q-tube reactor-assisted protocol is safe owing to facile pressing and sealing, a broad substrate scope, and simple work-up and purification processes, as well as being scalable and having a high atom economy. The proposed mechanistic route includes two sequential dehydrative stages. In this investigation, X-ray crystallographic analysis was performed to authenticate the targeted products.

TFA-catalyzed Q-Tube Reactor-Assisted Strategy for the Synthesis of Pyrido[1,2-b][1,2,4]triazine and Pyrido[1',2':2,3][1,2,4]triazino[5,6-b]indole Derivatives

An efficient high-pressure-assisted trifluoroacetic acid-catalyzed protocol for synthesizing unreported novel pyrido[1,2-b][1,2,4]triazine and pyrido[1',2':2,3][1,2,4]triazino[5,6-b]indole derivatives has been established. This strategy includes the condensation reactions of various 1-amino-2-imino-4-arylpyridine-3-carbonitrile derivatives with indoline-2,3-dione (isatin) derivatives and α-keto acids such as pyruvic acid and phenylglyoxylic acid. This strategy includes utilizing the Q-tube reactor as an efficient and safe tool to conduct these reactions under high-pressure conditions. In addition, trifluoroacetic acid was used to induce this transformation. In this research, conducting the targeted reactions under high pressure using the Q-tube reactor was found to be superb in comparison to that under the traditional refluxing conditions. X-ray single-crystal analysis was utilized in this study to authenticate the structure of the synthesized products.

High pressure assisted synthetic approach for novel 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-b]pyridine and 5,6-dihydrobenzo[h]quinoline derivatives and their assessment as anticancer agents

A novel, expedient and effective methodology for the synthesis of distinctly substituted 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-b]pyridine and 5,6-dihydrobenzo[h]quinoline systems has been developed with a new synthetic platform. This process includes ammonium acetate-mediated cyclocondensation reactions of 3-oxo-2-arylhydrazonopropanals with benzosuberone and tetralone precursors, respectively, using the high-pressure Q-tube reactor, which has been found to be superior to both conventional heating and microwave irradiation. The novel protocol benefits from its high atom efficiency, economy, ease of workup, broad substrate scope and is also applicable to gram-scale synthesis. To identify and confirm the newly synthesized targeted compounds, the X-ray single-crystal as well as all possible spectroscopic methods were utilized. The cytotoxicity of the newly synthesized 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-b]pyridine 4a-j and 5,6-dihydrobenzo-[h]quinolines derivatives 6a-e were preliminary examined toward three cell lines of human cancer; lung cancer (A549), breast cancer (MCF-7) and colon cancer (HCT-116), by applying the MTT colorimetric assay. The achieved results reflected the promising profile of the prepared compounds in this study against cancer cells and have shown that members from the synthesized 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-b]pyridine 4a-j exhibited promising cytotoxicity's against MCF-7, and A549 cancer cells respectively, while the HCT-116 (colon) cancer cells were inhibited by certain examples of 5,6-dihydrobenzo[h]quinoline derivatives 6c,d. These promising results could serve as a good primary base for further research into the design of anticancer drugs.

Increasing Scope of Clickable Fluorophores: Electrophilic Substitution of Ylidenemalononitriles

Recently, we demonstrated that ylidenemalononitriles (YMs) react with amines to form cyclic amidines and that the starting linear YMs are nonemissive in solution and the cyclic amidines are fluorescent. These turn-on systems were of interest to us because of their potential as biosensors and synthons for accessing functionalized pyridines. While our original method was promising, several limitations persisted, including access to more functionalized and polar-solvent-soluble structures as well as increased control over the rate of cyclization. Herein, we report a new approach that allows the electrophilic substitution of YMs. These substituted YMs exhibit faster turn-on rates, color tunability, access to polar-solvent-soluble species, and increased control over cyclization rate. This allowed us to significantly expand the fluorophore's chemical space.

The first Q-Tube based high-pressure synthesis of anti-cancer active thiazolo[4,5-c]pyridazines via the [4 + 2] cyclocondensation of 3-oxo-2-arylhydrazonopropanals with 4-thiazolidinones

A novel and efficient protocol for the synthesis of thiazolo[4,5-c]pyridazine derivatives was developed. The approach utilizes a high pressure Q-Tube reactor to promote cyclocondensation reactions between 3-oxo-2-arylhydrazonopropanals and 4-thiazolidinones. The process has a significantly high atom economy and a broad substrate scope, as well as being applicable to gram scale syntheses. The in vitro cytotoxic activities of the synthesized thiazolo[4,5-c]pyridazine derivatives were examined utilizing a MTT colorimetric assay with doxorubicin as a reference anti-cancer drug and three human cancer cell lines including HCT-116 (colon), MCF-7 (breast) and A549 (lung). The results show that thiazolopyridazines 7c, h, k and p have high cytotoxic activity against the MCF-7 cell line with respective IC50 values of 14.34, 10.39, 15.43 and 13.60 μM. Moreover, the thiazolopyridazine derivative 7s also show promising cytotoxic activity against the HCT-116 cell line with IC50 = 6.90 μM . Observations made in this effort serve as a basis for further investigations into the design and preparation of new anti-cancer drugs.

A facile, practical and metal-free microwave-assisted protocol for mono- and bis-[1,2,4]triazolo[1,5-a]pyridines synthesis utilizing 1-amino-2-imino-pyridine derivatives as versatile precursors

A facile and effective assembly of several substituted functionalized mono- and bis-[1,2,4]triazolo[1,5-a]pyridines from conveniently attainable 1-amino-2-imino-pyridines has been established. Using microwave irradiation speeds up the reaction efficiently, proceeding with a higher rate and yields than with conventional heating. In the presented protocol, a broad variety of carboxylic acids could be employed effectively to synthesize the respective derivatives via direct metal-free C–N bond construction. Interestingly, other substrates such as aldehydes (or their arylidene malononitriles), phenyl isothiocyanate, glyoxalic acid, and acrylonitriles could also provide the corresponding 1,2,4-triazolo[1,5-a]pyridines successfully. This versatile and convergent approach performs well with both deactivating and activating substrates in an environmentally benign manner compared with other already reported protocols. Other notable merits of the current strategy involve no need for column chromatography, no tedious work-up, and a direct pathway for the fast design of triazolopyridine frameworks. The identity of the newly synthesized compounds was established using several spectroscopic techniques, and X-ray single-crystal tools were employed to authenticate the suggested structures of some representative samples.

A novel and highly efficient, protocol for synthesizing mono- and bis-[1,2,4]triazolo[1,5-a]pyridines has been established utilizing the readily attainable 1-amino-2-imino-pyridines and microwave irradiation as green energy source.

Synthetic Strategy for Pyrazolo[1,5-a]pyridine and Pyrido[1,2-b]indazole Derivatives through AcOH and O2-Promoted Cross-dehydrogenative Coupling Reactions between 1,3-Dicarbonyl Compounds and N-Amino-2-iminopyridines

An efficient method has been developed for the synthesis of uniquely substituted pyrazolo[1,5-a]pyridine and pyrido[1,2-b]indazole derivatives, which involves acetic acid and molecular oxygen promoted cross-dehydrogenative coupling reactions of respective β-ketoesters and β-diketones (like ethyl acetoacetate, ethyl benzoylacetate, methyl propionylacetate, acetylacetone, dimedone, 1,3-cyclohexanedione, and 1,3-cyclopentanedione) with N-amino-2-iminopyridines. The proposed tentative mechanism involves formal acetic acid-promoted oxidative C(sp3)-C(sp2) dehydrogenative coupling followed by dehydrative cyclization under a catalyst-free condition within high atom economy processes.