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

Abstract

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.

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

“…Observations made in this effort serve as a basis for further investigations into the design and preparation of new anti-cancer drugs.Thiazolopyridazine derivatives comprise a broad range of structurally interesting substances that display a variety of medicinally interesting properties including activities against cancers 1,2 , microbes 3,4 , viruses 5 and bacteria 6 , as well as antioxidant 7 , analgesic and pesticidal activities 8,9 . As a result of these important properties, thiazolopyridazines remain the focus of our continuing investigations aimed at developing new and green routes for the synthesis of novel fused nitrogen containing heterocycles [10][11][12][13][14][15][16][17][18] . Until now, several methods have been developed for the synthesis of fused thiazolopyridazines, most of which are targeted at the synthesis of thiazolo[4,5-d] pyridazines 1-3,5 , thiazolo[3,2-b]pyridazine 19 and thiazolo[5,4-c]pyridazine 6 .…”

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 reasonable reaction mechanism for the synthesis of 1,2,4-triazole derivative (5a) was described in Table 1, based on experimental evidences and our reported studies. [31][32][33] As outlined in Table 1, the transformation of the non-isolable intermediate (A) to the target compound (5a) occurred under metal-free conditions. Now, the limitations and scope of the aforesaid reaction have then investigated.…”

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 little attention has been paid toward the biologically active thiochromeno­[2,3- b ]­pyridine derivatives , where few synthetic routes for some examples of thiochromeno­[2,3- b ]­pyridines were published. − Apart from this, only one publication for the synthesis of the thiochromeno­[4,3- b ]­pyridine skeleton was reported via a multicomponent reaction of thiochromanone with dimethylformamide-dimethylacetal and ethyl acetoacetate in the presence of ammonium acetate . In continuation to our work which aimed at developing new synthetic routes for new heterocyclic compounds, − herein the Q-tube reactor was used in this study. In comparison with conventional heating, the Q-tube reactor has several characteristics and features − including (1) better yield and performance, (2) a cleaner product profile that means light color and less impurities and byproducts, (3) energy savings, lower reaction time, and higher reproducibility, and (4) cheaper and safer because the sealing and pressing are easy.…”