Cu(I)/Fe(III) promoted dicarbonylation of aminopyrazole via oxidative C H coupling with methyl ketones

Synthetic routes to access dicarbonylated aryls and heteroaryls

1,2-Dicarbonyl compounds are privileged functionalities found in natural products, pharmaceuticals, bioactive molecules, and food items, and are important precursors in catalysis, asymmetric synthesis, polymer chemistry and synthesizing functionalized heterocycles. Herein, this comprehensive review focuses on various approaches for synthesizing 1,2-dicarbonylated aryls and heteroaryls in both intermolecular and intramolecular fashion, covering the dicarbonylation of indoles, imidazoheterocycles, indolizines, aminopyrazoles, pyrroloisoquinolines, coumarins, furan, anilines, phenols, anthranils, and benzil synthesis over the last decade (since 2015). Also, the present review highlights the scope and future perspectives of the approach.

Unveiling Na2-Eosin Y-Catalyzed and Water-Assisted Visible-Light Activation of Oxygen Molecules for the Dicarbonylation of Pyrazole Amines

A novel approach employing visible light-mediated activation of triplet oxygen molecules has been established. The reaction occurs at room temperature between pyrazole amine and phenylglyoxal monohydrate in the presence of Na2-eosin Y. Water played the dual role of solvent and reagent/additive. Photoactivation of triplet oxygen species was used to demonstrate the initiation of the hydrogen atom transfer (HAT) process. The conversion of the reaction mixture was found to be dependent on the amount of water present. Control experiments confirmed the importance of light, the photocatalyst, oxygen, the base, and water. The process tolerated various substitutions in both pyrazole amine and phenylglyoxal derivatives, enabling the synthesis of various dicarbonylpyrazole amines 15 and pyrazolooxazine derivatives 16 in moderate to good yields. 2 equiv of phenylglyoxal 10 gave a different reaction pathway, yielding highly diastereoselective pyrazolooxazine derivatives, confirmed by X-ray diffraction analysis. Collectively, this sustainable and environmentally friendly synthetic technique offers a promising method for the efficient preparation of pyrazole-based heterocyclic compounds. The high regioselectivity observed during the formation of trans-tetrahydropyrazolo[3,4-d][1,3]oxazine has been clarified through computational methods. These investigations emphasize the underlying factors and mechanisms that encourage the formation of this specific product, providing valuable insights into the reaction's selectivity and efficiency.

Copper-catalysed dehydrogenative self-coupling/cyclization of 5-aminopyrazoles: synthesis and photophysical study of pyridazines

An interesting self-coupling/cyclization of 5-aminopyrazoles is revealed, which provides a variety of pyridazine cores in reasonable yields. In this reaction, C(sp²)-C(sp²) and N-N bond formation occurs simultaneously in one reaction vessel. The photophysical properties of the synthesized compounds were also studied and some of them exhibited fluorescence properties with good quantum yields. A radical mediated reaction mechanism is proposed with the help of control experiments.

A new method for C(sp2)-H sulfonylmethylation with glyoxylic acid and sodium sulfinates

We herein describe a C4 sulfonylmethylation of pyrazol-5-amines with glyoxylic acid and sodium sulfinates. The reaction only needed to add water as the solvent, and it featured mild reaction condition,...

Metal- and Solvent-Free Cascade Reaction for the Synthesis of Amino Pyrazole Thioether Derivatives

We developed an iodine-mediated cascade strategy to synthesize amino pyrazole thioether derivatives (11) in the absence of metals as well as solvents. The present approach provides amino pyrazole thioethers in a highly selective manner without the formation of diaryl sulfide and sulfenyl-enaminonitrile with broad substrate scope. The reactivity of nine sulfenylation sources and synthetic applications of the synthesized compounds have been demonstrated. Thus, the overall iodine-mediated multicomponent reaction (MCR) is more economically feasible, efficient, and environmentally benign.

Ten Years of Glory in the α-Functionalizations of Acetophenones: Progress Through Kornblum Oxidation and C-H Functionalization

This review article focuses on the α-functionalization of acetophenones involving Kornblum oxidation and C-H functionalizations. Although various other strategies, such as classical approaches, enamine approaches and umpolung strategy are also known for this functionalization, here we discuss mainly the Kornblum oxidation approach and C-H functionalization strategy as they have advantages over the others. In Kornblum oxidation, the reaction uses iodine and dimethylsulfoxide and proceeds through the formation of arylglyoxal as the key intermediate. In C-H functionalization, the reaction requires metal, or metal-free catalyst, and generates radical intermediate in most cases. α-Functionalization of acetophenones is very important because of their huge applications in the synthesis of various natural products and pharmaceuticals and, therefore, a number of research articles have been published in this area. However, no review articles are available so far. In this article, we present a succinct discussion of various important and novel reactions, along with their mechanisms, published since 2012 to date. We believe that this first review article in this field will give readers one-stop information on this topic and encourage further intriguing work in this area.

L-Proline-catalyzed regioselective C1 arylation of tetrahydroisoquinolines through a multicomponent reaction under solvent-free conditions

Here we disclose the C1 arylation of tetrahydroisoquinolines (THIQ) through regioselective C(sp3)-H functionalization using a multicomponent reaction. The reaction was performed by reacting THIQ, aldehydes and aminopyrazoles or indoles under neat conditions with l-proline as a catalyst. The regioselectivity of the products was confirmed by X-ray analysis and spectroscopic data. The formation of an azomethine ylide intermediate is crucial for obtaining the regioselectivity.