Dimethyl Sulfoxide-Assisted, Iodine- and Ascorbic Acid-Catalyzed One-Pot Synthetic Approach for Constructing Highly Substituted Pyrazolo[1,5-a]quinoline Thioether Derivatives

Sodium Iodide-Promoted Construction of Fully Substituted 4-Sulfenyl-5-aminopyrazole Derivatives

Transition-metal-free synthesis of diversely substituted 4-sulfenyl-5-aminopyrazoles was developed under mild conditions through NaI-mediated three-component reaction of β-ketonitriles, disulfides, and hydrazines. The pyrazole products were constructed via consecutive cleavage of C-O and S-S bonds and recombination of C-N and C-S bonds. The methodology features broad substrate scope, mild transition-metal-free conditions, and easy manipulation.

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.

Electrocatalytic C-H/S-H Coupling of Amino Pyrazoles and Thiophenols: Synthesis of Amino Pyrazole Thioether Derivatives

A mild method for the C-H/S-H coupling of pyrazol-5-amines and thiophenols was developed via electrochemistry, giving diverse amino pyrazole thioether derivatives in 37-98% yields. This electrochemical reaction is sustainable and an atom-efficient approach with good functional group tolerance and scalability by avoiding metal and external chemical oxidants.

Transition-Metal-Free Dehydrogenation of Benzyl Alcohol for C-C and C-N Bond Formation for the Synthesis of Pyrazolo[3,4-b]pyridine and Pyrazoline Derivatives

A series of cascade reactions that produce a range of functionalized aromatic heterocyclic compounds with pyrazole/pyrazoline cores have been developed. The method relies on a metal-free dehydrogenative process to produce in-situ benzaldehydes. The produced benzaldehyde was then allowed to react with some other substances, including acetophenone, pyrazole amine, and phenylhydrazine. The intermediate produced from these substrates underwent several chemical processes, including electrocyclization, the aza-Diels-Alder reaction, and the formation of intramolecular C-N bonds. These positive outcomes would open up the possibility of producing biologically active pyrazolo[3,4-b]pyridine and pyrazoline derivatives through a variety of possible reactions.