On the formation of uncommon pyrazoloazepines from 5-aminopyrazoles as by-products in the Clauson-Kaas reaction

Applications of Clauson-Kaas Reaction in Organic Synthesis

Pyrrole-embedded organic molecules received a considerable importance due to their numerous biological and material applications. Hence, several synthetic strategies have been devised for the construction of diverse pyrrole analogues over the years. Among these, the Clauson-Kaas reaction is one of the most widely used protocols for the synthesis of various N-substituted pyrroles. This review briefly describes the Clauson-Kaas reaction along with modifications and a detailed account on its applications in the various sectors of organic synthesis.

Crystallographic, spectroscopic and thermal studies of 1-(4-bromophenyl)-5-(2,5-dimethyl-1H-pyrrol-1-yl)-3-methyl-1H-pyrazole

The new title pyrrole-pyrazole derivative, C16H16BrN3, was synthesized through a citric acid-catalyzed Paal-Knorr reaction between acetonylacetone and 1-(4-bromophenyl)-3-methyl-1H-pyrazol-5-amine under mild reaction conditions. This synthetic protocol is noteworthy for its utilization of stoichiometric amounts of the reactants, an ecofriendly solvent and a cost-effective, non-toxic and biodegradable organocatalyst. A comprehensive understanding of the molecular structure was gained through spectroscopic, thermal and X-ray crystallographic analyses. The crystal structure is characterized by weak interactions, where only C-H...π connections contribute to the hydrogen-bond contacts. The supramolecular assembly is controlled by dispersion forces. However, the energy frameworks demonstrate that these forces act in three dimensions, providing enough stability, as observed in TGA-DSC (thermogravimetric analysis-differential scanning calorimetry) studies.

Recent Advances in Synthesis and Properties of Pyrazoles

Pyrazole-containing compounds represent one of the most influential families of N-heterocycles due to their proven applicability and versatility as synthetic intermediates in preparing relevant chemicals in biological, physical-chemical, material science, and industrial fields. Therefore, synthesizing structurally diverse pyrazole derivatives is highly desirable, and various researchers continue to focus on preparing this functional scaffold and finding new and improved applications; this review highlights some of the most recent and strategic examples regarding the synthesis and properties of different pyrazole derivatives, mainly reported from 2017–present. The discussion involves strategically functionalized rings (i.e., amines, carbaldehydes, halides, etc.) and their use in forming various fused systems, predominantly bicyclic cores with 5:6 fusion taking advantage of our experience in this field and the more recent investigations of our research group.

Iodine-Mediated Pyridine Ring Expansion for the Construction of Azepines

A synthesis of azepines by the expansion of pyridine rings promoted by iodine in air is reported. The scope of the method is demonstrated with 27 examples. Two iodinations are involved in the reaction, in which the second iodination leads to the opening of the six-membered ring.

Machine learning prediction of 3CLpro SARS-CoV-2 docking scores

Molecular docking results of two training sets containing 866 and 8,696 compounds were used to train three different machine learning (ML) approaches. Neural network approaches according to Keras and TensorFlow libraries and the gradient boosted decision trees approach of XGBoost were used with DScribe’s Smooth Overlap of Atomic Positions molecular descriptors. In addition, neural networks using the SchNetPack library and descriptors were used. The ML performance was tested on three different sets, including compounds for future organic synthesis. The final evaluation of the ML predicted docking scores was based on the ZINC in vivo set, from which 1,200 compounds were randomly selected with respect to their size. The results obtained showed a consistent ML prediction capability of docking scores, and even though compounds with more than 60 atoms were found slightly overestimated they remain valid for a subsequent evaluation of their drug repurposing suitability.

Development of 19 F-detected 1,1-ADEQUATE for the characterization of polyfluorinated and perfluorinated compounds

Polyfluorinated and perfluorinated compounds in the environment are a growing health concern. ¹⁹ F-detected variants of commonly employed heteronuclear shift correlation experiments such as heteronuclear single quantum correlation (HSQC) and heteronuclear multiple bond correlation (HMBC) are available; ¹⁹ F-detected experiments that employ carbon-carbon homonuclear coupling, in contrast, have never been reported. Herein, we report the measurement of the ¹ J_CC and ⁿ J_CC coupling constants of a simple perfluorinated phthalonitrile and the first demonstration of a ¹⁹ F-detected 1,1-ADEQUATE experiment.

Mass spectrometrical and quantum-chemical study of pentafluorophenylhydrazones

Twenty-one pentafluorphenylhydrazones have been analyzed by means of tandem mass spectrometry (ESI MS/MS) conditions to compare their fragmentations with those ones obtained from quantum-chemical calculations of the hydrazone moiety depending on the substitution from the aldehyde site. The hydrazone N-N bond is disrupted under such conditions, and these results are in accordance with the facts that an electron-rich particle, such as an anion and or radical in a solution, can cause this disruption and simultaneous defluorination in para-position of the hydrazone part of the molecule.