Non-Decarboxylative Ruthenium-Catalyzed Rearrangement of 4-Alkylidene-isoxazol-5-ones to Pyrazole- and Isoxazole-4-carboxylic Acids

Bioactivity of novel isoxazole-fused heterocycles: comprehensive antimicrobial, antioxidant activities, SwissADME predictions, molecular docking, and DFT analysis

Among the foremost goals for organic chemists is to discover novel approaches for the synthesis of a particular heterocyclic and its design. Our approach focused on the vital precursor 4-acetyl-3-phenylisoxazol-5(4H)-one 3, as this molecule has an endocyclic carbonyl function in position 5 adjacent to the substituted acetyl function at site 4. Therefore, compound 3 was a crucial component of many types of fused isoxazole. The investigators provide a straightforward synthesis of fused isoxazole from the following categories: pyrano[3,2-d]isoxazole 4 & 6, isochromeno[4,3-d]isoxazole 5, isoxazolo[4',5':5,6]pyrano[3,4-c]pyridine 7, thieno[3',4':4,5]pyrano [3,2-d]isoxazole 8, pyrazolo[4,3-d]isoxazole 10a,b and 11a,b, and isoxazolo[4,5-c]pyridazine derivatives 14a,b. The target compounds and their structures were supported by the results of 1H-NMR, IR and mass spectroscopy. Molecular docking studies highlighted strong binding affinities to bacterial enzymes crucial for cell wall synthesis, while DFT calculations provided deep insights into their electronic properties and stability. Additionally, the antioxidant potential of compounds 11a,b was assessed using DPPH and ABTS assays, showing impressive concentration-dependent activity. Addressing the critical issue of antibiotic resistance, especially due to β-lactamases, molecular docking affirmed the high binding propensity of these derivatives with essential β-lactamase proteins (PDB: 1CK3, 6MU9, and 6W2Z). These findings underscore the promise of isoxazoline derivatives as powerful antimicrobial and antioxidant agents, paving the way for further development in combating bacterial resistance and oxidative stress.

Doubly Metathetic NiCl2-Catalyzed Coupling Between Bis(2-oxazolines) and Aldehydes: A Novel Access to Bis(ester-imine) Derivatives

The coupling between bis(2-oxazolines) and two equivalents of aromatic aldehydes in the presence of catalytic amounts of NiCl2 affords an ester-imine product in synthetically useful yields. This virtually unknown, 100% atom-economic transformation involves the formal metathesis between the C=N double bond of the bis(2-oxazoline) moiety, which undergoes ring-opening, and the C=O double bond of the aldehyde. The scope of this transformation is studied, and a mechanism is proposed based on DFT calculations.

Diastereoselective Palladaelectro-Catalyzed Construction of Bromomethyl Morpholines as Key Step To Access Morpholino Homonucleosides

A synthetic protocol for the preparation of a new class of morpholino homonucleosides in enantiopure form starting from readily available 1,2-aminoalcohols or glycidol has been developed. Key intermediates of the synthetic sequence are 2-bromomethyl morpholines, diastereoselectively achieved from the corresponding alkenols by palladaelectro-catalyzed alkoxybromination of unactivated alkenes. The so obtained bromo derivatives are in turn susceptible to functionalization with nucleic bases for easy access to morpholino homonucleosides.

Copper-Promoted Aerobic Oxidative [3+2] Cycloaddition Reactions of N,N-Disubstituted Hydrazines with Alkynoates: Access to Substituted Pyrazoles

A copper-promoted aerobic oxidative [3+2] cycloaddition reaction for the synthesis of various substituted pyrazoles from N,N-disubstituted hydrazines with alkynoates in the presence of bases is developed. This work involves a direct C(sp³)-H functionalization and the formation of new C-C/C-N bonds. In this strategy, inexpensive and easily available Cu₂O serves as the promoter and air acts as the green oxidant. The reaction exhibits the advantages of high atom and step economy, high regioselectivity, and easy operation.

Assembly of isoxazol-5-one with 2-unsubstituted imidazole N-oxides and aldehydes

A new synthetic protocol has been developed to construct polyfunctional isoxazol-5-one derivatives with imidazole moiety. It is based on the Knoevenagel condensation of isoxazol-5-one with aldehydes and subsequent Michael addition of imidazole N-oxides as part of a tandem three-component process. This reaction proceeds smoothly in moderate-to-good yield under catalyst-free conditions.

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.