A re-engineering approach: synthesis of pyrazolo[1,2-a]pyrazoles and pyrano[2,3-c]pyrazoles via an isocyanide-based four-component reaction under solvent-free conditions

Design, synthesis, characterization, and antioxidant activity studies of novel thienyl-pyrazoles

In a sustained search for novel and effective antioxidants, a potential therapeutic leads against renal, and neurological disorders. Amongst the heterocycles, pyrazole and their derivatives have been extensively studied for their biological potencies, particularly to a larger extent for their antioxidant properties. Although many of pyrazole derivatives displayed antioxidant activities, still there is a need of developing efficient protocol for their synthesis, involving ecofriendly conditions, molecules of greater antioxidant efficacy and lesser toxicity, etc. In this context, the current study presents an amberlyst-15 catalysed efficient synthesis of 2-pyrazoline derivatives, 5(a-g) via (3 + 2) annulation of chalcones with phenylhydrazines. Structure proofs of new pyrazoles offered by spectral studies, and the molecular structure of compound 5d of the series by crystallographic studies, which revealed an intra molecular hydrogen bond interactions (C–H⋯N type), and stabilization by C–H...π and π---π molecular interactions. Of the series, compounds 5g and 5h show excellent DPPH (IC₅₀ = 0.245 ± 0.01, and 0.284 ± 0.02 μM); and hydroxyl (IC₅₀ = 0.905 ± 0.01, and 0.892 ± 0.01μM) radical scavenging activities comparable with respective controls, ascorbic acid (IC₅₀ = 0.483 ± 0.01μM) and BHA (IC₅₀ = 1.739 ± 0.01μM). The molecular docking and ADME/Tox studies indicate that, these compounds have good antioxidant activity through π-π stacking with Catalase via Try337 and Phe140, and therefore, might be lead antioxidants for further study.

Copper-Catalyzed Sequential Cyclization/Migration of Alkynyl Hydrazides for Construction of Ring-Expanded N-N Fused Pyrazolones

A copper-catalyzed sequential cyclization/migration reaction of alkynyl hydrazides for the synthesis of ring-expanded N-N fused pyrazolones was developed. Control experiments indicate that the copper-ligand complex plays an essential role in the reaction. This approach features a broad scope including some functional group tolerance as well as a nucleophilic addition/1,3-migration/formal 1,2-migration sequence. This protocol provides simple manipulation and less waste due to high yield and atom economy. The synthetic utility of N-N fused pyrazolones was also demonstrated by further transformations.

Synthesis of Sulfamate-Fused 2-Aminopyrroles via an Isocyanide-Based Three Component [1+2+2] Annulation

An efficient preparation of sulfamate-fused 2-aminopyrroles was achieved through an isocyanide-based three-component [1+2+2] annulation of isocyanides, dialkyl acetylenedicarboxylates, and sulfamate-derived cyclic imines in good to excellent yields (up to 99 %). This reaction proceeds smoothly without any activation or modification of substances under neutral and metal-free conditions. The reaction could also be conveniently performed on a gram scale.

Synthesis and antimicrobial activity of new piperazine-based heterocyclic compounds

The hydrazide