Synthesis of 6-Amino-2,4-dihydropyrano[2,3-c]pyrazol-5-carbonitriles Catalyzed by Silica-Supported Tetramethylguanidine Under Solvent-Free Conditions

Review on advancements of pyranopyrazole: synthetic routes and their medicinal applications

Pyranopyrazoles are among the most distinguished, biologically potent, and exciting scaffolds in medicinal chemistry and drug discovery. Synthesis and design of pyranopyrazoles using functional modifications via multicomponent reactions (MCRs) are thoroughly found in synthetic protocols by forming new C-C, C-N, and C-O bonds. This review aims to focus on the biological importance of pyranopyrazoles as well as on a diverse synthetic approach for their synthesis using various catalytic systems such as acid-catalyzed, base-catalyzed, ionic liquids and green media-catalyzed, nano-particle-catalyzed, metal oxide-supported catalysts, and silica-supported catalysts. In this review, we have summarized data on the advancements in synthesizing pyranopyrazole from the last two decades to the mid-2023 and research papers describing the importance of these scaffolds. This review will be significant for synthetic organic chemists and researchers working in organic chemistry.

WITHDRAWN: Gellan gum-cellulose hydrogel incorporating with graphene oxide and magnetic nanoparticles as a novel nanocatalyst for the synthesis of dihydropyrano derivatives

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/policies/article-withdrawal.

Construction of a Dual-Functionalized Acid-Base Nanocatalyst via HEPES Buffer Functionalized on Fe3O4 as a Reusable Catalyst for Annulation Reactions

Herein, we present a highly efficient dual-functionalized acid-base nanocatalyst, denoted as Fe3O4@GLYMO-HEPES, featuring sulfuric acid and tertiary amines as its dual functional components. This catalyst is synthesized through the immobilization of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) as the source of these functionalities onto magnetite (Fe3O4) using 3-glycidoxypropyltriethoxysilane (GLYMO) as a linker. Characterization studies confirm the integrity of the Fe3O4 core, with the GLYMO-HEPES coating exhibiting no phase changes. Furthermore, Fe3O4@GLYMO-HEPES nanoparticles demonstrate a uniform size distribution without aggregation. Notably, the catalyst exhibits remarkable stability up to 200 °C and possesses a saturation magnetization value of 31.5 emu/g, facilitating easy recovery via magnetic separation. These findings underscore the potential of Fe3O4@GLYMO-HEPES as a versatile and recyclable nanocatalyst for various applications. Its catalytic ability was evaluated in the synthesis of various pyrano[2,3-c]pyrazoles and 2-amino-3-cyano-4H-chromenes through a tandem Knorr-Knoevenagel-Michael-Thorpe-Ziegler-type heterocyclization mechanism, using different aldehydes. A wide range of fused heterocycles was synthesized having good to excellent yields. The process is cost-effective, safe, sustainable, and scalable, and the catalyst can be reused up to five times. The prepared catalyst was found to be highly stable and heterogeneous and showed good recyclability.

An Fe3O4 supported O-phenylenediamine based tetraaza Schiff base-Cu(ii) complex as a novel nanomagnetic catalytic system for synthesis of pyrano[2,3-c]pyrazoles

In this research, we present a post-synthetic method for synthesizing a novel nanomagnetic Cu(II) Schiff base complex and investigate its efficiency in catalytic organic conversion reactions. Various spectroscopic analyses were employed to characterize the physiochemical characteristics of the resulting nanocomposite. The experimental results successfully demonstrate the catalytic application of the prepared Cu-complex in the preparation of pyrano[2,3-c]pyrazole heterocycles. This synthesis involved a one-pot three-component condensation reaction, wherein hydrazine hydrate, ethyl acetoacetate, malononitrile, and aromatic aldehydes were combined under reflux conditions using water as the solvent. Notably, the heterogenized complex exhibited exceptional catalytic performance, achieving remarkable conversion rates and selectivity, all accomplished using only 12 mg of the catalyst. Furthermore, thorough stability assessments of this catalyst were conducted through reusability and hot filtration tests, which confirmed its non-leaching properties and demonstrated excellent results over the course of five consecutive runs.

Yolk-shell structured magnetic mesoporous organosilica supported ionic liquid/Cu complex: an efficient nanocatalyst for the green synthesis of pyranopyrazoles

The preparation of yolk-shell structured magnetic mesoporous composites is a significant subject between researchers. Especially, modification of theses composites with ionic liquid/metal complex is very important for catalytic processes. In the present study, a novel magnetic methylene-based periodic mesoporous organosilica (PMO)-supported ionic liquid/Cu complex with yolk-shell structure (YS-Fe3O4@PMO/IL-Cu) was prepared via the soft template-assisted method. The TGA, FT-IR, SEM, EDX, XRD, VSM, nitrogen-sorption, and ICP techniques were employed to identify YS-Fe3O4@PMO/IL-Cu. The YS-Fe3O4@PMO/IL-Cu material was applied as a powerful nanocatalyst for the synthesis of pyranopyrazoles under ultrasonic media. The study demonstrated that the YS-Fe3O4@PMO/IL-Cu nanocatalyst is highly recyclable, selective, and effective. The leaching test was performed to investigate the nature of the designed catalyst under the applied conditions.

Design, preparation and application of the semicarbazide-pyridoyl-sulfonic acid-based nanocatalyst for the synthesis of pyranopyrazoles

A novel, efficient, and recoverable nanomagnetic catalyst bearing the semicarbazide linkers, namely, Fe₃O₄@SiO₂@OSi(CH₂)₃-N(3-pyridoyl sulfonic acid)semicarbazide (FSiPSS) was designed, synthesized and characterized by the use of various techniques such as FT-IR, EDX, elemental mapping analysis, XRD, SEM, TEM, TGA/DTA, BET, and VSM. Then, the catalytic capability of the novel prepared nanomagnetic FSiPSS catalyst was successfully investigated in the synthesis of diverse pyranopyrazoles through a one-pot four-component condensation reaction of ethyl acetoacetate, hydrazine hydrate, aromatic aldehydes, and malononitrile or ethyl cyano-acetate by the help of ultrasonication in very short reaction time, good to high yields and easy work-up (Fig. 1). Figure 1 Synthesis of diverse pyranopyrazoles by the FSiPSS nano-catalyst.

L-Cysteine Catalyzed Environmentally Benign One-pot Multicomponent Approach Towards the Synthesis of Dihydropyrano[2,3-c]pyrazole Derivatives

BACKGROUND

The pyrano[2,3-c]pyrazole derivatives are important building blocks of many biologically active compounds owing to their diverse biological potential for example, anti-inflammatory, anticancer, anti-microbial and anti-oxidant properties.

OBJECTIVE

Keeping in mind the wide range of applications of pyrano[2,3-c]pyrazoles, herein we intended to develop a novel synthetic methodology for dihydropyranopyrazoles. We were also interested in determining the influence of amino acids and dipeptides as a catalyst on the synthesis of pyrano[2,3-c]pyrazole derivatives.

METHODS

To achieve our objectives, we used a one-pot multi-component reaction of ethyl 3-oxobutanoate, propanedinitrile, hydrazine monohydrate and several substituted benzaldehydes by using different catalysts and solvents to synthesize our desired products in the presence of various catalysts.

RESULTS AND DISCUSSION

We found that optimal conditions for the preparation of pyrano[2,3-c]pyrazoles were L-cysteine (0.5 mol) in the presence of water:ethanol (9:1) at 90 °C. Various 1,4-dihydropyrano[2,3- c]pyrazoles were afforded by using several substituted benzaldehydes in 66-97% yields.

CONCLUSION

We described a green and environmentally benign method to synthesize pyrano[2,3-c]pyrazoles in a one-pot four component reaction of ethyl 3-oxobutanoate, propanedinitrile, hydrazine monohydrate and different substituted benzaldehyde in the presence of L-cysteine in aqueous ethanol (9:1) at 90 oC. Excellent yields of the products, simple work-up, easily available starting materials, use of green solvents, naturally occurring catalyst, non-toxicity, non-chromatographic purification and environmentally benign reaction conditions are some main advantages of this protocol.

DABA MNPs: a new and efficient magnetic bifunctional nanocatalyst for the green synthesis of biologically active pyrano[2,3-c]pyrazole and benzylpyrazolyl coumarin derivatives

A new core–shell magnetic silica functionalized with 3,4-diaminobenzoic acid nanocatalyst (Fe₃O₄@SiO₂@PTS-DABA) was prepared and characterized. The Fe₃O₄@SiO₂@PTS-DABA catalyst was applied for the synthesis of dihydropyranopyrazole and benzylpyrazolyl coumarin derivatives.

FeF3-mediated tandem annulation: a highly efficient one-pot synthesis of functionalized N-methyl-3-nitro-4H-pyrimido [2, 1-b] [1, 3] benzothiazole-2-amine derivatives under neat conditions

A straight forward and highly efficient one-pot annulation of 2-aminobenzothiazole, (E)-N-methyl-1-(methylthio)-2-nitroethenamine, and aldehydes in the presence of FeF₃ is described. Diverse functionalized N-methyl-3-nitro-4H-pyrimido [2, 1-b] [1, 3] benzothiazole-2-amine derivatives were obtained with excellent yields under neat conditions. The one-pot annulation was shown to be valid for the synthesis of highly functionalized derivatives of N-methyl-3-nitro-4H-pyrimido [2, 1-b] [1, 3] benzothiazole-2-amine from readily accessible substrates. The catalyst FeF₃ can be easily recovered and reused for the next reaction without any effects on the yields of the products. This green protocol provides structurally complex, biologically important N-methyl-3-nitro-4H-pyrimido [2, 1-b] [1, 3] benzothiazole-2-amine in a one-pot operation.

Core–shell structured magnetic silica supported propylamine/molybdate complexes: an efficient and magnetically recoverable nanocatalyst

A novel core–shell structured magnetic silica supported propylamine/molybdate complex (Fe₃O₄@SiO₂/Pr-NMo[Mo₅O₁₈]) is prepared, characterized and applied as an effective and easily recoverable nanocatalyst in the synthesis of pyrano-pyrazole derivatives.

An efficient and green approach for the synthesis of 2,4-dihydropyrano[2,3-c]pyrazole-3-carboxylates using Bi2O3/ZrO2 as a reusable catalyst

A novel material of bismuth loaded on zirconia (Bi2O3/ZrO2) is synthesized by simple wet-impregnation method and characterized by several techniques (P-XRD, TEM, SEM, BET, etc.). Bi2O3/ZrO2 proved to be a good catalyst for the four-component, one-pot reaction to produce a new series of 2,4-dihydropyrano[2,3-c]pyrazole-3-carboxylate derivatives with excellent yields (91 to 98%) under mild conditions at RT with short reaction times (≈20 min). The structures of the target molecules were confirmed by 1H NMR, 13C NMR, 15N NMR, HRMS and FT-IR. The catalyst is easily separable and can be reused for six cycles without ostensible loss of activity. This method is inexpensive, atom-efficient and no chromatographic separations are needed.