DOI : https://doi.org/10.5281/zenodo.19882444
- Open Access
- Authors : Jyoti Jain, Deepti Saini, Sukhbeer Kumari
- Paper ID : IJERTV15IS042419
- Volume & Issue : Volume 15, Issue 04 , April – 2026
- Published (First Online): 29-04-2026
- ISSN (Online) : 2278-0181
- Publisher Name : IJERT
- License:
This work is licensed under a Creative Commons Attribution 4.0 International License
Recent Developments for Eco-compatible And Environmentally Benign Synthesis of Pyranopyrazole Derivatives: A Review
Jyoti Jain,
Department of Chemistry, University of Rajasthan, Jaipur
Deepti Saini and Sukhbeer Kumari
Department of Chemistry, S. S. Jain Subodh PG (Autonomous) College, Jaipur
Abstract: Owing to biological and medicinal properties of pyranopyrazoles, synthesis of these bioactive heterocycles has attracted the interest of medicinal and organic chemists. This review focuses on the recent advances in greener and one-pot synthesis of pyranopyrazole derivatives. The present review describes the literature reports for the period 2011 to 2025. The reported methodologies encompass both conventional and alternative reaction conditions, with recent studies predominantly emphasizing environmentally sustainable protocols. These include the application of microwave and ultrasound irradiation, the use of catalytic systems, eco-friendly solvents, and solvent-free approaches.
Key Words: Pyranopyrazoles, one-pot synthesis, energy efficient synthesis, solvent-free condition
Table of Content:
-
Introduction
-
Synthesis of pyranopyrazoles
-
Using nano catalyst under solvent free condition
-
Using green solvent
-
Using green catalyst
-
Using energy resources
-
-
Conclusion
-
Acknowledgment
-
Conflict of interest
-
References
-
Introduction:
To develop safer and more sustainable organic synthetic protocols, methodologies addressing the principles of green chemistry have received considerable attention in recent years. This approach emphasizes the use of environmentally acceptable chemicals and solvents, long-lifetime and recyclable catalysts, and atom-efficient procedures. [13] With growing awareness of environmental issues, the need for clean and sustainable synthetic approaches has become increasingly important in modern research. In this regard, heterogeneous organic reactions have attracted significant attention due to their practical benefits, such as convenient handling, straightforward separation of products, reusability of catalysts, and reduced environmental impact. [49]
Heterocyclic compounds are widely distributed in nature and play an essential role in various biological processes. [10,11] Heterocyclic compounds play a pivotal role in medicinal chemistry due to their unique structural features and diverse physicochemical characteristics. [12,13] During the last two to three decades, significant progress has been
made in heterocyclic chemistry, with considerable attention directed toward the synthesis and diverse applications of medium-sized ring systems. [1416]
In recent years, pyranopyrazoles and their derivatives have gained considerable attention as an important class of heterocyclic compounds owing to their wide range of biological activities, such as antioxidant, anticancer, antimicrobial, anti-inflammatory, antifungal, insecticidal, antitumor, antipyretic, antidepressant, and anti-HIV properties [1722]. Furthermore, certain pyranopyrazole-based compounds have demonstrated potential applications in the agricultural sector. As a result, the construction of heterocyclic systems incorporating both pyran and pyrazole moieties has become an area of significant research interest. To address environmental concerns, a variety of eco-friendly synthetic approaches have been developed, particularly those employing heterogeneous and recyclable nanocatalysts. For instance, zwitterionic sulfamic acid-functionalized nanoclay has been reported as an efficient catalyst for the synthesis of dihydropyrano[2,3-c]pyrazoles and spiro-pyranopyrazole derivatives under green reaction conditions [79]. Consequently, due to the presence of these valuable structural motifs in biologically active molecules, extensive efforts have been directed toward the development of sustainable and efficient synthetic methodologies for pyranopyrazole derivatives.
-
Synthesis of pyranopyrazoles
-
Using solvent free condition
Dwivedi et al. [23] reported an environmentally friendly and efficient method for synthesizing pyrano[2,3-c] pyrazoles at ambient temperature, employing WEB as the reaction medium. (Scheme1-2)
Ar = Ph, 2-NO2Ph, 3-FPh, 4-FPh, 2-ClPh, 4-ClPh, 4-BrPh, 4-OMePh, 4-OH,2-OMePh,
Furan, Thiophene, Isatin, 5-Cl Isatin, 5-Br Isatin, N-Bn Isatin
Scheme1. An efficient solvent-free approach was employed for the synthesis of pyrano[2,3-c] pyrazole derivatives at ambient temperature using WEB.
Entry
Solvent
ToC
Time (min)
Yield (%)
1
MeOH
R.T.
300
5
2
EtOH
R.T.
300
5
3
MeOH + WEB (1:1)
R.T.
240
20
4
EtOH + WEB (1:1)
R.T.
120
25
5
MeOH + WEB (2:8)
R.T.
120
55
6
EtOH + WEB (2:8)
R.T.
120
60
7
DCM + WEB (1:1)
R.T.
240
25
8
DCM + WEB (2:8)
R.T.
120
40
9
WEB
R.T.
30
96
Table 1. Optimization of the solvent system for the efficient synthesis of pyrano[2,3-c]pyrazoles using WEB at ambient temperature
Scheme 2. A plausible reaction mechanism for the formation of pyrano[2,3-c]pyrazole derivatives in the WEB medium.
Chavan et al. [24] reported the synthesis of pyranopyrazoles under solvent-free conditions using a catalytic amount of silicotungstic acid (Scheme 3)
R1 = Ph, 2-NO2Ph, 3-NO2Ph, 4-NO2Ph, 3-ClPh, 2,4-diClPh, 2,6-diClPh, 3-BrPh, 4-BrPh, 4-FPh, 2-OMePh,
3,4-diOMePh, 2-OHPh, 2,4-diFPh, 4-OMePh, 4-OHPh, 4-MePh, 2-Furanyl, 2-Thiophenyl, Propyl, n-Hexyl
Scheme 3. A one-pot multicomponent strategy was employed for the synthesis of pyrano[2,3-c]pyrazole derivatives using H[SiWO] as a catalyst under solvent-free conditions at 60 °C
Entry
Catalyst
Catalyst (mol %)
Time (min)
Yild (%)
1
None
–
180
–
2
FeCl3
2
10
20
3
SnCl4
2
10
38
4
ZnCl2
2
10
25
5
P2O5
2
10
32
6
CAN
2
10
15
7
H4[SiW12O40]
2
10
96
8
H4[SiW12O40]
0.5
10
34
9
H4[SiW12O40]
1
10
68
10
H4[SiW12O40]
5
10
95
Table 2.Screening of catalysts and optimization of catalyst loading for the synthesis of pyrano[2,3-c]pyrazoles.
Scheme 4. A plausible reaction mechanism for the formation of pyrano[2,3-c]pyrazoles via Knoevenagel condensation is proposed.
Ebrahimi et al. [25] reported an efficient and environmentally benign method for synthesizing substituted
pyranopyrazoles using [(CH)SOMIM][HSO] as a catalyst. (Scheme 5)
R1 = Ph, 3-NO2Ph, 4-NO2Ph, 2-ClPh, 3-ClPh, 4-ClPh, 3-BrPh, 4-BrPh, 4-OMePh, 4-MePh,
Scheme 5. Pyrano[2,3-c]pyrazoles were synthesized under solvent-free conditions using
[(CH)SOHMIm][HSO] as a catalystShaabani et al. [26] reported a straightforward and efficient four-component reaction involving dialkyl acetylenedicarboxylates, isocyanides, and ethyl acetoacetate with hydrazine hydrate or phenylhydrazine, affording pyrazolo[1,2-a]pyrazoles and pyrano[2,3-c]pyrazoles under solvent-free conditions at mild temperatures with good to excellent yields. (Scheme 6)
Scheme 6. A one-pot, solvent-free approach for the synthesis of pyrazolo[1,2-a]pyrazoles and pyrano[2,3-c]pyrazoles
Mirjalili et al. [27] reported the synthesis of a nano-eggshell/Ti(IV) (NEST) catalyst and demonstrated its application as a heterogeneous natural nanocatalyst for the efficient synthesis of dihydropyrano[2,3-c]pyrazoles at ambient temperature under solvent-free conditions through the
condensation of hydrazine hydrate, ethyl acetoacetate, malononitrile, and aromatic aldehydes.(
Scheme 7)
ArCHO NH2NH2.H2O
Ar = C6H5, 2-OCH3C6H4, 3-O2NC6H4, 4-H3CC6H4, 4-O2NC6H4, 3-BrC6H4, 4-BrC6H4, 4-ClC6H5, 4-OHC6H4, 3,4-(OH)C6H3, 2,4-(Cl)C6H3,
3-OCH3 4-OH, C6H4, 4-FC6H4, 2-Furyl, 1-Naphthyl
Scheme 7. One-pot multicomponent synthesis of dihydropyrano[2,3-c]pyrazoles under solvent-free conditions.
Safari et al. [28] reported the synthesis and characterization of MMT-ZSA as a non-toxic and environmentally benign zwitterionic catalyst for the preparation of pyrano[2,3-c]pyrazole and spiro[indoline-3,4-pyrano[2,3-c]pyrazole] derivatives. They developed a novel methodology for heterocycle synthesis employing a heterogeneous zwitterionic sulfamic acid catalytic system based on MMT-ZSA nanoclay. The catalyst demonstrated excellent reusability, maintaining its catalytic efficiency for up to five cycles without significant loss of activity.( Scheme 8)
Scheme 8. One-pot multicomponent synthesis of pyrano[2,3-c]pyrazole and spiro[indoline-3,4-pyrano[2,3-c]pyrazole] derivatives.
Yarie et al. [29] reported the synthesis of a novel nanosized molten salt and its application in the preparation of dihydropyrano[2,3-c]pyrazole derivatives through a three-component reaction. The developed protocol offers several advantages, including mild reaction conditions, high catalytic efficiency, simple work-up, shorter reaction times, and excellent yields.( Scheme 9)
R = 4-Cl, 2- Cl, 2,4-Cl2, 4-Br, 4-F, 2,6-F2, 3,4-F2, 3,5-F2, 4-CF3, 3,5-(CF3)2, 4-CN, 2-NO2,
3-NO2, 4-NO2, H, 4-Me, 2-OMe, 4-OMe, 4-OH, 3-OEt, 1-cinnamaldehyde, 1- napthaldehyde
Scheme 9. One-pot multicomponent synthesis of dihydropyrano[2,3-c]pyrazole derivatives.
Vasava et al. [30] reported the synthesis of a series of novel and biologically active 6-amino-1-(2,4-dinitrophenyl)-4-phenyl-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile derivatives via a multicomponent reaction involving various substituted aromatic aldehydes, 2,4-dinitrophenylhydrazine, ethyl acetoacetate, and malononitrile in the presence of SnCl as an efficient catalyst. The reaction was carried out using both microwave irradiation and conventional methods. The synthesized compounds were evaluated for in vitro antibacterial, antitubercular, and cytotoxic activities using the MTT assay. Additionally, in silico ADME pharmacokinetic studies were performed to assess their bioavailability. Furthermore, molecular docking studies with enoyl-ACP reductase (oxidoreductase) were conducted to determine the binding affinity of the compounds. (Scheme 10)
Scheme 10. One-pot multicomponent synthesis of 6-amino-1-(2,4-dinitrophenyl)-4-phenyl-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile derivatives
A.R. Moosavi-Zare et al. [31] investigated an acetic acid-functionalized pyridinium salt, 1-(carboxymethyl)pyridinium iodide {[cmpy]I}, as a reusable catalyst for the green, simple, and efficient synthesis of 6-amino-4-(4-methoxyphenyl)-5-cyano-3-methyl-1-phenyl-1,4-dihydropyrano[2,3-c]pyrazoles. The reaction was carried out via a one-pot tandem four-component condensation of aryl aldehydes, ethyl acetoacetate, malononitrile, and hydrazine
hydrate at 100 °C under solvent-free conditions. This methodology offers several advantages, including high efficiency, broad applicability, excellent yields, shorter reaction times, cost-effectiveness, a cleaner reaction profile, simple product isolation, and adherence to green chemistry principles. (Scheme 11)
R = Ph, 4-ClPh, 2-ClPh, 4-MePh, 2-OMePh, 4-FPh, 2-OHPh, OH
3-OHPh, 3-NO2Ph, 4-NO2Ph, 3,4,5-triOMePh, S
Scheme 11. One-pot synthesis of 6-amino-4-(4-methoxyphenyl)-5-cyano-3-methyl-1-phenyl-1,4-dihydropyrano[2,3-c]pyrazole.
-
Using green solvent
Mandha et al. [32] reported an efficient, cost-effective, and environmentally friendly multicomponent approach for the synthesis of pyrano[2,3-c]pyrazoles under catalyst-free conditions.(Scheme 12)
R = 3-OHC6H4, 4-BrC6H4, 4-CH3C6H4, 4-OHC6H4, C6F5, 3-C5H4N, 2-C4H3S, 4-C11H5Cl3NO, 3-OC6H5C6H4, 3-C11H5Cl3NO, C6H5, 4-OHC6H4, 4-OCH3C6H4, 4-NO2C6H4, 3-OC6H5C6H4, 3-C5H4N, 3-C11H5Cl3NO
Scheme 12. Preparation of pyrano[2,3-c]pyrazoles in ethanol without the use of a catalyst.
D.M. Pore et al. [33] reported a catalyst-free multicomponent reaction (MCR) for the synthesis of spiro pyranopyrazole derivatives via the reaction of acetylenic esters with hydrazine hydrate, followed by their interaction with isatin and malononitrile in water as a green solvent at room temperature. (Scheme 13)
R = H, CH3, C2H5; R1 = H, Cl, I,OMe, Me,
Scheme 13. Preparation of spiro pyranopyrazole derivatives using ethanol as the solvent in the absence of a catalyst.
Bhosle et al. [34] reported a facile and environmentally friendly method for the synthesis of biologically active substituted pyranopyrazoles via a one-pot cyclocondensation of various aromatic aldehydes, ethyl acetoacetate, hydrazine hydrate, and malononitrile using a deep eutectic solvent system composed of choline chloride and urea. (Scheme 14)
CN
RCHO + NH2NH2.H2O + + CN
R = 4-OCH3-Ph, Ph, 4-Cl-Ph, 4-CH3-Ph, 4-F-Ph, 3-Br-Ph, 4-NO2-Ph, 4-OH-Ph, 2-Cl-Ph,
3-NO2-Ph, 3,4-(OMe)2-Ph, 4-OH-3-OMe-Ph, 2-furyl, 2-thiophenyl, 4-pyridyl
Scheme 14. Synthesis of biologically active substituted pyranopyrazoles malononitrile in a deep eutectic solvent, choline chloride: urea.
Dalal et al. [35] investigated the synthesis of pyranopyrazole derivatives through a one-pot four-component reaction involving aldehydes or isatins, hydrazine hydrate, malononitrile, and a -keto ester in an HOEtOH (9:1) system at 80 °C. This study represents the first report of such a transformation under neutral conditions using supramolecular -cyclodextrin (-CD) as an efficient, biodegradable, and reusable catalyst. (Scheme 15)
-
R2 = H, CH3, C2H5, CH2Ph
R = H, 2-Cl, 4-Cl, 2-NO2, 3-NO2, 4-NO2, 4-F, 4-Br, 3-Br, 2-OH,
4-OH, 4-Me, 4-OMe, 4-N(CH3)2, 3-OMe, 4-OH, Thionyl
Scheme 15. A green approach for the synthesis of pyranopyrazole derivatives using -cyclodextrin (-CD) as a supramolecular, biodegradable, and recyclable catalyst.
Yang et al. [36] developed a green method for the synthesis of novel dihydropyrano[2,3-c]pyrazoles employing lignin-derived aromatic aldehydes, and the resulting compounds were assessed for their in vitro antioxidant and cytotoxic properties. ( Scheme 16)
Scheme 16. An efficient approach for the synthesis of dihydropyrano[2,3-c]pyrazoles.
Azzam et al. [37] demonstrated a simple and novel one-pot four-component synthesis of pyranopyrazol-6-one derivatives via the reaction of Meldrums acid, ethyl acetoacetate, hydrazine hydrate, and aromatic aldehydes in water, using Ba(OH) as a readily available, inexpensive, and efficient catalyst. (Scheme 17)
Ar = 3,4,5-(MeO)3C6H2, 4-MeOC6H4, 3-MeOC6H4, 2-ClC6H4,
-
HOC6H4, 4-FC6H4, 3-NO2C6H4, H, CH3, CH3CH2, CH3CH2CH2
Scheme 17. Synthesis of pyranopyrazol-6-one derivatives in water using Ba(OH) as a catalyst.
N
Zonouz et al. [38] reported a green and catalyst-free approach for the synthesis of novel pyranopyrazole derivatives via a four-component reaction in water.( Scheme 18)
H CN
+ +
Ar O CN
H2N NH2.H2O +
COOMe
COOMe
H2O, 1.5-2.5 h
50-60 OC
NC H2N
Ar COOMe NH
Ar = C6H5, 2-MeC6H4, 3-MeC6H4, 2-BrC6H4, 4-BrC6H4, 2-NO2C6H4, 3-NO2C6H4, 4-NO2C6H4, 3-HOC6H4, 3-OMeC6H4,
Scheme 18. Synthesis of pyranopyrazole derivatives in an aqueous medium at 5060 °C.
Tamaddon et al. [39] reported a protocol for the rapid multicomponent synthesis of dihydropyrano[2,3-c]pyrazoles using cocamidopropyl betaine (CAPB) as a biodegradable surfactant in a novel water-based worm-like micellar medium at 5060 °C. ( Scheme 19)
CAPB (0.02 mol%) H2O, 50-60oC
Ar = 2-furyl, 2 C6H5, 3,4-O2NC6H4, 2-O2NC6H4, 3-O2NC6H4, 4-ClC6H4, 2-ClC6H4, 3-ClC6H4, 4-FC6H4, 3-BrC6H4, 4-H3CC6H4, 3-H3CC6H4,
4-MeOC6H4, 4-HOC6H4, 2-HOC6H4, 3-HOC6H4, CH3, CH3CH2CH2
Scheme 19. Synthesis of dihydropyrano[2,3-c]pyrazoles using cocamidopropyl betaine (CAPB) in an aqueous worm-like micellar medium
-
-
Using green catalyst
Ali et al. [40] reported sulfonated carboxymethylcellulose (SCMC), a biopolymer-derived solid acid, as a green heterogeneous catalyst for the one-pot multicomponent synthesis of pyrano[2,3-c] pyrazole derivatives. The reaction involved ethyl acetoacetate, hydrazine hydrate, malononitrile, and various aldehydes in ethanol, serving as a green solvent. (Scheme 20)
NH2
R = H, 4-Cl, 2-Cl, 4-OH, 2-Cl, 4-Br, 4-NO2,3, 4-diOMe, 3-OMe, 4-OH, 3-NO2, 4-F
Scheme 20. Synthesis of pyrano[2,3-c] pyrazole derivatives using sulfonated carboxymethylcellulose (SCMC) as a catalyst.
Tekale et al. [41] reported a one-pot four-component synthesis of dihydropyrano[2,3-c]pyrazoles in an aqueous medium using zinc oxide nanoparticles as an efficient catalyst.(Scheme 21)
-
-
R1
CN NH2
CN NH2
R1 = Ph, 2-ClPh, 2,4-diClPh, 2-OMePh, 2-NO2Ph, 3-ClPh, 3,4-diOMePh, 3-NO2Ph, 3-BrPh, 3-OHPh, 3-FPh,
4-ClPh, 4-OMePh, 4-NO2Ph, 4-BrPh, 4-OHPh, 4-MePh
HN
O N O H
O R1
HN
O N O H
CN NH2
Scheme 23. An efficient synthesis of pyranopyrazole derivatives via. knoevengel cyclocondensation
Sangshetti et al. [44] described a green and eco-friendly protocol for the one-pot, four-component synthesis of methyl 6-amino-5-cyano-4-aryl-2,4-dihydropyrano[2,3-c]pyrazole-3-carboxylates in water, catalyzed by titanium dioxide (TiO).( Scheme 24)
COOMe
+ COOMe
CN + CN
NH2NH2.H2O
+ R1CHO
TiO2 (10 mol %) H2O, rt
R
O
N
NC H2N
CO2CH3 NH
R1 = Ph,4-NO2Ph, 4-MePh,3-OHPh, 3-OMePh, 4-BrPh,
-
MePh, 2-NO2Ph, 2-MePh, 3-NO2Ph,, Thiophene
Scheme 24. Preparation of methyl 6-amino-5-cyano-4-aryl-2,4-dihydropyrano[2,3-c]pyrazole-3-carboxylates using TiO as a catalyst.
Keyume et al. [45] reported an efficient and straightforward one-pot method for the synthesis of functionalized, multisubstituted 2,4-dihydropyrano[2,3-c]pyrazole dicarboxylates from -ketoesters, hydrazine, dimethyl acetylenedicarboxylate, and malononitrile in ethanol.( Scheme 25)
H3CO2C CO2CH3 H3CO2C CO2CH3
COOMe
+ COOMe
CN + CN
NH2NHR3
+ R1COCH2CO2Me
DABCO EtOH, 50OC
NC
H2N O
R1
NH OR
N
NC R1
N
H2N O N R3
R1 = Me, Et, n-Pro, Me, iso-Pro, Ph, R3 = H, Me, Ph, o-ClPh, p-ClPh
Scheme 25. An efficient synthesis of 2,4-dihydro-pyrano[2,3-c]pyrazole dicarboxylates
Lavanya et al. [46] reported a rapid, clean, and highly efficient method for the green synthesis of pyrano[2,3-c]pyrazole-3-carboxylate and pyrano[2,3-c]pyrazole-5-carbonitrile derivatives via a one-pot four-component reaction catalyzed by Mn/ZrO under ultrasonication.( Scheme 26)
CHO
CN )))))), RT, 10 min
COOMe COOMe
R
O
NH
O
N
NC H2N
OMe
R + NH2NH2.H2O + CN
Mn/ZrO2
R
O
N
O O
R = 2,3-(OMe)2, 2-OMe, 4-Br, 2,4,6-(OMe)3, 3-OH, 2-F,
2,5-(OMe)2, 2,3-(OMe)2, 2-OMe, 4-Br, 2,4,6-(OMe)3,
3-OH, 2-F, 2,5-(OMe)2
OEt
NC
NH
H2N
Scheme 26. One-pot synthesis of pyrano[2,3-c]pyrazole-3-carboxylate and pyrano[2,3-c]pyrazole-5-carbonitrile derivatives.
Muramulla et al. [47] demonstrated a novel catalytic role of MDOs, where they function as Lewis base catalysts in a tandem Michael additioncyclization reaction between 3-methyl-2-pyrazolin-5-one and benzylidene malononitriles.(Scheme 27)
CN
R CN
+
H
R
N N
MDO
O N
H
CH2Cl2, rt N O
CN NH2
R = C6H5, 4-MeOC6H4, 4-MeC6H4, 4-FC6H4, 4-ClC6H4, 4-BrC6H4, 4-CNC6H4, 4-NO2C6H4, 3-BrC6H4, 2-FC6H4, 2-ClC6H4, 2-BrC6H4, 2-MeC6H4, n-C5H11
MDO =
N COOH H
,
F3C
S
N
NH
H
N
N
H
OMe
F3C
Scheme 27. MDO-catalyzed tandem Michael additioncyclization reaction between 3-methyl-2-pyrazolin-5-one and benzylidene malononitriles.
Iravani et al. [48] synthesized tin sulfide nanoparticles (SnS-NPs) on activated carbon (AC) in an aqueous medium at room temperature and utilized the resulting nanocomposite as a heterogeneous Lewis acid catalyst for the one-pot three-component synthesis of 4H-pyrano[2,3-c]pyrazole derivatives in ethanol at 80 °C.( Scheme 28)
ArCHO
+ CN + CN
N N O
Ph
SnS-NPs @AC
EtOH, reflux at 80oC
Ar
O
N
CN
N
NH2
Ph
Ar = C6H5, 4-PhC6H4, 4-MeC6H4, 4-CHOC6H4, 4-MeOC6H4, 3,4,5-(MeO)3C6H2,
3-NO2C6H4, 4-NO2C6H4, 2-ClC6H4, 4-ClC6H4,3-ClC6H4, 2,4-(Cl)2C6H3,4-FC6H4,
-
OHC6H4, 2-OHC6H4, 4-BrC6H4, 4-CNC6H4, Naphthyl
Scheme 28. Synthesis of 4H-pyrano [2,3-c]pyrazole derivatives in ethanol at 80°C.
Krishnapillai et al. [49] synthesized a novel porphyrin-initiated amine-functionalized poly(BCMO) dendritic polymer and evaluated its catalytic performance in the one-pot, four-component solvent-free synthesis of pyrazolopyranopyrimidinones and pyranopyrazoles.( Scheme 29)
O
R
O O N
NH R
O O
CHO
CN CN
PBCMO-amine
EtO
+
R
((((, 10 min
NH2NH2
O
N NH
O
N N O
H H
H
PBCMO-amine ((((, 15 min
CN
N
O
H
-
NH2
R = H, 4-Br, 1-Napth, 4-Cl, 4-NO2, 4-OCH3, 2-Thiophene, Cinnamaldehyde, Anthraldehyde
Scheme 29. Preparation of pyrazolopyrano pyrimidinone and pyranopyrazole
Padmini et al. [50] demonstrated an efficient grinding-assisted protocol for the synthesis of dihydropyrano[2,3-c]pyrazole derivatives from acetylenic esters, hydrazine hydrate, aryl aldehydes, and malononitrile under solvent-free conditions, affording excellent yields.( Scheme 30)
COOEt
+
COOEt
NH2NH2.H2O +
CHO CN
+
R CN
L-Proline Solvent free,
Grinding for 10 min
R
EtOOC
CN
HN
R = Ph, 4-CH3Ph, 2-ClPh, 4-ClPh, 4-FPh, 2-furanyl, 2-thionyl, 4-CH2CH3Ph, 4-OHPh, 2-OCH3Ph,
3-OCH3,4-OHPh, 4-OCH3Ph, 4-NO2Ph
-
O NH2
Scheme 30.Prepration of dihydropyrano[2,3-c]pyrazole derivatives
Siddekha et al. [51] reported an efficient and practical protocol for the synthesis of pyranopyrazoles, employing imidazole as an organocatalyst in aqueous medium, affording high yields. (Scheme 31)
-
O
+ NH NH
H O + ArCHO +
Ar
CN imidazole CN
OEt
2 2.
2 CN
H2O, 80OC
N
2
-
O NH H
Ar = 4-OMePh, Ph, 4-NO2Ph, 4-ClPh, 4-OHPh, 2-OMePh, 3-OMePh, 3-NO2Ph, 3-ClPh, 2-Furan
Scheme 31. Preparation of pyranopyrazoles employing imidazole as an organocatalyst.
Paul et al. [52] developed a novel strategy utilizing uncapped SnO quantum dots (QDs) as catalysts for the one-pot multicomponent synthesis of substituted pyrano[2,3-c]pyrazole and spiro-2-oxindole derivatives in an aqueous medium.(Scheme 32)
R2CHO
R3 CN
+
R’
R1NHNH2 O O
O
OEt
R2
R3
N
N
R1
O NH2
Uncapped SnO2 QDs
H2O, rt
R = CN, COOEt
R’ = H, Ph, 4-NO2Ph
Ar = C6H5, 2-ClC6H4, 4-BrC6H4, 3-NO2C6H4,
4-CH3OC6H4, 3-CH3C6H4, thionyl, alkyl
Scheme 32. An efficient SnO quantum dot-catalyzed synthesis of pyrano[2,3-c]pyazole and spiro-2-oxindole derivatives.
Zhang etal. [53] developed a highly efficient and greener approach for the one-pot, four-component synthesis of pyranopyrazole derivatives using meglumine as an inexpensive, biodegradable and reused catalyst. (Scheme 33)
NC CN
O
O +
Carbonyl Compounds
R1 R2 CN
Meglumine EtOH-H2O, rt
N
O
H
N NH2
O
EtO
NH2NH2.H2O
HN
O O
R
O N
N N O
H H
R
CN
NH2
Carbonyl Compounds
R = H, CH3, F, Cl, Br, NO2
PhCHO, 2-OCH3C6H4CHO, 4-OCH3C6H4CHO, 4-CH3(CH2)2OC6H4CHO, 4-CH3(CH2)4OC6H4CHO, 2-OMe-5-CHMe2C6H3CHO, 2,3,4-(OMe)3C6H2CHO, 3-CH3C6H4CHO, 4-C(CH3)3C6H4CHO, 4-SCH3C6H4CHO, 4-OHC6H4CHO, 2-FC6H4CHO, 3-FC6H4CHO, 4-FC6H4CHO, 2-ClC6H4CHO, 3-ClC6H4CHO, 4-ClC6H4CHO, 2,4-Cl2C6H3CHO, 2-
NO2C6H4CHO, 4-NO2C6H4CHO, 3-CF3C6H4CHO, 4-CF3C6H4CHO, 4-((4-Nitrobenzyl)oxy) benzaldehyde, Furan-2-carbaldehyde, Thiophene-2-carbaldehyde, Pyridine-4-carbaldehyde, 1-Naphthaldehyde, Decanal, Cyclohexanecarbaldehyde
Scheme 33. Synthesis of pyranopyrazole derivatives using meglumine as a biodegradable and reused catalyst.
Babaie et al. [54] reported a four-component reaction involving hydrazine hydrate or phenylhydrazine, ethyl 3-alkyl-3-oxopropanoate, aldehydes, and malononitrile in the presence of a highly efficient heterogeneous nanosized magnesium oxide catalyst, leading to the formation of 6-amino-3-alkyl-4-aryl-5-cyano-1,4-dihydropyrano[2,3-c]pyrazole derivatives in excellent yields within a short reaction time.( Scheme 34)
ArCHO
CN CN
+
R’
RNHNH2 O O
O
OEt
O
R’
N
N
R
Ar
CN
NH2
nanosized MgO
CH3CN
Ar = C6H5, 2-ClC6H4, 4-ClC6H4, 3-BrC6H4, 4-NO2C6H4,
4-CH3OC6H4, C6H5, 4-CH3C6H4, 4-CH3OC6H4, 4-ClC6H4,
2,4-Cl2C6H3, 4-BrC6H4, 4-ClC6H4, 4-ClC6H4, 2,4-Cl2C6H3 R = H, Ph
R’ = CH3, Isopropyl
Scheme 34. Preparation of 6-amino-3-alkyl-4-aryl-5-cyano-1,4-dihydropyrano[2,3-c]pyrazole
derivatives.
CN
CN
+
NH2NH2
O O
R
L-proline (10 mol%)
CN
N
RCHO
O
OEt
H2O, 10-20 min, reflux
N
O
NH2
H
Mecadon et al. [55] demonstrated that L-proline (10 mol%) serves as an effective organocatalyst for the four-component synthesis of 6-amino-4-alkyl/aryl-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles in aqueous medium. ( Scheme 35)
R = C6H5, 4-CH3C6H4, 4-CH3O6H4, 2-ClC6H4, 4-ClC6H4, 3-BrC6H4, 4-BrC6H4 4-HOC6H4, 4-N(CH3)2C6H4, 2-NO2C6H4, 3-NO2C6H4,
4-NO2C6H4, 3-CH3O-4-HOC6H3, 3,4-(CH3O)2C6H3, 2,5-(CH3O)2C6H,
3,4,5-(CH3O)3C6H2, 1-Naphthyl, 9-Anthranyl, Butyryl
Scheme 35. A green approach for the synthesis of 6-amino-4-alkyl/aryl-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles in water.
Bora et al. [56] reported an environmentally friendly and efficient protocol for the four-component synthesis of dihydropyrano[2,3-c]pyrazoles in ethanol using a catalytic amount of the biocatalyst ANL (lipase from Aspergillus niger) at room temperature. ( Scheme 36)
R1
O
R
+ CN
CN
+ NH2NH2.H2O +
-
-
-
O
-
OEt
ANL, Ethanol
O
R R1
N
1-50 hr, 30o C
HN
CN NH2
R, R1 = H, alkyl, aryl
Scheme 36. An efficient biocatalytic synthesis of dihydropyrano[2,3-c]pyrazoles in ethanol using ANL derived from Aspergillus niger.
Karami et al. [57] examined first application of SSC (silica sodium carbonate) as a green, highly efficient and recyclable catalyst to synthesis of new 1,4-dihydropyrano[2,3-c]pyrazoles. ( Scheme 37)
CHO
+
CN
R + N
R
O
N
SSC (1 mol%)
O EtOH / H O CN
CN N
Ph
2
80oC
N
Ph
NH2
R = H, 2-Cl, 3-Br, 4-CH3, 4-OMe, 4-OH, 3-OEt, 4-CH(CH3)2, 4-Ph, 4-OCH2Ph
Scheme 37. An efficient synthesis of 1,4-dihydropyrano[2,3-c]pyrazoles using SSC as a recyclable green catalyst.
Farahi et al. [58] described tungstate sulfuric acid as an efficient and environmentally friendly catalyst for the synthesis of 6-amino-4-aryl-5-cyano-3-methyl-1-phenyl-1,4-dihydropyrano[2,3-c]pyrazoles via the reaction of 3-methyl-1-phenyl-2-pyrazolin-5-one, aromatic aldehydes, and malononitrile. (Scheme 38)
ArCHO
+ CN + CN
NN O
Ph
TSA (10 Mol%)
EtOH, Reflux
Ar
O
N
CN
N
NH2
Ph
Ar = C6H5, 2-Cl-C6H4, 3-Br-C6H4, 3-NO2-C6H4, 4-MeO-C6H4, 4-Me-C6H4, 4-Br-C6H4, 4-NO2-C6H4,
4-Iso-propyl-C6H4, 4-Bisphenyl-C6H4, 4,-Benzyloxy-C6H4 1-Naphthyl2,4-Cl2-C6H3, 3-OEt-4-HO-C6H3
Scheme 38. Preparation of 6-amino-4-aryl-5-cyano-1,4-dihydropyrano[2,3-c]pyrazoles via the reaction of 3-methyl-1-phenyl-2-pyrazolin-5-one, aromatic aldehydes, and malononitrile.
Remaily et al. [59] reported a one-pot four-component synthesis of a series of pyranopyrazoles using magnetically recoverable FeO nanoparticles as a heterogeneous catalyst. The reaction involved hydrazine hydrate, ethyl acetoacetate, aldehydes or ketones, and malononitrile, and was carried out in water at room temperature. ( Scheme 39)
R1
O + CN +
CN
R
O
NH2NH2 +
O
O OEt
Fe3O4-MNPs / H2O
O
R R1
N
rt, 1-5 min
HN
CN NH2
R1 = H, CH3, Ph
R = H, 2-NO2, 4-NO2, 2-Cl, 4-Cl, 2,4-DiCl, 4-F, 3-Br, 4-CH3, 4-OMe, 2-OMe, 2-OH, 4-OH, 3-OH, 4-N(Me)2, 2,5-di OMe, 3,4,5-tri OMe,
Scheme 39. Synthesis of pyranopyrazoles using magnetically recoverable FeO nanoparticles as a
heterogeneous catalyst in aqueous medium at room temperature.
O
N
Valiey et al. [60] developed an environmentally benign organocatalytic protocol for the synthesis of functionalized dihydropyrano[2,3-c]pyrazole and benzylpyrazolyl coumarin scaffolds using bio-based melamine-modified chitosan (Cs-Pr-Me) as a catalyst. ( Scheme 40)
CHO
CN
R + CN
O
+ R2NHNH2 + R2 = H, Ph
O
O OEt
Cs-Pr-Me
N
R2
R CN NH2
R = H, 2-NO2, 4-NO2, 2-Cl, 4-Cl, 2,4-DiCl, 4-F, 3-Br, 4-CH3, 4-OMe, 2-OMe, 2-OH, 4-OH, 3-OH, 4-N(Me)2
Scheme 40. Synthesis of dihydropyrano[2,3-c]pyrazole and benzylpyrazolyl coumarin scaffolds using Cs-Pr-Me as a catalyst.
O
N
Zolfigol et al. [61] reported the use of an environmentally benign [nano-FeO@SiO@(CH)-Imidazole-SOH]Cl catalyst for the efficient synthesis of 1,8-dioxooctahydroxanthenes and dihydropyrano[2,3-c]pyrazole derivatives under mild and solvent-free conditions. ( Scheme 41)
CHO
+
CN
R +
CN
N N O
Ph
[MNP-PIm-SO3H]Cl catalystN
Ph
R CN NH2
R = H, 2-NO2, 3-NO2, 4-NO2, 2-Cl, 3-Cl, 4-Cl, 2,4-DiCl, 4-F, 3-F, 4-Br, 2-Br, 4-CH3, 4-OMe, Naphthalene-2-
carbaldehyde, Naphthalene-1-carbaldehyde, 4-N,N-Dimethylaminobenzaldehyde, 2-Hydroxy-3,5-dichlorobenzaldehyde
Scheme 41. Efficient synthesis of 1,8-dioxooctahydroxanthenes and dihydropyrano[2,3-c]pyrazoles
using FeO@SiO@(CH)-imidazole-SOH]Cl.
Zhou et al. [62] have developed an efficient method for the synthesis of a diverse range ofdihydropyrano[2,3-c]pyrazoles using Lewis acid MorT as an eco-friendly catalyst.( Scheme 42)
O O
R -NHNH
+ R CHO +
CN MorT CN
+ 2
OEt
2 1 CN
EtOH-H2O,
Reflux
N
R2
NH2
O
R1
N
R1 = C6H5, 4-FC6H4, 2-ClC6H4, 4-ClC6H4, 2-BrC6H4, 4-BrC6H4, 2-HOC6H4, 3-HOC6H4, 3-CH3C6H4, 4-CH3C6H4, 3-CH3OC6H4, 4-CH3OC6H4, 4-CF3C6H4, 4-NO2C6H4, 4-iPr6H4, 4-(CH3)2NC6H4, 2-F-6-Cl-C6H3, 2,4-Cl2C6H3, 3,4-(CH3)2C6H3, 2,4,5-(CH3O)3C6H2, 3-C6H5O, 4-F-C6H3, CH3CH2CH2, (CH3)2CH, (CH3)3C, 2-Furan, 3-Pyridine
R2 = H, Ph
Scheme 42. Synthesis of dihydropyrano[2,3-c]pyrazoles using eco-friendly Lewis acid MorT catalyst.
Shahbazi et al. [63] demonstrated that the CoO@SiONH nanocomposite functions as a green, efficient, and robust heterogeneous nanocatalyst for multicomponent reactions involving ethyl acetoacetate, hydrazine hydrate, aldehydes, and malononitrile. This approach offers several advantages, including excellent yields, short reaction times, facile separation, catalyst recyclability, simple purification, and environmentally benign reaction conditions. Furthermore, the synthesized pyranopyrazole nanocomposites were evaluated for their antibacterial and antifungal activities against Gram-positive bacteria such as Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA), Gram-negative bacteria including Escherichia coli and Pseudomonas aeruginosa, as well as Candida albicans, using disc diffusion and minimum inhibitory concentration (MIC) methods. The results indicated that derivatives bearing (4-Br), (4-F), and (2,4-Cl) substituents exhibited the most significant activity against S. aureus. (Scheme 43)
O O +
NH2
H2N
O
Ar H
NC CN
Co3O4@SiO2-NH2 H2O/EtOH, RT
Ar
CN
N
O
H
N NH2
Ar = 4-BrPh, 4-OMePh, 4-ClPh, 4-OHPh, 4-NO2Ph, 4-CH3Ph, 4-SCH3Ph, 3-NO2Ph, 2-ClPh, 4-FPh, 2,4-diClPh, 2-NO2Ph, 4-N(CH3)2Ph, 4-CNPh
Scheme 43. Synthesis of pyranopyrazoles using CoO@SiONH nanocomposite as a green
heterogeneous catalyst.
Xingtian Huang et al. [64] developed a novel, efficient, and environmentally friendly protocol employing BSA as a reusable biocatalyst for the synthesis of a wide range of pyrano[2,3-c]pyrazole derivatives. This method offers several advantages, including eco-compatibility, mild reaction conditions, shorter reaction times, high yields, and operational simplicity. ( Scheme 44)
CHO +
NH2.H2O + + O O
R
BSA, 45oC CN
2
N
R H2N
NC CN OEt
90% aq. EtOH
-
O NH H
R = 4-ClPh, 2-ClPh, 2,4-diClPh,4-BrPh, 2-BrPh, 3-BrPh, 4-NO2Ph, 3-NO2Ph, 2-NO2Ph, 4-MePh, 4-OMePh, 4-OHPh,
Ph, 3-OMe,4-OHPh, 4-NMe2 Ph, O O O O O O
O CHO
N O
H CHO
Scheme 44. Synthesis of pyrano[2,3-c]pyrazole derivatives using BSA as a reusable biocatalyst
Fatahpour et al. [65] reported a simple and environmentally friendly method for the cascade synthesis of biologically significant dihydropyrano[2,3-c]pyrazole scaffolds, employing Ag/TiO nano-thin films as a durable and recyclable catalyst in a one-pot multicomponent process. (Scheme 45)
CHO
+
NH2.H2O + + O O
R
EtOH:H2O (2:1) 70oC, CN
O
H
Ag/TiO2 nano-thin films N
R H2N
NC CN OEt
-
NH2
R= H,4-F, 4-Cl, 2-Cl, 2,4-diCl, 4-Br, 3-Br, 4-NO2, 2-NO2, 4-Me, 4-OH, 3-OMe-4-OH,
Scheme 45. Preparation of dihydropyrano[2,3-c]pyrazoles employing Ag/TiO nano-thin films as an eco-friendly and reusable catalyst.
Hajizadeh et al. [66] synthesized a novel, environmentally benign, stable, magnetically retrievable, and reusable poly(ethyleneimine)-functionalized magnetic halloysite nanotube nanocomposite (FeO@HNTs-PEI). The catalytic performance of this material was evaluated in the synthesis of dihydropyrano[2,3-c] pyrazole derivatives. The nanocomposite exhibits notable features, including nanotubular morphology, high thermal stability, well-defined crystalline structure, and magnetic properties. ( Scheme 46)
CHO
NH H O + + O O
R
O
N
Fe3O4-Halloysite-PEI CN
+
R H2N
2. 2
NC CN
OMe
EtOH, 400C
HN
NH2
R= H,4-Cl, 4-Br, 3-Br, 4-NO2, 3-NO2, 4-Me, 4-OH, 4-OMe-4-OH, 4-CN, 2-OH-5-Br, 3,4,5-OMe, Furane
Scheme 46. A green and sustainable approach for the synthesis of dihydropyrano[2,3-c]pyrazoles
using FeO@HNTsPEI as a reusable magnetic catalyst.
Balaskar et al. [67] introduced an alternative route for the synthesis of 1,4-dihydropyrano[2,3-c]pyrazol-5-yl cyanide derivatives using triethylammonium acetate (TEAA) as a catalyst in a green reaction medium. The method offers several advantages, including solvent-free conditions, low cost, ease of handling, and recyclability of the catalyst. ( Scheme 47)
N
R + +
N
O TEAA N
N
N
O
R
N
N
NH2
Stirring /R.T.
Scheme 47. Synthesis of 1,4-dihydropyrano[2,3-c]pyrazol-5-yl cyanide derivatives using TEAA as catalyst.
ArCHO
RNHNH2
CN
CN
+
R’
O
O
Ni0.5Zn0.5Fe2O4@ Hap-Cs2CO3
O
OEt
H2O/ EtOH
O
R’
Ar
CN
N
N
NH2
R
Moeinpour et al. [68] hadreported Ni0.5Zn0.5Fe2O4@ Hap-Cs2CO3 as a basic green nanocatalyst for the new efficient and green synthesis of 5-cyano-1,4-dihydropyrano[2,3-c]pyrazoles at room temperature in water/ethanol. ( Scheme 48)
R = H, Ph
R’ = CH3, Isopropyl
Ar = C6H5, 3-BrC6H4, 3-ClC6H4, 4-CH3OC6H4, 4-NO2C6H4, 4-ClC6H4,
4-BrC6H4, 4-CH3C6H4, 3-NO2C6H4, C6H5, 4-MeC6H4, 4-CH3OC6H4,
4-ClC6H4, 4-BrC6H4 4-ClC6H4, 4-Cl2C6H3
Scheme 48. Prepration of 5-cyano-1,4-dihydropyrano[2,3-c]pyrazoles using Ni.Zn.FeO@HApCsCO as a green nanocatalyst
CN
CN
+
NH2NH2
O O
R
RCHO
Ni0.5Cu0.3Zn0.2Fe2O4
EtOH
CN
N
N
O
O
OEt
NH2
H
Mandle et al. [69] developed magnetically recoverable Cu2+ doped Ni-Zn Nano Ferrite catalyst for efficient one pot multicomponent synthesis of Pyrano (2,3-C) Pyrazoles from ethyl acetoacetate, hydrazine hydrate, aromatic aldehydes and malononitrile. (Scheme 49)
R = Ph, 4-OCH3, 4-ClPh, 4-OHPh
Scheme 49. An efficient synthesis of pyrano[2,3-c]pyrazoles using Cu²-doped NiZn nano ferrite as an efficient catalyst.
Pandit et al. [70] reports DABCO as an efficient catalyst to promote rapid one-pot multicomponent reaction between aromatic aldehydes, malanonitrile, ethyl acetoacetate and hydrazine hydrate in aqueous media to give substituted pyrano[2,3-c]pyrazole. (Scheme 50)
-
CN
Ar
O O DABCO, H2O, CN
Ar H
+ + NH2NH2.H2O + CN
OEt
REFLUX
HN
-
O NH2
Scheme 50. Synthesis of substituted pyrano[2,3-c]pyrazoles via rapid one-pot multicomponent reaction in aqueous medium.
Dandia et al. [71] reports on-water chemoselective synthesis of pyranodipyrazolones via the reaction of various carbonyl compounds with 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one using Ag NPs decorated reduced graphene oxide (Ag NPs/GO) composite which is a facile, leach free and easily recyclable heterogeneous catalyst at room temperature. (Scheme 51)
Ph
-
O N
Ag NP’s/ GO composite
Ph Ph
+ N
CHO R O
O
N H
R
O
N
N
OHC
N N
O
O
S
CHO
R= H, OMe, Me, Cl, Br, F, No2
R= H, Cl, Br,
Me, No2 N
H
Scheme 51. Synthesis of pyranodipyrazolones using Ag NPs/rGO as a catalyst.
Subrahmanyam et al. [72] designed and utilized a highly effective and costeffectiveprotocol for the synthesisofpyranopyrazole analogues via one-pot multi-component reactionusingiron-doped heteropoly acid [(Fe5(PW10V2O40)3] (FePWV) as an efficient catalyst at room temperature andethanol as the solvent. (Scheme 52)
-
-
CN
R
O O FePWV, EtOH, CN
+
R H CN
+ NH2NH2.H2O +
OEt
R.T., 15 min.
HN
-
O NH2
R = 2,3-OMe-C6H3, 2,4,6-OMe-C6H2, 2,4-OMe-C6H3, 2-Br-C6H4, 2-Cl-C6H4, 2-NO2-C6H4, 3-OMe-C6H4, 4-Cl-C6H4, 3-OH-C6H4, C6H5, C4H4S, C4H4O
Scheme 52. Synthesis of pyranopyrazole analogues via one-pot multicomponent reaction using FePWV as an efficient catalyst.
Mirjalili et al. [73] has been reported an efficient approachfor the synthesis of pyranopyrazoles (PPzs) using ball milling and metal-free nano-catalyst (Nano-silica/aminoethylpiperazine [AEP]), under solvent-free conditions. (Scheme 53)
O
Ar H
CN
+ + NH2NH2.H2O + CN
-
O Nano-SiO2 / AEP OEt Ballmilling,
Sol. Free, R. T.
Ar
CN
HN
N O NH2
Ar = 4-NO2-C6H4, 4-Cl-C6H4, 2,4-diCl-C6H3, 4-F-C6H4, 4-Br-C6H4, 3-OMe-4-OH-C6H3, 4-OH-C6H4,
4-CH3-C6H4, C6H5, 3,4-diOH-C6H3, Furan-2-Carbaldehyde, Pyrole-2-Carbaldehyde, 2-OMe-C6H4
Scheme 53. Synthesis of pyranopyrazoles using Nano-silica/AEP as a metal-free nanocatalyst under solvent-free ball-milling conditions
NH2
R = H, 4Cl, 4-NMe2, 4-SMe, 4-OH, 2-Cl, 4-Me, 4-Br, 4-NO2, 4-OMe, 3-OMe, 4-OH, 3-NO2, 2-Furyl
Scheme 21. Peparation of dihydropyrano[2,3-c]pyrazoles catalyzed by zinc oxide nanoparticles.
Shrinivas et al. [42] demonstrated an efficient green approach for the one-pot four-component synthesis of pyranopyrazoles in a non-aqueous medium using bakers yeast at room temperature under neutral pH conditions. (Scheme 22)
CHO
R
CN O
+ NH2NH2 + + CN
O
OEt
Baker’s Yeast EtOH, 34 hrs, rt
N
NH O
R
CN NH2
R = H, 4-NO2, 4-Cl, 4-Me, 4-OMe, 4-N(Me)2, 2-Cl, 3-NO2,
4-(2-chloroquinolin), 4-CF3, 4-F, 2,3,4-(OMe)3, 2-OH, 4-Et
Scheme 22. Prepration of pyranopyrazoles in non-aqueous medium using a bakers yeast
Mohamadpour et al. [43] developed a green and facile saccharin-catalyzed method for the convenient one-pot synthesis of pyranopyrazole derivatives via a multicomponent tandem Knoevenagelcyclocondensation reaction. (Scheme 23)
R1CHO + NH2NH2.H2O +
CN Saccharin (25 mol%) CN EtOH, 60oC
O O
OEt
O
O
O
R1
N
O
N H
O
-
-
-
Using energy resources
Mengnisa Seydimemet et al. [74] discussed an environmentally benign simple and novel four component synthesis of coumarin based dihydropyrano[2,3-c] pyrazoles by the reaction of -dicarbonyl compound, phenylhydrazine, aromatic aldehydes and malononitrile in ethanol in presence of l-proline as catalyst under ultrasonic irradiation. (Scheme 54)
O
O
+
NC
NH2
L-proline (10 mol%) EtOH
Sonication )))))
r.t., 50 min, 78-90 %
O
Ar
N
N
R
O
O
O O
O
Ph
ArCHO
R
PhNHNH2
NC CN
R = OH, OCH3, N(Et)2
Ar = 2,4-Cl2C6H3, 2,3-Cl2C6H3, 2-BrC6H4,C6H5, 2-ClC6H4, 3-NC5H4, 4-BrC6H4, 4-ClC6H4,
Scheme 54. Synthesis of coumarin-based dihydropyrano[2,3-c]pyrazoles using L-proline in ethanol under ultrasonic irradiation.
Mohamadpour et al. [75] developed an atom economic and facial synthesis of dihydropyrano[2,3-c]pyrazole via multi-component tandem Knoevenagel cyclo-condensation reaction. ( Scheme 55)
O
O
O
R1
Saccharin (25 %)
H O EtOH, 60oC
+
R1
CN
N
N O NH2
CN H
NH2NH2.H2O CN
Scheme 55. Synthesis of dihydropyrano[2,3-c] pyrazoles via atom-economical multicomponent Knoevenagel cyclo condensation.
Khoobi et al. [76] designed a novel series of tacrine-based compounds consisting pyrano[2,3-c]pyrazole substructure. The poly-functionalized hybrid molecules were efficiently synthesized through multi-component reaction and subsequent Friedländer reaction between the obtained pyrano[2,3-c]pyrazoles and cyclohexanone using ultrasonic irradiation. (Scheme 56)
CN
CN
NH2NH2.H2O
O O
ArCHO
O
OEt
)))), (S) – proline
H2O/ EtOH,rt, (10-35 min)
Ar
CN
+
N
N
H
O
NH2
Ar
NH2
N
N
H
O N
O
AlCl3, ClCH2CH2Cl
Ar = Naphthalen-1-yl, Thiophen-2-yl, 4-tolyl, 2-F Ph, 4-F Ph, 3-NO2Ph, 4-MeOPh, 2-MeOPh, 2,5-diMeOPh, 3,4-diMeOPh, 3,4,5-triMeOPh,
Scheme 56. Synthesis of tacrine-based pyrano[2,3-c]pyrazole hybrids via multicomponent and Friedländer reactions under ultrasonic irradiation.
-
Misllaneous condition
-
Pawar et al. [77] developed a green protocol for the synthesis of pyranopyrazoles using energy-efficient microwave irradiation or room-temperature stirring in the presence of ammonium chloride as a mild, cost-effective, and eco-friendly catalyst, with water serving as the green solvent. ( Scheme 57)
O O
CHO
O
+ R
R
NH4Cl, H2O
CN
RT or mw
H2N
NH2.H2O
NC CN
N
O
H
N NH2
R = H, 4-Cl, 2-Cl, 4-OH, 2-Cl, 4-Br, 4-NO2,3, 4-diOMe, 3-OMe, 4-OH, 3-NO2, 4-F
Scheme 57. Preparation of pyranopyrazoles employing NHCl as an eco-friendly catalyst in aqueous medium under microwave or ambient conditions.
Thakare et al. [78] developed a novel magnetically recoverable CoFeO@SiOHClO nanocatalyst for the synthesis of pyranopyrazoles and their derivatives under solvent-free conditions using microwave irradiation. (Scheme 58)
CN Ar
CN CoFe2O4@SiO2-HClO4 CN
+ N N O NN
ArCHO H
mw, 100oC, Solvent-free Condition
H O NH2
Ar =C6H5, 3-NO2C6H4, 4-ClC6H4, 4-OHC6H4, 3-OC2H5,4-OH-C6H4, 4-OCH3-C6H5, 3,4-OCH3-C6H4, 3,4,5-OCH3-C6H3, 4-
CH3-C6H5, 4-(CH3)2CH-C6H5, 4-(CH3)2N-C6H5, 2-furyl-C6H5, 2-Thiophene-C6H5, 3-Indolyl-C6H5, Terepthalaldehyde
,
Scheme 58. Microwave-assisted, solvent-free synthesis of pyrano[2,3-c]pyrazoles employing
CoFeO@SiOHClO as a recyclable magnetic nanocatalyst.
-
Conclusion
This review summarizes recent green and efficient strategies reported for the synthesis of pyranopyrazole derivatives during the period from 2011 to 2025. The focus is on environmentally friendly protocols, including sonochemical methods, microwave-assisted techniques, solvent-free conditions, and the use of green solvents, particularly water. In addition, the application of heterogeneous catalysts such as nanocatalysts, heteropoly acids, and ionic liquids has significantly enhanced the accessibility of these important heterocyclic compounds. Pyranopyrazole derivatives have been reported to exhibit a wide range of biological activities, including antibacterial, antifungal, antioxidant, anti-inflammatory, anti-ulcerogenic, analgesic, anticonvulsant, and insecticidal properties. Structural characterization of these compounds has been carried out using spectroscopic and analytical techniques such as NMR, mass spectrometry, IR spectroscopy, elemental analysis, and X-ray diffraction to confirm their structures and the position of hydrogen atoms in the pyrazolone ring.
-
Acknowledgments
The authors gratefully acknowledge the support and encouragement provided by the Principal, Head of the Department, and teaching staff of S. S. Jain Subodh P.G. (Autonomous) College, Jaipur. J. Jain acknowledges the financial assistance provided by the University Grants Commission (MHRD), New Delhi, under the Start-Up Grant scheme (Award No. 30-572/2021(BSR)).
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Conflict of interest
The authors declare that there are no conflicts of interest.
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