A summary of microwave-assisted pyrano[2,3-c]pyrazole and spiropyrano[2,3-c] pyrazole synthesis.

Product	Reactants	Catalyst	Solvent	Method employed	Reaction time	Yield	Ref.
Indol-3-yl substituted pyrano[2,3-c]pyrazoles	(a) Three-component system: 2-phenyl-1H-indole-3-carbaldehydes, malononitrile, and 3-methyl-1H-pyrazole-5(4H)-one	Piperidine	Ethanol	Conventional reflux	2–2.5 h	59–74%	Kathrotiya et al.33
	(b) Four-component system: 2-phenyl-1H-indole-3-carbaldehydes, ethyl acetoacetate, malononitrile, and hydrazine hydrate	NaOH		Microwave	5–6 min	68–84%
Quinolylpyrano[2,3-c]pyrazoles and indolylpyrano[2,3-c]pyrazoles	Three-component system: indole- or quinol carbaldehyde, pyrazolone, and enol ethers	—	Triethyl-ammonium acetate (TEAA)	Microwave	6–12 min	82–92%	J. Parmar et al.34
Substituted pyrano[2,3-c]pyrazoles	Four-component system: acetoacetic ester, hydrazine hydride, aldehydes, and malononitrile	l-Tyrosine	H2O–ethanol	Microwave	5–8 min	86–94%	D. Rupnar et al.36
Pyrano[2,3-c]pyrazoles	Four-component system: ethyl acetoacetate, hydrazine, malononitrile, and aldehydes	Triethylamine	Ethanol	Conventional reflux	1–4.5 h	68–95%	P. Shukla et al.35
				Microwave	2–5 min	57–88%
Pyrano[2,3-c]pyrazoles	Four-component system: substituted aldehyde, 2,4-dinitrophenyl hydrazine, ethyl acetoacetate, and malononitrile	SnCl2	Methanol	Conventional reflux	1.5–2 h	50–80%	S. Vasava et al.37
			Solvent-free	Microwave	10–20 min	60–88%
4H-Pyrano[2,3-c] pyrazoles	Four-component system: ethyl acetoacetate, hydrazine hydrate, malononitrile, and aromatic aldehydes	Potassium t-butoxide (base)	Methanol	Microwave	2–5 min	80–90%	Yallappa et al.38