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. 2019 Mar 6;4(3):4955-4962.
doi: 10.1021/acsomega.8b02013. eCollection 2019 Mar 31.

Serendipitous Formation of 2 H-Pyrazolo[3,4- d]pyridazin-7(6 H)-ones from 3-Arylsydnones

Mahadev N Kumbar  1 , Saba Kauser J Shaikh  1 , Ravindra R Kamble  1 , Praveen K Bayannavar  1 , Atulkumar A Kamble  1 , Raveendra K Hunnur  2
Affiliations

Serendipitous Formation of 2 H-Pyrazolo[3,4- d]pyridazin-7(6 H)-ones from 3-Arylsydnones

Mahadev N Kumbar et al. ACS Omega. .

Abstract

Fused nitrogen heterocyclesnamely, pyrazolo[3,4-d]pyridazin-7(6H)-ones have been obtained by exploiting the 1,3-dipolar nature of N-arylsydnones, from hydrazones of 3-aryl-4-acetylsydnones via the Vilsmeier-Haack strategy. Facile intramolecular nucleophilic addition followed by CO2 elimination under reflux or upon microwave irradiation was presented. Plausible mechanisms for the formation of the title compounds are proffered. Structure confirmatory evidence came from single-crystal X-ray crystallography.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1. Tautomeric Structures of Pyrazolo[3,4-d]pyridazine
Scheme 2
Scheme 2. Previous Reported Synthesis of Pyrazolopyridazines/ones (Yield = <70%)
Scheme 3
Scheme 3. Synthetic Route for Title Compounds 7a–l
7a: Ar = −C6H5, Ar′ = −C6H5; 7b: Ar = −C6H5, Ar′ = 4-Cl–C6H4; 7c: Ar = −C6H5, Ar′ = 4-Br–C6H4; 7d: Ar = 4-CH3O–C6H4, Ar′ = −C6H5; 7e: Ar = 4-CH3O–C6H4, Ar′ = 4-Cl–C6H4; 7f: Ar = 4-CH3O–C6H4, Ar′ = 4-Br–C6H4; 7g: Ar = 4-Cl–C6H4, Ar′ = −C6H5; 7h: Ar = 4-Cl-C6H4, Ar′ = 4-Cl–C6H4; 7i: Ar = 4-Cl–C6H4, Ar′ = 4-Br–C6H4; 7j: Ar = 4-H3C–C6H4, Ar′ = −C6H5; 7k: Ar = 4-H3C–C6H4, Ar′ = 4-Cl–C6H4; 7l: Ar = 4-H3C–C6H4, Ar′ = 4-Br–C6H4.
Scheme 4
Scheme 4. Plausible Mechanism for Formation of Pyrazolo[3,4-d]pyridazin-7(6H)-ones 7a–l
Figure 1
Figure 1
ORTEP structure of compound 7d (displacement ellipsoids are drawn at the 50% probability level) and packing structure of compound 7d.
See this image and copyright information in PMC

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