Regioselective Synthesis, Spectroscopic Characterization, and Computational Chemical Study of Spiro[Indoline-3,4’-Pyrazolo[3,4-b] Pyridine Derivatives as Agrochemical Agents

Herein, new four-component domino reactions are described and utilized to synthesize spiro[indoline-3,4’-pyrazolo[3,4-b]pyridine derivatives via one-pot reaction. Different hydrazine derivatives such as hydrazine hydrate, methyl hydrazine, and phenylhydrazine were allowed to react with active methylene precursors (CH₂CN) as malononitrile, ethyl cyanoacetate, isatin, and 1,3-dicarbonyl compounds in the presence of (+)-camphor-10-sulfonic acid (CSA) as the acid catalyst under microwave condition using water as the solvent. Two and three fused heterocyclic rings were obtained in a single synthetic operation with a facile work-up and less waste generation due to the absence of extraction and purification steps. Structural features of the obtained compounds were confirmed by utilizing elemental analyses, mass spectrometry, ¹H-NMR, and ¹³C-NMR microanalyses. Insecticidal assessments for some of the synthesized pyrazole derivatives against the cotton leafworm <i>Spodoptera littoralis</i> were conducted. In addition, fungicidal activities against <i>Rhizoctonia solani</i> and <i>Fusarium solani</i> soil-borne fungi were also performed. The tested compounds showed poor insecticidal activity compared with the standard insecticide chlorpyrifos ethyl. Meanwhile, they showed remarkable fungicidal activity against tested pathogens. Analysis of the fungicidal study indicated that <i>R. solani</i> fungus was found to be more sensitive to the tested compounds than <i>F. solani</i> fungus. Some pyrazole derivatives particularly possessed close or even higher fungicidal activities than the standard fungicide Pencycuron (Monceren 25%WP). The density functional theory was then applied to explore the structural and electronic characteristics of these materials.