Microwave Assisted Synthesis of a Novel Schiff Base Scaffolds of Pyrazole Nuclei: Green Synthetic Method

Abstract

Aim: The research aims to develop a sustainable microwave-assisted scheme for Synthesizing 5-(benzylidene amino)-1-phenyl-1H-pyrazole-4-carbonitrile congeners. Background: 5-(benzylideneamino)-1-phenyl-1H-pyrazole-4-carbonitrile scaffolds are novel molecules having various pharmacological activities such as neurodegenerative, anti-microbial, anticancer. Schiff base congeners are considered as efficient pharmacophores for research. These activities are due to the presence of azomethine (CH=N) group in the Schiff base compounds. Objectives: To synthesise different novel Schiff base compounds of pyrazole nuclei by green chemistry with a decent yield. Methods: The 5-(benzylideneamino)-1-phenyl-1H-pyrazole-4-carbonitrile scaffolds were prepared by two-step reactions. Both steps were microwave-assisted. The first step was to synthesize 5- amino-1-phenyl-1H-pyrazole-4-carbonitrile as an intermediate compound. This compound was synthesized by using phenyl hydrazine and 2-(ethoxymethylene)malononitrile. The temperature, pressure, and time required for this reaction were 102°C, 300W, and 45 minutes respectively. In the second step, the final Schiff base congeners were attained by reacting this compound with several aromatic aldehydes. The yield, reaction condition, and time consumption were all acceptable for the green synthetic methods rather than the conventional schemes. Results: The microwave-assisted method was more efficient. The reactions were less timeconsuming, and the overall yield of the all-synthesized compounds was 75-82%. Different spectroscopic methods characterized the synthesized congeners. The IR peak is considered the main functional group (azomethine) at 1611 cm-1 wavelength. Conclusions: This microwave-assisted synthetic scheme thus appears more environmentally due to a significant reduction in organic solvents, resulting in fewer hazardous residues. Using this scheme, we prepared different Schiff base congeners with satisfactory chemical yields.