Biochar: a robust and renewable basic carbocatalyst for sustainable synthesis of diversified spirooxindoles

In this study, biochars have been utilized as reusable basic carbocatalysts to get quick access to multi-functionalized spirooxindoles using a sustainable approach. Various organic wastes and manure sources were pyrolyzed into corresponding biochars through a pyrolysis-carbonization process. Compelling evidence supporting the basic nature of the synthesized biochars was provided through the potentiometric titration analysis and chemical characteristics. These analyses substantiated the pronounced alkalinity of the biochar derived from cow manure pyrolyzed at 600 °C (CB600), positioning it as the optimal carbocatalyst in this investigation. The catalytic performance of the biochars was subsequently assessed in the three-component one-pot synthesis of spirooxindoles under benign reaction conditions, with CB600 demonstrating superior activity as a result of its elevated total basicity. This breakthrough achievement clarifies the critical role of basic biochars in Knoevenagel condensation-based reactions, highlighting their unprecedented utility for facilitating multicomponent synthesis of diverse heterocyclic compounds.