Pumice-based sulfonic acid: a sustainable and recyclable acidic catalyst for one-pot synthesis of pyrazole anchored 1,4-dihydropyridine derivatives at room temperature

In the present investigation, we have developed an efficient and eco-friendly protocol for the synthesis of pyrazole anchored 1,4-dihydropyridine analogs using pumice-based sulfonic acid (pumice@SO3H) as a recyclable solid acid catalyst under simple stirring at room temperature. The present protocol proceeded smoothly with 1,3-diaryl pyrazole-4-carbaldehydes, ethyl acetoacetate, and NH4OAc in ethanol as a solvent with excellent yield. The pumice-based sulfonic acid catalyst is easily prepared from naturally occurring pumice by simple agitation with chlorosulfonic acid. The key features of this catalyst are its heterogeneous nature, high porosity, non-corrosive and non-toxic nature, recyclability, stable and highly efficient at room temperature. The application of this catalyst makes the protocol more environmentally benign.