Chitosan-SO3H: An Efficient and Biodegradable Catalyst for the Green Syntheses of 1,4-dihydropyridines

Nowadays, biodegradable polymers are attractive candidates to create highperformance and environmentally friendly catalytic species. Polymeric materials for catalytic processes must be biocompatible and preferably biodegradable. Sulfonic acid functionalized chitosan (CS-SO3H) was easily prepared by the reaction of chitosan with chlorosulfonic acid. CS-SO3H is found to catalyze the Hantzsch reaction to produce 1,4-dihydropyridines (1,4DHPs) via the condensation reaction of aldehydes, ethyl acetoacetate and ammonium acetate with high efficiency. The use of heterogeneous and biodegradable CS-SO3H makes this synthetic methodology quite simple, more convenient and economically viable compared to homogeneous chitosan catalyzed method. CS-SO3H with nanopore structure, with encapsulated reactants may be applied as a nanoreactor for this chemical reaction. The main advantages of this protocol are the eco-friendly catalyst system, heterogeneous nature, freedom from organic solvents, and ease of the workup procedure. The present method can be used for the green design of heterocyclic compounds, and has potential for biological applications and drug discovery.