Ugi-Functionalized Magnetic Carbon Quantum Dots: an Efficient and Environmentally Friendly Catalyst for the Synthesis of 1,4-Dihydropyridines

This research presents the synthesis of Ugi-modified magnetic carbon quantum dots (MCQD-AP-Ugi) via a one-pot process to improve functionality. For the first time, the Ugi reaction was utilized to modify the surface of carbon quantum dots (CQDs), thereby creating an environmentally friendly hydrogen-bonding nanocatalyst. The CQDs were produced using a hydrothermal method with citric acid and urea, then coated onto magnetic Fe₃O₄ nanoparticles. The surface was further modified with 3-aminopropyltriethoxysilane (APTES) to produce amine-modified MCQD (MCQD-AP). A one-pot Ugi four-component reaction (Ugi-4CR) was conducted with MCQD-AP, glacial acetic acid, tert-butylisocyanide, and 2-nitrobenzaldehyde. Characterization of the catalysts utilized various analytical techniques, including X-ray diffraction (XRD), vibrating sample magnetometer (VSM), dynamic light scattering (DLS), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDX), EDS mapping, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and elemental analysis. The catalytic performance of MCQD-AP-Ugi was evaluated as a hydrogen bonding catalyst for producing 1,4-dihydropyrimidines (1,4-DHPs), achieving yields of 80 %–97 % at 40 °C over 10–25 min. This method offers several advantages, such as operating under milder reaction conditions, achieving higher product yields, and allowing for easy catalyst separation with an external magnet, all while requiring shorter reaction times compared to traditional methods. These factors improve the efficiency, reliability, and practicality of the synthetic method, highlighting MCQD-AP-Ugi's potential as a versatile catalyst for chemical reactions. Its capacity for reuse over nine cycles demonstrates its sustainability and cost-effectiveness, making it well-suited for large-scale production. Utilizing the Ugi-4CR to modify magnetic carbon quantum dots offers several advantages, including a simplified one-pot process, a variety of functional groups such as Carboxamide [-C(O)NH–], reduced costs, and lower pollution levels. Furthermore, the design of the catalyst, characterized by the incorporation of Carboxamide, not only enhances catalytic activity but also promotes homogeneity, thereby improving overall performance.