A novel micro-flow system under microwave irradiation for continuous synthesis of 1, 4-dihydropyridines in the absence of solvents via Hantzsch reaction

Wei He^a,b, Zheng Fang^b, Kai Zhang^b, Tao Tu^a, Niuniu Lv^b, Chuanhong Qiu^b, Kai Guo^b,c

• ^a Department of Chemistry, Fudan University, No. 220 Handan Road, Shanghai, 200433, PR China
• ^b College of Biotechnology and Pharmaceutical Engineering, Nanjing Technology University, No. 30 Puzhu South Road, Nanjing, 211816, PR China
• ^c State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Technology University, No. 30 Puzhu South Road, Nanjing, 211816, PR China

γ-Fe2O3 nanoparticles were synthesized in the valve-assisted micromixer. The resulting nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM). In the packed bed flow reactor, the investigation concerning the comparison of different heating methods demonstrated that microwave irradiation displayed the best reaction efficiency compared with air heating and oil-bath heating. A novel micro-flow system under microwave irradiation was designed and employed in the condensation of aldehyde, ethyl acetoacetate and ammonia. Under optimized conditions, Hantzsch reaction conducted well, resulting in a yield of 98.7% and excellent selectivity. In addition, this novel process worked well for other substrates.

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