Organic Electrosynthesis: A Promising Alternative Methodology for the Synthesis of Nanosized Particles of Pyrans

An electrochemical strategy is presented herein for the synthesis of pyran nanoparticles by an electro-generated base from a propanol anion in a one-pot, three-component reaction. This reaction includes the condensation of isatin or an aromatic aldehyde, ethyl acetoacetate, and malononitrile in propanol in the presence of sodium bromide as an electrolyte in an undivided cell. The effects of current, temperature, solvent, time and anode type were studied. The optimized current and temperature is 20 mA cm-2 and 25 °C for the synthesis of spiropyrans nanoparticles, and is 40 mA cm-2 and 50 °C for producing nanosized particles of 4H pyrans. The formation of propanol anions on the surface of the cathode-generated malononitrile anion proceeded by Knoevenagel condensation which is followed by a Michael addition and ended by the intramolecular ring-closing strategy. The products were characterized after purification using infrared spectroscopy (IR), 1H and 13C nuclear magnetic resonance, scanning electron microscope (SEM), and dynamic light scattering (DLS). The proposed method produces pyran nanoparticles directly from initial compounds in a safe and mild condition.