Metal-free cascade reactions for one-pot tetrahydroquinoxaline construction through nitroarene reduction and imine hydrogenation with water

A metal-free one-pot cascade process involving reduction of nitroarenes, cyclization, and sequential hydrogenation of imines with B2cat2 and water was developed to construct dihydroquinoxalinones and tetrahydroquinoxalines directly from readily available 2-nitroanilines or o-dinitrobenzenes with α-ketoesters and α-diketones. This strategy provides various dihydroquinoxalinones and tetrahydroquinoxalines in good to excellent yields and tolerance to many functional groups. Mechanism studies by control experiments and density functional theory (DFT) calculations show that this cascade procedure involves the deoxygenative reduction of nitroarenes, the Maillard reaction, and hydrogenation to produce dihydroquinoxalinones and tetrahydroquinoxalines. This method aims to reduce the environmental impact while maintaining high yields and selectivity for both nitroarene reduction and the synthesis of dihydroquinoxalinones and tetrahydroquinoxalines.