Direct Synthesis of 6H-Chromeno[3,4-b]quinolin-6-ol Derivatives from Substituted 3-Nitro-2H-chromenes and 2-Nitrobenzaldehydes Mediated by Fe/AcOH System

Abstract

An efficient iron/acetic acid system-mediated reductive cyclization reaction of substituted 2-aryl-3-nitro-2H-chromenes with substituted 2-nitrobenzaldehydes for the synthesis of 6-aryl-6H-chromeno[3,4-b]quinolines was developed. This reaction involves the sequential reduction, hydrolysis, aldol condensation, intramolecular addition, and the nucleophilic addition of substituted 2-aryl-3-nitro-2H-chromenes with substituted 2-nitrobenzaldehydes to give the corresponding 6H-chromeno[3,4-b]quinolines. This transformation provides a straightforward synthetic protocol for constructing substituted 6H-chromeno[3,4-b]quinoline derivatives. The structures of three typical products were confirmed by X-ray crystallography.