Accessing 2-aryl quinolines via AIBN/dithionite-promoted sequential oxidative radical α-hydroxymethylation/cyclization of imine employing ethanol as ethyne surrogate

Abstract

Ethanol, rather than dioxane, vinylene carbonate, or acrylic acid, acted as the ethyne surrogate in sodium hydrosulfite/AIBN-promoted multicomponent reactions (MCRs) involving amines and aldehydes toward 2-aryl quinolines under O₂ atmosphere. This procedure likely started with the formation of α-hydroxy carbon centered nucleophilic radical in the presence of sodium dithionite and O₂. Then the reaction proceeded with sequential oxidative radical α-hydroxymethylation of in situ-formed imine, elimination of one equivalent of H₂O, and 6 π electrocyclization followed by aromatization. As such, this metal-free procedure represents a sustainable and efficient pathway to access a series of 2-aryl quinolines.