Synthesis of Functionalized Quinolines from 4‐(o‐Nitroaryl)‐Substituted 3‐Acyl‐4,5‐Dihydrofurans: Reductive Cyclization and C=C Bond Cleavage

Abstract

A new synthetic approach to functionalized quinolines was developed based on the application of Zn–AcOH system as a simple and efficient reductive agent towards 4‐(o‐nitroaryl)‐3‐acyl‐substituted 4,5‐dihydrofurans. Reduction of 3‐carbonyl‐substituted dihydrofurans is accomplished by C=C double‐bond cleavage in the dihydrofuran ring and 1,6‐cyclization, which leads to 3,4‐dihydroquinolines. The latter can be easily oxidized to quinolines or reduced to tetrahydroquinolines. For dihydrofuran‐3‐carboxylates, reduction proceeds with retention of the dihydrofuran ring and affords a tricyclic dihydrofuroquinoline core under harsher conditions. The proposed general reaction pattern was supported by results of DFT calculations. Moreover, a similar reductive system can be successfully applied in the conversion of dihydrofuran acyclic precursors, γ‐(o‐nitroaryl) α,β‐unsaturated carbonyl compounds, into quinoline derivatives.