Mg–Al hydrotalcite-based catalysts for one-pot synthesis of quinoline derivatives

This mini-review discusses Mg–Al hydrotalcite-based catalyst systems used for modified Friedländer quinoline synthesis. The metal-grafted Mg–Al hydrotalcites consist of both active metal species and base sites capable of advancing catalytic activity. The Ru-grafted catalysts are active for the oxidative dehydrogenation of 2-aminobenzyl alcohol to 2-aminobenzaldehyde, followed by the base-catalyzed condensation with ketones to 2-substituted quinolines. Fe-grafted Mg–Al hydrotalcites also act as heterogeneous catalysts for the one-pot synthesis at a slightly higher reaction temperature. For pure Mg–Al hydrotalcite, hydrogen transfer reactions occur to afford 2-aminobenzaldehyde intermediate with an alcohol, resulting in the consequent production of the corresponding quinolines. The reaction mechanism and substrate scope of each catalyst system are also discussed.