Aerobic, metal-free synthesis of 6<i>H</i>-chromeno[4,3-<i>b</i>]quinolin-6-ones

Abstract

A Friedländer-based method for transition-metal free, aerobic synthesis of chromene-fused quinolinones is reported. The coupling of 4-hydrocoumarins and 2-aminobenzyl alcohols proceeds in the presence of acetic acid solvent and oxygen oxidant, affording 6<i>H</i>-chromeno[4,3-<i>b</i>]quinolin-6-ones in good to excellent yields. The reactions are tolerant of functionalities such as alkyl, methoxy, bromo, chloro, and <i>N</i>-heterocycle. Isosteric cyclic 1,3-diketones and 2-amino acetophenones also give fused quinolinones under reaction conditions. The method herein offers a rapid and benign synthesis of hitherto challenging <i>N</i>-heterocycles. To our best knowledge, such a convenient pathway to obtain chromene-fused quinolinones have not been known in the literature.