Chromium-catalysed selective synthesis of 3-oxo and 3-amino quinolines using β-O-4′ lignin models or α-amino ketones

Abstract

Chromium-catalyzed annulation of 2-aminoaryl alcohol with phenoxyacetophenone to 3-oxo-quinoline derivatives is reported. Phenoxyacetophenones are employed as β-O-4′ lignin models for this conversion. The efficacy of this process was further extended by producing 3-aminoquinolines using α-amino ketones. Notably, these are hard to prepare using conventional methods. The catalyst tolerates numerous functional groups, including hydrogenation-sensitive groups, and is applicable for even problematic α-hydroxyacetophenone as a substrate. This process can be further extended to a gram-scale reaction and late-stage functionalization of natural products. Experimental studies suggested that the reaction is a highly coupled cascade reaction involving dehydrogenation, aldol condensation, C–N bond formation and nitrogen-heterocyclic ring construction.