Divergent Iron Catalysis with Zincke Imines: Access to C5-Amidated Pyridines and Oxazole Derivatives from 2-Substituted Pyridines

Abstract

The transformation of electron-deficient pyridines into electron-rich Zincke imines is a well-established strategy for selective C3/C5 functionalization via electrophilic or radical pathways. Despite this, the reactivity of these imines toward metal nitrenoids has remained unexplored. Addressing this gap, we herein disclose an iron-catalyzed divergent reaction of Zincke imines with dioxazolones. Depending on the conditions, this protocol provides access to either C5-amidopyridines or substituted oxazoles, primarily starting from 2-substituted pyridines. This highly regioselective C5-amidation proceeds under mild conditions to furnish biologically relevant 2-substituted 5-amidopyridines, providing direct access to valuable scaffolds that are otherwise challenging and costly to access via conventional routes. Conversely, oxidative conditions at elevated temperatures favor the formation of oxazole derivatives with versatile synthetic handles. Mechanistic and theoretical insights support the generation of a reactive Fe(III)-imidyl intermediate that undergoes selective addition at the C5 position of the Zincke imine.