Visible light-driven direct access to imine-containing azaarene-substituted highly functionalized pyrroles

Abstract

Radical-based functionalization-oriented construction (FoC) has recently been developed as a powerful protocol to access imine-containing azaarene (Im-azaarene) derivatives. Different from the well-established strategies of construction and functionalization, it enables the direct synthesis of important but difficult-to-synthesize Im-azaarene-substituted azaarenes. Nonetheless, it is still in its infancy as only one successful example has been established. Herein, we report a novel FoC method towards the direct synthesis of Im-azaarene-substituted highly functionalized pyrroles. The readily accessible β/α-azaarene-substituted enones were demonstrated as viable partners to react with α-amino acids when irradiated with visible light and using p-toluenesulfonic acid (TsOH) as an additive to generate an electron donor–acceptor (EDA) complex with enones to trigger the transformation. Two series of products were obtained in high yields and with broad substrate scope. In addition to the capability to readily modulate diverse Im-azaarenes and functional groups as the substituents of pyrroles, the method is capable of preparing attractive fully aryl-functionalized variants with satisfactory results.