Radical pathways for 2,4-chromandione synthesis via photoexcitation of 4-hydroxycoumarins†

Abstract

4-Hydroxycoumarins are well-known for their ground-state nucleophilic behavior, which has been widely exploited for their functionalization. Herein, we reveal a previously unexplored photochemical reactivity: upon deprotonation and excitation with purple light, 3-substituted 4-hydroxycoumarins reach an excited state and act as single-electron transfer (SET) reductants, generating radicals from stable substrates. This newfound reactivity enables the direct synthesis of 3,3-disubstituted 2,4-chromandiones via a radical dearomatization process. By enabling the incorporation of alkyl and perfluoroalkyl fragments, this protocol offers a straightforward and mild route to access synthetically valuable chromanone scaffolds featuring a quaternary stereocenter. Comprehensive photophysical studies confirmed that deprotonated 4-hydroxycoumarins are potent SET reductants in their excited state, making them suitable for initiating radical-based transformations.