Advancing Photocatalytic Diels–Alder Conversion of Biomass-derived Compounds on Red Phosphorus via C–H Activation

Photocatalytic conversion of biomass-derived compounds into valuable chemicals represents an important advancement for solar-energy conversion. However, conventional semiconductor photocatalysts, composed of multiple elements, exhibit nonuniform catalytic surfaces, complicating catalyst design and mechanistic understanding. Here, we present single-element semiconductors, red phosphorus (RP), to facilitate visible-light-driven Diels–Alder transformations of biomass-derived compounds into high-value products in moderate to good yields. The electron-rich phosphorus atoms effectively adsorb p-toluquinone and activate C–H bonds, leading to the formation of a cationic intermediate via photogenerated holes that promote Diels–Alder electronic matching with a diene into a cationic cyclized adduct. Accompanied by an O 2 -mediated process, wherein O 2 accepts conduction-band electrons and transfers them to the cationic cyclized adduct, the D–A transformation is accomplished without requiring any sacrificial agents. This approach operates under milder and greener conditions, advancing the biomass conversion and highlighting RP’s potential in organic synthesis. Additionally, the single-element photocatalyst allows for valuable insights into mechanistic studies.