Aldehyde/Triazolium-Catalyzed Transformation of C(sp ³ )–H Bonds via HAT Photocatalysis and Electron-Shuttle Process: Unexplored Merging of Aldehyde and Triazolium

The direct activation of C–H bonds remains a central challenge in synthetic chemistry, with photochemical hydrogen atom transfer (HAT) offering a mild and powerful strategy. Aldehydes represent an attractive, readily available class of potential HAT photocatalysts, yet their short-lived excited states often result in inefficient catalyst turnover dominated by competing pathways. Herein, we report an unexplored merging of aldehyde and triazolium photocatalytic systems that overcomes these intrinsic limitations and enables aldehydes to function as effective and regenerable HAT photocatalysts. In this electron-shuttle manifold, triazolium salts rapidly intercept α-hydroxybenzyl radicals formed via excited aldehyde-mediated HAT, facilitating efficient catalyst turnover while generating reducing radicals that convert benzylic radicals into carbanions. This strategy activates a broad range of C(sp 3 )–H bonds and enables a broad range of three-component coupling with alkenes and electrophiles, including alkyl-deuteration, alkylative cyclization, aryl-alkylation, and alkylative carboxylation transformations. Furthermore, the functionalized products exhibit potent antimicrobial activity against various fungi, underscoring their potential as fungicidal agrochemical leads. The merger of simple benzaldehyde with a triazolium as a mechanistically distinct electron-shuttle catalyst establishes a practical HAT platform that expands the synthetic potential of aldehyde photocatalysis for direct C–H functionalization.