Highly stable quinacridone-based photocatalyst for selective thioether oxidation

Quinacridone derivatives have recently emerged as promising organic photocatalysts due to their availability, strong visible-light absorption and accessible redox properties; however, their broader application in homogeneous photocatalysis has been hindered by poor solubility and stability. Herein, we report an optimized and resource‐efficient N -alkylation protocol that enables simple access to soluble quinacridone derivatives under significantly milder conditions than those commonly employed. With this approach, a new N , N ′-substituted quinacridone derivative was prepared, fully characterized, and evaluated as an organic photocatalyst. This catalyst promotes efficiently the visible‐light‐driven aerobic oxidation of sulfides to sulfoxides in homogeneous conditions, operating at very low catalyst loading (0.1 mol %) and displaying excellent chemoselectivity, with no detectable overoxidation to sulfones. The reaction proceeds smoothly in HFIP using molecular oxygen as oxidant and shows broad tolerance across different substrates. Notably, the photocatalytic system remained active over multiple consecutive substrate addition cycles without requiring catalyst reloading and consistently maintained high sulfoxide yields, a level of robustness that contrasts with the degradation typically observed for quinacridone-based photocatalysts under analogous conditions.