Photochemical Oxidation of Thiazolidines and Oxazolidines Enables Access to Reactive Oxygen Species (ROS) Sensitive and Chitin‐Derived Heterocycles

The development of sustainable synthetic methodologies is crucial to advancing greener processes. In this work, a mild and chemoselective photochemical oxidation of thiazolidines to the corresponding thiazolines under an oxygen‐free atmosphere and oxazolidines to oxazolines under an oxygen atmosphere is described. The transformation proceeds efficiently with the inexpensive organophotocatalyst 9‐fluorenone for thiazolidines, while both [Ru(bpy) 3 ](PF 6 ) 2 and 3CzClIPN proved effective for oxazolidines. The reaction tolerates a wide range of functional groups, including oxidation‐sensitive moieties such as dimethylamines and boronic acids, and delivers up to 94% yield across 28 substrates. Importantly, this methodology enables the late‐stage functionalization of the chitin‐derived synthon 3‐acetamido‐5‐formylfuran (3A5F), a challenging aldehyde prone to decomposition, expanding the chemical space of nitrogen‐containing renewable scaffolds. The synthetic utility of the process is further demonstrated through the total synthesis of the antibacterial natural product Aerugine in 20% overall yield. This sustainable and versatile approach opens new avenues for the preparation of heterocycles and bioactive molecules from renewable resources.