Cerium-Doped Manganese Oxide Catalyst for the Oxidative Coupling Synthesis of Fluorescent 2-Amino-1,9-dimethyl-3H-phenoxazin-3-one Using Atmospheric Oxygen

The heterogeneous catalytic oxidative coupling synthesis of 2-amino-3H-phenoxazin-3-one (APXO) from the oxidative coupling of 2-aminophenol has important practical significance, due to its significant antiproliferative properties. However, the use of noble metals, alkaline additives, and explosive H2O2 seriously restricts its applicability in industrial settings. Herein, through preparing a cerium-doped manganese oxide catalyst, we achieved the green synthesis of APXOs, using atmospheric oxygen as an oxidant, and without any additives. Its high activity can be attributed to the greatly enhanced oxidation capacity, oxygen activation capacity, and alkalinity that comes from doping with cerium. Remarkably, we found that 2-amino-1,9-dimethyl-3H-phenoxazin-3-one possesses excellent fluorescence properties and could be applied as a fluorescent molecular probe in various detection and labeling studies. This methodology provides an environmentally friendly and economical strategy for the synthesis of APXO in industrial applications, preserving the stability of the heterogeneous catalyst, which showed minimal metal leaching.