The photochemical oxidation of lignin models in the presence of singlet oxygen was studied. The treatment of the non-phenolic β-O-4 aryl ether derivatives 6, 7, and 8 in the presence of both oxygen and Rose Bengal gave products deriving from a formal β-CO cleavage formation. By this way, the derivatives 12, 13, and 15 were obtained. The photochemical oxidation of the phenolic β-O-4 aryl ehter 9 gave the same type of product confirming that, ...