Manganese(III)-Mediated Selective Cascade Phosphorylation-Cyclization of Tertiary Enamides for the Synthesis of Multi-Substituted 3-Phosphorylpyridines

A novel regioselective manganese(III)-mediated radical cascade cyclization of N-propargyl enamides with various H-phosphine oxides, H-phosphinates and H-phosphonates was developed. Mechanistic studies show that the reaction is mainly composed of the selective addition of phosphonyl radical to C≡C bond and the intramolecular 6-endo-trig cyclization of vinyl radical. Utilizing this protocol, we successfully synthesized a diverse range of 3-phosphorylpyridines in high efficiency with good functional group compatibility and simple operation.