Domino Reactions Involving the Branched C-N and C=C Cleavage of Enaminones Toward Pyridines Synthesis

The copper-catalyzed cascade reactions of enaminones and ammonium chloride have led to the unprecedented synthesis of 4-unsubstituted pyridines of both symmetrical and unsymmetrical structures. Under the aerobic copper-catalyzed conditions, the branched transformations of enaminones with C-N and C=C bond cleavage provide the C2-C3/C5-C6 and C4 building blocks to construct the pyridine ring, respectively. The C=C cleavage that provides the C4 atom in the pyridine product is the first example showing the reactivity of an enaminone as the donor of one carbon synthon.