New routes to nitrogen heterocycles through intramolecular amidocarbonylation of alkenamides catalyzed by rhodium complexes

Intramolecular amidocarbonylation of 3-butenamide catalyzed by a rhodium complex with excess PPh₃ gives 3,4-dihydro-2-pyridone selectively, whereas the same reaction using P(OPh)₃ affords a unique heterodimer in excellent yield. The reaction of 4-pentenamide gives 4-methyl-3,4-dihydro-2-pyridone exclusively regardless of the structure of rhodium catalysts.