H• Transfer-Initiated Synthesis of γ-Lactams: Interpretation of Cycloisomerization and Hydrogenation Ratios

A cobaloxime/H-2 system used to synthesize valuable gamma-lactams from acrylamide molecules is described. In addition to cycloisomerized lactams, linear hydrogenated products were also observed. The amounts of the hydrogenation product were observed to correlate with the bulk of the substituent on the acrylamide nitrogen. Further analysis of the product distributions with experimental and computational studies suggested that while cyclization can occur from one C=C acrylamide rotamer, hydrogenation can occur from both. This observation was further evinced through calculation of the hydrogenation rate constant, which was observed to be ca. 10(2) faster than previously determined for a related system using (Bu3SnH)-Bu-n.