The preparation of β-lactams through four different radical cyclization reactions was studied by density functional theory calculations at the UB3LYP/6-311＋＋G(3df, 2p) level. Thermodynamics and kinetics of these radical cyclizations were analyzed using the Marcus theory. The calculated results showed that the 4-exo cyclization of carbamoyl radical was an ideal kinetic-control process. The 4-exo cyclization of carbamoylalkyl radical was predicted to be kinetically competitive with the 5-endo process. The 4-exo cyclization of amido radical was less favorable both kinetically and thermodynamically. Finally, the 4-exo ring closure of an acyl radical onto an imine acceptor was thermodynamically competitive with the 5-endo process but less favorable kinetically.

Key words: radical cyclization, β-lactam, density functional theory, Marcus theory