Intramolecular cyclization reaction mechanism and regioselectivities of unsubstituted and benzene-substituted 4-penteniminyl radicals: A DFT investigation

► A stereoelectronic effect results in the 5-exo cyclization as the dominant pathway for 4-penteniminyl radical. ► The preferred 6-endo cyclization for Ph-substituted 4-penteniminyl radical can be attributed to thermodynamic contribution. ► Kinetic and thermodynamic effects on a reaction barrier can be evaluated by Marcus theory.