[1–5] Sigmatropic rearrangement in the confined cavity of self-assembled nanotube under oriented external electric field

Supramolecular nanotubes, such as the belt[12]pyridine nanotube, provide a confined environment that significantly alters the reactivity of organic reactions through nanoconfinement. This study investigates the confinement effects on the 1,5 sigmatropic rearrangement, focusing on the impact of non-bonding interactions between the 1,3 diene and the belt[12]pyridine nanotube. We utilized density functional theory (DFT) to optimize transition states and evaluate activation energies (Ea), which are found to be reduced to 35.64 kcal/mol compared to the unconfined reaction (36.35 kcal/mol). The application of an oriented external electric field (OEEF) further lowered the activation energy to 33.12 kcal/mol, demonstrating the dual influence of confinement and electric fields on reaction dynamics. The study revealed that the interaction distances and bond lengths between reactants and transition states varied significantly within the nanotube cavity, with noncovalent interaction indices indicating enhanced stabilization. QTAIM and NCI analyses confirmed these interactions, reinforcing the concerted mechanism of the reaction as established by the synchronicity (Sy) calculations, which were found to be 0.95, 0.95, and 0.91 for bare, confined without field, and confined with field reactions. Overall, our findings suggest that employing belt[12]pyridine nanotubes can effectively promote the efficiency of organic reactions, opening new avenues for catalytic applications in confined environments.