Distortion Rules: Diene Ring Size Effects in Diels-Alder Reactions with Triazolinediones

Triazolinediones (TADs) are highly reactive electrophiles used in several processes within the field of organic chemistry, especially in Diels-Alder cycloadditions. The reactions of TADs with cyclic dienes have been observed to depend on the diene structure and size. To investigate the role of diene structure in the reactivity of TADs, computational chemistry based on DFT and Activation Strain Model were employed to quantitatively assess the impact of distortion and interaction energies on the observed reactivity. Calculations suggest that the reactions are endo selective based on lower energy barriers compared to the exo pathway. Additionally, the trends in reactivity agree with experimental observations: cyclopentadiene is the more reactive diene, followed by cyclohexadiene and cycloheptadiene. The ASM analysis reveals that this trend is a consequence of the degree of distortion the reactants along the reaction coordinate. These distortion energies also allowed to explain why the endo selective route is preferred over the exo one. We studied the reaction between a triazolinedione with cyclic dienes using the activation stain model. The distortion of the diene structure controls the reactivity of cyclic dienes cyclopentadiene, cyclohexadiene and cycloheptadiene toward triazolinediones. We offer a clue on the preference of the endo selective pathway based on lower distortion energies for the endo transition state compared to the exo one. The distortion of the diene structure from the isolated state controls the reactivity of cyclic dienes in Diels-Alder cycloadditions with triazolinediones.image