Solvent-trap reaction of triazolinediones with simple alkenes: An experimental/theoretical study of thermodynamic and kinetic parameters

The reaction of N-phenyltriazolinedione with simple alkyl-substituted alkenes in a series of simple alcohols as nucleophilic solvents affords two products: a solvent-addition product (trap) and the ene adduct. Herein we present different experimental data which allow the estimation of different kinetic parameters ( DDHs ene,trap and DDSs ene,trap). The values of those parameters are found to be lower with a longer nucleophile-solvent molecule. Solvent isotope effects are also estimated and found in favour of the heavier (and smaller) deuterated compounds. Results from competition experiments in equimolar binary mixtures of different alcohols as solvents also point to the prevalence of the smaller alcohol. A length limitation is observed in the competition of EtOH versus PrOH couple, the absence of any competition for the formation of the two solvent-addition (trap) products. All the results are consistent with an SN2-‘like’ nucleophilic attack of the nucleophile-solvent to a closed aziridinium imide (AI) intermediate. Computational models were investigated in order to both confirm the stability of the different possible intermediates and to confirm the experimentally observed trends and kinetic profiles. Furthermore, the results show the existence of a single transition state from which both products are formed.