Kinetics and thermochemistry of the unusual [2π + 2σ + 2σ]‐cycloaddition of quadricyclane with some dienophiles |
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| Authors: | Vladimir D Kiselev Dmitry A Kornilov Oleg V Anikin Igor A Sedov Alexander I Konovalov |
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| Institution: | 1. Butlerov Institute of Chemistry, Kazan Federal University, Kazan, Russia;2. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center of Russian Academy of Sciences, Kazan, Russia |
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| Abstract: | Kinetic parameters of the unusual 2π + 2σ + 2σ]‐cycloaddition reactions of quadricyclane ( 1 ) with tetracyanoethylene ( 2 ), 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione ( 3 ), N‐phenylmaleimide ( 4 ), and diethyl azodicarboxylate ( 5 ) are determined experimentally. Additionally, the enthalpies of 1 + 2 reaction in 1,4‐dioxane solution (?236.6 ± 1.0 kJ mol?1) and 1 + 3 reaction in toluene (?255.0 ± 2.8 kJ mol?1) are determined calorimetrically and shown to be the largest in absolute magnitude among all known cycloaddition reactions involving these dienophiles. Solvent effect on the rate of 1 + 3 reaction in 11 solvents is studied and found to be moderate and similar to that of the conventional Diels‐Alder and ene reactions. The difference in the reaction rate constants of 1 with different dienophiles can be up to 9 orders of magnitude and is mainly caused by the difference in activation enthalpies. This difference is not correlated with the standard enthalpies of reactions and is likely the result of high sensitivity of the 2π + 2σ + 2σ] reaction rates to the energy of donor‐acceptor interactions between the reactants. |
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| Keywords: | [2π + 2σ + 2σ ] reaction 4‐phenyl‐1 2 4‐triazoline‐3 5‐dione quadricyclane rate constants reaction heat tetracyanoethylene |
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