Factors Governing the Diels-Alder Reactivity of (2,7)Pyrenophanes

The physical factors governing the Diels-Alder reactivity of (2,7)pyrenophanes have been computationally explored using state-of-the-art Density Functional Theory calculations. It is found that the [4 + 2]-cycloaddition reactions between these cyclophanes and tetracyanoethylene, which occur concertedly through highly asynchronous transition states, proceed with lower activation barriers and are more exothermic than the analogous process involving the parent planar pyrene. The influence of the bent equilibrium geometry of the pyrenophane as a function of the length of the bridge as well as the nature of the tether on the transformation are analyzed in detail. By means of the Activation Strain Model of reactivity and the Energy Decomposition Analysis methods, a detailed quantitative understanding of the reactivity of this particular family of cyclophanes is presented.