The effect of charge-transfer complexation/π-stacking interactions in lowering the activation barrier of the bergman cyclization

Abstract

To elaborate the concept of weak interactions and their effect on Bergman Cyclization (BC), several 1,2-dikynyl benzenes incorporating various combinations of donor and acceptor units in the two arms of the enediynes were designed and synthesized, and their charge-transfer interactions followed by UV/Vis spectroscopy. The thermal reactivities, as studied by DSC, show an increase in reactivity for the donor/acceptor or donor/donor combinations relative to the acceptor/acceptor pair. Such an increase in reactivity can be explained on the basis of intramolecular charge transfer and π-stacking interactions between the two arms, which may lower the distance between the two acetylenic ends.