Actuating Cycloaromatization of a Bicyclo[7.3.1]enediyne by Annelation: An Example of Inverse Dependence on Bridge Atom Hybridization

Abstract

Although the acetylenic carbon atoms in 2 are closer together than those in 1, only the latter undergoes Bergman cyclization. In contrast, in analogous enediynes without an annelated cyclohexane ring a change in the hybridization of the bridging carbon atom from sp to sp leads to a dramatic increase in the cyclization rate.