Electronic Effects on the Bergman Cyclisation of Enediynes. A Review

Abstract

The thermal cyclisation of enediynes to benzene-1,4-diyl diradicals (Bergman cyclisations) is affected by geometrical and electronic conditions. While the effect of ring strain or conformational constrains on the cyclisation temperature has been investigated in detail, electronic contributions have been less studied. Often geometrical and electronic contributions cannot be clearly distinguished. In most cases metal ion chelation does involve both. We have summarised clear-cut observations of electronic substituents effects on the thermal enediyne reactivity.