Geometric and Electronic Control of Thermal Bergman Cyclization

The geometric and electronic contributions to Bergman cyclization of simple enediynes are compared and contrasted to those of recently developed metalloenediyne analogues. The comparison reveals that metals can have more diverse, subtle, and in some cases, more dramatic geometric effects upon Bergman cyclization than simple substitution chemistry. In addition to geometric consequences imposed by metals, electronic control of metalloenediyne cyclization is emerging as a complementary parameter in complex design.