Demoniac Intervention in the Thermal Electrocyclic Ring Opening of Cyclobutenes: Fe(CO)3 Complexation of Pericyclic Transition Structures

Abstract

Dedicated to Professor Edgar Heilbronner on the occasion of his 80th birthday Can metal complexation of organic p-systems alter the stereoselectivity of pericyclic reactions? We address this question for the Fe(CO) 3 -templated electrocyclic ring opening of cyclobutene using hybrid HF-DFT calculations. These calculations show that the preferred pericyclic pathway in the presence of Fe(CO) 3 corresponds to the pathway that is orbital-symmetry-forbidden in its absence, validating predictions made previously based on extended Hückel calculations. The three-dimensional aromaticity of the preferred metalcomplexed transition state is revealed by NICS calculations.

6 Reaction mechanisms : Part (ii) Pericyclic reactions

“…55 High-level calculations reveal that Fe(CO) 3 complexation alters the aromaticity of the disrotatory transition state, such that it becomes more favorable than conrotation, which is relatively unaffected by complexation. This aromatic stabilization of the disrotatory transition state is further supported by calculated nucleus-independent chemical shift values.…”