Abstract
In conclusion, the dihapto coordination of benzene by the π-basic metal fragment {[TpRe(CO)(MeIm)} effectively dearomatizes benzene. The electron-donating metal activates the arene to such an extent that the unbound portion of the ligand acts as an electron-rich diene undergoing a Diels−Alder cycloaddition with NMM with a specific rate that is 60% greater than that observed for cyclohexadiene. Furthermore, the metal controls the stereochemistry of the cycloaddition and protects the resulting cycloadduct from undergoing a retrocycloaddition by blocking one of the π bonds. Oxidation of the rhenium metal center promotes decomplexation, providing access to the bicyclo[2.2.2]octadiene. Optionally, decomplexation accompanied by oxygen insertion yields bicyclo[2.2.2]octenone products. The strategy of using a transition metal to “switch off” resonance stabilization in arenes and aromatic heterocycles could prove to be a powerful new tool for synthetic chemists.
