Diastereo- and Enantioselective Dearomatization of Rhenium-Bound Naphthalenes

Dihapto-coordinated naphthalene complexes of the form TpRe(CO)(L)(η2-naphthalene) (L = PMe3,
pyridine, or 1-methylimidazole) undergo electrophilic addition with dimethoxymethane and with
various Michael acceptors to generate 1H-naphthalenium species. These naphthalenium complexes
undergo intra- or intermolecular nucleophilic addition reactions with stabilized enolates, silyl ketene
acetals, or enols to form the corresponding dihydronaphthalene complexes. Oxidative decomplexation
generates the free dihydronaphthalene. When a resolved form of the rhenium dearomatization
agent is used, these reactions can be performed enantioselectively. DFT calculations provide a useful
guide in explaining the observed stereochemistry. Depending on reaction conditions, a Michael−Michael ring-closure sequence (MIMIRC) or a net [2 + 4] cycloaddition with the bound naphthalene
is also observed, and the corresponding tricyclic molecules can be removed from the metal in high
yield.