Rare-Earth Metal-Enabled Ring-Opening Metathesis of Benzene.

Activation and transformation of inert C-C bonds within arenes are challenging and important topics in synthetic chemistry. While there have been some reports on the activation of C-C bonds in arene rings, the realm of metathesis reactions involving arene C-C bonds remains unexplored. Here, we report a rare-earth metal-enabled intramolecular metathesis reaction of one benzene C-C bond and another C-C single bond, assisted by the high reactivity and unique synergistic effect of rare-earth metallacycles. Mechanistic studies disclose an intriguing pathway that forms a fused tricyclic intermediate bearing a 4-membered ring through stepwise [2 + 2] cycloaddition, followed by stepwise [2 + 2] cycloreversion. The distinct reaction discovered here extends the reactivity of arenes and is expected to inspire the development of aromatic ring-opening metathesis reactions.