Rare-Earth Metal-Enabled\nRing-Opening Metathesis of\nBenzene

Activation and transformation of inert C–C bonds\nwithin\narenes are challenging and important topics in synthetic chemistry.\nWhile there have been some reports on the activation of C–C\nbonds in arene rings, the realm of metathesis reactions involving\narene C–C bonds remains unexplored. Here, we report a rare-earth\nmetal-enabled intramolecular metathesis reaction of one benzene C–C\nbond and another C–C single bond, assisted by the high reactivity\nand unique synergistic effect of rare-earth metallacycles. Mechanistic\nstudies disclose an intriguing pathway that forms a fused tricyclic\nintermediate bearing a 4-membered ring through stepwise [2 + 2] cycloaddition,\nfollowed by stepwise [2 + 2] cycloreversion. The distinct reaction\ndiscovered here extends the reactivity of arenes and is expected to\ninspire the development of aromatic ring-opening metathesis reactions.