2 H ‐Phosphindole‐Enabled Dearomatization and [4+2] Cycloaddition of (Hetero)Arenes

The heavier main group multiple bonds offer an effective tool for small molecule activation. Transient 2 H ‐phosphinidole working as a reactive phosphadiene system undergoes phospha‐Diels‐Alder reaction with a wide range of non‐activated aromatic carbocycles and heterocycles, including naphthalene, anthracene, phenanthrene, furan, thiophene, pyrrole, pyridine, and benzo‐fused heterocycles, affording concise access to a range of polycyclic fused rings feature with phosphorus at the bridgehead. These results demonstrate that non‐activated (hetero)arenes are capable of acting as 2π systems in [4+2] cycloaddition with highly reactive 2 H ‐phosphindole complex.