Transition Metal-Free Heteroarene Insertion Into C─C Bonds of Benzocyclobutenones.

The insertion of five-membered heteroarenes into the C─C bonds of benzocyclobutenones (BCBs) has been achieved. This process proceeds under mild conditions and does not require the use of a transition metal catalyst. A variety of fused polycyclic compounds based on indoles, 7-azaindoles, benzothiophenes, benzofurans, and thiophenes relevant to bioactive scaffolds are efficiently accessed through this approach. The reaction is scalable, and the products are suitable for various late-stage derivatizations. Preliminary mechanistic studies reveal a catalytic role of base in facilitating C─C bond cleavage to generate a reactive intermediate which likely engages in subsequent dearomative cycloaddition with heteroarenes.