On-Surface Heptagon Contraction Enables Rearrangement Driven Selective C–C Coupling

Abstract On-surface synthesis commonly relies on preinstalled C–X activation sites to initiate intermolecular coupling, which limits reactivity to precursor-encoded positions and can be impractical for frameworks that are difficult to halogenate in solution. Here, we report a rearrangement-driven coupling reaction on Au(111) in which a heptagon undergoes a [7 → 6 + 1] contraction before intermolecular bond formation, thereby generating reactive termini for subsequent covalent growth. A dibromotropone model establishes the mechanistic feasibility of this process and reveals a facile contraction that can be directly interrogated on the surface. A dual-heptagon precursor then demonstrates the synthetic consequence of the same principle, where contraction-generated termini drive intermolecular coupling with in situ formation of ethynylene bridges. This reaction sequence provides a complementary on-surface strategy for precursors whose coupling sites cannot be readily pre-encoded by conventional halogen substitution.