A photoredox-enabled functionalized carbon-atom insertion reaction has been developed for the ring expansion of indene to access 2-substituted naphthalenes. This method utilizes α-iodonium diazo compounds as masked carbyne precursors, which can be activated by visible light to generate radical intermediates that facilitate ring expansion and functionalization. The reaction is mild, operationally simple, and tolerant of a wide range of functional groups, including trifluoromethyl, ester, phosphate ester, sulfonate ester, sulfone, nitrile, amide, aryl ketone, and aliphatic ketone fragments. The methodology was applied to the skeletal editing of pharmaceutical compounds, demonstrating its utility in accessing a library of 2-substituted naphthalenes. The reaction mechanism involves a radical chain process, with key steps including the generation of a carbyne intermediate, ring expansion, and rearomatization. DFT calculations support the proposed mechanism, showing that the reaction proceeds via a single-electron transfer and subsequent radical addition to the indene ring. The method offers a versatile approach for skeletal editing, enabling the synthesis of complex molecules with high efficiency and functional group tolerance. The study highlights the potential of photoredox catalysis in enabling new transformations for molecular scaffolding and drug discovery.A photoredox-enabled functionalized carbon-atom insertion reaction has been developed for the ring expansion of indene to access 2-substituted naphthalenes. This method utilizes α-iodonium diazo compounds as masked carbyne precursors, which can be activated by visible light to generate radical intermediates that facilitate ring expansion and functionalization. The reaction is mild, operationally simple, and tolerant of a wide range of functional groups, including trifluoromethyl, ester, phosphate ester, sulfonate ester, sulfone, nitrile, amide, aryl ketone, and aliphatic ketone fragments. The methodology was applied to the skeletal editing of pharmaceutical compounds, demonstrating its utility in accessing a library of 2-substituted naphthalenes. The reaction mechanism involves a radical chain process, with key steps including the generation of a carbyne intermediate, ring expansion, and rearomatization. DFT calculations support the proposed mechanism, showing that the reaction proceeds via a single-electron transfer and subsequent radical addition to the indene ring. The method offers a versatile approach for skeletal editing, enabling the synthesis of complex molecules with high efficiency and functional group tolerance. The study highlights the potential of photoredox catalysis in enabling new transformations for molecular scaffolding and drug discovery.