Merging photocatalysis with C-H insertions enabled switchable synthesis of indoles and indolines

C–H insertion offers a powerful route to C–C bond formation, yet it has often proven challenging to integrate into cascade synthetic sequences for further molecular elaboration. This limitation stems primarily from the aggressive conditions required for carbene generation and the high sensitivity of carbene species, which lead to premature termination and incapability with downstream transformations. Although intramolecular C–H insertion provides direct access to indolines, conventional approaches tend to produce ungoverned mixtures of indolines and indoles, owing to harsh conditions. To address these limitations, we have developed an integrated platform that enables controlled access to both triplet and singlet carbene pathways, allowing for selective synthesis of either indoles or indolines. By leveraging energy transfer, C-H insertions and consecutive photoredox dehydrogenation, triplet carbene was accommodated in cascade reactions to afford N -fused indoles selectively. Alternatively, indolines were synthesized controllably through singlet carbene-mediated C-H insertion. The incorporation of indoline and indole motifs into drug scaffolds demonstrates practical applicability. Moreover, the mechanism was elucidated through a combination of experimental mechanistic studies and density functional theory (DFT) calculations. Notably, compound 5b was identified as a promising ferroptosis inhibitor after comprehensive pharmacological studies, underscoring the potential of photochemical synthesis in drug discovery.