Accessing SuFExable Cyclobutane‐Fused Indolines via Photocatalytic Intermolecular [2+2] Cycloaddition of Indoles

Abstract Indoline‐fused polycycles are commonly found as a key structural component in numerous natural products and biologically active compounds. In recent times, the incorporation of sulfonyl fluoride groups has drawn significant attention in research due to their potential to enhance or confer new biological activities to molecules. In this study, we report the development of a modular approach for synthesizing FSO 2 ‐functionalized cyclobutane‐fused indolines by employing an intermolecular [2+2] cycloaddition reaction between indoles and SuFExable ethenesulfonyl fluoride under triplet energy‐transfer catalysis. This method features mild reaction conditions, metal‐free photocatalysts, and excellent tolerance to various functional groups. Moreover, we demonstrate the feasibility of further modifying the FSO 2 ‐functionalized indoline products via SuFEx click reactions, enabling their conjugation with other molecules.