Radical-Mediated Functional Group Migration and Cyclization Cascade for the Synthesis of Sulfonylated Oxindoles.

Herein, we report the development of a three-component radical cascade for the synthesis of sulfonylated oxindoles from a sulfonamide derivative, bis(1,4-diazabicyclo[2.2.2]octane) sulfur dioxide (DABSO), and benzenediazonium tetraarylborate salts. Remarkably, the transformation operates under both photocatalytic and nonphotocatalytic conditions, providing flexible access to the desired products. The reaction proceeds through in situ generation of a sulfonyl radical, followed by addition to the alkene, a Truce-Smiles-type 1,4-cyano migration, and subsequent intramolecular cyclization to construct the oxindole framework. This one-pot cascade enables the formation of C-S and C-C bonds under mild conditions. The method delivers a broad range of sulfonylated oxindoles in generally good yields with wide functional group tolerance and high atom economy, and in situ capture of substrate-released SO2 by the diazonium salt enabled the use of only 0.5 equiv of DABSO as the SO2 surrogate, offering a concise and efficient route to highly substituted oxindole derivatives.