Bromide‐Catalyzed Remote C5‐H Selenylation of Indolines with Se Powder and Boronic Acids: Dual Role of DMSO Both as Solvent and Oxidant

Herein, we report an efficient and metal‐free platform for the synthesis of selenylated indolines via bromide‐catalyzed radical three‐component coupling of indolines, Se powder, and boronic acids. This strategy offers a sustainable and alternative pathway to access organoselenylated indolines in 43%–89% yields by employing industry feedstock Se powder as the selenylation reagent. The key to success is attributed to the synergistic work of dimethyl sulfoxide and bromide. The synthetic utility of this strategy is demonstrated by its wide substrate scope, the employment of commercially available and stable selenyl precursors, broad functional group tolerance, gram‐scale reaction, and downstream functionalizations of selenyl‐substituted indolines.