Sequential Aerial Oxidation and Atom‐Economical C‐3 Chalcogenation of Indolines Facilitated by Potassium <i>tert</i>‐Butoxide

Abstract An operationally straightforward and highly efficient potassium tert ‐butoxide facilitated protocol for the C‐3 chalcogenation of indolines under catalyst and additive‐free conditions has been established under ambient temperature. The salient features of the process include the development of transition metal‐free, oxidant‐free and iodine‐free, atom‐economic and cost‐effective reaction conditions at room temperature in DMSO as solvent for regioselective generation of 3‐chalcogenyl indoles in high yields. The mechanistic interpretation through controlled experiments and analysis of intermediates suggests the prevalence of the ionic pathway. The reaction is scalable to gram‐scale without a significant decrease in product yield, indicating its potential for large‐scale applications. This protocol offers a practical and environment friendly approach to accessing a diverse range of 3‐arylthioindoles and 3‐arylselenylindoles withstanding electron releasing and withdrawing substituents in good to excellent yields. Interestingly, the biological evaluation of the 3‐arylselenylindole products exhibited significant activity against breast cancer and triple‐negative breast cancer cell lines MCF‐7, and MDA‐MB 231. These results indicate the derivatives to be potent candidates for further SAR study.