Oxidative dearomatization of 3-substituted indoles with sulfonium salts: direct access to 3-hydroxyoxindoles

Abstract

The development of a mild, green, and metal-free oxidative dearomatization process of substituted indoles into 3-hydroxyoxindole derivatives is highly desirable in modern organic chemistry. This emphasis stems from the significance of oxindole cores as an essential and prevalent reactive intermediate in the synthesis of natural products and pharmaceutically relevant molecules. Herein, we report the dual vicinal functionalization of 3-substituted indoles into 3-hydroxy-2-oxindole scaffolds using a sulfonium intermediate generated in situ by activating DMSO with alkyl bromides. Water acts as an oxygen source in this process, allowing the indoles to be 2,3-dioxygenated products. This reaction is a unique approach for generating 3-hydroxy-2-oxindoles and has a broad substrate scope. The transformation takes place in a single step at mild and ambient temperature, allowing access to a variety of 3-hydroxyoxindoles, including natural products, such as donaxaridine.