From Benzofurans to Indoles: Palladium‐Catalyzed Reductive Ring‐Opening and Closure <i>via</i> β‐Phenoxide Elimination

Abstract

Abstract Benzofurans can undergo ring‐opening by a palladium‐catalyzed process resulting in C−O bond breaking. Benzofuran‐tethered 2‐iodoanilines give synthetically interesting 2‐(3‐indolylmethyl)phenols in an overall reductive process. Mechanistic studies suggest that this unusual reaction proceeds by carbopalladation of benzofuran giving a 3‐palladated 2,3‐dihydrobenzofuran intermediate, which then fragments by an uncommon trans ‐elimination of the phenoxide group β to the metal. In this transformation, N , N ‐diisopropylethylamine (DIPEA) acts as a base and as a reducing agent: it regenerates palladium(0) from palladium(II), thus allowing catalytic turnover. magnified image