Brønsted Acid Catalyzed Oxygenative Bimolecular Friedel–Crafts‐type Coupling of Ynamides

A non‐metal approach for accessing α‐oxo carbene surrogates for a C−C bond‐forming bimolecular coupling between ynamides and nucleophilic arenes was developed. This acid‐catalyzed coupling features mild temperature, which is critical for the required temporal chemoselectivity among nucleophiles. The scope of nucleophiles includes indoles, pyrroles, anilines, phenols and silyl enolethers. Furthermore, a direct test of SN2′ mechanism has been provided by employing chiral N,N′‐dioxides which also enlightens the nature of the intermediates in related metal‐catalyzed processes. A synthetic surrogate of α‐oxo carbene is accessed by Brønsted acid catalysis on ynamides. Keteniminium ions generated by the protonation of ynamides are chemoselectively attacked by pyridine‐N‐oxides and form potent electrophiles for Friedel–Crafts‐type SN2′ addition of nucleophiles. This metal‐free approach is milder (room temperature) than related transition‐metal‐catalyzed processes.