The Isocyanide SN2 Reaction

Abstract

The nucleophilic substitution reaction (SN2) is one of the oldest, yet very useful organic transformations and has found widespread applications for the synthesis of drugs and natural products. Typically, cyanide, oxygen, nitrogen, sulfur, or phosphorous nucleophiles replace a halogen or sulfonyl ester leaving group to form a new bond between the nucleophile and the electrophile. Isocyanides display an unusual versatile chemistry based on their C-centered lone pair s and the C-centered p* frontier orbitals leading to radical, and multicomponent reactions. Surprisingly, the nucleophilic character of isocyanides has never been explored in SN2 reactions. We discovered that isocyanides react as versatile nucleophiles in SN2 reactions with alkyl halides in a general manner to afford highly substituted secondary amides by in situ hydrolysis of the intermediate nitrilium ion. The innovative 3-component reaction has a broad scope regarding the structures of the isocyanide and electrophile components, functional group compatibility, scalability, use for late-stage modification of a drug and synthesis of highly complex compounds otherwise not easily accessible from simple precursors. The chemical space of the new reaction is not only different but nearly doubled in size compared to the classical amid coupling. Significantly, the isocyanide nucleophile comprises an unusual Umpolung amide carbanion synthon R-NHC(-)=O, useful as an alternative to the classical amide coupling.