Azide- and Transition-Metal-Free Access to Sulfonyl Amidines via C(sp2)-N Coupling of Trifluoroborate-Iminiums with N-Fluorobenzenesulfonimide

Amidines are an important class of organic compounds with widespread application as superbases, nucleophilic cata-lysts, and building blocks of heterocyclic compounds in organic synthesis. Moreover, they represent an important struc-tural motif in medicinal chemistry. This work describes an application of primary trifluoroborate‐iminiums in unprece-dented azide- and transition-metal-free transformation to N-sulfonyl amidines in the presence of N-fluorobenzenesulfonimide. This novel C(sp2)-N bond-forming reaction proceeds without excess of any reagent under mild conditions and provides good to high yields of N-sulfonyl amidines by a simple isolation procedure. Density functional theory mechanistic studies into this novel transformation support that the use of a base is required to activate either the trifluoroborate-iminium or the NFSI and promote the C(sp2)-N bond formation via nucleophilic attack of the nitrogen. The utility of the developed methodology is showcased with the synthesis of two bioactive compounds.