Access to amidines via C(sp2)-N coupling of trifluoroborate-iminiums with N-fluorobenzenesulfonimide.

Abstract

Amidines are an important class of organic compounds with widespread application as superbases, nucleophilic catalysts, and building blocks of heterocyclic compounds in organic synthesis. Moreover, they represent an important structural motif in medicinal chemistry. This work describes an application of primary trifluoroborate-iminiums in unprecedented azide- and transition-metal-free transformation to N-sulfonyl amidines in the presence of N-fluorobenzenesulfonimide (NFSI). 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 (DFT) 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.