Transition metal-free stereospecific access to (E)-(1-fluoro-2-arylvinyl)phosphine borane complexes

This work describes the first transition metal-free stereospecific synthesis of (E)-(1-fluoro-2-arylvinyl)phosphine boranes through the addition of diarylphosphine-boranes to gem-bromofluoroalkenes in the presence of a base at room temperature. The reaction proceeds well under very mild conditions and tolerates a variety of functionalities. Scope and limitations of the reaction are discussed. Mechanistic investigations have been undertaken and revealed that the reaction takes place through an S_RN1 mechanism. The formation of the fluorinated vinyl radical has been evidenced by electron paramagnetic resonance (EPR) experiment.