Andrew T. Parsons, Todd D. Senecal and Stephen L. Buchwald Angew. Chem. Int. Ed.
Trifluoromethylation of vinyl borates can be achieved with Togni’s reagent with mild reaction conditions and an iron(II) catalyst. Togni’s reagent is prepared in three steps from 2-iodobenzoic acid. The reaction works best with conjugated aryl substrates where selectivity for the E isomer is high. More flexible substrates undergo trifluoromethylation with reduced stereoselectivity.
Regarding the mechanism, it was found that Z-substrates also give selectivity for the E isomer. Based on this, the authors suggest that the reaction is likely to proceed by a cationic intermediate.
Evidence for this hypothesis was found when alternative Lewis acid catalysts, particularly tin(II) triflate, were also shown to catalyse the reaction.