Iron(II)-Catalyzed Trifluoromethylation of Potassium

An iron(II)-catalyzed trifluoromethylation of potassium vinyltrifluoroborates has been developed. The reactions proceed under mild conditions and provide E/Z selectivities of> 95:5 for 2-aryl and-heteroarylvinyl substrates. Experimental observations suggest that the reaction does not proceed through a transmetallation of the RBF3K to the iron catalyst. Keywords trifluoromethylation; fluorine; iron; catalysis The incorporation of fluorinated functional groups in pharmaceutical and agrochemical molecules has had a significant impact on the discovery and development of biologically active compounds.[1,2] Due to its metabolic stability, lipophilicity, and electron-withdrawing character,[3] use of the trifluoromethyl (CF3) substituent has gained considerable attention in recent years. New methods for direct C–CF3 bond-formation have had a prominent presence in current literature, highlighting the importance of this transformation.[4,5] Efforts in our lab have focused on the development of new fluorination[6] and trifluoromethylation[7] reactions through the use of transition metal catalysis and promotion. Herein, we report a facile method to access vinyl–CF3 functional groups through an iron(II)-catalyzed trifluoromethylation of potassium vinyltrifluoroborates (1) using Togni’s reagent 2[8] (eq 1). Recently, we reported an oxidative trifluoromethylation of terminal olefins, providing rapid access to allyl–CF3 containing products of type 4.[9,10] During the course of our studies, we observed 5, a side product resulting from chloride counterion transfer from CuCl to the olefin substrate subsequent to C–CF3 bond formation (Figure 1, A). We hypothesized several possible intermediates (summarized as 6) leading to the formation of both 4 and 5