Aminotrifluoromethylation of Olefins via Cyclic Amine Formation: Mechanistic Study and Application to Synthesis of Trifluoromethylated Pyrrolidines

We examined the mechanism of our previously reported aminotrifluoromethylation reaction, which proceeds via intramolecular cyclization of alkenylamines in the presence of the combination of copper catalyst and Togni reagent (1). Kinetic studies revealed that the initial rate of the reaction was first order with respect to Togni reagent and CuI, as well as the substrate. Changes of the 19F NMR chemical shift of Togni reagent during the reaction suggested the existence of a dynamic equilibrium involving coordination of not only Togni reagent, but also the substrate amine and the product aziridine to copper. ESI-MS analysis provided evidence of involvement of reactive Cu­(II) intermediates in the catalytic cycle. Overall, our results indicate that the reaction proceeds at the hypervalent iodine moiety of Togni reagent, which is activated by Cu­(II) species acting as a Lewis acid catalyst. On the basis of these mechanistic considerations, we developed an efficient synthesis of trifluoromethylated pyrrolidine derivatives. This transformation exhibited a remarkable rate enhancement upon addition of Et3N.