Organic Brønsted acids are one of the most important classes of homogeneous and heterogeneous catalysts.[1] In particular, trifluoromethanesulfonyl (triflyl; Tf)-derived acids such as TfOH and Tf2NH and their conjugated bases are attracting much attention from a wide field of chemical sciences.[2] Methane derivatives substituted by at least two Tf groups have been also known to show strong Brønsted acidity.[3, 4] However, the development of ...