The bis(trifluoromethanesulfonyl)methyl (Tf₂CH; Tf = CF₃SO₂) group is a very strong acidic functionality that has an active hydrogen atom on an electronically neutral carbon atom. Hikaru Yanai and co-workers, Tokyo University of Pharmacy and Life Sciences, Japan, have developed two kinds of acid catalysts on the basis of this carbon acid.

The first one is a triple carbon acid that has three Tf₂CH groups in the molecular structure (see picture above). This catalyst was used in the first example of an organocatalytic olefination of arene-fused lactones by reaction with a silicon enolate (see scheme below).

The second one is a zwitterion that contains a highly stabilized carbanion moiety, which is an intermolecular salt between Tf₂CH functionality and aniline functionality. By using this zwitterion instead of the triple carbon acid, similar reactions to those conducted with the first catalyst gave aldol adducts in a selective manner (see scheme below). Furthermore, the adducts were successfully converted into highly substituted 1-naphthols, which are common in the structure of biologically active naphthalenes.

It is hoped that these findings on carbon-acid and zwitterion catalysis will provide the basis for the Tf₂CH group to be a useful acidic functionality for molecular design of organocatalysts.

• Organic Acid Catalysts in Reactions of Lactones with Silicon Enolates,
  Hikaru Yanai, Nobuyuki Ishii, Takashi Matsumoto, Takeo Taguchi,
  Asian J. Org. Chem. 2013.
  DOI: 10.1002/ajoc.201300157