Asymmetric counteranion directed catalysis (ACDC)[1] or chiral anion catalysis [2] in enantioselective synthesis is the "induction of enantioselectivity in a reaction proceeding through a cationic intermediate by means of ion pairing with a chiral, enantiomerically pure anion provided by the catalyst".
Hence, some authors may exclude ion pair formation by proton transfer as a type of chiral counteranion catalysis.
However, the observation that enantioinduction occurred only in nonpolar solvents supports the proposed role of the borate as the chiral counteranion.
The term asymmetric counteranion-directed catalysis was coined in 2006 by List in the context of organocatalytic iminium reduction in the presence of a chiral phosphate anion:[4]
In the example below, the fluorinating reagent Selectfluor exhibits extremely limited solubility in nonpolar solvents and is therefore unreactive as an insoluble bulk solid.