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Asymmetric counteranion directed catalysis (ACDC) or chiral anion catalysis in 
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:
Chiral anions have been combined with 
Subsequently, Toste and coworkers advanced the concept of ''chiral anion phase transfer catalysis'', in which phase segregation (solid/organic or aqueous/organic) is used as a tactic to enforce the pairing of a cationic reagent or intermediate with a chiral counteranion. In the example below, the fluorinating reagent 
enantioselective synthesis
Enantioselective synthesis, also called asymmetric synthesis, is a form of chemical synthesis. It is defined by IUPAC as "a chemical reaction (or reaction sequence) in which one or more new elements of chirality are formed in a substrate molecul ...
is the "induction of enantioselectivity
In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical ant ...
in a reaction proceeding through a cationic intermediate by means of ion pairing with a chiral, enantiomer
In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical ant ...
ically pure anion provided by the catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
". Although chiral Brønsted acid catalyzed reactions may well fall into this category of catalysis under the definition given here (e.g., protonation of an imine by a chiral phosphoric acid), the extent of proton transfer and the demarcation between hydrogen bonding and full proton transfer is often ambiguous. Hence, some authors may exclude ion pair formation by proton transfer as a type of chiral counteranion catalysis. The discussion below will focus on chiral ion pairs generated through means other than proton transfer. (''For a discussion about chiral Brønsted acid catalyzed reactions, see the article on hydrogen bond catalysis.'')
The concept of utilizing the counteranion as the source of chirality in catalysis was first proposed by Arndtsen and coworkers in 2000, who applied chiral borate anions to copper-catalyzed olefin
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
aziridination and cyclopropanation. The enantioselectivities observed were low: <10% ee in cases where the chiral borate was the only source of chirality. 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:
Chiral anions have been combined with homogeneous catalyst
In chemistry, homogeneous catalysis is catalysis by a soluble catalyst in a solution. Homogeneous catalysis refers to reactions where the catalyst is in the same phase as the reactants, principally in solution. In contrast, heterogeneous catalysis ...
s, illustrated by chiral phosphate anions for intramolecular allene hydrofunctionalization reactions catalyzed by phosphinegold(I) complexes:
:
Subsequently, Toste and coworkers advanced the concept of ''chiral anion phase transfer catalysis'', in which phase segregation (solid/organic or aqueous/organic) is used as a tactic to enforce the pairing of a cationic reagent or intermediate with a chiral counteranion. In the example below, the fluorinating reagent Selectfluor
Selectfluor, a trademark of Air Products and Chemicals, is a reagent in chemistry that is used as a fluorine donor. This compound is a derivative of the nucleophillic base DABCO. It is a colourless salt that tolerates air and even water. It has ...
exhibits extremely limited solubility in nonpolar solvents and is therefore unreactive as an insoluble bulk solid. Exchange of its tetrafluoroborate anions with two equivalents of a chiral, lipophilic phosphate anion brings the reagent into solution as an ion-triplet which behaves as a source of chiral "F+":
References
{{Reflist Catalysis