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Phase transfer catalysis is the transport of a reactant from one immiscible phase into another, where the desired transformation occurs, by a catalyst that shuttles the reactive ion or molecule across the phase boundary ^[1][2]. In advanced synthetic organic chemistry the concept is bounded by a biphasic (or interfacial) reaction medium and by a catalyst—commonly a quaternary ammonium or phosphonium salt, a crown ether, or a chiral ion-pairing species—that is not itself the stoichiometric nucleophile. Essential features are ion exchange or complexation that solubilizes an otherwise phase-restricted anion, and return of the catalyst to the source phase so that turnover is achieved. Enantioselective variants use a chiral quaternary ammonium cation to ion-pair with a prochiral enolate, most classically a glycine Schiff-base ester, and thereby differentiate the faces of alkylation ^[1][3][4]. Chiral anion phase-transfer catalysis inverts the ion-pairing logic: a chiral phosphate or related anion associates with a cationic reagent and delivers it enantioselectively ^[2]. The concept is distinguished from micellar catalysis, in which rate effects arise from compartmentalization within aggregates rather than from stoichiometric ion transport, and from homogeneous organocatalysis conducted in a single phase.