Enantioselective halogenation via asymmetric phase‐transfer catalysis

The asymmetric phase‐transfer catalysis (PTC) is a flourishing field of contemporary synthetic organic chemistry, and this prominent methodology has been tremendously successful in enantioselective halogenations. Both electrophilic and nucleophilic reaction manifolds were enabled through the exploitation of highly ordered ion pairing and/or hydrogen‐bonding interactions around a carefully designed chiral phase‐transfer catalyst with an insoluble halogenating reagent as well as a suitable substrate. Fluorination has been the most fruitful, and encouraging results have also been documented with heavier halogens. This review surveys examples of various enantioselective halogenations via the asymmetric PTC from its beginning to prosperity over the past decade. The asymmetric phase‐transfer catalysis enabled mechanistically intriguing reaction manifolds for enantioselective halogenations by exploiting highly ordered noncovalent interactions between the chiral catalyst and the reactants. This review provides a compilation of the successful examples over the past decade with brief comments on the essential mechanistic rationales.