Recent Developments in Enantioselective Organocatalytic Cascade Reactions for the Construction of Halogenated Ring Systems

Chiral halogenated substances have many applications in pharmaceuticals, agrochemicals, and materials, such as polymers, liquid crystals and as intermediates in synthesis. The presence of a halogen atom in a molecule can have a large effect in its properties; for instance, halogens are used in drugs to improve lipophilicity, membrane permeability and absorption, and even the blood-brain barrier permeability. As highlighted in this review, there are nowadays a range of highly selective, versatile halogenating reagents, electrophilic, nucleophilic or radical in nature, which operate under mild conditions, allowing late-stage functionalization of complex molecules in cascade reactions. Recent developments in organocatalyst design revealed novel Cinchona alkaloids derivatives, chiral phosphoric acids, amines, phosphines and several bifunctional catalysts, mostly thiourea- or squaramide-based, which introduced chirality, with high levels of enantio- and diastereoselection, in the formation of one or multiple chiral centers in a single synthetic operation, as shown. In this review we survey the literature published in this field from 2014 to 2020. © 2021 Wiley-VCH GmbH