Asymmetric Nickel-Catalyzed Reactions

Abstract

The primary objective of synthetic organic chemists is the efficient synthesis of carbon–carbon bonds. The asymmetric reaction has emerged as a valuable tool for this aim among the many other techniques. Asymmetric synthesis is useful in synthesizing stereoisomeric compounds for various applications as different enantiomers of particular compounds are found to exert different biological activities. This chapter describes the C–C bond formation via asymmetric nickel-catalyzed reactions through seven different types of synthetic methodologies. Herein we cover asymmetric nickel-catalyzed cascade reactions, aldol type reactions, cyclization strategy, hydrofunctionalization, addition reaction, cross-coupling techniques, and C–H functionalization reactions. Aldol reactions have undergone major recent advancements, most of which focused on the activation of the aldol acceptor employing chiral nickel complexes as catalysts. Recent advances in homogeneous catalysis, particularly, in the field of enantioselective hydrofunctionalization of alkenes are shown to use of earth-abundant nickel-catalysts. In the nickel-catalyzed asymmetric addition reactions, several chiral nickel complexes based on chiral ligands have been studied, including chiral bidentate imine ligands, chiral oxazoline ligands, chiral bisoxazoline ligands, and chiral NHC ligands. Cross-coupling reactions provide another alternate route to synthesize C–C bonds using a different variety of chiral nitrogen and phosphorous ligands with high enantioselectivity. Various metals (Grignard, zinc), boron reagents, and aryl or alkyl halides are well studied as nucleophiles and electrophiles for the coupling reaction. Chiral nickel compounds have particularly been important in the development of catalytic Friedel–Crafts alkylation processes that are enantioselective. Nickel-based catalysts were shown to produce the Friedel–Crafts adducts in high yields and with excellent stereocontrol for the production of biologically relevant compounds. Asymmetric allylation have also been executed using several nickel-complexes with chiral ligands. These catalytic asymmetric reactions are helpful for the synthesis of diverse compounds with high enantioselectivity since double bonds and triple bonds are so versatile in terms of synthesis. The stereochemical characteristics of asymmetric nickel-catalyzed reactions with proper mechanistic approaches are covered in this chapter.