Halides as versatile anions in asymmetric anion-binding organocatalysis

Abstract

This review intends to provide an overview on the role of halide anions in the development of the research area of asymmetric anion-binding organocatalysis. Key early elucidation studies with chloride as counter-anion confirmed this type of alternative activation, which was then exploited in several processes and contributed to the advance and consolidation of anion-binding catalysis as a field. Thus, the use of the halide in the catalyst–anion complex as both a mere counter-anion spectator or an active nucleophile has been depicted, along with the new trends toward additional noncovalent contacts within the HB-donor catalyst and supramolecular interactions to both the anion and the cationic reactive species.

Branching out: redox strategies towards the synthesis of acyclic α-tertiary ethers

“…401 Recently, Seidel developed a reductive etherification reaction using anion-binding catalysis. 402,403 A derivative of Schreiner's thiourea catalyst was designed to facilitate the formation and increase the electrophilicity of the intermediate oxocarbenium ion and enabled the synthesis of an a-tertiary example in 65% yield. 404 Boron-based reducing agents have also been employed to generate a-tertiary ethers using this reductive etherification strategy; Scheunemann utilised decaborane as a mild and fairly stable reducing agent to yield a tert-butyl ether while investigating a onestep reductive etherification of 4-[ 18 F] fluoro-benzaldehyde for use in positron emission tomography.…”

Organocatalysis: A Tool of Choice for the Enantioselective Nucleophilic Dearomatization of Electron-Deficient Six-Membered Ring Azaarenium Salts

“…Nevertheless, in the last fifteen years and due to the advent of organocatalysis [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36], which was recently highlighted through the Nobel Prize of Prof. B. List and Prof. D. MacMillan, several enantioselective organocatalytic dearomatization reactions of azaarenium salts have been reported [11,[13][14][15][16]18,19,37,38]. Organocatalysts can be classified following the mode of activation of either the electrophilic and/or nucleophilic partners involved in a given reaction [24,25].…”

New advances in asymmetric organocatalysis

“…The evolution of the understanding of noncovalent activation modes led to the realization that anion-binding is a critical feature in many transformations. Halide anions are highly relevant and widely occurring within many reactions and a variety of organocatalysts can engage with them [ 18 ].…”