scholarly journals A radical approach to the copper oxidative addition problem: Trifluoromethylation of bromoarenes

Science ◽  
2018 ◽  
Vol 360 (6392) ◽  
pp. 1010-1014 ◽  
Author(s):  
Chip Le ◽  
Tiffany Q. Chen ◽  
Tao Liang ◽  
Patricia Zhang ◽  
David W. C. MacMillan
Keyword(s):  
Oxidative Addition ◽  
Open Shell ◽  
Past Century ◽  
Aryl Radical ◽  
Aryl Bromides ◽  
Addition Problem ◽  
Molecular Synthesis ◽  
Metal Catalyzed ◽  
High Valent ◽  
Radical Approach

Transition metal–catalyzed arene functionalization has been widely used for molecular synthesis over the past century. In this arena, copper catalysis has long been considered a privileged platform due to the propensity of high-valent copper to undergo reductive elimination with a wide variety of coupling fragments. However, the sluggish nature of oxidative addition has limited copper’s capacity to broadly facilitate haloarene coupling protocols. Here, we demonstrate that this copper oxidative addition problem can be overcome with an aryl radical–capture mechanism, wherein the aryl radical is generated through a silyl radical halogen abstraction. This strategy was applied to a general trifluoromethylation of aryl bromides through dual copper-photoredox catalysis. Mechanistic studies support the formation of an open-shell aryl species.

scholarly journals HARC as an open-shell strategy to bypass oxidative addition in Ullmann–Goldberg couplings

2020 ◽  
Vol 117 (35) ◽  
pp. 21058-21064
Author(s):  
Marissa N. Lavagnino ◽  
Tao Liang ◽  
David W. C. MacMillan
Keyword(s):  
Room Temperature ◽  
Elevated Temperatures ◽  
Large Range ◽  
Aryl Halide ◽  
Oxidative Addition ◽  
Open Shell ◽  
Bond Forming ◽  
Aryl Bromides ◽  
Sterically Demanding ◽  
Rapid Diversification

The copper-catalyzed arylation of unsaturated nitrogen heterocycles, known as the Ullmann–Goldberg coupling, is a valuable transformation for medicinal chemists, providing a modular disconnection for the rapid diversification of heteroaromatic cores. The utility of the coupling, however, has established limitations arising from a high-barrier copper oxidative addition step, which often necessitates the use of electron-rich ligands, elevated temperatures, and/or activated aryl electrophiles. Herein, we present an alternative aryl halide activation strategy, in which the critical oxidative addition (OA) mechanism has been replaced by a halogen abstraction–radical capture (HARC) sequence that allows the generation of the same Cu(III)-aryl intermediate albeit via a photoredox pathway. This alternative mechanistic paradigm decouples the bond-breaking and bond-forming steps of the catalytic cycle to enable the use of many previously inert aryl bromides. Overall, this mechanism allows access to both traditional C–N adducts at room temperature as well as a large range of previously inaccessible Ullmann–Goldberg coupling products including sterically demandingortho-substituted heteroarenes.

Monodentate Trialkylphosphines: Privileged Ligands in Metal-catalyzed Crosscoupling Reactions

2020 ◽  
Vol 24 (3) ◽  
pp. 231-264 ◽  
Author(s):  
Kevin H. Shaughnessy
Keyword(s):  
Transition Metal ◽  
Cross Coupling ◽  
Coupling Reactions ◽  
Cross Coupling Reactions ◽  
Aryl Bromides ◽  
Wide Range ◽  
Sterically Demanding ◽  
Transition Metal Catalyzed ◽  
Catalyzed Reactions ◽  
Metal Catalyzed

Phosphines are widely used ligands in transition metal-catalyzed reactions. Arylphosphines, such as triphenylphosphine, were among the first phosphines to show broad utility in catalysis. Beginning in the late 1990s, sterically demanding and electronrich trialkylphosphines began to receive attention as supporting ligands. These ligands were found to be particularly effective at promoting oxidative addition in cross-coupling of aryl halides. With electron-rich, sterically demanding ligands, such as tri-tertbutylphosphine, coupling of aryl bromides could be achieved at room temperature. More importantly, the less reactive, but more broadly available, aryl chlorides became accessible substrates. Tri-tert-butylphosphine has become a privileged ligand that has found application in a wide range of late transition-metal catalyzed coupling reactions. This success has led to the use of numerous monodentate trialkylphosphines in cross-coupling reactions. This review will discuss the general properties and features of monodentate trialkylphosphines and their application in cross-coupling reactions of C–X and C–H bonds.

scholarly journals Protecting group-free, selective cross-coupling of alkyltrifluoroborates with borylated aryl bromides via photoredox/nickel dual catalysis

2015 ◽  
Vol 112 (39) ◽  
pp. 12026-12029 ◽  
Author(s):  
Yohei Yamashita ◽  
John C. Tellis ◽  
Gary A. Molander
Keyword(s):  
Small Molecules ◽  
Functional Group ◽  
Cross Coupling ◽  
Differential Protection ◽  
Coupling Reactions ◽  
Protecting Group ◽  
Cross Coupling Reactions ◽  
Aryl Bromides ◽  
Rapid Construction ◽  
Metal Catalyzed

Orthogonal reactivity modes offer substantial opportunities for rapid construction of complex small molecules. However, most strategies for imparting orthogonality to cross-coupling reactions rely on differential protection of reactive sites, greatly reducing both atom and step economies. Reported here is a strategy for orthogonal cross-coupling wherein a mechanistically distinct activation mode for transmetalation of sp3-hybridized organoboron reagents enables C-C bond formation in the presence of various protected and unprotected sp2-hybridized organoborons. This manifold has the potential for broad application, because orthogonality is inherent to the activation mode itself. The diversification potential of this platform is shown in the rapid elaboration of a trifunctional lynchpin through various transition metal-catalyzed processes without nonproductive deprotection or functional group manipulation steps.

scholarly journals Oxidative Addition of Aryl Halides to a Ni(I)-Bipyridine Complex

2022 ◽  
Author(s):  
Stephen Ting ◽  
Wendy Williams ◽  
Abigail Doyle
Keyword(s):  
Oxidative Addition ◽  
Aryl Halides ◽  
Solution Phase ◽  
Nickel Catalysis ◽  
Mechanistic Studies ◽  
Redox Equilibrium ◽  
Aryl Bromides ◽  
First Time

The oxidative addition of aryl halides to bipyridine- or phenanthroline-ligated nickel(I) is a commonly proposed step in nickel catalysis. However, there is a scarcity of complexes of this type that both are well-defined and undergo oxidative addition with aryl halides, hampering organometallic studies of this process. We report the synthesis of a well-defined Ni(I) complex, [(CO2Etbpy)NiCl]4 (1). Its solution-phase speciation is characterized by a significant population of monomer and a redox equilibrium that can be perturbed by π-acceptors and σ-donors. 1 reacts readily with aryl bromides, and mechanistic studies are consistent with a mechanism proceeding through an initial Ni(I) → Ni(III) oxidative addition. Such a process was demonstrated stoichiometrically for the first time, affording a structurally characterized Ni(III) aryl complex.

ChemInform Abstract: Low-Temperature Formation of Functionalized Grignard Reagents from Direct Oxidative Addition of Active Magnesium to Aryl Bromides.

ChemInform ◽  
2000 ◽  
Vol 31 (48) ◽  
pp. no-no
Author(s):  
Jun-sik Lee ◽  
Raffet Velarde-Ortiz ◽  
Albert Guijarro ◽  
Joshua R. Wurst ◽  
Reuben D. Rieke
Keyword(s):  
Low Temperature ◽  
Oxidative Addition ◽  
Grignard Reagents ◽  
Aryl Bromides
Sign in / Sign up

Export Citation Format

Share Document