Self-control tames the coupling of reactive radicals

Abstract

ABSTRACT:The mechanism of gold-catalyzed coupling of arenes with aryltrimethylsilanes has been investigated employing an improved precatalyst (thtAuBr3) to facilitate kinetic analysis. In combination with linear free-energy relationships, kinetic isotope effects, and stoichiometric experiments, the data support a mechanism involving an Au(I) / Au(III) redox cycle in which sequential electrophilic aromatic substitution of the arylsilane and the arene by Au(III) precedes productforming reductive elimination and subsequent, cycle-closing reoxidation of the metal. Despite the fundamental mechanistic similarities between the two auration events, high selectivity is observed for heterocoupling (C-Si then C-H auration) over homocoupling of either the arylsilane or the arene (C-Si then C-Si, or C-H then C-H auration): this chemoselectivity originates from differences in the product-determining elementary steps of each electrophilic substitution. The turnover-limiting step of the reaction involves associative substitution en route to an arene π-complex. The ramifications of this insight for implementation of the methodology are discussed.

Nickel-Catalyzed Cross-Coupling of Photoredox-Generated Radicals: Uncovering a General Manifold for Stereoconvergence in Nickel-Catalyzed Cross-Couplings

“…Herein, we report a detailed density functional theory (DFT) study of the catalytic cross-coupling of alkyl­trifluoro­borates and aryl bromides via single-electron transmetalation. Results reveal that the final reductive elimination accounts for the origin of stereo­induction for this important transformation . A stereo­chemical model is proposed and, for the first time, supported by experiments with a series of substituted aryl bromides.…”

“…Results reveal that the final reductive elimination accounts for the origin of stereoinduction for this important transformation. 8 A stereochemical model is proposed and, for the first time, supported by experiments with a series of substituted aryl bromides. These mechanistic findings are proposed to have far-reaching implications related to other stereoconvergent CCRs.…”

Photoredox Cross-Coupling: Ir/Ni Dual Catalysis for the Synthesis of Benzylic Ethers

“…Furthermore, the controlled radical generation afforded by these catalysts opens the door to a host of net redox neutral transformations that would have been previously impossible using stoichiometric reagents, where unproductive reductant/oxidant quenching and radical side products are an inevitable shortcoming. 4 To date, many new and innovative reactions have been designed around the use of photoredox single-electron transfer (SET) catalysts, leading to a resurgence in radical-mediated methods for C–C bond formation.…”

“…Visible-light mediated photoredox catalysis has become recognized as an empowering technology for radical-mediated chemistry in recent years. − By transiently generating catalytic quantities of both a single-electron oxidant and reductant within the confines of the same flask, typically inert substrates can be activated for reaction. Furthermore, the controlled radical generation afforded by these catalysts opens the door to a host of net redox neutral transformations that would have been previously impossible using stoichiometric reagents, where unproductive reductant/oxidant quenching and radical side products are an inevitable shortcoming . To date, many new and innovative reactions have been designed around the use of photoredox single-electron transfer (SET) catalysts, leading to a resurgence in radical-mediated methods for C–C bond formation.…”

Eine Iod‐katalysierte Hofmann‐Löffler‐Reaktion

“…[19b] Demgegenüber verlangt unser Szenario zweier miteinander verflochtener,s ynergistischer Zyklen einen kinetisch effizienten Iodkatalysator im Zusammenspiel mit der parallel verlaufenden Radikalkettenreaktion, da die beiden Te ilzyklen nicht unabhängig voneinander ablaufen kçnnen. [20] [21] Des Wei-Angewandte Chemie teren geht das Tr yptaminderivat 1ae eine selektive Aminierung zum cyclischen Aminal 2ae ein, wodurch der Synthese von Cyclotryptamin-Alkaloiden [22] neue Mçglichkeiten erçffnet werden.…”