Silyldefluorination of Fluoroarenes by Concerted Nucleophilic Aromatic Substitution

Abstract

The reaction of readily generated silyl lithium reagents with various aryl fluorides to provide the corresponding aryl silanes is reported. DFT calculations reveal that the nucleophilic aromatic substitution of the fluoride anion by the silyl lithium reagent proceeds through concerted ipso substitution. In contrast to the classical nucleophilic aromatic substitution, this concerted ionic silyldefluorination also occurs on more electron‐rich aryl fluorides.

Konzertierte nukleophile aromatische Substitutionen

“…Arylfluoride wurden kürzlich von Würthwein, Studer et al. einer ganz anderen cS N Ar‐Reaktion unterzogen, wobei Silyllithiumreagentien als Nukleophile verwendet wurden . Dies stellte insofern eine interessante Entwicklung dar, als in früheren Reaktionen von Arylhalogeniden (insbesondere Iodiden) mit ähnlichen Reagenzien direkt am Halogenatom ein Silylhalogenid und ein Aryllithium als reaktive Zwischenprodukte erhalten wurden.…”

In Situ Generation of Silyl Anion Species through Si−B Bond Activation for the Concerted Nucleophilic Aromatic Substitution of Fluoroarenes

“…It has been reported that R 3 Si−B(pin) can efficiently form a silyl‐borate complex with alkoxides, but it was not clear whether a highly reactive silyl anion equivalent could be generated from the silyl‐borate species and practically utilized. We selected the defluorosilylation reaction of Ph−F as a model reaction, based on the experimental observation by Würthwein and Studer that the S N Ar (nucleophilic aromatic substitution) reaction of unactivated fluoroarenes with silyllithiums proceeds smoothly without any transition metal (TM) catalyst . S N Ar reaction has long been considered to proceed in a stepwise manner via the Meisenheimer intermediate, though more recently an in‐depth mechanistic study by Jacobsen demonstrated that S N Ar reaction also occurs via a concerted pathway…”

“…We selected the defluorosilylation reaction [11][12] of PhÀ F as a model reaction, based on the experimental observation by Würthwein and Studer that the S N Ar (nucleophilic aromatic substitution) reaction of unactivated fluoroarenes with silyllithiums proceeds smoothly without any transition metal (TM) catalyst. [13] S N Ar reaction has long been considered to proceed in a stepwise manner via the Meisenheimer intermediate, [14] though more recently an in-depth mechanistic study by Jacobsen [15] demonstrated that S N Ar reaction also occurs via a concerted pathway. [16] The possible S N Ar reaction pathways of PhÀ F are shown in Figure 1.…”

Defluorosilylation of Industrially Relevant Fluoroolefins Using Nucleophilic Silicon Reagents

“…[5][6][7] In contrast, s-block silyl anions (M-SiR 3 ;M= Li, Na, K) have been invoked as intermediates in highly efficient methods for the defluorosi-lylation of sp 2 C À Fbonds of fluoroarenes and terminal sp 3 C À Fb onds of fluoroalkanes. [8][9][10][11] In related studies we,a nd others,h ave shown that main group nucleophiles are exceptional reagents for the CÀFfunctionalisation of fluoroarenes, fluoroalkenes and fluoroalkanes. [12][13][14][15][16][17] Strong M-F interactions provide al arge thermodynamic driving force for the reaction and can also play arole in determining the selectivity of which C À Fbond reacts.…”

“…[5][6][7] An umber of lithium and magnesium silyls were synthesized. [8,9] Magnesium silyl reagents (1-4)w ere prepared by at wo-step procedure involving sequential deprotonation of the pro-ligand (b-diketiminate,i minoanilide or guanidine) with [Mg n/s Bu 2 ]f ollowed by am etathesis reaction with R 3 Si-Bpin ( Figure 1). [18] In an alternative approach, lithium silyls (5·THF, 5·TMEDA, 5·PMDETA)w ere synthesised by direct metalation of PhMe 2 SiCl with Li metal (Figure 1).…”