3976-34-9Relevant academic research and scientific papers
Dual Roles for Potassium Hydride in Haloarene Reduction: CSNAr and Single Electron Transfer Reduction via Organic Electron Donors Formed in Benzene
Barham, Joshua P.,Dalton, Samuel E.,Allison, Mark,Nocera, Giuseppe,Young, Allan,John, Matthew P.,McGuire, Thomas,Campos, Sebastien,Tuttle, Tell,Murphy, John A.
supporting information, p. 11510 - 11518 (2018/09/12)
Potassium hydride behaves uniquely and differently than sodium hydride toward aryl halides. Its reactions with a range of haloarenes, including designed 2,6-dialkylhaloarenes, were studied in THF and in benzene. In THF, evidence supports concerted nucleophilic aromatic substitution, CSNAr, and the mechanism originally proposed by Pierre et al. is now validated through DFT studies. In benzene, besides this pathway, strong evidence for single electron transfer chemistry is reported. Experimental observations and DFT studies lead us to propose organic super electron donor generation to initiate BHAS (base-promoted homolytic aromatic substitution) cycles. Organic donor formation originates from deprotonation of benzene by KH; attack on benzene by the resulting phenylpotassium generates phenylcyclohexadienylpotassium that can undergo (i) deprotonation to form an organic super electron donor or (ii) hydride loss to afford biphenyl. Until now, BHAS reactions have been triggered by reaction of a base, MOtBu (M = K, Na), with many different types of organic additive, all containing heteroatoms (N or O or S) that enhance their acidity and place them within range of MOtBu as a base. This paper shows that with the stronger base, KH, even a hydrocarbon (benzene) can be converted into an electron-donating initiator.
Evidence of single electron transfer from the enolate anion of an: N, N ′-dialkyldiketopiperazine additive in BHAS coupling reactions
Emery, Katie J.,Tuttle, Tell,Murphy, John A.
, p. 8810 - 8819 (2017/11/03)
A designed N,N′-dialkyldiketopiperazine (DKP) provides evidence for the role of DKP additives as initiators that act by electron transfer in base-induced homolytic aromatic substitution reactions, involving coupling of haloarenes to arenes.
KOtBu: A Privileged Reagent for Electron Transfer Reactions?
Barham, Joshua P.,Coulthard, Graeme,Emery, Katie J.,Doni, Eswararao,Cumine, Florimond,Nocera, Giuseppe,John, Matthew P.,Berlouis, Leonard E. A.,McGuire, Thomas,Tuttle, Tell,Murphy, John A.
supporting information, p. 7402 - 7410 (2016/07/06)
Many recent studies have used KOtBu in organic reactions that involve single electron transfer; in the literature, the electron transfer is proposed to occur either directly from the metal alkoxide or indirectly, following reaction of the alkoxide with a solvent or additive. These reaction classes include coupling reactions of halobenzenes and arenes, reductive cleavages of dithianes, and SRN1 reactions. Direct electron transfer would imply that alkali metal alkoxides are willing partners in these electron transfer reactions, but the literature reports provide little or no experimental evidence for this. This paper examines each of these classes of reaction in turn, and contests the roles proposed for KOtBu; instead, it provides new mechanistic information that in each case supports the in situ formation of organic electron donors. We go on to show that direct electron transfer from KOtBu can however occur in appropriate cases, where the electron acceptor has a reduction potential near the oxidation potential of KOtBu, and the example that we use is CBr4. In this case, computational results support electrochemical data in backing a direct electron transfer reaction.
Resorcinarenyl-phosphines in suzuki-miyaura cross-coupling reactions of aryl chlorides
Monnereau, Laure,El Moll, Hani,Sémeril, David,Matt, Dominique,Toupet, Lo?c
supporting information, p. 1364 - 1372 (2015/04/27)
Two phosphines built on a bowl-shaped resorcin[4]arene skeleton, namely 5-diphenylphosphanyl- and 5-diisopropylphosphanyl-4(24),6(10),12(16),18(22)-tetramethylenedioxy-2,8,14,20-tetrapentylresorcin[4]arene, have been synthesised and tested in the Suzuki-Miyaura cross-coupling reaction of aryl halides. Combining these ligands with [Pd(OAc)2] resulted in highly active catalysts that allowed the formation of o,o-biphenyls starting from aryl chlorides. The remarkable activities observed possibly arise from 1) the capacity of the phosphines to operate transiently as P,O chelators, thereby increasing the electron density of the metal, and 2) the ability of the ligands to embed metal-organic units, which, when occurring, makes the ligand considerably bulkier so as to disfavour the coordination of a second phosphine. Both features are known to facilitate the oxidative addition step. Palladium complexes containing cavitand-phosphines based on a resorcinarene skeleton display high reactivity in Suzuki-Miyaura cross-coupling reactions. The unusual performance of these ligands essentially relies on their bulkiness and ability to bind the metal centre in a hemilabile fashion.
Palladium-catalyzed arylation of simple arenes with iodonium salts
Storr, Thomas E.,Greaney, Michael F.
supporting information, p. 1410 - 1413 (2013/05/09)
The development of an arylation protocol for simple arenes with diaryliodonium salts using the Herrmann-Beller palladacycle catalyst is reported. The reaction takes simple aromatic feedstocks and creates valuable biaryls for use in all sectors of the chem
Facile access to sterically hindered aryl ketones via carbonylative cross-coupling: Application to the total synthesis of luteolin
O'Keefe, B. Michael,Simmons, Nicholas,Martin, Stephen F.
scheme or table, p. 4344 - 4351 (2011/07/29)
A general and mild protocol for achieving the carbonylative cross-coupling of sterically hindered, ortho-disubstituted aryl ketones is reported. The commercially available PEPPSI-IPr catalyst is shown to efficiently promote the carbonylative cross-coupling of hindered ortho-disubstituted aryl iodides to give diaryl ketones; traditional phosphine catalysts are less effective. Carbonylative Suzuki-Miyaura cross-couplings provide a diverse array of biaryl ketones in good to excellent yields. The same catalyst is also shown to catalyze a carbonylative Negishi cross-coupling reaction, utilizing a variety of alkynyl-zinc reagents to give the corresponding alkynyl aryl ketones. Application of this new methodology to the synthesis of the natural product luteolin is reported.
Application of a readily available and air stable monophosphine HBF4 salt for the Suzuki coupling reaction of aryl or 1-alkenyl chlorides
Lü, Bo,Fu, Chunling,Ma, Shengming
supporting information; experimental part, p. 1284 - 1286 (2010/04/27)
In this Letter, a readily available monophosphine HBF4 salt was applied for the Suzuki coupling reactions of organoboronic acids to afford the cross-coupling products in high to excellent yields. Both aryl or 1-alkenyl boronic acids and chlorides may be used. It is also suitable for sterically hindered cases.
Carbonylative cross-coupling of ortho-disubstituted aryl iodides. Convenient synthesis of sterically hindered aryl ketones
Michael O'Keefe,Simmons, Nicholas,Martin, Stephen F.
supporting information; experimental part, p. 5301 - 5304 (2009/06/18)
(Chemical Equation Presented) A mild and general protocol for the carbonylative cross-coupling of sterically hindered ortho-disubstituted aryl iodides is reported. Carbonylative Suzuki-Miyaura couplings of a variety of aryl boronic acids provide an array of substituted biaryl ketones in modest to excellent yield. A carbonylative Negishi coupling that utilizes alkynyl nucleophiles is also described.
Iron-mediated direct arylation of unactivated arenes
Wen, Jun,Zhang, Ji,Chen, Shan-Yong,Li, Jing,Yu, Xiao-Qi
supporting information; experimental part, p. 8897 - 8900 (2009/05/26)
(Chemical Equation Presented) Inexpensive and straightforward: An iron-mediated cross-coupling reaction generates biaryl compounds through C-H bond activation, using easily handled reagents with low toxicity. Under the optimized reaction conditions a series of substituted phenylboronic acids were coupled with several simple unactivated arenes.
Ligands for metals and improved metal-catalyzed processes based thereon
-
, (2008/06/13)
One aspect of the present invention relates to ligands for transition metals. A second aspect of the present invention relates to the use of catalysts comprising these ligands in transition metal-catalyzed carbon-heteroatom and carbon-carbon bond-forming reactions. The subject methods provide improvements in many features of the transition metal-catalyzed reactions, including the range of suitable substrates, reaction conditions, and efficiency.
