- Palladium-Catalyzed ipso-Borylation of Aryl Sulfides with Diborons
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A catalytic Miyaura-type ipso-borylation of aryl sulfides with diboron reagents has been achieved, providing arylboronate esters of synthetic use. The key conditions to transform inherently reluctant C-S bonds into C-B bonds include a palladium-NHC (N-heterocyclic carbene) precatalyst, bis(pinacolato)diboron, and lithium hexamethyldisilazide. This protocol is applicable to a reasonable range of aryl alkyl sulfides. Twofold borylation was observed in the reaction of diphenyl sulfide.
- Bhanuchandra,Baralle, Alexandre,Otsuka, Shinya,Nogi, Keisuke,Yorimitsu, Hideki,Osuka, Atsuhiro
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supporting information
p. 2966 - 2969
(2016/07/06)
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- Ipso-Fluorination of aryltrimethylsilanes using xenon difluoride
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Reaction of aryltrimethylsilanes with xenon difluoride in C 6F6/Pyrex at room temperature gives aryl fluorides in good yield. The reaction is inhibited when acetonitrile is used as solvent but proceeds well in CFCl3/Pyrex or CH 2Cl2/Pyrex. Pyrex appears to be a very effective heterogeneous catalyst for this ipso-fluorination. The reaction does not proceed in PTFE, quartz, soda glass or glassy-carbon flasks or Pyrex flasks pre-rinsed with 2 M NaOH. Aryltrimethylstannanes and arylboronic acids and their esters do not undergo ipso-fluorination under similar conditions. Plausible mechanisms involving electrophilic addition of polarised xenon difluoride [FXeδ+?F→Pyrex δ-] followed by ligand coupling are discussed.
- Lothian, Aileen P.,Ramsden, Christopher A.,Shaw, Maxine M.,Smith, Rachel G.
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experimental part
p. 2788 - 2793
(2011/05/02)
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- Palladium-catalyzed silylation of aryl chlorides with hexamethyldisilane
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A method for the palladium-catalyzed silylation of aryl chlorides has been developed. The method affords desired product in good yield, is tolerant of a variety of functional groups, and provides access to a wide variety of aryltrimethylsilanes from commercially available aryl chlorides. Additionally, a one-pot procedure that converts aryl chlorides into aryl iodides has been developed.
- McNeill, Eric,Barder, Timothy E.,Buchwald, Stephen L.
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p. 3785 - 3788
(2008/02/12)
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- Metallation reactions. Part 35: A change of the regiochemistry in the metallation of (alkylthio)arenes
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The metallation reaction of bromo(alkylthio)benzenes is described. The results show the complementarity of these reactions with the metal-hydrogen exchange reaction. In fact, monometallation of bromo(methylthio)benzenes afforded products substituted in para or meta or ortho to the thioethereal function while bimetallation led to αS,para, αS,meta and αS,ortho disubstituted products. Analogously, the monometallation of 4-bromo-(isopropylthio)benzene afforded para-monosubstituted and ortho,para-disubstituted products.
- Cabiddu, Maria G.,Cabiddu, Salvatore,Cadoni, Enzo,De Montis, Stefania,Fattuoni, Claudia,Melis, Stefana
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p. 3915 - 3920
(2007/10/03)
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- Arylcalcium hydrides as precursors to alkoxides and aryloxides of calcium
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Calcium atoms react with +I-substituted benzene derivatives under cocondensation conditions to yield arylcalcium hydrides. With toluene, tert-butylbenzene, and trimethyl(phenyl)silane the reaction showed no selectivity for C-H activation, resulting in the formation of each of the three possible isomers, while with m-xylene the reaction resulted in selective activation of the bond meta to the CH3 groups. Treatment of (tert-butylphenyl)calcium hydride with di- and trisubstituted phenols such as 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, and 2,4,6-tri-tert-butylphenol resulted in the formation of calcium aryloxides in yields > 95%. [Ca(2,4,6-tBu3C6H2O)2 (THF)3] crystallises from a THF solution as a distorted trigonal bipyramid, with two THF ligands in the trans-axial positions and the third THF ligand and both aryloxide groups in equatorial positions. The Ca-OAryl bond length was found to average at 2.181(3). A. The Ca-O-CAryl angles are almost linear, with Cal-O1-C1 and Ca1-O2-C19 being 173.9(3)° and 178.8(3)°, respectively, while the O1-Cal-O2 angle was determined as 157.04(12)°. A reaction between (tert-butylphenyl)calcium hydride and triphenylmethanol resulted in the formation of the corresponding monomeric calcium bis(alkoxide) Ca(OCPh3)2(THF)4 in 95% yield. The structure was determined as a distorted octahedron with the alkoxide ligands in a cis-equatorial arrangement. The Ca-O bond length was determined at 2.1609(17) A. The Ca-O-CAryl angle of 177.46(16)° is almost linear, while the O1-Cal-O1A angle was determined at 110.12(19)°. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).
- Dunne, John P.,Tacke, Matthias,Selinka, Carola,Stalke, Dietmar
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p. 1416 - 1425
(2007/10/03)
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- A mild and efficient protocol for the catalytic silylation of aryl bromides
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New catalyst systems were developed which facilitate palladium-catalyzed silylation of various functionalized aryl and heteroaryl bromides with hexamethyldisilane under unprecedented mild conditions. The use of two different sets of ligands and bases for electron-rich and electron-poor substrates, respectively, is crucial for achieving excellent product selectivities at 100 °C and atmospheric pressure. For electron-rich substrates, diphenyl-2'-pyridylphosphine in combination with K2CO3 gives the best results, whereas for electron-poor substrates, 2-(di-t-butylphosphino)biphenyl/KF is preferred. Even base-sensitive arylsilanes, which are inaccessible by the traditional routes via organolithium species or Grignard reagents, can be prepared in a single step and high yields.
- Goossen,Ferwanah
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p. 1801 - 1803
(2007/10/03)
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- Transmission of electronic effects via a SiMe2 spacer in 4-mono- and 4,4'-disubstituted diphenyldimethylsilanes: 29Si and 13C NMR spectroscopy and PM3 semi-empirical calculations
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Some 29Si and 13C NMR studies were performed of series of 4-substituted phenyltrimethylsilanes and 4-substituted and 4,4'-disubstituted diphenyldimethylsilanes.Within each series linear relationships are found between the chemical shifts and (a) the Hammett substituent constants ?p and (b) the PM3-calculated total atomic charges.It is inferred that the SiMe2 ?-type spacer weakly mediates substituent effects in the ground state via a bond polarization mechanism.A comparison with available data for 4-substituted and 4,4'-disubstituted diphenylmethanes shows that the SiMe2 group is a better transmitter of electronic effects that the CH2 group. Keywords: Silicon; 29Si NMR; 13C NMR; Substituent effects; MO calculations
- Walree, Cornelis A. van,Lauteslager, Xavier Y.,Wageningen, Andreas M. A. van,Zwikker, Jan W.,Jenneskens, Leonardus W.
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p. 117 - 126
(2007/10/02)
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