The Suzuki-Miyaura cross-coupling of sterically hindered and electron-rich ortho,ortho'-substituted aryl halides with potassium vinyltrifluoroborate utilizing microwave irradiation has been conducted while adjusting solvent ratio, irradiation time, and catalyst loading to find optimal conditions. Coupling of benzyl 3,5-bis(benzyloxy)-4-bromobenzoate leads to a mixture of the desired styrene derivative, and the reduced product. 4-Bromo-1,3,5-trimethoxybenzene, methyl 4-bromo-3,5-dimethoxybenzoate, and mesitylene bromide were also coupled to test the breadth and scope of this methodology. Of these substrates tested only 4-bromo-1,3,5-trimethoxybenzene was not vinylated successfully, which is believed to be due to the electron rich nature of this system. KeywordsSuzuki-Miyaura; Potassium vinyltrifluoroborate; Styrenes; Palladium catalysis; Hindered aryl bromides Substituted styrenes (typically assembled using a transition metal-mediated cross-coupling) are useful intermediates in both the formation of new polymeric material and in the formation of specialty chemicals. 1 Mild vinylation of aryl bromides and/or iodides using trivinylcyclotriboroxane,1 vinylmagnesium bromide,2 vinyltrimethylsilane,3 and vinylpolysiloxanes 4 has been observed. N-Heterocyclic carbenes bearing palladium (II) catalysts have demonstrated high catalytic activity capable of coupling unactivated aryl chlorides. 5 Aryl bromides and activated aryl chlorides also undergo mild palladiumcatalyzed couplings at room temperature with alkenes utilizing dicyclohexylmethylamine as © 2010 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: 843-953-6587; fax 843-953-1404; wyattj@cofc.edu.Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. (2) with the assistance of microwave irradiation. NIH Public AccessScheme 1 illustrates the first reaction of interest, and the two possible products of the crosscoupling reaction; the desired vinylated product, benzyl 3,5-bis(benzyloxy)-4-vinylbenzoate (3), and reduced product, benzyl 3,5-bis(benzyloxy)benzoate (4). As with conventional conditions 14 the reduced product was observed under microwave conditions, but only in trace amounts (less than 1% of the total product distribution). Product ratios were determined, if necessary, using 1 H NMR integration of the crude reaction mixture using the methylene hydrogens from the benzyl ethers of the starting material 1, as well as for the vinyl product 3; chemical shifts of 5.18 ppm (s, 4H) and 5.14 ppm (s, 4H), respectively. The amount of reduced product 4, if any, was determined by integration of the triplet at 6...
Abstractortho,ortho′‐Substituted aryl bromides are vinylated in a Pd‐catalyzed Suzuki—Miyaura reaction.
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