Enantioselective conjugate additions of arylboronic acids to β-substituted cyclic enones have been previously reported from our laboratories. Air- and moisture-tolerant conditions were achieved with a catalyst derived in situ from palladium(II) trifluoroacetate and the chiral ligand (S)-t-BuPyOx. We now report a combined experimental and computational investigation on the mechanism, the nature of the active catalyst, the origins of the enantioselectivity, and the stereoelectronic effects of the ligand and the substrates of this transformation. Enantioselectivity is controlled primarily by steric repulsions between the t-Bu group of the chiral ligand and the α-methylene hydrogens of the enone substrate in the enantiodetermining carbopalladation step. Computations indicate that the reaction occurs via formation of a cationic arylpalladium(II) species, and subsequent carbopalladation of the enone olefin forms the key carbon-carbon bond. Studies of nonlinear effects and stoichiometric and catalytic reactions of isolated (PyOx)Pd(Ph)I complexes show that a monomeric arylpalladium-ligand complex is the active species in the selectivity-determining step. The addition of water and ammonium hexafluorophosphate synergistically increases the rate of the reaction, corroborating the hypothesis that a cationic palladium species is involved in the reaction pathway. These additives also allow the reaction to be performed at 40 °C and facilitate an expanded substrate scope.
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http://dx.doi.org/10.1021/ja401713g | DOI Listing |
Org Lett
December 2024
School of Chemistry & Chemical Engineering, Yangzhou University, Yangzhou, Jiangsu 225002, China.
We present a tandem aza-Heck/Suzuki cross-coupling reaction of -phenyl hydroxamic ethers with readily available arylboronic and alkenyl boronic acids. This protocol is enabled by a palladium catalyst paired with chiral phosphoramidite ligands, particularly under mild reaction conditions, yielding efficient and succinct synthetic routes to chiral isoindolinones with high enantioselectivity. Furthermore, this reaction exhibits excellent functional group compatibility and a rich diversity of subsequent transformations.
View Article and Find Full Text PDFJ Org Chem
December 2024
Department of Chemistry, Jadavpur University, Kolkata 700032, India.
We have developed a novel protocol for carbonylative homocoupling of arylboronic acids using dithiocarbamate esters as the carbonyl alternative. A series of arylboronic acids underwent smooth reaction with dithiocarbamate ester (MeNCSMe) in the presence of Pd(PPh)Cl catalyst, Cu(OAc)·HO additive, and NaCO in DCE solvent, producing the biaryl ketones efficiently. The mechanism has been studied with the help of several control experiments that reveal the probability of thioamide intermediacy.
View Article and Find Full Text PDFOrg Biomol Chem
December 2024
Department of Chemistry, Southern Federal University, Zorge str. 7, 344090 Rostov-on-Don, Russian Federation.
6-Bromo- and 6,7-dibromo-1,3-dimethyl-1-perimidin-2(3)-ones were arylated with arylboronic acids under Suzuki-Miyaura reaction conditions to afford 6-aryl-, 6-bromo-7-aryl- and 6,7-diaryl-1,3-dimethyl-1-perimidin-2(3)-ones. A comparison of the X-ray structural parameters of -diaryl derivatives of 1,3-dimethyl-1-perimidin-2(3)-one, naphthalene and 1,8-bis(dimethylamino)naphthalene (proton sponge) was performed. Based on the data of dynamic H NMR spectroscopy and quantum-chemical calculations, barriers to /-isomerization of 6,7-diaryl-1,3-dimethyl-1-perimidin-2(3)-ones were estimated.
View Article and Find Full Text PDFOrg Lett
December 2024
School of Life Sciences and Medicine, Shandong University of Technology, Zibo 255000, Shandong, P. R. China.
A nickel-catalyzed intermolecular three-component 1,1-difunctionalization of unactivated alkenes with quinoxaline/naphthoquinone and arylboronic acids via organometallic-radical relay is developed. This efficient protocol provides a new method to access a variety of arylalkanes in moderate to good yields with a broad substrate scope and excellent functional group tolerance. The mechanistic studies provide insights into the mechanism and origin of chemo- and regioselectivity as well as confirm the generation of functionalized benzylic radicals.
View Article and Find Full Text PDFJ Org Chem
December 2024
Department of Chemistry, University of Idaho, Moscow, Idaho 83844, United States.
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