10.1002/anie.202007030
The study presents a novel light-driven approach to Grubbs metathesis, facilitated by the gem-hydrogenation of internal alkynes using [(NHC)(cymene)RuCl2] (NHC = N-heterocyclic carbene) complexes. This method results in the formation of discrete Grubbs-type ruthenium carbene species, which can be harnessed for a "hydrogenative metathesis" reaction that converts enyne substrates into cyclic alkenes. The research explores the unique reactivity of these complexes under UV irradiation, leading to the efficient formation of various cycloalkene products. The study also discusses the potential and limitations of this new catalyst system, as well as providing experimental evidence for the formation of Grubbs-type carbenes through alkyne gem-hydrogenation. This innovative method offers a non-canonical entry into the field of metathesis chemistry, expanding the scope of catalytic hydrogenation and Grubbs catalysis.
10.1002/chem.201100160
The research focuses on the doping effect of fluorinated aromatic solvents (FAHs) on the rate of olefin metathesis reactions catalyzed by ruthenium complexes with N-heterocyclic carbene (NHC) ligands. The study explores how the use of FAHs as solvents can significantly enhance the yields of desired products in olefin metathesis reactions, particularly for complex and biologically active molecules. Through a series of experiments, including ring-closing metathesis (RCM), enyne reactions, and cross-metathesis (CM), the researchers observed substantial improvements in turnover numbers (TONs) and yields when using FAHs compared to traditional solvents like 1,2-dichloroethane and toluene. The experiments involved the use of standard commercially available ruthenium pre-catalysts and a variety of substrates to test the efficiency of the reactions under different conditions. Analyses such as X-ray structure analysis, 31P NMR, and computational studies were employed to understand the interactions between the FAHs and the ruthenium catalysts, which were found to improve the efficiency of the olefin metathesis transformation. The study suggests that FAHs can be an attractive alternative medium for promoting challenging olefin metathesis reactions and potentially lead to the design of new improved ruthenium catalysts.
10.1016/j.chempr.2019.07.023
This study presents a novel dimeric gold-catalyzed oxidative cross-coupling method for the synthesis of a diverse range of biaryl compounds using arylboronates and arylsilanes. The method overcomes the limitations of traditional gold-catalyzed o,p-orientation rules and is effective for electron-rich arenes through C–H bond activation. It exhibits excellent tolerance for various functional groups and offers a flexible synthetic approach to (pseudo)halogenated biaryls. The research demonstrates the unique catalytic efficiency of a dimeric gold complex and the preparation of biaryl pharmacophores under pseudoneutral conditions, which is significant for the synthesis of complex organic materials and pharmaceuticals. The study also includes the successful synthesis of several biaryl pharmacophores and p-conjugated organic materials, highlighting the method's synthetic value and versatility.
10.1016/S0040-4020(00)00626-8
The study presents an eco-friendly and cost-effective method for the tosylation of alcohols and selective monotosylation of diols using p-toluenesulfonic acid with metal-exchanged montmorillonite clay as a catalyst. The Fe3+-montmorillonite clay demonstrated the highest effectiveness among the tested catalysts, outperforming Zn2+, Cu2+, Al3+-exchanged montmorillonites and K10 montmorillonite. This method allows for the regioselective tosylation of diols to monotosylated derivatives with high purity, favoring the primary hydroxy group in the presence of secondary hydroxy groups. The catalyst's reusability over several cycles was consistent, as shown in the tosylation of cyclohexanol. This approach minimizes by-product formation, typically just water, and offers advantages such as ease of catalyst recovery, recyclability, and enhanced stability compared to traditional methods using sulfonyl chloride or anhydride with organic bases.
10.1002/chem.201002563
The research primarily focuses on the development of an asymmetric conjugate addition reaction of 3-substituted oxindoles to 2-chloroacrylonitrile, utilizing a chiral alkyl thiourea as a catalyst. This reaction is significant for the construction of chiral pyrroloindoline structures, which are key components in many biologically active indole alkaloids. The experiments involved screening various bifunctional tertiary amine thioureas or urea catalysts to optimize the reaction conditions, ultimately achieving high yields and excellent stereoselectivity. Reactants included 3-substituted oxindoles and 2-chloroacrylonitrile, with the catalysts being screened at low temperatures. Analyses used to determine the success of the reactions included 1H NMR spectroscopy for diastereomeric ratios and chiral HPLC analysis for enantiomeric excess. The optimized conditions were identified as using 4a catalyst in 1,2-dichloroethane at -20°C with 4 ? molecular sieves, yielding products with up to >30:1 dr and up to 99% ee.
10.1002/jhet.5570370603
The research aimed to develop a new and convenient method for the synthesis of 3-substituted 4,5-dihydro-5-oxo-1,2,4-thiadiazoles, which are potentially useful as nonpeptide angiotensin II receptor antagonists. The study focused on the reaction of amidoximes with 1,1'-thiocarbonyldiimidazole (TCDI) in the presence of Lewis acids such as silica gel or boron trifluoride diethyl etherate (BF3-OEt2). The reaction yielded 3-substituted 4,5-dihydro-5-oxo-1,2,4-thiadiazoles in moderate yields, with the Lewis acids promoting the rearrangement of thioxocarbamate intermediates to thiolcarbamate intermediates, which then cyclize to form the desired thiadiazoles. The researchers concluded that their method provided a facile synthesis of these compounds, which could be applied to a variety of aromatic and aliphatic amidoximes bearing different substituents. Key chemicals used in the process included amidoximes, TCDI, silica gel, BF3-OEt2, and various solvents such as tetrahydrofuran, dichloromethane, and 1,2-dichloroethane.
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