Enantioselective Brønsted Acid Catalysis in the Friedel-Crafts Reaction of Indoles with Secondary ortho-Hydroxybenzylic Alcohols
Contributors: Wilcke, David, Herdtweck, Eberhardt, Bach, Thorsten
... Abstract The reaction of indole and various methyl-substituted indoles with the title compounds was studied in the presence of chiral phosphoric acids, which act as Brønsted acid catalysts. While yields were generally high (>90%), significant enantioselectivities (up to 77% ee) were only achieved for certain substrate-catalyst combinations. In addition, a kinetic resolution of the starting material was observed, which led to an enrichment of one chiral alcohol to up to 68% ee after 76% conversion. The Friedel-Crafts reaction is not stereospecific (no direct SN2-type substitution), but rather is likely to proceed via a cation, which is bound to the chiral Brønsted acid or its anion in a close contact ion pair.
A Novel Catalyst-Free Tandem Reaction for the Synthesis of 5-Hydroxy-1,5-dihydro-2H-pyrrol-2-ones in Water Medium
Contributors: Wu, Ming-Yu, Li, Kun, Wang, Na, He, Ting, Yu, Xiao-Qi
... Abstract A novel catalyst-free, water-medium, tandem reaction for the synthesis of 5-hydroxy-1,5-dihydro-2H-pyrrol-2-ones was developed through a one-pot strategy from nitroethylenes and 1,3-dicarbonyl compounds. A series of 1-aryl-2-nitroethenes and 1-nitroalk-1-enes were surveyed to determine the scope of this tandem reaction with moderate to good yield.
Contributors: Lu, Yongzhong, Wang, Ruiping, Qiao, Xixue, Shen, Zengming
... Abstract The copper-catalyzed C-H halogenation of 2-arylpyridines containing a variety of electron-withdrawing and electron-donating substituents was described. It is worth noting that cheap and easy-to-handle lithium halides were utilized as the halogen sources.
Lithium Dibenzylamide, a Simple, Selective and Highly Efficient Catalyst for Isocyanate Cyclotrimerization to Isocyanurate
Contributors: Shi, Jingchao, Guo, Zhiqiang, Wei, Xuehong, Liu, Diansheng, Lappert, Michael F.
... Abstract Lithium dibenzylamide catalyzed the rapid and essentially quantitative cyclotrimerization of a variety of isocyanates under mild conditions and could be recycled for six times in high yield.
An Efficient Synthesis of 2-Aminofuran-3-carbonitriles via Cascade Stetter-γ-Ketonitrile Cyclization Reaction Catalyzed by N-Heterocyclic Carbene
Contributors: Liu, Peng, Lei, Min, Ma, Lei, Hu, Lihong
... Abstract An efficient method for the synthesis of 4,5-disubstituted 2-aminofuran-3-carbonitriles via a cascade Stetter-γ-ketonitrile cyclization reaction of aromatic aldehydes with acylidenemalononitriles, catalyzed by N-heterocyclic carbenes, has been developed. This procedure provides the corresponding products in moderate to high yields under mild conditions.
Synthesis of 2,3,4,11b-Tetrahydro-1H-pyridazino[6,1-a]isoquinolines via the Three-Component Reaction of 2-Alkynylbenzaldehydes, a Sulfonohydrazide and Dimethyl Cyclopropane-1,1-dicarboxylate
Contributors: Yu, Xingxin, Qiu, Guanyinsheng, Liu, Jianping, Wu, Jie
... Abstract A three-component reaction of 2-alkynylbenzaldehydes, a sulfonohydrazide and dimethyl cyclopropane-1,1-dicarboxylate, co-catalyzed by silver(I) triflate and nickel(II) perchlorate hexahydrate, is described, which affords 2,3,4,11b-tetrahydro-1H-pyridazino[6,1-a]isoquinolines in moderate to good yields. A possible reaction pathway that proceeds via a tandem 6-endo-cyclization and [3+3] cycloaddition sequence is proposed.
Contributors: Wang, Tong, Shen, Li-Tao, Ye, Song
... Abstract The Wittig olefination of trifluromethyl ketones and allylic carbonates mediated by tributylphosphine was realized to give corresponding trifluoromethyl dienes in good yields with excellent E-selectivities.
Titanium-Catalyzed Cyclopropanation of Boc-Protected Cyanohydrins: A Short Access to Aminocyclopropanecarboxylic Acid Derivatives
Contributors: Pearson-Long, Morwenna S. M., Beauseigneur, Alice, Karoyan, Philippe, Szymoniak, Jan, Bertus, Philippe
... Abstract The preparation of protected 1-aminocyclopropanecarboxylic acid was performed from readily available and inexpensive starting materials, using titanium-catalyzed cyclopropanation as the key step. As an extension of this methodology, a diastereoselective synthesis of the cis-2-vinyl-substituted analogue is presented.
Contributors: Li, Yingfa, Cooksey, John P., Gao, Zhanghua, Kocieński, Philip J., McAteer, Stephen M., Snaddon, Thomas N.
... Abstract Key steps in a synthesis of the C17-C32 fragment of ionomycin are (a) an auxiliary-directed oxidative cyclisation of a diene with potassium permanganate to construct a tetrahydrofuran ring and four stereogenic centres in a single operation, and (b) a chain-appendage reaction featuring the alkylation of an enolsilane by an oxocarbenium ion generated from a 2-phenylsulfonyl-substituted tetrahydrofuran.
Contributors: Liu, Xiaoyan, Zhang, Songlin
... Abstract Low catalytic amount CuI and Fe(acac)3 were found to effectively promote the C-O cross-coupling reaction in the presence of K2CO3 as the base. A serious of diaryl ethers with different substitutents can be synthesized in good to excellent yields. This efficient and economic method is attractive for applications on an industrial scale.