- Preparation of Imidazole Derivatives via Bisfunctionalization of Alkynes Catalyzed by Ruthenium Carbonyl
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A one-step, oxidative bisfunctionalization of alkynes to generate cis -enediol diacetates catalyzed by ruthenium carbonyl (triruthenium dodecacarbonyl) is presented. The reaction was performed using the alkyne, (diacetoxyiodo)benzene, Ru 3 (CO) 12 as the catalyst, and toluene as the solvent at 100 °C to give the cis -enediol diacetates in up to 82percent yields. This method overcomes the shortcomings of existing methods, such as tedious reaction steps, substrate limitations, and the use of toxic reagents. Furthermore, the reaction of module cis -enediol diacetates with ammonium carbonate [(NH 4) 2 CO 3 ] in an alcohol solvent gave imidazole derivatives in 37-84percent yields, thus providing a simple and mild new method for the synthesis of imidazole compounds.
- Chen, Yue-Peng,Gu, Ling-Hui,He, Ling,Luo, Yang,Ruan, Yi-Tong,Yang, Ze
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- Thermal and photochemical solvolysis of (E)- and (Z)-2-phenyl-1-propenyl(phenyl)iodonium tetrafluoroborate: Benzenium and primary vinylic cation intermediates
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The thermal and photochemical solvolysis of the two stereoisomeric 2-phenyl-1-propenyl(phenyl)-iodonium tetrafluoroborates has been investigated in alcoholic solvents of varying nucleophilicity. The product profiles and rates of product formation in the thermal reaction are all compatible with a mechanism involving cleavage of the vinylic C - I bond assisted by the group in the trans position (methyl or phenyl), always leading to rearranged products. Depending on the nucleophilicity of the solvent, the primarily formed cations may or may not further rearrange to more stable isomers. The less reactive Z compound also yields some unrearranged vinyl ether product in the more nucleophilic solvents via an in-plane SN2 mechanism. The mechanism of the photolysis involves direct, unassisted cleavage of the vinylic, and aromatic, C - I bond in an SN1 mechanism. This produces a primary vinyl cation, which is partially trapped prior to rearrangement in methanol. The unrearranged vinyl ethers are mainly formed with retention of configuration via a λ3-iodonium/solvent complex in an SNi mechanism. Thermal and photochemical solvolyses of iodonium salts are complementary techniques for the generation of different cation intermediates from the same substrate.
- Gronheid,Lodder,Ochiai,Sueda,Okuyama
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- Ru(II)-Catalyzed Difunctional Pyridyloxy-Directed Regio-and Stereospecific Addition of Carboxylic Acids to Internal Alkynes
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A highly efficient Ru(II)-catalyzed regio- and stereospecific hydro-oxycarbonylation of unsymmetrical internal alkynes bearing a difunctional 2-pyridyloxy directing group with carboxylic acids has been developed, which provides allylic (Z)-enol esters in good to excellent yields with a broad substrate scope under mild conditions. The difunctional directing group can be diversely derivatized, particularly undergoing allylic substitution with various nucleophiles to afford β-functionalized (Z)-enol esters without directing groups.
- Wang, Qin,Shi, Yan,Huang, Xiaoli,Wang, Yongzhuang,Jiao, Jiao,Tang, Yuhai,Li, Jing,Xu, Silong,Li, Yang
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p. 379 - 384
(2022/01/11)
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- Rh-catalyzed asymmetric hydrogenation of α-aryl-β-alkylvinyl esters with chiral ferrocenylphosphine-phosphoramidite ligand
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An enantioselective Rh-catalyzed hydrogenation of E/Z mixtures of trisubstituted vinyl esters has been disclosed. With a combination of [Rh(COD)2]BF4 and a structurally fine-tuning chiral ferrocenylphosphine-phosphoramidite ligand as the catalyst, a variety of E/Z mixtures of α-aryl-β-alkylvinyl esters have been successfully hydrogenated in high yields and with good to high enantioselectivities (up to 96% ee). The presence of a small amount of tBuOH proved to be beneficial to improve the hydrogenation outcome.
- Dong, Chao,Liu, Dao-Sheng,Zhang, Lei,Hu, Xiang-Ping
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supporting information
(2021/02/03)
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- Asymmetric Oxidation of Enol Derivatives to α-Alkoxy Carbonyls Using Iminium Salt Catalysts: A Synthetic and Computational Study
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We report herein the first examples of asymmetric oxidation of enol ether and ester substrates using iminium salt organocatalysis, affording moderate to excellent enantioselectivities of up to 98% ee for tetralone-derived substrates in the α-hydroxyketone products. A comprehensive density functional theory study was undertaken to interpret the competing diastereoisomeric transition states in this example in order to identify the origins of enantioselectivity. The calculations, performed at the B3LYP/6-31G(D) level of theory, gave good agreement with the experimental results, in terms of the magnitude of the effects under the specified reaction conditions, and in terms of the preferential formation of the (R)-enantiomer. Just one of the 30 characterized transition states dominates the enantioselectivity, which is attributed to the adoption of an orientation relative to stereochemical features of the chiral controlling element that combines a CH interaction between a CH2 group in the substrate and one of the aromatic rings of the biaryl section of the chiral auxiliary with a good alignment of the acetoxy group with the other biaryl ring, and places the smallest substituent on the alkene (a hydrogen atom) in the most sterically hindered position.
- Page, Philip C. Bulman,Almutairi, Saud M.,Chan, Yohan,Stephenson, G. Richard,Gama, Yannick,Goodyear, Ross L.,Douteau, Alice,Allin, Steven M.,Jones, Garth A.
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p. 544 - 559
(2019/01/11)
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- Stereoselective Ketone Rearrangements with Hypervalent Iodine Reagents
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The first stereoselective version of an iodine(III)-mediated rearrangement of arylketones in the presence of orthoesters is described. The reaction products, α-arylated esters, are very useful intermediates in the synthesis of bioactive compounds such as ibuprofen. With chiral lactic acid-based iodine(III) reagents product selectivities of up to 73 % ee have been achieved.
- Malmedy, Florence,Wirth, Thomas
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p. 16072 - 16077
(2016/10/30)
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- C-H alkenylations with alkenyl acetates, phosphates, carbonates, and carbamates by cobalt catalysis at 23 °C
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Inexpensive cobalt catalysts with N-heterocyclic carbene ligands enable direct arene alkenylations with easily accessible alkenyl acetates through regioselective C-H/C-O functionalizations in a stereoconvergent fashion. The versatile cobalt catalyst was b
- Moselage, Marc,Sauermann, Nicolas,Richter, Sven C.,Ackermann, Lutz
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supporting information
p. 6352 - 6355
(2015/05/20)
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- Copper-catalyzed regioselective reaction of internal alkynes and diaryliodonium salts
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The copper-catalyzed highly regioselective reaction of internal alkynes with diaryliodonium salts was achieved for the first time. α-Arylketones were obtained in moderate to good yields from arylpropargylic alcohols or aryl alkyl alkynes under mild condit
- Xu, Ze-Feng,Cai, Chen-Xin,Liu, Jin-Tao
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supporting information
p. 2096 - 2099
(2013/06/05)
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- First lipase catalysed resolution of epoxy enol esters
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We report the first enzyme-catalysed kinetic resolution of epoxy enol esters. The lipase-promoted hydrolysis of these compounds provided α-hydroxyketones or α-hydroxyaldehydes (arising from the spontaneous rearrangement of the epoxy enols) and the residual esters with moderate to good enantioselectivity (E up to 100).
- Gravil, Sébastien,Veschambre, Henri,Chênevert, Robert,Bolte, Jean
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p. 6153 - 6157
(2007/10/03)
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- Homolytic carbostannylation of alkenes and alkynes with tributylstannyl enolates
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matrix presented In the presence of AIBN, tributylstannyl enolates derived from aromatic ketones reacted with electron-deficient alkenes and a variety of alkynes to give the corresponding carbostannylated adducts. The reactions with methyl acrylate gave α-tributylstannylmethyl-γ-ketoesters, unlike the known Michael-type reaction of stannyl enolates forming δ-ketoesters. The carbostannylation of alkynes proceeded in an anti addition mode to afford β,γ-unsaturated ketones. The reactivity of stannyl enolates as radical transfer agents could be utilized for radical cyclization of 1,6-enynes.
- Miura, Katsukiyo,Saito, Hiroshi,Fujisawa, Naoki,Wang, Di,Nishikori, Hisashi,Hosomi, Akira
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p. 4055 - 4057
(2007/10/03)
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- Regio- and Stereo-selectivity of Acetoxymercuration of Acetylenes
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Acetoxymercuration of alkylphenylacetylenes (PhCCR; R = Me, Et, Prn, or Bun) (1) in acetic acid at 20 - 60 deg C proceeds completely in a trans-fashion to afford a regioisomeric mixture of two vinylmercury(II) compounds, Ph(OAc)C=C(HgCl)R (2) and Ph(HgCl)C=C(OAc)R (3), the extent of attack of Hg at the carbon α to alkyl group to form (2) being increased upon increasing the carbonyl chain length of the alkyl group .A bridged mercurinium ion intermediate in which phenyl and alkyl groups are bent toward the attacking side of acetate anion is proposed for explaining a marked dependence of the isomer ratio (2):(3) on the kind of alkyl groups.Similar treatment of diphenylacetylene at 20 - 95 deg C gives only the cis-adduct as reported previously, while that of diethyl-acetylene affords the trans-adduct and a mixture of trans- and cis-adduct at 20 deg C and at 65 deg C, respectively.The NaBH4 reduction of (2, R = Me) in neutral condition produces a mixture of (Z)- and (E)-1-acetoxy-1-phenylpropene (ca. 3-5:1) in contrast to the reduction of thallium analogue of (2) which gives only the Z-isomer.
- Uemura, Sakae,Miyoshi, Haruo,Okano, Masaya
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p. 1098 - 1103
(2007/10/02)
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