- Enantioselective Construction of Quaternary Carbon Stereocenter via Palladium-Catalyzed Asymmetric Allylic Alkylation of Lactones
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An efficient and practical method for the synthesis of α,α-disubstituted six-membered lactones was developed. Enantioselective construction of quaternary carbon centers by utilizing Pd-catalyzed asymmetric allylic alkylation proved its feasibility.
- Li, Xiao-Hui,Wan, Shi-Li,Chen, Di,Liu, Qing Rong,Ding, Chang-Hua,Fang, Ping,Hou, Xue-Long
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supporting information
p. 1568 - 1572
(2016/05/24)
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- A General and mild catalytic α-alkylation of unactivated esters using Alcohols
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Catalytic α-alkylation of esters with primary alcohols is a desirable process because it uses low-toxicity agents and generates water as the by-product. Reported herein is a NCP pincer/Ir catalyst which is highly efficient for α-alkylation of a broad scope of unactivated esters under mild reaction conditions. For the first time, alcohols alkylate unactivated α-substituted acyclic esters, lactones, and even methyl and ethyl acetates. This method can be applied to the synthesis of carboxylic acid derivatives with diverse structures and functional groups, some of which would be impossible to access by conventional enolate alkylations with alkyl halides. In a pinch: An NCP pincer/iridium catalyst is highly efficient for the α-alkylation of unactivated esters using alcohol under mild reaction conditions. The reaction is simple, clean, and scalable (1-10 mmol), and the scope with respect to the ester is wide.
- Guo, Le,Ma, Xiaochen,Fang, Huaquan,Jia, Xiangqing,Huang, Zheng
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supporting information
p. 4023 - 4027
(2015/03/30)
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- One-pot sequential 1,4- and 1,2-reductions of α,β-unsaturated δ-lactones to the corresponding δ-lactols with CuCl and NaBH 4 in methanol
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An efficient, one-pot method for the highly chemoselective synthesis of δ-lactols from α,β-unsaturated δ-lactones using CuCl and NaBH4 in methanol was developed. Georg Thieme Verlag Stuttgart. New York.
- Matsumoto, Yasunobu,Yonaga, Masahiro
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supporting information
p. 1764 - 1768
(2014/08/05)
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- The stereochemical course of intramolecular michael reactions
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We present a general model for understanding the stereochemical course of intramolecular Michael reactions. We show that the addition of β- ketoester enolates to α,β-unsaturated esters and imides bearing adjacent stereocenters (X, Y = H, Me, OR) leads to high levels of asymmetric induction. Reinforcing and nonreinforcing stereochemical relationships are evaluated from the syn and anti reactant diastereomers. On the basis of synthetic, spectroscopic, and computational studies, we propose that the outcomes of these reactions can be rationalized by a dipole-minimized chair transition-state model.
- Kwan, Eugene E.,Scheerer, Onathan R.,Evans, David A.
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supporting information
p. 175 - 203
(2013/04/10)
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- Highly enantioselective iridium-catalyzed hydrogenation of α,β-unsaturated esters
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α,β-Unsaturated esters have been employed as substrates in iridium-catalyzed asymmetric hydrogenation. Full conversions and good to excellent enantioselectivities (up to 99 % ee) were obtained for a broad range of substrates with both aromatic- and aliphatic substituents on the prochiral carbon. The hydrogenated products are highly useful as building blocks in the synthesis of a variety of natural products and pharmaceuticals. Asymmetric hydrogenation: A variety of α,β-unsaturated esters were hydrogenated with high enantioselectivities (see scheme). The hydrogenated products have been used in synthetic transformations as well as in formal total syntheses. Copyright
- Li, Jia-Qi,Quan, Xu,Andersson, Pher G.
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supporting information
p. 10609 - 10616
(2012/11/07)
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- Branched-regioselective hydroformylation with catalytic amounts of a reversibly bound directing group
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(Chemical Equation Presented) Phosphinites do the trick and work as reversibly bound catalyst-directing groups in catalytic amounts to allow for the highly regioselective hydroformylation of homo-allylic alcohols with terminal and internal alkene functions in favor of the branched product.
- Gruenanger, Christian U.,Breit, Bernhard
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supporting information; experimental part
p. 7346 - 7349
(2009/04/07)
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- Highly Enantioselective Intermolecular Cu(I)-Catalyzed Cyclopropanation of Cyclic Enol Ethers. Asymmetric Total Synthesis of (+)-Quebrachamine
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A set of cyclic enol ethers derived from 2,3-dihydrofuran 35 and 3,4-dihydropyran 8 with a varying substitution pattern at the olefinic system were synthesized. Evans's ligand 5 with Cu(I)OTf was found to be an effective catalyst in the cyclopropanation reaction between cyclic enol ethers 14, 19, 28-31, and 33 and ethyl diazoacetate 6 to give diastereoselectivities up to exo/endo = 95:5 and enantioselectivities higher than 95% in nearly all cases. Because of the selective building of a quarternary carbon center and good yields in the formation of bicyclic structures 34c-h, the reaction was used as a key step in the asymmetric synthesis of (+)-quebrachamine 7, an indole alkaloid of the Aspidosperma family. After acid-induced ring opening of bicyclic compound 34f to lactone 40 followed by LiAlH4 reduction to the masked aldehyde 41, a reaction with tryptamine gave intermediate 42. This alcohol was efficiently converted into the indole alkaloid (+)-quebrachamine 7 in an overall yield of 37% starting from the chiral synthon 34f. Moreover it revealed the absolute configuration of the quarternary center of the cyclopropanation product 34f to be S.
- Temme, Oliver,Taj, Shabbir-Ali,Andersson, Pher G.
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p. 6007 - 6015
(2007/10/03)
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- Mechanism-based inactivation of serine proteases by dichlorocyclopropane fused lactone derivatives
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A dichlorocyclopropane fused lactone derivative was prepared as a novel mechanism-based inactivator of serine protease, α-chymotrypsin. The lactone derivative showed transient irreversible inhibitory activity toward α-chymotrypsin with the value of k(obsd)/[I] = 54 M-1s-1 and the enzyme activity recovered perfectly after 6 hours.
- Ohba, Tsuyoshi,Ikeda, Eitatsu,Tsuchiya, Naoki,Nishimura, Kuniko,Takei, Hisashi
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p. 2629 - 2634
(2007/10/03)
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- Photoinduced Molecular Transformations. Part 144. One-Carbon Intercalation of γ- and δ-Lactones involving the β-Scission of Alkoxyl Radicals as the Key Step: Synthesis of δ- and ε-Lactones with α-Substituents
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A new general method of a one-carbon intercalation of γ-lactones to δ-lactones and δ-lactones to ε-lactones in three steps involving a selective β-scission of the alkoxyl racicals as the key step is described.The reactions of γ- and δ-lactones with lithioalkyl acetate gave an equilibrium mixture of alkyl (2-hydroxytetrahydrofuran-2-yl)acetates and alkyl (2-hydroxytetrahydropyran-2-yl)acetates, as well as their ring-opened isomers in 62-95percent yields, respectively.The photolysis of the hypoiodites of these lactols in benzene containing mercury(II) oxide and iodine with Pyrex-filtered light resulted in a selective endocyclic β-scission of the corresponding alkoxyl radicals to give alkyl iodoalkyl propanedioates in 33-70percent yields.Treatment of the iodoalkyl propanedioates with tetraethylammonium bromide and sodium hydride gave alkyl 3,4,5,6-tetrahydro-2-oxo-2H-pyran-3-carboxylates or alkyl 2,3,4,5,5a,6,7,8,9,9a-decahydro-2-oxobenzoxepine-3-carboxylate in 61-81percent yields.On the other hand, succesive treatment of ω-iodoalkyl propanedioates with tetraethylammonium bromide-sodium hydride and then benzyl bromide gave a α-disubstituted δ-lactone, which gave a α-monosubstituted δ-lactone upon heating in trifluoroacetic acid under reflux.Cyclopentanone can similarly be transformed into 2-substituted cyclohexanone via a three-step procedure.
- Kobayashi, Kazuhiro,Minakawa, Hiroki,Sakurai, Hideo,Kujime, Sachiko,Suginome, Hiroshi
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p. 3007 - 3010
(2007/10/02)
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- Catalytic iron-mediated ene carbocyclizations: Formal [4+4]-ene reactions of triene esters
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2-Substituted-2,7,9-decatrienoates undergo an iron-catalyzed carbocyclization to yield trans-disubstituted cyclopentanes in moderate-to-good chemical yields. The cyclization products are formally the result of a [4+4]-ene reaction in which cis-propenyl and 2-acroyl functionalities are introduced as appendages to the newly formed cyclopentane ring by the cyclization. Triene ester substrates bearing an alkyl substituent at the 4- or 6-positions cyclize with high 1,2-stereoinduction to yield trisubstituted cyclopentanes in which the relative stereochemistry between three contiguous stereocenters is controlled.
- Takacs, James M.,Newsome, Peter W.,Kuehn, Cynthia,Takusagawa, Fusao
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p. 5507 - 5522
(2007/10/02)
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- Acyl and Sulfonyl Isocyanates ib β-Lactam Synthesis
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The preparation of β-lactams from the reactions of several acyl and sulfonyl activated isocyanates with alkenes was studied.Three compounds, (2,2,2-trichloroethoxy)sulfonyl, 2,2,2-trichloroethane sulfonyl, and trifluoroacetyl isocyanates, were shown to be
- Barrett, Anthony G. M.,Betts, Michael J.,Fenwick, Ashley
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p. 169 - 175
(2007/10/02)
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