- Ru-Based Catechothiolate Complexes Bearing an Unsaturated NHC Ligand: Effective Cross-Metathesis Catalysts for Synthesis of (Z)-α,β-Unsaturated Esters, Carboxylic Acids, and Primary, Secondary, and Weinreb Amides
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Despite notable progress, olefin metathesis methods for preparation of (Z)-α,β-unsaturated carbonyl compounds, applicable to the synthesis of a large variety of bioactive molecules, remain scarce. Especially desirable are transformations that can be promoted by ruthenium-based catalysts, as such entities would allow direct access to carboxylic esters and amides, or acids (in contrast to molybdenum-or tungsten-based alkylidenes). Here, we detail how, based on the mechanistic insight obtained through computational and experimental studies, a readily accessible ruthenium catechothiolate complex was found that may be used to generate many α,β-unsaturated carbonyl compounds in up to 81% yield and ≥98:2 Z/E ratio. We show that through the use of a complex bearing an unsaturated N-heterocyclic carbene (NHC) ligand, for the first time, products derived from the more electron-deficient esters, acids, and Weinreb amides (vs primary or secondary amides) can be synthesized efficiently and with high stereochemical control. The importance of the new advance to synthesis of bioactive compounds is illustrated through two representative applications: An eight-step, 15% overall yield, and completely Z-selective route leading to an intermediate that may be used in synthesis of stagonolide E (vs 11 steps, 4% overall yield and 91% Z, previously), and a five-step, 25% overall yield sequence to access a precursor to dihydrocompactin (vs 13 steps and 5% overall yield, formerly).
- Liu, Zhenxing,Xu, Chaofan,Del Pozo, Juan,Torker, Sebastian,Hoveyda, Amir H.
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supporting information
p. 7137 - 7146
(2019/05/10)
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- Dienolates of Cycloalkenones and α,β-Unsaturated Esters Form Diels–Alder Adducts by a Michael/Michael-Tandem Reaction Rather Than in One Step
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α,β-Unsaturated esters and lithium 1,3-dien-2-olates are known to furnish bicyclic lithium enolates by anionic Diels–Alder reactions. However, in principle, the respective products might form not only in a single step but also in two consecutive – or “tandem” – Michael additions, the first of which occurs intermolecularly, the second intramolecularly. Three cyclic lithium dienolates and four esters with a stereogenic Cα=Cβ bond reacted to give Diels–Alder adducts (10 times) or failed to react (2 times). Seven of the reactive combinations furnished adducts wherein the configuration of the former ester moiety had in part inverted. This precludes concerted pathways as their origins. This was a surprise since donors at C-2 of the 1,3-diene accelerate normal electron-demand Diels–Alder reactions in the order alkyl ⊕O? being a far better donor still, it is not obvious why the mechanism is non-concerted rather than concerted (and still more asynchronous).
- Loesche, Ann-Christine,Brückner, Reinhard
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supporting information
p. 562 - 573
(2018/12/11)
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- Electrochemical anion pool synthesis of amides with concurrent benzyl ester synthesis
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An electrosynthesis method for amide bond formation has been developed in an attempt to increase the atom economy for this class of reactions. This "anion pool" method electrochemically generates strong nucleophiles from amine substrates. The amine nucleophiles then react with acid anhydrides to generate amides, and the by-product from this reaction undergoes further chemical transformations to generate pharmaceutically relevant benzoic esters. These one-pot reactions are operationally simple, are performed at room temperature, and avoid rare transition metals and added bases. The amide synthesis is amenable to primary and secondary amines and a variety of anhydrides with yields up to 90% obtained. Atom economy and process mass index (PMI) values calculated for this procedure indicate that this process can be considered greener compared to traditional amide synthesis routes used by industry. Furthermore, this electrochemical approach showed unique selectivity when substrates that contained two inequivalent amine moieties were examined.
- Mevan Dissanayake,Melville, Alex D.,Vannucci, Aaron K.
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supporting information
p. 3165 - 3171
(2019/06/18)
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- Carboxylative Suzuki coupling reactions of benzyl chlorides with allyl pinacolborate catalyzed by palladium nanoparticles
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Palladium-catalyzed carboxylative Suzuki coupling reactions of benzyl chlorides with allyl pinacolborate were successfully conducted in the absence of any extra ligand to produce β,γ-unsaturated esters in satisfactory to good yields. The carboxylative Suzuki coupling reaction proceeded smoothly under mild conditions in the presence of palladium nanoparticles generated in situ through the formation of a π-benzylpalladium chloride intermediate.
- Sun, Jian,Wang, Jiasheng,Feng, Xiujuan,Yamamoto, Yoshinori,Almansour, Abdulrahman I.,Arumugam, Natarajan,Kumar, Raju Suresh,Bao, Ming
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p. 1258 - 1262
(2018/06/21)
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- Chemoselective Transesterification of Acrylate Derivatives for Functionalized Monomer Synthesis Using a Hard Zinc Alkoxide Generation Strategy
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A new practical method for the synthesis of functionalized acrylate derivatives with the view to prepare functional polymers was explored. Hard zinc alkoxide generation enabled the highly chemoselective transesterification of acrylate derivatives over the undesired conjugate addition, which caused polymerization. The combined use of the catalytic zinc cluster Zn4(OCOCF3)6O and 4-(dimethylamino)pyridine delivered various functionalized acrylate derivatives through the transesterification of commercially available methyl acrylate derivatives with functionalized alcohols under mild conditions.
- Nakatake, Daiki,Yazaki, Ryo,Ohshima, Takashi
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supporting information
p. 3696 - 3699
(2016/08/20)
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- Use of diethoxymethane as a solvent for phase-transfer esterification of carboxylic acids
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The esterification of carboxylic acids with selected primary alkyl halides in diethoxymethane (DEM) utilizing solid-liquid phase-transfer catalysis has been studied. The use of DEM as the solvent simplifies the process in that a single solvent can be used for both reaction and workup.
- Coleman, M. Todd
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scheme or table
p. 1911 - 1913
(2012/06/04)
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- Well-defined binuclear chiral spiro copper catalysts for enantioselective N-H insertion
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An asymmetric N-H insertion of α-diazoesters with anilines catalyzed by well-defined copper complexes of chiral spiro bisoxazoline ligands was studied in detail. The copper-catalyzed asymmetric N-H insertion of a wide range of α-alkyl-α-diazoacetates with anilines was accomplished with excellent enantioselectivity (up to 98% ee) and provided an efficient method for the preparation of optically active α-amino acid derivatives. A correlation study of the electronic properties of the substrates with the enantioselectivity of the N-H insertion reaction supports a stepwise insertion mechanism, and the significant first-order kinetic isotope effect proves that the proton transfer is most likely the rate-limiting step. A binuclear chiral spiro copper catalyst having 14-electron copper centers, a trans coordination model, a perfect C2-symmetric chiral pocket, and significant Cu-Cu interaction was isolated and extensively studied. The novel structure of the binuclear chiral spiro copper catalyst leads to unique reactivity as well as enantioselectivity in the N-H insertion reaction.
- Zhu, Shou-Fei,Xu, Bin,Wang, Guo-Peng,Zhou, Qi-Lin
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supporting information; experimental part
p. 436 - 442
(2012/03/07)
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- Scalable synthesis of enantiomerically pure syn -2,3-dihydroxybutyrate by sharpless asymmetric dihydroxylation of p -phenylbenzyl crotonate
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An efficient four-step synthetic route to the useful chiral building block (2R,3S)-dihydroxybutyric acid acetonide in >95% ee is detailed. The sequence is readily scaled, requires no chromatography, and allows for efficient recycling of p-phenylbenzyl alcohol, an expedient for enantio- and diastereoenrichment by recrystallization.
- Smaltz, Daniel J.,Myers, Andrew G.
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body text
p. 8554 - 8559
(2011/12/03)
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- PREPARATION OF ALKENES BY MILD THERMOLYSIS OF SULFOXIDES
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Embodiments of this disclosure, among others, encompass methods for generating alkenes under mild thermolytic conditions that can provide almost total conversion of a precursor compound to an alkene without isomerization or the need to chromatographically purify the final product By selectively blocking the amino and carboxy groups of the depvatized amino acid, the methods of the disclosure provide for the synthesis of a peptide having the vinylglycine moiety at either the carboxy or the amino terminus of the peptide The mild conditions for the thermolytic removal of an o-NO2-phenyl substituted aryl group ensure that there is minimal if any damage to thermally sensitive conjugates such as a peptide bearing the vinylglycine The methods of the present disclosure have practical applications for the preparation of unsaturated compounds under mild, thermolytic conditions.
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Page/Page column 5
(2010/07/02)
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- Copper-catalyzed enantioselective carbenoid insertion into S-H bonds
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An asymmetric carbenoid insertion into S-H bonds catalyzed by copper-chiral spiro bisoxazoline complexes has been developed, in which a series of α-mercaptoesters were produced in high yields with moderate to good enantioselectivities (up to 85% ee); this
- Zhang, Yong-Zhen,Zhu, Shou-Fei,Cai, Yan,Mao, Hong-Xiang,Zhou, Qi-Lin
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body text
p. 5362 - 5364
(2009/12/08)
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- The effect of fluoromethyl groups on the diastereoselectivity in the electrophilic alkylation
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The effect of fluoromethyl groups on the diastereoselectivity in the electrophilic alkylation is described. In particular, the electrophilic alkylation of enolates with a trifluoromethyl group was proceeded with highly diastereofacial selectivity based on the steric and/or electrostatic effect of substituent with strong electron withdrawing.
- Tamura, Kenji,Yamazaki, Takashi,Kitazume, Tomoya,Kubota, Toshio
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p. 918 - 930
(2007/10/03)
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