- Asymmetric aminolysis of aromatic epoxides: A facile catalytic enantioselective synthesis of anti-β-amino alcohols
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The first asymmetric aminolysis of trans-aromatic epoxides with anilines is described. The process affords enantioenriched anti-β-amino alcohols in up to 99% ee. The complete regio- and diastereoselectivity observed uses commercially available [Cr(Salen)CI] as a Lewis acid catalyst and in combination with a very simple experimental procedure renders the present reaction a facile and practical tool for the synthesis of chiral nonracemic anti-β-amino alcohols.
- Bartoli, Giuseppe,Bosco, Marcella,Carlone, Armando,Locatelli, Manuela,Massaccesi, Massimo,Melchiorre, Paolo,Sambri, Letizia
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- Copper-Catalyzed Transfer Hydrodeuteration of Aryl Alkenes with Quantitative Isotopomer Purity Analysis by Molecular Rotational Resonance Spectroscopy
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A copper-catalyzed alkene transfer hydrodeuteration reaction that selectively incorporates one hydrogen and one deuterium atom across an aryl alkene is described. The transfer hydrodeuteration protocol is selective across a variety of internal and terminal alkenes and is also demonstrated on an alkene-containing complex natural product analog. Beyond using 1H, 2H, and 13C NMR analysis to measure reaction selectivity, six transfer hydrodeuteration products were analyzed by molecular rotational resonance (MRR) spectroscopy. The application of MRR spectroscopy to the analysis of isotopic impurities in deuteration chemistry is further explored through a measurement methodology that is compatible with high-throughput sample analysis. In the first step, the MRR spectroscopy signatures of all isotopic variants accessible in the reaction chemistry are analyzed using a broadband chirped-pulse Fourier transform microwave spectrometer. With the signatures in hand, measurement scripts are created to quantitatively analyze the sample composition using a commercial cavity enhanced MRR spectrometer. The sample consumption is below 10 mg with analysis times on the order of 10 min using this instrument - both representing order-of-magnitude reduction compared to broadband MRR spectroscopy. To date, these measurements represent the most precise spectroscopic determination of selectivity in a transfer hydrodeuteration reaction and confirm that product regioselectivity ratios of >140:1 are achievable under this mild protocol.
- Alansari, Isabella Y.,Clark, Joseph R.,Holdren, Martin S.,Neill, Justin L.,Pate, Brooks H.,Reyes, Albert,Sloane, Samantha E.,Sonstrom, Reilly E.,Vang, Zoua Pa
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supporting information
p. 7707 - 7718
(2021/06/21)
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- Copper-catalyzed formal transfer hydrogenation/deuteration of aryl alkynes
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A copper-catalyzed reduction of alkynes to alkanes and deuterated alkanes is described under transfer hydrogenation and transfer deuteration conditions. Commercially available alcohols and silanes are used interchangeably with their deuterated analogues as the hydrogen or deuterium sources. Transfer deuteration of terminal and internal aryl alkynes occurs with high levels of deuterium incorporation. Alkyne-containing complex natural product analogues undergo transfer hydrogenation and transfer deuteration selectively, in high yield. Mechanistic experiments support the reaction occurring through a cis-alkene intermediate and demonstrate the possibility for a regioselective alkyne transfer hydrodeuteration reaction.
- Sloane, Samantha E.,Reyes, Albert,Vang, Zoua Pa,Li, Lingzi,Behlow, Kiera T.,Clark, Joseph R.
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p. 9139 - 9144
(2020/11/30)
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- Iterative synthesis of alkenes by insertion of lithiated epoxides into boronic esters
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The insertion of lithiated epoxides into boronic esters followed by thermal syn-elimination provides a stereospecific entry to alkenes. This process avoids transition metals and is amenable to iteration to provide higher substitution patterns.
- Bojaryn, Kevin,Fritsch, Stefan,Hirschhaüser, Christoph
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supporting information
p. 2218 - 2222
(2019/04/10)
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- Diastereoselective borocyclopropanation of allylic ethers using a boromethylzinc carbenoid
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A borocyclopropanation of (E)- and (Z)-allylic ethers and styrene derivatives via the Simmons-Smith reaction using a novel boromethylzinc carbenoid is described. The carbenoid precursor is prepared via a 3-step sequence from inexpensive and commercially available starting materials. This methodology allows for the preparation of 1,2,3-substituted borocyclopropanes in high yields and diastereoselectivities. Several postfunction-alization reactions were also performed to illustrate the versatility of these building blocks.
- Benoit, Guillaume,Charette, André B.
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supporting information
p. 1364 - 1367
(2017/02/10)
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- The synthesis of (R,S)-reboxetine employing a tandem cyclic sulfate rearrangement - Opening process
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(R,S)-Reboxetine was synthesized in nine steps and with 43% overall yield starting from trans-cinnamyl alcohol. Following silylation and AD steps, the two hydroxyl groups at C-1 and C-2 were simultaneously activated to the cyclic sulfate. A series of tandem reactions initiated by desilylation transposed the activation to C-3, then to C-1, where nucleophilic displacements took place in succession. During this process, the configuration at C-2 was inverted while that at C-1 was retained through a double inversion.
- Yu, Jin,Ko, Soo Y.
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experimental part
p. 650 - 654
(2012/09/22)
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- Biomimetic iron-catalyzed asymmetric epoxidation of aromatic alkenes by using hydrogen peroxide
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A novel and general biomimetic non-heme Fe-catalyzed asymmetric epoxidation of aromatic alkenes by using hydrogen peroxide is reported herein. The catalyst consists of ferric chloride hexahydrate (FeCl3·OH 2O), pyridine-2,6-dicarboxylic acid (H2-(pydic)), and readily accessible chiral N-arenesulfonyl-N′-benzyl-substituted ethylenediamine ligands. The asymmetric epoxidation of styrenes with this system gave high conversions but poor enantiomeric excesses (ee), whereas larger alkenes gave high conversions and ee values. For the epoxidation of trans-stilbene (1a), the ligands (S,S)-N-(4-toluenesulfonyl)-1,2- diphenylethylenediamine ((S,S)-4a) and its N′-benzylated derivative ((S,S)-5a) gave opposite enantiomers of trans-stilbene oxide, that is, (S,S)-2a and (R,R)-2a, respectively. The enantioselectivity of alkene epoxidation is controlled by steric and electronic factors, although steric effects are more dominant. Preliminary mechanistic studies suggest the in situ formation of several chiral Fe-complexes, such as [FeCl(L*)2-(pydic)] ·HCl (L* = (S,S)-4a or (S,S)-5a in the catalyst mixture), which were identified by ESIMS. A UV/Vis study of the catalyst mixture, which consisted of FeCl3·6H2O, H2(pydic), and (S,S)-4a, suggested the formation of a new species with an absorbance peak at λ = 465 nm upon treatment with hydrogen peroxide. With the aid of two independent spin traps, we could confirm by EPR spectroscopy that the reaction proceeds via radical intermediates. Kinetic studies with deuterated styrenes showed inverse secondary kinetic isotope effects, with values of k H/kD = 0.93 for the β carbon and kH/k D=0.97 for the a carbon, which suggested an unsymmetrical transition state with stepwise O transfer. Competitive epoxidation of para-substituted styrenes revealed a linear dual-parameter Hammett plot with a slope of 1.00. Under standard conditions, epoxidation of la in the presence of ten equivalents of H218O resulted in an absence of the isotopic label in (S,S)-2a. A positive non-linear effect was observed during the epoxidation of la in the presence of (S,S)-5a and (R,R)-5a.
- Gelalcha, Feyissa Gadissa,Anilkumar, Gopinathan,Tse, Man Kin,Brueckner, Angelika,Beller, Matthias
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experimental part
p. 7687 - 7698
(2009/08/07)
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- Direct, iridium-catalyzed enantioselective and regioselective allylic etherification with aliphatic alcohols
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(Chemical Equation Presented) From alcohol to ether: Iridium-catalyzed allylations yield α chiral ether derivatives directly from aliphatic alcohols with a simple alkali metal base (see equation). These reactions form ethers from primary, secondary, and tertiary alkoxides with high enantioselectivity. By-products from isomerization were suppressed by the use of an alkyne additive.
- Ueno, Satoshi,Hartwig, John F.
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p. 1928 - 1931
(2008/12/22)
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- Iridium-catalyzed enantioselective synthesis of allylic alcohols: Silanolates as hydroxide equivalents
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(Chemical Equation Presented) Masked hydroxide: A highly regio- and enantioselective Ir-catalyzed allylic etherification of acyclic, achiral allylic carbonates can be achieved by using potassium silanolates as nucleophiles. The use of these hydroxide equi
- Lyothier, Isabelle,Defieber, Christian,Carreira, Erick M.
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p. 6204 - 6207
(2007/10/03)
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- Efficient and stereoselective synthesis of allylic ethers and alcohols
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(Chemical Equation Presented) A short and efficient synthesis of allylic TBS ethers and allylic alcohols has been developed, based upon a unique Kocienski-Julia olefination reaction. Allylic alcohols and allylic ethers are obtained in good to excellent yields and with high (E)-selectivity. The conditions are mild and the procedure is broadly applicable.
- Pospisil, Jiri,Marko, Istvan E.
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p. 5983 - 5986
(2007/10/03)
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- Sulfoxide-modified Julia-Lythgoe olefination: Highly stereoselective di-, tri-, and tetrasubstituted double bond formation
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A novel modification of the classical Julia-Lythgoe olefination, using sulfoxides instead of sulfones, affords, after in situ benzoylation and SmI 2/HMPA or SmI2/DMPU-mediated reductive elimination, 1,2-di-, tri- and tetrasubstituted olefins in moderate to good yields and E/Z selectivity. The conditions are mild and the procedure is widely applicable. The reaction mechanism was studied and a general model, describing the reaction selectivity, is proposed.
- Pospisil, Jiri,Pospisil, Tomas,Marko, Istvan E.
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p. 1953 - 1969
(2007/10/03)
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- Sulfoxides in Julia-Lythgoe olefination: Efficient and stereoselective preparation of di-, tri-, and tetrasubstituted olefins
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(Chemical Equation Presented) A novel modification of the classical Julia-Lythgoe olefination, using sulfoxides instead of sulfones, affords, after in situ benzoylation and Sml2/HMPA- or DMPU-mediated reductive elimination, 1,2-di-, tri-, and tetrasubstituted olefins in moderate to excellent yields and E/Z selectivity. The conditions are mild, and the procedure is broadly applicable.
- Pospisil, Jiri,Pospisil, Tomas,Marko, Istvan E.
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p. 2373 - 2376
(2007/10/03)
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- Solvent-modulated Pd/C-catalyzed deprotection of silyl ethers and chemoselective hydrogenation
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Recently we have reported undesirable and frequent deprotection of the TBDMS protective group of a variety of hydroxyl functions occurred under neutral and mild hydrogenation conditions using 10% Pd/C in MeOH. The deprotection of silyl ethers is susceptible to significant solvent effect. TBDMS and TES protecting groups were selectively cleaved in the presence of acid-sensitive functional groups such as TIPS ether, TBDPS ether and dimethyl acetal under hydrogenation condition using 10% Pd/C in MeOH. In contrast, chemoselective hydrogenation of reducible functional groups such as acetylene, olefin and benzyl ether, proceeds in the presence of TBDMS or TES ethers in AcOEt or MeCN.
- Ikawa, Takashi,Hattori, Kazuyuki,Sajiki, Hironao,Hirota, Kosaku
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p. 6901 - 6911
(2007/10/03)
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- Catalytic asymmetric epoxidation
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A compound and method for producing an enantiomerically enriched epoxide from an olefin using a chiral ketone and an oxidizing agent is disclosed.
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Page column 28
(2010/01/30)
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- Palladium-catalyzed tandem reactions to form 1-vinyl-1H-isochromene derivatives
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The palladium-catalyzed reaction of pinacolone with tert-butyldimethyl(3-(2-bromophenyl)allyloxy)-silane results in direct formation of 1-vinyl-3-tert-butyl-1H-isochromene. This is the result of a ketone arylation followed by an intramolecular cyclization of the enolate with the allylic system. The use of a lithium diamide base appears to be essential for success. The tert-butyldimethylsilyl protecting group is also an essential choice as it furnishes the appropriate reactivity to promote allylic substitution after the aryl coupling process. The use of more effective leaving groups, such as acetate, results in reaction of the allylic group, and no aryl coupling is observed. Through the appropriate selection of phosphine ligand and solvent, either the cyclized isochromene product or the noncyclized intermediate may be formed selectively. A short combinatorial study of the scope and limitations of the reaction, involving 24 ketones, is described.
- Mutter,Campbell,de la Nava,Merritt,Wills
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p. 3284 - 3290
(2007/10/03)
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- A novel and efficient method for the silylation of alcohols with methallylsilanes catalyzed by Sc(OTf)3
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Reaction of alcohols with methallylsilanes in the presence of a catalytic amount of Sc(OTf)3 provides efficiently the corresponding alkyl silyl ethers. By using microencapsulated (MC) Sc(OTf)3, which can be easily recovered and reused, yields of alkyl silyl ethers are improved and the work-up process after completion of the reaction is considerably simplified. (C) 2000 Elsevier Science Ltd.
- Suzuki,Watahiki,Oriyama
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p. 8903 - 8906
(2007/10/03)
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- Direct formation of 1-vinyl-1H-isochromene derivatives via a palladium-catalysed coupling reaction
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The palladium-catalysed reaction of the tert-butyldimethylsilyl ether of a 3-(o-bromophenyl)allylic alcohol with a methyl ketone leads directly to a 1-vinyl-1H-isochromene via a tandem ketone arylation-allylic cyclisation reaction.
- Mutter,Martin de la Neva,Wills
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p. 1675 - 1676
(2007/10/03)
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- Efficient and chemoselective protection of alcohols and phenols with tert-butyldimethylchlorosilane (TBDMCS) under solvent-free conditions
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Various types of primary and secondary alcohols and phenols can be converted efficiently to their corresponding TBDMS ethers using TBDMCS/imidazole under solvent-free conditions. Elimination of DMF, accompanied with an easy non-aqueous work-up and a high rate enhancement of the reaction are worthy to be mentioned for the presented method. The reactions show absolute chemoselectivity for the protection of primary in the presence of secondary alcohols.
- Firouzabadi, Habib,Etemadi, Shahrad,Karimi, Babak,Jarrahpour, Ali Asghar
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