- Interrupting the Barton?McCombie reaction: Aqueous deoxygenative trifluoromethylation of o-alkyl thiocarbonates
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The site-selective trifluoromethylation of aliphatic systems remains an important challenge. This work describes a light-driven, copper-mediated trifluoromethylation of O-alkyl thiocarbonates. The reaction provides broad functional group tolerance (e.g., alkyne, alkene, phenol, free alcohol, electron-rich and -deficient arenes), thereby offering orthogonality and practicality for trifluoromethylation. A radical organometallic mechanism is proposed.
- Liu, Zhi-Yun,Cook, Silas P.
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supporting information
p. 808 - 813
(2021/02/01)
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- Deracemization and Stereoinversion of Alcohols Using Two Mutants of Secondary Alcohol Dehydrogenase from Thermoanaerobacter pseudoethanolicus
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We developed a one-pot sequential two-step deracemization approach to chiral alcohols using two mutants of Thermoanaerobacter pseudoethanolicus secondary alcohol dehydrogenase (TeSADH). This approach relies on consecutive non-stereospecific oxidation of alcohols and stereoselective reduction of their prochiral ketones using two mutants of TeSADH with poor and good stereoselectivities, respectively. More specifically, W110G TeSADH enables a non-stereospecific oxidation of alcohol racemates to their corresponding prochiral ketones, followed by W110V TeSADH-catalyzed stereoselective reduction of the resultant ketone intermediates to enantiopure (S)-configured alcohols in up to > 99 percent enantiomeric excess. A heat treatment after the oxidation step was required to avoid the interference of the marginally stereoselective W110G TeSADH in the reduction step; this heat treatment was eliminated by using sol-gel encapsulated W110G TeSADH in the oxidation step. Moreover, this bi-enzymatic approach was implemented in the stereoinversion of (R)-configured alcohols, and (S)-configured alcohols with up to > 99 percent enantiomeric excess were obtained by this Mitsunobu-like stereoinversion reaction.
- Hamdan, Samir M.,Musa, Musa M.,Nafiu, Sodiq A.,Takahashi, Etsuko,Takahashi, Masateru
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- Selective Cross-Dehydrogenative C(sp3)-H Arylation with Arenes
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Selective C(sp3)-C(sp2) bond construction is of central interest in chemical synthesis. Despite the success of classic cross-coupling reactions, the cross-dehydrogenative coupling between inert C(sp3)-H and C(sp2)-H bonds represents an attractive alternative toward new C(sp3)-C(sp2) bonds. Herein, we establish a selective inter-and intramolecular C(sp3)-H arylation of alcohols with nondirected arenes that thereby provides a general pathway to access a wide range of β-arylated alcohols, including tetrahydronaphthalen-2-ols and benzopyran-3-ols, with high to excellent chemo-and regioselectivity.
- Hao, Hong-Yan,Mao, Yang-Jie,Xu, Zhen-Yuan,Lou, Shao-Jie,Xu, Dan-Qian
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supporting information
p. 2396 - 2402
(2020/03/13)
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- Iron-catalyzed protodehalogenation of alkyl and aryl halides using hydrosilanes
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A simple and efficient iron-catalyzed protodehalogenation of alkyl and aryl halides using phenylhydrosilane is disclosed. The reaction utilizes FeCl3 without the requirement of ligands. Unactivated alkyl and aryl halides were successfully reduced in good yields; sterically hindered tertiary halides were also reduced including the less reactive chlorides. The scalability of this methodology was demonstrated by a gram-scale synthesis with a catalyst loading as low as 0.5 mol%. Notably, disproportionation of phenylsilane leads to diphenylsilane that further reduces the halides. Preliminary mechanistic studies revealed a non-radical pathway and the source of hydrogen is PhSiH3via deuterium labeling studies. Our methodology represents simplicity and provides a good alternative to typical tin, aluminum and boron hydride reagents.
- Pilli, Ramadevi,Balakrishnan, Venkadesh,Chandrasekaran, Revathi,Rasappan, Ramesh
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supporting information
p. 1749 - 1753
(2019/02/20)
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- Ti-Catalyzed Radical Alkylation of Secondary and Tertiary Alkyl Chlorides Using Michael Acceptors
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Alkyl chlorides are common functional groups in synthetic organic chemistry. However, the engagement of unactivated alkyl chlorides, especially tertiary alkyl chlorides, in transition-metal-catalyzed C-C bond formation remains challenging. Herein, we describe the development of a TiIII-catalyzed radical addition of 2° and 3° alkyl chlorides to electron-deficient alkenes. Mechanistic data are consistent with inner-sphere activation of the C-Cl bond featuring TiIII-mediated Cl atom abstraction. Evidence suggests that the active TiIII catalyst is generated from the TiIV precursor in a Lewis-acid-assisted electron transfer process.
- Wu, Xiangyu,Hao, Wei,Ye, Ke-Yin,Jiang, Binyang,Pombar, Gisselle,Song, Zhidong,Lin, Song
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supporting information
p. 14836 - 14843
(2018/11/10)
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- Expanding the Substrate Specificity of Thermoanaerobacter pseudoethanolicus Secondary Alcohol Dehydrogenase by a Dual Site Mutation
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Here, we report the asymmetric reduction of selected phenyl-ring-containing ketones by various single- and dual-site mutants of Thermoanaerobacter pseudoethanolicus secondary alcohol dehydrogenase (TeSADH). The further expansion of the size of the substrate binding pocket in the mutant W110A/I86A not only allowed the accommodation of substrates of the single mutants W110A and I86A within the expanded active site but also expanded the substrate range of the enzyme to ketones bearing two sterically demanding groups (bulky–bulky ketones), which are not substrates for the TeSADH single mutants. We also report the regio- and enantioselective reduction of diketones with W110A/I86A TeSADH and single TeSADH mutants. The double mutant exhibited dual stereopreference to generate the Prelog products most of the time and the anti-Prelog products in a few cases.
- Musa, Musa M.,Bsharat, Odey,Karume, Ibrahim,Vieille, Claire,Takahashi, Masateru,Hamdan, Samir M.
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p. 798 - 805
(2018/02/21)
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- Cobalt-Catalyzed Silylcarbonylation of Unactivated Secondary Alkyl Tosylates at Low Pressure
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A catalytic preparation of silyl enol ethers from unactivated secondary alkyl tosylates is reported. An inexpensive cobalt catalyst is used under mild conditions with low pressures of carbon monoxide. Nucleophilic, anionic cobalt carbonyls facilitate the catalytic activation of a range of alkyl tosylates. The silylcarbonylation offers a practical approach to synthetically valuable silyl enol ethers from simple starting materials.
- Roque Pena, Joan E.,Alexanian, Erik J.
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supporting information
p. 4413 - 4415
(2017/09/11)
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- Multifunctional supported bimetallic catalysts for a cascade reaction with hydrogen auto transfer: Synthesis of 4-phenylbutan-2-ones from 4-methoxybenzyl alcohols
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We report the one-pot tandem synthesis of 4-(4-methoxyphenyl)butan-2-one directly from 4-methoxybenzyl alcohol and acetone using a multifunctional supported AuPd nanoalloy catalyst. This one-pot synthesis involves dehydrogenation, aldol condensation and hydrogenation of CC. In this supported AuPd catalyst, the bimetallic sites catalyse the dehydrogenation and hydrogenation steps and, in combination with the support, catalyse the C-C coupling (aldol) process. This supported bimetallic catalyst is also effective in utilizing hydrogen from the dehydrogenation reaction for the hydrogenation of 4-(4-methoxyphenyl)but-3-en-2-one to 4-(4-methoxyphenyl)butane-2-one via a hydrogen auto transfer route. These multifunctional catalysts were characterised using transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy.
- Morad, Moataz,Nowicka, Ewa,Douthwaite, Mark,Iqbal, Sarwat,Miedziak, Peter,Edwards, Jennifer K.,Brett, Gemma L.,He, Qian,Morgan, David,Alshammari, Hamed,Bethell, Donald,Knight, David W.,Sankar, Meenakshisundaram,Hutchings, Graham J.
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p. 1928 - 1936
(2017/07/15)
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- Nickel-Catalyzed C-Alkylation of Nitroalkanes with Unactivated Alkyl Iodides
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Enabled by nickel catalysis, a mild and general catalytic method for C-alkylation of nitroalkanes with unactivated alkyl iodides is described. Compatible with primary, secondary, and tertiary alkyl iodides; and tolerant of a wide range of functional groups, this method allows rapid access to diverse nitroalkanes.
- Rezazadeh, Sina,Devannah, Vijayarajan,Watson, Donald A.
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supporting information
p. 8110 - 8113
(2017/06/28)
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- Manganese-Catalyzed Borylation of Unactivated Alkyl Chlorides
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The use of low-cost manganese(II) bromide (MnBr2) and tetramethylethylenediamine (TMEDA) catalyzes the cross coupling of (bis)pinacolatodiboron with a wide range of alkyl halides, demonstrating the first manganese-catalyzed coupling with alkyl electrophiles. This method allows access to primary, secondary, and tertiary boronic esters from the parent chlorides, which were previously inaccessible as coupling partners. The reaction proceeds in high yield with as little as 1000 ppm catalyst loading, while 5 mol % can provide high yields in as little as 30 min. Finally, radical-clock experiments revealed that at 0 °C direct borylation outcompetes alternative radical processes, thereby providing synthetically useful, temperature-controlled reaction outcomes.
- Atack, Thomas C.,Cook, Silas P.
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supporting information
p. 6139 - 6142
(2016/06/09)
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- Palladium-Catalyzed Alkoxycarbonylation of Unactivated Secondary Alkyl Bromides at Low Pressure
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Catalytic carbonylations of organohalides are important C-C bond formations in chemical synthesis. Carbonylations of unactivated alkyl halides remain a challenge and currently require the use of alkyl iodides under harsh conditions and high pressures of CO. Herein we report a palladium-catalyzed alkoxycarbonylation of secondary alkyl bromides that proceeds at low pressure (2 atm CO) under mild conditions. Preliminary mechanistic studies are consistent with a hybrid organometallic-radical process. These reactions efficiently deliver esters from unactivated alkyl bromides across a diverse range of substrates and represent the first catalytic carbonylations of alkyl bromides with carbon monoxide.
- Sargent, Brendon T.,Alexanian, Erik J.
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supporting information
p. 7520 - 7523
(2016/07/06)
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- Dual enzymatic dynamic kinetic resolution by Thermoanaerobacter ethanolicus secondary alcohol dehydrogenase and Candida antarctica lipase B
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The immobilization of Thermoanaerobacter ethanolicus secondary alcohol dehydrogenase (TeSADH) using sol-gel method enables its use to racemize enantiopure alcohols in organic media. Here, we report the racemization of enantiopure phenyl-ring-containing secondary alcohols using xerogel-immobilized W110A TeSADH in hexane rather than the aqueous medium required by the enzyme. We further showed that this racemization approach in organic solvent was compatible with Candida antarctica lipase B (CALB)-catalyzed kinetic resolution. This compatibility, therefore, allowed a dual enzymatic dynamic kinetic resolution of racemic alcohols using CALB-catalyzed kinetic resolution and W110A TeSADH-catalyzed racemization of phenyl-ring-containing alcohols.
- Karume, Ibrahim,Musa, Musa M.,Bsharat, Odey,Takahashi, Masateru,Hamdan, Samir M.,El Ali, Bassam
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p. 96616 - 96622
(2016/10/25)
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- Thermoanaerobacter ethanolicus secondary alcohol dehydrogenase mutants with improved racemization activity
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Controlled racemization of enantiopure alcohols is a key step in dynamic kinetic resolution. We recently reported the racemization of enantiopure phenyl-ring-containing alcohols using W110A Thermoanaerobacter ethanolicus secondary alcohol dehydrogenase (W110A TeSADH), which relies on selectivity mistakes. Trp-110 lines the large pocket of the active site of TeSADH, which allows W110A TeSADH mutant to accommodate phenyl-ring-containing substrates in Prelog mode, albeit with selectivity mistakes. Here, we report the racemization of enantiopure phenyl-ring-containing alcohols using several Trp-110 mutants of TeSADH in the presence of the oxidized and reduced forms of nicotinamide-adenine dinucleotide. We observed a noticeable enhancement in racemization efficiency when W110G TeSADH was used compared with W110Q, W110M, W110L, W110I, and W110V. This observation was anticipated because the W110G mutation is expected to open the large pocket of the active site to a greater extent compared to other mutants of TeSADH at W110. Both enantiomers of 1-phenyl-2-propanol and 4-phenyl-2-butanol were fully racemized by W110G TeSADH. We also constructed a triple mutant of TeSADH, W110A/I86A/C295A, by site-directed mutagenesis with the aim of opening the two pockets of the active site of TeSADH. The W110A/I86A/C295A mutant was employed to racemize enantiopure phenyl-ring-containing alcohols. The current study demonstrates that W110G and W110A/I86A/C295A TeSADH are more efficient catalysts for the racemization of enantiopure secondary alcohols than the previously reported mutant W110A TeSADH [6].
- Musa, Musa M.,Patel, Jay M.,Nealon, Christopher M.,Kim, Chang Sup,Phillips, Robert S.,Karume, Ibrahim
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supporting information
p. 155 - 159
(2015/03/30)
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- Oxidation and β-Alkylation of Alcohols Catalysed by Iridium(I) Complexes with Functionalised N-Heterocyclic Carbene Ligands
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The borrowing hydrogen methodology allows for the use of alcohols as alkylating agents for C-C bond forming processes offering significant environmental benefits over traditional approaches. Iridium(I)-cyclooctadiene complexes having a NHC ligand with a O- or N-functionalised wingtip efficiently catalysed the oxidation and β-alkylation of secondary alcohols with primary alcohols in the presence of a base. The cationic complex [Ir(NCCH3)(cod)(MeIm(2- methoxybenzyl))][BF4] (cod=1,5-cyclooctadiene, MeIm=1-methylimidazolyl) having a rigid O-functionalised wingtip, shows the best catalyst performance in the dehydrogenation of benzyl alcohol in acetone, with an initial turnover frequency (TOF0) of 1283 h-1, and also in the β-alkylation of 2-propanol with butan-1-ol, which gives a conversion of 94 % in 10 h with a selectivity of 99 % for heptan-2-ol. We have investigated the full reaction mechanism including the dehydrogenation, the cross-aldol condensation and the hydrogenation step by DFT calculations. Interestingly, these studies revealed the participation of the iridium catalyst in the key step leading to the formation of the new C-C bond that involves the reaction of an O-bound enolate generated in the basic medium with the electrophilic aldehyde.
- Jiménez, M. Victoria,Fernández-Tornos, Javier,Modrego, F. Javier,Pérez-Torrente, Jesús J.,Oro, Luis A.
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supporting information
p. 17877 - 17889
(2015/12/08)
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- Iron-catalyzed borylation of alkyl electrophiles
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The use of low-cost iron(III) acetoacetate (Fe(acac)3) and tetramethylethylenediamine (TMEDA) enables the direct cross-coupling of alkyl halides with bis(pinacolato)diboron. This approach allows for the borylation of activated or unactivated primary, secondary, and tertiary bromides. Moreover, even the borylation of benzylic or allylic chlorides, tosylates, and mesylates are possible. The reactions proceed under mild conditions at room temperature and show broad functional-group compatibility and "robustness" as measured by a modified Glorius robustness screen.
- Atack, Thomas C.,Lecker, Rachel M.,Cook, Silas P.
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supporting information
p. 9521 - 9523
(2014/07/22)
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- Poly(n-butyl-4-vinylpyridinium) borohydride as a new stable and efficient reducing agent in organic synthesis
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Sodium borohydride is stabilized on poly(n-butyl-4-vinylpyridinium) chloride, and it is used as an efficient and regenerable polymer-supported borohydride reagent for the reduction of a variety of carbonyl compounds, such as aldehydes, ketones, α,β-unsaturated carbonyl compounds, α-diketones, and acyloins.
- Khaligh, Nader Ghaffari,Ghasem-Abadi, Parisa Ghods,Mihankhah, Taraneh
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- Iron-catalyzed cross-coupling of unactivated secondary alkyl thio ethers and sulfones with aryl grignard reagents
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The first systematic investigation of unactivated aliphatic sulfur compounds as electrophiles in transition-metal-catalyzed cross-coupling are described. Initial studies focused on discerning the structural and electronic features of the organosulfur substrate that enable the challenging oxidative addition to the C(sp3)-S bond. Through extensive optimization efforts, an Fe(acac)3-catalyzed cross-coupling of unactivated alkyl aryl thio ethers with aryl Grignard reagents was realized in which a nitrogen "directing group" on the S-aryl moiety of the thio ether served a critical role in facilitating the oxidative addition step. In addition, alkyl phenyl sulfones were found to be effective electrophiles in the Fe(acac) 3-catalyzed cross-coupling with aryl Grignard reagents. For the latter class of electrophile, a thorough assessment of the various reaction parameters revealed a dramatic enhancement in reaction efficiency with an excess of TMEDA (8.0 equiv). The optimized reaction protocol was used to evaluate the scope of the method with respect to both the organomagnesium nucleophile and sulfone electrophile.
- Denmark, Scott E.,Cresswell, Alexander J.
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supporting information
p. 12593 - 12628
(2014/01/17)
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- Poly(1,4-butyl-bis-vinylpyridinium) borohydride as a new stable and efficient reducing agent in organic synthesis
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The unstable sodium borohydride is stabilized on modified poly(4-vinylpyridinium), and it is used as an efficient and regenerable polymer-supported borohydride reagent for the reduction of a variety of carbonyl compounds, such as aldehydes, ketones, α,β-unsaturated carbonyl compounds, α-diketones and acyloins, in good to excellent yields.
- Khaligh, Nader Ghaffari
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p. 721 - 727
(2013/08/23)
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- N-heterocyclic carbene-catalyzed hydrosilylation of styryl and propargylic alcohols with dihydrosilanes
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Reducing alkenes to tears: Addition of structurally diverse N-heterocyclic carbenes (NHCs) to silicon allows the reduction of propargylic and styryl alcohols through an organocatalyzed silylation/direct hydride transfer tandem reaction (see scheme). Catalytic turnover is enabled by the switch to and from hypervalent silicon. This provides a new synthetic application of NHC-main group element complexes. Copyright
- Zhao, Qiwu,Curran, Dennis P.,Malacria, Max,Fensterbank, Louis,Goddard, Jean-Philippe,Lacote, Emmanuel
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supporting information; experimental part
p. 9911 - 9914
(2011/10/05)
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- Chemoselective conjugate reduction of α,β-unsaturated ketones catalyzed by rhodium amido complexes in aqueous media
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Although a notable feature of Noyori's Ru-TsDPEN complex is that the transfer hydrogenation reaction is highly chemoselective for the C-O functional group and tolerant of alkenes, our early report indicated that the chemoselectivity could be switched from C-O to C-C bonds in the transfer hydrogenation of activated α,β-unsaturated ketones. Now we have found that a variety of α,β-unsaturated ketones, even without other electron-withdrawing functional groups, could be reduced on the alkenic double bonds with high selectivities employing amido-rhodium hydride complex in aqueous media, and up to 100% chemoselectivity has been achieved. It is notable that the chemoselectivity was improved significantly on going from organic solvent to water. Moreover, a 1,4-addition mechanism has been proposed on the basis of the corresponding experimental details and computational analysis.
- Li, Xuefeng,Li, Liangchun,Tang, Yuanfu,Zhong, Ling,Cun, Linfeng,Zhu, Jin,Liao, Jian,Deng, Jingen
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experimental part
p. 2981 - 2988
(2010/07/05)
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- Asymmetric reduction and oxidation of aromatic ketones and alcohols using W110A secondary alcohol dehydrogenase from Thermoanaerobacter ethanolicus
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An enantioselective asymmetric reduction of phenyl ring-containing prochiral ketones to yield the corresponding optically active secondary alcohols was achieved with W110A secondary alcohol dehydrogenase from Thermoanaerobacter ethanolicus (W110A TESADH) in Tris buffer using 2-propanol (30%), v/v) as cosolvent and cosubstrate. This concentration of 2-propanol was crucial not only to enhance the solubility of hydrophobic phenyl ring-containing substrates in the aqueous reaction medium, but also to shift the equilibrium in the reduction direction. The resulting alcohols have S-configuration, in agreement with Prelog's rule, in which the nicotinamide-adenine dinucleotide phosphate (NADPH) cofactor transfers its pro-R hydride to the re face of the ketone. A series of phenyl ring-containing ketones, such as 4-phenyl-2-butanone (1a) and 1-phenyl-1,3-butadione (2a), were reduced with good to excellent yields and high enantioselectivities. On the other hand, 1-phenyl-2-propanone (7a) was reduced with lower ee than 2-butanone derivatives. (R)-Alcohols, the anti-Prelog products, were obtained by enantiospecific oxidation of (S)-alcohols through oxidative kinetic resolution of the rac-alcohols using W110A TESADH in Tris buffer/acetone (90:10, v/v).
- Musa, Musa M.,Ziegelmann-Fjeld, Karla I.,Vieille, Claire,Zeikus, J. Gregory,Phillips, Robert S.
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- TRANSITION METAL COMPLEXES AS LINKERS
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The invention relates to new traceless linkers which use transition metal complexes to link a pi-orbital containing substrate for subsequent synthesis by, for example, combinatorial chemistry or multiple parallel synthesis (MPS) to a support.
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- Reduction of ketones to alcohols using a decaborane/pyrrolidine/cerium(III) chloride system in methanol
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Decaborane was found to be an effective agent for the chemoselective reduction of ketones to alcohols in the presence of pyrrolidine and cerium(III) chloride heptahydrate in methanol.
- Bae, Jong Woo,Lee, Seung Hwan,Jung, Yeon Joo,Yoon, Choon-Ock Maing,Yoon, Cheol Min
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p. 2137 - 2139
(2007/10/03)
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- Transition metal complexes as linkers for solid phase synthesis: Chromium carbonyl complexes as linkers for arenes
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Substrates containing aromatic rings have been attached to 'polymer supported triphenylphosphine' using a chromium carbonyl linker, chemically manipulated, and released from the polymer to demonstrate the potential use π-bound ligands in linker chemistry. Immobilisation of the phenylalanine derivative Fmoc-Phe-OtBu via its aromatic ring has been achieved and the resulting resin successfully subjected to standard amino acid deprotection and coupling procedures.
- Comely,Gibson,Hales,Peplow
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p. 2526 - 2531
(2007/10/03)
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- Triisobutylaluminium promoted reductive rearrangement of substituted vinyl ethers to homologous alcohols
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Substituted vinyl ethers carrying electron-donating groups in the ether moiety undergo smooth oxygen to carbon rearrangement with triisobutylaluminium to afford chain extended alcohols.
- Du Roizel,Sollogoub,Pearce,Sinay
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p. 1507 - 1508
(2007/10/03)
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- Chromium carbonyl complexes as novel traceless linkers
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Substrates containing aromatic rings have been attached to 'polymer supported triphenylphosphine' using a chromium carbonyl linker, chemically manipulated, and released from the polymer to demonstrate the use of π- arene chromium complexes as traceless linkers.
- Gibson,Hales,Peplow
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p. 1417 - 1418
(2007/10/03)
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- 2-Aryl-2-[1-(2-hydroxypropyl)]-1,3-dithianes as versatile building blocks for the preparation of enantiomerically pure drugs
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An efficient access to chiral, non racemic arylbutanols 1a-c (ee > 98%) as drug intermediates is described. Thioacetalization of substituted benzaldehydes 3a-c with 1,3-propanedithiol gave 2-aryl-1,3-dithianes 4a-c. Lithiation of 4a-c followed by reaction with racemic, (R)- or (S)-propylene oxide, respectively, gave racemic, (R)- or (S)-hydroxyalkyldithianes 5a-c in high yields. Subsequent desulfurization with tributyltin hydride (TBTH) resulted in almost quantitative formation of the arylbutanols 1a-c. Ketols 6 were obtained by hydrolysis of the hydroxyalkyldithianes 5a.
- Bracher,Litz
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p. 235 - 238
(2007/10/02)
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- Propanamine derivatives
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Substituted propanamines having anticoagulant or antifungal activity are disclosed. Also disclosed are methods of use involving the substituted propanamines as well as pharmaceutical compositions containing them.
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- Temperature and Substituent Effects on Regioselectivity in the Insertion of Arylcarbene into Alcohols
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Photolysis of aryldiazomethanes in methanol, ethanol, and 2-propanol gave OH insertion products along with small amounts of CH insertion products at ambient temperature.However, the CH insertion products increased significantly at the expense of the ether as the temperature was lowered.The attempted sensitized decomposition of the diazomethane did not lead to an increase in the CH insertion products presumably because of a rapid singlet-triplet equilibrium.The key intermediate leading to the CH insertion is suggested to be ground-state triplet arylcarbene, based on the accumulated spectroscopic as well as chemical evidence for the intervention of the triplet arylcarbene in the low-temperature photolysis of aryldiazomethanes.Substituents on the phenyl ring also have an appreciable effect on the insertion selectivity.At room temperature, the OH/CH insertion selectivity increased with the electron-donating ability of the substituents.This is interpreted in terms of the substituent effect on the transition state of OH insertion, where there is a deficiency of electrons at the benzylic carbon atom, rather than on the stability of singlet carbene.At low temperature, both electron-donating and -withdrawing substituents facilitate OH insertion, indicating the change in substituents induces a concomitant change in the insertion mechanism, presumably due to decreasing nucleophilicity of carbene with increasing electron-withdrawing ability as well as decreasing proton-donor activity of alcohol with decreasing temperature.This may also reflect the effect of the substituent on the singlet-triplet energy gap.
- Tomioka, Hideo,Suzuki, Shinji,Izawa, Yasuji
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p. 3156 - 3162
(2007/10/02)
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