- Synthesis and stereoselective evaluation of a (1R)-(–)-myrtenal-derived pseudo C2-symmetric dodecaheterocycle as a potential heterofunctional chiral auxiliary
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The synthesis and diastereoselective performance of the pseudo C2-symmetric dodecaheterocycle 3 in nucleophilic and electrophilic reactions are reported. Compound 3 proved to be a highly diastereoselective template to generate a pair of enantiomeric moieties within its structure in a programmed manner. Hence, this study describes the synthesis of a novel potential heterobifunctional chiral auxiliary.
- Sánchez-Chávez, Anahí C.,Elena Vargas-Díaz, Ma.,Ontiveros-Rodríguez, Julio C.,Pérez-Estrada, Salvador,Flores-Bernal, Gustavo G.,Mendoza-Espinosa, Daniel,álvarez-Hernández, Alejandro,Delgado, Francisco,Tamariz, Joaquín,Gerardo Zepeda-Vallejo
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- The Bovine Serum Albumin-2-Phenylpropane-1,2-diolatodioxo-osmium(VI) Complex as an Enantioselective Catalyst for cis-Hydroxylation of Alkenes
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The 1:1 complex between an osmate ester and bovine serum albumin was found to be effective as an enantioselective catalyst in the cis-hydroxylation of alkenes, affording diols in up to 68percent e.e. and turnover of the catalyst with tert-butyl hydroperoxide.
- Kokubo, Toshio,Sugimoto, Toyonari,Uchida, Toshio,Tanimoto, Shigeo,Okano, Masaya
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- Chiral-auxiliary-controlled diastereoselectivity in the epoxidation of enecarbamates with DMD and mCPBA
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(Matrix presented) Chiral oxazolidinone-substituted enecarbamates 1 are epoxidized in a diastereoselectivity up to 93:7 for both DMD and mCPBA. The diastereofacial differentiation depends on the steric interaction between the R1 substituent on the oxazolidinone ring and the incoming electrophile. The stereochemical course of epoxidation was assessed by chemical correlation with the known optically active diols.
- Adam, Waldemar,Bosio, Sara G.,Wolff, Barbara T.
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- New 2-acyl-1,3-dioxane derivatives from (1R)-(-)-myrtenal: stereochemical effect on their relative ability as chiral auxiliaries
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Four 3,10-pinanediol derivatives 1a-d, prepared in 50-72% global yields from (1R)-(-)-myrtenal 2, were treated with (RO)2CHCOR3 (R3 = CH3, Ph) to afford 2-acyl-1,3-dioxanes 3a-f. The latter were submitted to nucleophilic additions using several Grignard reagents to mainly afford carbinols generated by re diastereofacial attack (85-99% yield, ≥88:12 dr). The lowest diastereoselectivity was observed when PhLi or hydrides were used as nucleophiles. Only an equatorial substituent at C-3 modifies the diastereoselectivity of the nucleophilic additions.
- Becerra-Martinez, Elvia,Velazquez-Ponce, Pedro,Sanchez-Aguilar, Miguel A.,Rodriguez-Hosteguin, Alfredo,Joseph-Nathan, Pedro,Tamariz, Joaquin,Zepeda, L. Gerardo
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- An improved version of the Sharpless asymmetric dihydroxylation
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The osmium catalyzed asymmetric dihydroxylation of olefins (Sharpless AD) was studied under controlled pH conditions. It was found that providing a constant pH value of 12.0 leads to improved reaction rates for internal olefins. Hydrolysis aids such as methanesulfonamide can be omitted. For terminal olefins, working at a constant pH of 10.0 at room temperature leads to higher enantioselectivities compared to AD reactions without pH control. (C) 2000 Elsevier Science Ltd.
- Mehltretter,Dobler,Sundermeier,Beller
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- Catalytic asymmetric dihydroxylation of α-methylstyrene by air
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Dioxygen is able, under visible irradiation, to promote the high yielding and highly asymmetric dihydroxylation of α-methylstyrene in the presence of catalytic amounts of Os(VI), phthalazine dihydroquinidine chiral ligand [(DHQD)2PHAL].
- Krief, Alain,Colaux-Castillo, Catherine
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- Absolute stereochemical determination of 1,2-diols via complexation with dinaphthyl borinic acid
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Rapid derivatization of chiral 1,2-diols with dinaphthyl borinic acid (DBA) leads to a cyclic boronate, enabling the absolute stereochemical prediction via exciton-coupled circular dichroic (ECCD) of the naphthyl groups. Aryl- and alkyl-substituted 1,2-diols derivatized with DBA yield a predictable ECCD, which is also in agreement with theoretical predictions derived from computationally minimized structures.
- Torabi Kohlbouni, Saeedeh,Sarkar, Aritra,Zhang, Jun,Li, Xiaoyong,Borhan, Babak
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supporting information
p. 817 - 823
(2020/03/26)
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- Racemic or enantioselective osmium-catalyzed dihydroxylation of olefins under near-neutral conditions
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K3Fe(CN)6 and NaIO4 serve as catalytic co-oxidants for osmium-catalyzed dihydroxylations that are performed under near-neutral conditions with K2S2O8 as the stoichiometric oxidant and Na2HPO4 as the base. By using either quinuclidine or hydroquinidine 1,4-phthalazinediyl ether [(DHQD)2Phal], good yields of racemic or enantioenriched diols are obtained. This simple, biphasic procedure offers advantages over other neutral dihydroxylation protocols that use N-methylmorpholine oxide as the stoichiometric oxidant, by suppressing the secondary catalytic cycle that leads to reduced enantioselectivities. The utility of the procedure, which is nicely suited for base-labile starting materials or products, is demonstrated by performing the dihydroxylation in the presence of an aliphatic aldehyde moiety.
- Blumberg, Shawn,Martin, Stephen F.
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- Syn-dihydroxylation of alkenes using a sterically demanding cyclic diacyl peroxide
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The syn-dihydroxylation of alkenes is a highly valuable reaction in organic synthesis. Cyclic acyl peroxides (CAPs) have emerged recently as promising candidates to replace the commonly employed toxic metals for this purpose. Here, we demonstrate that the structurally demanding cyclic peroxide spiro[bicyclo[2.2.1]heptane-2,4′-[1,2]dioxolane]-3′,5′-dione (P4) can be effectively used for the syn-dihydroxylation of alkenes. Reagent P4 also shows an improved selectivity for dihydroxylation of alkenes bearing β-hydrogens as compared to other CAPs, where both diol and allyl alcohol products compete with each other. Furthermore, the use of enantiopure P4 (labeled P4′) demonstrates the potential of P4′ for a metal-free asymmetric syn-dihydroxylation of alkenes.
- Pilevar, Afsaneh,Hosseini, Abolfazl,Becker, Jonathan,Schreiner, Peter R.
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p. 12377 - 12386
(2019/10/11)
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- Ligand-Controlled Regiodivergent Enantioselective Rhodium-Catalyzed Alkene Hydroboration
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Regiocontrol in the rhodium-catalyzed boration of vinyl arenes is typically dominated by the presence of the conjugated aryl substituent. However, small differences in TADDOL-derived chiral monophosphite ligands can override this effect and direct rhodium-catalyzed hydroboration of β-aryl and β-heteroaryl methylidenes by pinacolborane to selectively produce either chiral primary or tertiary borated products. The regiodivergent behavior is coupled with enantiodivergent addition of the borane. The nature of the TADDOL backbone substituents and that of the phosphite moiety function synergistically to direct the sense and extent of regioselectivity and enantioinduction. Twenty substrates are shown to undergo each reaction mode with regioselectivity values reaching greater than 20:1 and enantiomer ratios reaching up to 98:2. A variety of subsequent transformations illustrate the potential utility of each product.
- Bochat, Andrew J.,Shoba, Veronika M.,Takacs, James M.
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p. 9434 - 9438
(2019/06/27)
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- Production Of Enantiopure alpha-Hydroxy Carboxylic Acids From Alkenes By Cascade Biocatalysis
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The invention provides compositions comprising an alkene epoxidase and a selective epoxide hydrolase, such as a recombinant microorganism comprising a first heterologous nucleic acid encoding an alkene epoxidase and a second heterologous nucleic acid encoding a selective epoxide hydrolase. Exemplary alkene epoxidases include StyAB, while exemplary selective epoxide hydrolases include epoxide hydrolases from Sphingomonas, Solanum tuberosum, or Aspergillus. The invention also provides non-toxic methods of making enantiomerically pure vicinal diols or enantiomerically pure alpha-hydroxy carboxylic acids using these compositions and microorganisms.
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Paragraph 0097-0099
(2016/05/02)
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- Enantioselective Bromo-oxycyclization of Silanol
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Relying on the nucleophilicity of silanol for building up silicon-incorporated scaffold with an enantiopure tetrasubstituted carbon center remains elusive. In this report, asymmetric bromo-oxycyclization of olefinic silanol by using chiral anionic phase-transfer catalyst is described. This protocol provided a facile entry to a wide arrangement of enantiopure benzoxasilole in moderate to excellent enantioselectivities depending on the unique reactivity of bromine/N-benzyl-DABCO complex.
- Xia, Zilei,Hu, Jiadong,Shen, Zhigao,Wan, Xiaolong,Yao, Qizheng,Lai, Yisheng,Gao, Jin-Ming,Xie, Weiqing
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- Mechanistic Insights into Enantioselective C-H Photooxygenation of Aldehydes via Enamine Catalysis
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Organocatalytic photooxygenation of aldehydes at the α-position proceeds via enamine catalysis, though enamines should be easily oxidized by singlet oxygen respectively to amides and carbonyl compounds. Moreover, the formation of a zwitterionic enamine peroxide intermediate was postulated based on experimental and theoretical data. The reaction affords desired diols (after in situ reduction) in a decent yield and (S)- or (R)-enantioselectivity depending on a catalyst used. The (S)-enantiomer predominated in imidazolidinone-catalyzed reactions, while prolineamides assured the formation of the (R)-stereoisomer. DFT calculation suggests that the enamine-oxygen complex with the lowest energy has the E,s-cis conformation for the prolineamide derivative and E,s-trans for the imidazolidinone catalyst, explaining the opposite stereoselectivity in the photooxygenation reaction.
- Walaszek, Dominika J.,Rybicka-Jasińska, Katarzyna,Smoleń, Sabina,Karczewski, Maksymilian,Gryko, Dorota
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supporting information
p. 2061 - 2070
(2015/06/23)
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- Resolution of diols via catalytic asymmetric acetalization
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A highly enantioselective kinetic resolution of diols via asymmetric acetalization has been achieved using a chiral confined imidodiphosphoric acid catalyst. The reaction is highly efficient for the resolution of tertiary alcohols, giving selectivity factors of up to >300. Remarkably, even in cases where the selectivity factors are only moderate, highly enantioenriched diols are obtained via a stereodivergent resolution to diastereomeric acetals.
- Kim, Ji Hye,ori, Ilija,Palumbo, Chiara,List, Benjamin
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supporting information
p. 1778 - 1781
(2015/03/04)
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- A simple primary amine catalyst for enantioselective α-hydroxylations and α-fluorinations of branched aldehydes
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A new primary amine catalyst for the asymmetric α-hydroxylation and α-fluorination of α-branched aldehydes is described. The products of the title transformations are generated in excellent yields with high enantioselectivities. Both processes can be performed within short reaction times and on gram scale. The similarity in results obtained in both reactions, combined with computational evidence, implies a common basis for stereoinduction and the possibility of a general catalytic mechanism for α-functionalizations. Promising initial results in α-amination and α-chlorination reactions support this hypothesis.
- Witten, Michael R.,Jacobsen, Eric N.
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supporting information
p. 2772 - 2775
(2015/06/16)
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- Enantioselective trans-dihydroxylation of aryl olefins by cascade biocatalysis with recombinant escherichia coli coexpressing monooxygenase and epoxide hydrolase
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Cascade biocatalysis via intracellular epoxidation and hydrolysis was developed as a green and efficient method for enantioselective dihydroxylation of aryl olefins to prepare chiral vicinal diols in high ee and high yield. Escherichia coli (SSP1) coexpressing styrene monooxygenase (SMO) and epoxide hydrolase SpEH was developed as a simple and efficient biocatalyst for S-enantioselective dihydroxylation of terminal aryl olefins 1a-15a to give (S)-vicinal diols 1c-15c in high ee (97.5-98.6% for 10 diols; 92.2-93.9% for 3 diols) and high yield (91-99% for 6 diols; 86-88% for 2 diols; 67% for 3 diols). Combining SMO and epoxide hydrolase StEH showing complementary regioselectivity to SpEH as a biocatalyst for the cascade biocatalysis gave rise to R-enantioselective dihydroxylation of aryl olefins, being the first example of this kind of reversing the overall enantioselectivity of cascade biocatalysis. E. coli (SST1) coexpressing SMO and StEH was also engineered as a green and efficient biocatalyst for R-dihydroxylation of terminal aryl olefins 1a-15a to give (R)-vicinal diols 1c-15c in high ee (94.2-98.2% for 7 diols; 84.2-89.9% for 6 diols) and high yield (90-99% for 6 diols; 85-89% for 5 diols; 65% for 1 diol). E. coli (SSP1) and E. coli (SST1) catalyzed the trans-dihydroxylation of trans-aryl olefin 16a and cis-aryl olefin 17a with excellent and complementary stereoselectivity, giving each of the four stereoisomers of 1-phenyl-1,2- propanediol 16c in high ee and de, respectively. Both strains catalyzed the trans-dihydroxylation of aryl cyclic olefins 18a and 19a to afford the same trans-cyclic diols (1R,2R)-18c and (1R,2R)-19c, respectively, in excellent ee and de. This type of cascade biocatalysis provides a tool that is complementary to Sharpless dihydroxylation, accepting cis-alkene and offering enantioselective trans-dihydroxylation.
- Wu, Shuke,Chen, Yongzheng,Xu, Yi,Li, Aitao,Xu, Qisong,Glieder, Anton,Li, Zhi
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p. 409 - 420
(2014/03/21)
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- A chiral benzyl group as a chiral auxiliary and protecting group for the synthesis of optically active 1,2-Diols and (+)-Frontalin
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Chelation-controlled asymmetric nucleophilic addition of a Grignard reagent to chiral α-benzyloxy ketones gives the corresponding alcohols with high diastereoselectivities (up to 96% de) by 1,4-asymmetric induction. A chiral benzyl group is used as a chiral auxiliary as well as a protecting group for the synthesis of optically active 1,2-diols and (+)-frontalin. Georg Thieme Verlag Stuttgart, New York.
- Kim, Tae Hyun,Kim, Young-Kyo,Yang, Zunhua,Jung, Jung Wha,Jeong, Lak Shin,Kim, Hee-Doo
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supporting information
p. 251 - 254
(2014/02/14)
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- Asymmetric diboration of terminal alkenes with a rhodium catalyst and subsequent oxidation: Enantioselective synthesis of optically active 1,2-diols
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Pin it down: A highly enantioselective diboration of terminal alkenes with chiral 1 and bis(pinacolato)diboron (B2pin2) was realized. Subsequent oxidation of the diboron adducts with sodium peroxoborate readily gave the corresponding optically active 1,2-diols in high yields and high enantioselectivities. Copyright
- Toribatake, Kenji,Nishiyama, Hisao
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supporting information
p. 11011 - 11015
(2013/10/22)
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- Stereoselective selenium catalyzed dihydroxylation and hydroxymethoxylation of alkenes
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The selenium atom of the selenocysteine plays a crucial role in the reduction of peroxides. Herein we showed that, in the absence of a thiol cofactor, the same aminoacid efficiently catalyzed the dihydroxylation of carbon-carbon double bonds leading to the stereoselective formation of 1,2-diols at room temperature and in on water conditions. Alternatively, in the presence of methanol, the corresponding β-methoxyalcohol can be prepared. The stereoselectivity of the reaction will be discussed and NMR evidences of the actual catalyst are here reported.
- Santi, Claudio,Di Lorenzo, Rosalia,Tidei, Caterina,Bagnoli, Luana,Wirth, Thomas
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p. 10530 - 10535,6
(2012/12/12)
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- Organocatalytic asymmetric α-benzoyloxylation of α-branched aldehydes and enals: A useful approach to oxygenated quaternary stereocenters
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Direct asymmetric α-benzoyloxylation of α-branched aldehydes and α-branched enals via enamine and dienamine catalysis was used to construct quaternary oxygenated stereocenters with good yields and moderate to good enantioselectivity. This method uses an inexpensive and readily available cinchona alkaloid-derived primary amine as the catalyst, benzoyl peroxide as the oxygen source, and stoichiometric amounts of the aldehyde substrates, providing simple metal-free access to valuable protected 2-hydroxyaldehyde derivatives.
- Demoulin, Nicolas,Lifchits, Olga,List, Benjamin
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supporting information; scheme or table
p. 7568 - 7574
(2012/09/21)
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- Highly homogeneous stereocontrolled construction of quaternary hydroxyesters by addition of dimethylzinc to α-ketoesters promoted by chiral perhydrobenzoxazines and B(OEt)3
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A highly efficient enantioselective addition of Me2Zn to α-ketoesters, assisted by a chiral perhydro-1,3-benzoxazine ligand, is described. This novel catalytic system offers homogeneous elevated enantioselectivities in the preparation of α-hydroxyesters that bear a quaternary stereocenter, with a minor dependence on electronic and steric effects when aromatic, heteroaromatic, or aliphatic α-ketoesters are employed. The catalyst can be recovered and reused without loss of activity.
- Infante, Rebeca,Nieto, Javier,Andres, Celia
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supporting information; experimental part
p. 4375 - 4379
(2012/05/20)
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- Alkyl 2-(2-benzothiazolylsulfinyl)acetates as useful synthetic reagents for alkyl 4-hydroxyalk-2-enoates by sulfinyl-Knoevenagel reaction
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Isopropyl, ethyl, and methyl 2-(2-benzothiazolylsulfinyl)acetates have been found to be useful synthetic reagents for sulfinyl-Knoevenagel reaction with various aldehydes to give directly the corresponding 4-hydroxyalk-2-enoates [R′CH(OH)CHCHCO2R], which are ubiquitous structures in biologically active natural products and useful building blocks for organic synthesis of chiral compounds. From the optically pure (R)-2-(2- benzothiazolylsulfinyl)acetates (>99% ee) prepared by the enzymatic kinetic resolution of (±)-2-(2-benzothiazolylsulfinyl)acetates, optically active 4-hydroxyalk-2-enoates (up to 91% ee) have been obtained in good yields.
- Du, Zhenjun,Kawatani, Toshihiro,Kataoka, Kazuhide,Omatsu, Rikiya,Nokami, Junzo
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experimental part
p. 2471 - 2480
(2012/04/10)
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- OsO4?streptavidin: A tunable hybrid catalyst for the enantioselective cis-dihydroxylation of olefins
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Taking control: Selective catalysts for olefin dihydroxylation have been generated by the combination of apo-streptavidin and OsO4. Site-directed mutagenesis allows improvement of enantioselectivity and even inversion of enantiopreference in certain cases. Notably allyl phenyl sulfide and cis-β-methylstyrene were converted with unprecedented enantiomeric excess.
- Koehler, Valentin,Mao, Jincheng,Heinisch, Tillmann,Pordea, Anca,Sardo, Alessia,Wilson, Yvonne M.,Knoerr, Livia,Creus, Marc,Prost, Jean-Christophe,Schirmer, Tilman,Ward, Thomas R.
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supporting information; experimental part
p. 10863 - 10866
(2012/02/01)
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- An achiral manganese salen catalyst encapsulated in a peptidic phosphonate homochiral solid for the enantioselective formation of diols by consecutive epoxidation and hydration reactions
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An insoluble, porous, amorphous, homochiral material based on a polypeptide titanium-phosphonate scaffold with an encapsulated achiral Mn III-salen was prepared and characterized. Consecutive epoxidation and hydration of styrene and its derivatives by aqueous hypochlorite in THF showed the highly enantioselective (>99%) formation of styrene diol derivatives.
- Milo, Anat,Neumann, Ronny
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supporting information; experimental part
p. 2535 - 2537
(2011/04/26)
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- A recyclable dendritic osmium catalyst for homogeneous dihydroxylation of olefins
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A series of osmate (OsO42-) core dendrimers was prepared by an ion-exchange technique through the mixing of K 2OsO4 and a bis(quaternary ammonium bromide) core dendrimer, which consisted of poly(benzyl ether) dendron. By employing an osmate core dendrimer as a homogeneous catalyst, dihydroxylation reactions of olefins proceeded rapidly, and the dendritic osmium catalyst was recovered by reprecipitation and then reused. Furthermore, a dendritic effect on the recyclability of a catalyst was observed. In the case of asymmetric dihydroxylation reactions, the corresponding diol was obtained in a high chemical yield with a fair enantiomeric excess (ee). In this case, not only the dendritic osmium catalyst but also the chiral ligand could be recovered by reprecipitation and reused efficiently up to five times.
- Fujita, Ken-Ichi,Yamazaki, Manabu,Ainoya, Taku,Tsuchimoto, Teruhisa,Yasuda, Hiroyuki
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experimental part
p. 8536 - 8543
(2010/11/18)
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- Access to enantiopure aromatic epoxides and diols using epoxide hydrolases derived from total biofilter DNA
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Metagenomic DNA is a rich source of genes encoding novel epoxide hydrolases (EHs). We retrieved two genes encoding functional EHs from total DNA isolated from biofilter-derived biomass, using PCR with EH-specific degenerate primers followed by genome-walking PCR. The degenerate primers were based on two EH-specific consensus sequences: HGWP and GHDWG. The resulting recombinant EHs, Kau2 and Kau8, were expressed in Escherichia coli, and their enantioselectivity and regioselectivity were determined using 13 different epoxide substrates. The EH Kau2 had broad substrate specificity and preferentially hydrolyzed epoxides with S-configuration. It showed high enantioselectivity towards aromatic epoxides such as styrene oxide, p-nitrostyrene oxide, and trans-1-phenyl-1,2-epoxypropane. In addition, Kau2 showed enantioconvergent hydrolysis activity. The EH Kau8 also showed broad substrate specificity and preferentially hydrolyzed epoxides with R-configuration. High enantioselectivity was observed for p-nitrostyrene oxide, and the hydrolysis activity of Kau8 was less enantioconvergent than that of Kau2. To determine the usefulness of Kau2 for synthetic applications, preparative-scale biohydrolysis reactions were performed. Specifically, two kinetic resolutions were carried out with 80 g/L of racemic trans-1-phenyl-1,2-epoxypropane, affording both (1R,2R)-epoxide and the corresponding (1R,2S)-diol in high enantiomeric excess (>99%) and good yield (>45%). In addition, a process based on enantioconvergent hydrolysis by the EH Kau2 was established for racemic cis-1-phenyl-1,2-epoxypropane at a concentration of 13 g/L, resulting in the formation of the corresponding (1R,2R)-diol with a 97% yield and an enantiomeric excess exceeding 98%.
- Kotik, Michael,Stepanek, Vaclav,Grulich, Michal,Kyslik, Pavel,Archelas, Alain
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experimental part
p. 41 - 48
(2010/12/19)
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- A new type of oxidation-reduction condensation by the combined use of phenyl diphenylphosphinite and oxidant
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A new type of oxidation-reduction condensation of alcohols with sulfur, nitrogen, and oxygen nucleophiles by the combined use of phenyl diphenylphosphinite (PhOPPh2) and oxidants such as azides or diethyl azodicarboxylate (DEAD) are described. In these reactions, chiral secondary and tertiary alcohols are converted into the corresponding chiral sulfides, azides, esters and ethers under mild and neutral conditions with almost complete inversion of stereochemical configuration.
- Mukaiyama, Teruaki,Kuroda, Kiichi,Maruyama, Yuji
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scheme or table
p. 63 - 82
(2010/04/23)
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- A tripodal peptidic titanium phosphonate as a homochiral porous solid medium for the heterogeneous enantioselective hydration of epoxides
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A porous, homochiral titanium-phosphonate material based on a tripodal peptide scaffold was used as a heterogeneous reaction medium for the enantioselective hydration (>99%) of styrene oxide. This titanium-phosphonate material, which was shown to contain confined chiral spaces, was prepared by polymerization of L-leucine onto a tris(2-aminoethyl)amine initiator, followed by capping with phosphonate groups and completed by non-aqueous condensation with titanium isopropoxide. Circular dichroism confirmed that the peptide tethers yielded a secondary structure. X-ray powder diffraction and transmission electron microscopy supported by a semi-empirical model showed the likely formation of a porous, lamellar material that was quantified by nitrogen adsorption.
- Milo, Anat,Neumann, Ronny
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supporting information; experimental part
p. 2159 - 2165
(2010/12/18)
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- New general method for regio- and stereoselective allylic substitution with aryl and alkenyl coppers derived from grignard reagents
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Allylic substitution with sp2-carbon reagents (aryl and alkenyl anions) was realized by using allylic picolinates and copper reagents derived from RMgBr and CuBr-Me2S to afford anti SN2 products regioand stereoselectively. Steric and electronic factors in the reagents and the size of the methylene substituents around the allylic moiety marginally affected the selectivity. The reaction system was compatible with alkyl reagents as well. Furthermore, the substitution was applied to construction of a quaternary center and synthesis of (-)-sesquichamaenol. Electron-withdrawing nature of the pyridyl group and chelation of the C(=O)-C5H4N to MgBr2 generated in situ were found to be responsible for the high efficiency of the substitution.
- Kiyotsuka, Yohei,Katayama, Yuji,Acharya, Hukuni P.,Hyodo, Tomonori,Kobayashi, Yuichi
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experimental part
p. 1939 - 1951
(2009/08/07)
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- Osmium-catalyzed asymmetric dihydroxylation by carbon dioxide-activated hydrogen peroxide and N-methylmorpholine
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An improved process has been developed for the osmium-catalyzed dihydroxylation of olefins via in situ formation of NMO from NMM using CO2 catalysis and H2O2. All olefins examined were selectively cis-dihydroxylated to their corresponding diols in good to excellent yields, and by the use of chiral ligands, high enantiomeric excesses were obtained.
- Balagam, Bharathi,Mitra, Ranjan,Richardson, David E.
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p. 1071 - 1075
(2008/09/18)
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- Sharpless asymmetric dihydroxylation of olefins in water-surfactant media with recycling of the catalytic system by membrane nanofiltration
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This paper presents a new and more sustainable alternative approach for the Sharpless catalytic asymmetric dihydroxylation (AD) of olefins using a water/surfactant systemas reaction media. The AD reaction was performed using several cationic and anionic surfactants allowing yields and enantiomeric excesses higher or comparable with the conventional systems (using organic mixtures). The use of this water/surfactant medium offers the additional advantage of performing the reactions without the need of a slow addition of olefins. Asymmetric dihydroxylation of 1-hexene in a 1.5 mM sodium cholate aqueous solution, using N-methylmorpholine N-oxide (NMO) as co-oxidant was selected as model systemto evaluate the feasibility of recycling the Sharpless catalytic systemby nanofiltration. The reaction media was processed by nanofiltration, the product was isolated in the permeate, whereas the catalytic systemand surfactant were retained by the membrane and recycled through six successive reactions, improving the catalyst turn-over number. The experimental results were compared with the ones calculated on the basis of mass balances, membrane rejections to product and reaction yields.
- Branco, Luis C.,Ferreira, Frederico Castelo,Santos, Jose L.,Crespo, Joao G.,Afonso, Carlos A. M.
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supporting information; experimental part
p. 2086 - 2098
(2009/09/07)
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- Preparation of substituted enol derivatives from terminal alkynes and their synthetic utility
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Stereodefined enol derivatives of aldehydes are prepared from terminal alkynes. Specifically, terminal alkynes are known to undergo Cp2ZrCl2-catalyzed methylalumination. Here, we show that the resultant vinylalanes can be oxygenated with peroxyzinc species to generate trisubstituted enolates. Electrophilic trapping with carboxylic anydrides or silyl triflates yields trisubstituted enol esters or silanes, respectively. The tandem carbometalation/oxygenation tolerates free and protected alcohols, heterocycles, olefins, and nitriles. Stereodefined enol esters can undergo asymmetric dihydroxylation to yield optically active α-hydroxy aldehydes. Reduction with NaBH4 provides the diols of 1,1-disubstituted olefins in excellent ee. An application of this methodology to the enantioselective synthesis of the insect pheromone frontalin is presented. Finally, α-hydroxy aldehydes are shown to undergo homologation to a terminal alkyne, reductive amination, oxidation and olefination. Preliminary results indicate that tandem carbometalation/amination can be accomplished with azodicarboxylates. In this way, ene-hydrazines are formed in excellent yield. Copyright
- DeBergh, John R.,Spivey, Kathleen M.,Ready, Joseph M.
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supporting information; experimental part
p. 7828 - 7829
(2009/02/01)
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- Catalytic Asymmetric Dihydroxylation of Olefins Using a Recoverable and Reusable Ligand
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A free bis-cinchona alkaloid derivative ligand was prepared by a simple synthetic manipulation. With ligand/olefin mole ratio of 1%, the asymmetric dihydroxylation reactions of six olefins proceeded smoothly to give the chiral vicinal diols in high chemical yields and optical yields. The ligand itself could be recovered quantitatively by a simple operation and reused five times without loss of enantioselectivity.
- Wang, Qiao Feng,Sun, Xiao Li,Zhang, Sheng Yong,Qin, Xiang Yang,Zhao, Yan
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- Synthesis of a new (1R)-(-)-myrtenal-derived dioxadithiadodecacycle and its use as an efficient chiral auxiliary
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(Chemical Equation Presented) The new macrocycle 9 (>70% yield from hydroxythiol 10) was treated with several nucleophilic reagents (RMgX, RLi, and LiAlH4) affording carbinols 12a-j (80-96% yield, >99:1 dr). Oxidative hydrolysis of 12a,c,e, followed by LiAlH4 reduction of the resulting mixture, gave 16a,c,e in >95% ee,16c being a key precursor for the preparation of fungicide 17. The absolute configuration of 9 and 12j (Nu = H) was established by single-crystal X-ray diffraction analyses and chemical correlation.
- Vargas-Diaz, M. Elena,Joseph-Nathan, Pedro,Tamariz, Joaquin,Zepeda, L. Gerardo
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- Filtration-free recyclable catalytic asymmetric dihydroxylation using a ligand immobilized on magnetic mesocellular mesoporous silica
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A new magnetic mesocellular mesoporous silica support featuring a 3D open-pore structure has been developed for highly efficient, filtration-free recycling of chiral ligands for catalytic asymmetric dihydroxylation. Reactions using the ligand immobilized on this magnetic silica system exhibited almost the same reactivity and enantioselectivity as those obtained in the homogeneous reaction. Magnetically recovered ligand could be recycled eight times with good to excellent conservation of reaction rates and enantioselectivities.
- Lee, Daewon,Lee, Jinwoo,Lee, Honggeun,Jin, Sunmi,Hyeon, Taeghwan,Kim, B. Moon
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- A novel chemoentrapment approach for supportless recycling of a catalyst: Catalytic asymmetric dihydroxylation
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A simple method of recycling a metal catalyst through chemoentrapment in an aqueous layer using ethyl vinyl ether has been developed. Using this new methodology, a highly efficient, filtration-free recycling of osmium for catalytic asymmetric dihydroxylation was accomplished. By means of the formation of a water-soluble OsO42- using EVE, AD reactions of mono- and disubstituted olefins with 1 mol % of OsO4 proceeded for up to 9 cycles without any loss of yields and enantioselectivities.
- Lee, Daewon,Lee, Honggeun,Kim, Seyoung,Yeom, Chang-Eun,Kim, B. Moon
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p. 1021 - 1024
(2007/10/03)
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- Preparation, characterization and catalytic properties of polyaniline-supported metal complexes
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Polyaniline-supported Sc, In, Pd, Os and Re catalysts were prepared by using a simple protocol and the thus prepared catalysts were well characterized using FTIR, XPS, UV-Vis/DRS, TGA-DTA. All the catalysts were successfully employed in a wide range of organic transformations such as cyanation and allylation of carbonyl compound, Suzuki coupling of aryl halides and boronic acids, and, most importantly, in asymmetric dihydroxylation of olefins to afford optically active vicinal diols. All the catalysts were separated from the reaction mixture by simple filtration and reused with consistent activity for five cycles without noticeable leaching of metal from the support.
- Choudary, Boyapati M.,Roy, Moumita,Roy, Sarabindu,Kantam, M. Lakshmi,Sreedhar, Bojja,Kumar, Karasala Vijay
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p. 1734 - 1742
(2007/10/03)
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- Clean osmium-catalyzed asymmetric dihydroxylation of olefins in ionic liquids and supercritical CO2 product recovery
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The combination of ionic liquids (ILs) as solvents in the asymmetric Sharpless dihydroxylation (AD) with the use of ScCO2 in the separation process allows a very simple, efficient, clean and robust system for the reuse of the AD catalytic system, which also does not need the use of organic solvents either for the reaction or for the separation of products and allows the isolation of the diol, in high yield and enantiomeric excess and basically without contamination with osmium.
- Branco, Luis C.,Serbanovic, Ana,Da Ponte, Manuel Nunes,Afonso, Carlos A. M.
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p. 107 - 109
(2007/10/03)
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- A novel microencapsulated osmium catalyst using cross-linked polystyrene as an efficient catalyst for asymmetric dihydroxylation of olefins in water
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A novel microencapsulated osmium catalyst (PSresin-MC Os) was developed using cross-linked polystyrene. The concept of this method may go beyond that of microencapsulation. The catalyst was successfully used in asymmetric dihydroxylation in water, and it was recovered quantitatively by simple filtration and reused several times without loss of activity. The shape of the catalyst was maintained even after several uses. Moreover, no leaching of the Os component was detected.
- Ishida, Tasuku,Akiyama, Ryo,Kobayashi, Shu
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p. 1189 - 1192
(2007/10/03)
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- Probing competitive enantioselective approach vectors operating in the Jacobsen-Katsuki epoxidation: A kinetic study of methyl-substituted styrenes
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This paper describes a study of reactivity and enantioselectivity for a series of methyl-substituted styrenes in the Jacobsen-Katsuki (Mn(salen)-catalyzed) epoxidation reaction. Competition experiments provided kinetic data for the reactivity of the seven possible methyl-substituted styrenes (mono-, di- and trisubstituted) relative to styrene itself, ee values were measured by chiral GC, and absolute configurations were secured by chemical correlation. Of particular interest was the switch in absolute configuration at the benzylic position of the epoxides derived from (Z)- and (E)-α,β-dimethylstyrene, respectively. The results could be rationalized in terms of an approach vector with the phenyl substituent proximal to the salen. As opposed to alkyl groups, a proximal phenyl group has very little effect on the rate of the reaction. Consideration of distal vs proximal approach allows prediction of absolute stereochemistry as a function of alkene substitution pattern. Trisubstituted alkenes with one phenyl group cis to the alkene hydrogen can be identified as a favored substrate class in the title reaction, with both rate and selectivity close to the classic (Z)-β-substituted styrene substrates.
- Fristrup, Peter,Dideriksen, Brian B.,Tanner, David,Norrby, Per-Ola
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p. 13672 - 13679
(2007/10/03)
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- CATALYZED ENANTIOSELECTIVE TRANSFORMATION OF ALKENES
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Enantioselective catalytic reactions that operate directly on unactivated alkenes for the preparation of chiral organic building blocks and new materials. More particularly, a catalyzed enantioselective reaction that operates on an unsaturated hydrocarbon, such as an alkene, to provide an enantiomerically enriched reactive organometallic intermediate, which can be converted to a variety of multifunctional optically active reaction products.
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Page/Page column 36
(2010/02/10)
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- Diastereoselective addition of grignard reagents to chiral α-ketoimides derived from Oppolzer's sultam
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Additions of various Grignard reagents to N-pyruvoyl- (3) and N-phenylglyoxyloyl-(2R)-bornane-10,2-sultam (4) under thermal and Lewis-acid catalytic conditions are studied. High diastereoselectivity was observed in these reactions, and in the case of vinylmagnesium bromide additions to α-ketoimide 4 a change of direction of asymmetric induction was found.
- Raszplewicz,Sikorska,Kiegiel,Balakier,Jurczak
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p. 1901 - 1907
(2007/10/03)
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- An electrophilic cleavage procedure for the asymmetric dihydroxylation: Direct enantioselective synthesis of cyclic boronic esters from olefins
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A variation within the osmium-catalysed asymmetric dihydroxylation (AD) of olefins is described that yields cyclic boronic esters from olefins in a straight-forward manner. This process represents the first real product alteration in asymmetric dihydroxylation, since all previous protocols lead to free diols exclusively. A protocol based on the Sharpless AD conditions (for enantioselective oxidation of prochiral olefins) was developed that gives cyclic boronic esters with excellent enantiomeric excesses (ee's). Some of the ee's are higher than those reported for conventional AD. The unprecedented role of phenyl boronic acid on the course of the AD reaction was investigated in detail. PhB(OH)2 does not interfere with the chiral ligand. leaving the enantioselective step of olefin oxidation intact. The main role of the boronic acids - apart from protecting the diol products against potential overoxidation-relies on removing the diol entity in an electrophilic cleavage, which is in contrast to the conventional hydrolylic cleavage of the AD protocols. Thus, a mechanistically new cleavage for enantioselective dihydroxylation reactions is introduced within the present work.
- Hoevelmann, Claas H.,Muniz, Kilian
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p. 3951 - 3958
(2007/10/03)
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- Sodium chlorite as an efficient oxidant and hydroxy ion pump in osmium-catalyzed asymmetric dihydroxylation
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Sodium chlorite is an efficient stoichiometric oxidant in Sharpless asymmetric dihydroxylation. One sodium chlorite provides the reaction with the stoichiometric number of electrons and hydroxide ions needed to dihydroxylate two olefins without the consumption of any additional base. 100% conversion in sodium chlorite asymmetric dihydroxylation of styrene was achieved twice as fast as in the established Sharpless K3[Fe(CN)6] dihydroxylation. Even internal olefins were dihydroxylated fast with sodium chlorite without hydrolysis aids. Eight olefins were dihydroxylated to corresponding vicinal diols with yields and ees as good as those reported in the literature for other similar processes.
- Junttila, Mikko H.,Hormi, Osmo E. O.
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p. 4816 - 4820
(2007/10/03)
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- Ionic liquids as a convenient new medium for the catalytic asymmetric dihydroxylation of olefins using a recoverable and reusable osmium/ligand
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The use of room-temperature ionic liquids (RTILs) in the Sharpless catalytic asymmetric dihydroxylation (AD) as a cosolvent or replacement of the tert-butanol was studied in detail by screening 11 different RTILs. The AD reaction is faster in 1-n-butyl-3-methylimidazolium hexafiuorophosphate [C 4mim][PF6] as a cosolvent than in the conventional system of tert-butanol/H2O. For the range of six substrates tested, comparable or even higher yields and enantiomeric excess (ee) were found using [C4mim] [PF6] or 1-n-octyl-3-methylimidazolium hexafiuorophosphate [C8mim] [PF6] compared to the conventional solvent system. Due to high affinity of the catalytic osmium/quiral ligand system to the ionic liquid, the use of ionic liquid/water (biphasic) or ionic liquid/water/tert-butanol (monophasic) solvent systems provides a recoverable, reusable, robust, efficient, and simple system for the AD reaction. Using 1-hexene and [C4mim] [PF6] as RTIL it was possible to reuse the catalytic system for 9 cycles with only a 5% of yield reduction from the first cycle, allowing an overall yield of 87%, TON = 1566, and with similar ee. Additionally, for each cycle, after extraction of the reaction mixture with diethyl ether, the osmium content in the organic phase (containing the AD product) and in the aqueous phase was in the range of the detection limit (≤3%, ≤7 ppb) and 3-6% of initial amount, respectively. In contrast, the ionic liquid phase retained more than 90% of the osmium content of the previous cycle.
- Branco, Luis C.,Afonso, Carlos A. M.
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p. 4381 - 4389
(2007/10/03)
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- Bifunctional catalysts stabilized on nanocrystalline magnesium oxide for one-pot synthesis of chiral diols
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New bifunctional catalysts composed of PdCl42-, OsO42- and OsO42-, WO 42- designed and prepared by a counterionic stabilization technique involving the reactions of Na2PdCl4-K 2OsO4 and K2OsO4-Na 2WO4 with nanocrystalline MgO are well characterized. These bifunctional catalysts, NAP-Mg-PdOs and NAP-Mg-OsW perform tandem Heck asymmetric dihydroxylation and asymmetric dihydroxylation-N-oxidation reactions, respectively, in the presence of the chiral ligand 1,4-bis(9-o- dihydroquinidinyl)phthalazine [(DHQD)2PHAL] in a single pot. It is quite impressive to note that H2O2 is used as a terminal oxidant to provide N-methylmorpholine N-oxide (NMO) in situ by the oxidation of N-methylmorpholine (NMM) in the asymmetric dihydroxylation-N-oxidation catalyzed by NAP-Mg-OsW.
- Choudary, Boyapati M.,Jyothi, Karangula,Roy, Moumita,Kantam, Mannepalli L.,Sreedhar, Bojja
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p. 1471 - 1480
(2007/10/03)
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- Polysiloxane-bound ligand accelerated catalysis: A modular approach to heterogeneous and homogeneous macromolecular asymmetric dihydroxylation ligands
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Polysiloxane acts as a modular scaffold for macromolecular reagent development. Two separate components were covalently integrated into one material, one constituent provided reagent functionality, the other modulated solubility. In particular cinchona alkaloid based ligands used in the osmium tetroxide catalyzed asymmetric dihydroxylation (AD) reaction were covalently attached to commercially available polysiloxane. To enhance the reactivity of these polymeric ligands, multifunctional reagents were designed to include both the cinchona alkaloid and an alkoxyethylester solubilizing moiety providing random co-polymers. While the mono-functional materials led to heterogeneous conditions, the bifunctional polymers resulted in homogeneous reaction mixtures. Although both reagent types provided diol products with excellent yield and selectivity (>99% ee in nearly quantitative yield) the homogeneous analog has nearly twice the reactivity. Every repeat unit in the heterogeneous material was functionalized along the polysiloxane backbone while approximately half of these sites contained ligand in the homogeneous version. This approach led to macromolecular catalysts with high loadings of ligand and therefore materials with very low equivalent weights. Although these polymers are highly loaded they do maintain reactivity on a par with their free ligand counterpart. Using straightforward purification techniques (i.e. precipitation, simple filtration, or ultrafiltration) these polymeric ligands were easily separated from diol product and reused multiple times. Polysiloxane is a viable support for the catalysis of AD reactions and may provide a generally useful backbone for other catalytic systems.
- DeClue, Michael S.,Siegel, Jay S.
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p. 2287 - 2298
(2007/10/03)
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- A triazine core for a new class of Sharpless asymmetric dihydroxylation ligands
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Sharpless asymmetric dihydroxylation ligands were synthesized using a triazine spacer group in two, high yielding steps and gave good enantioselectivities in the asymmetric dihydroxylation of alkenes. Sharpless asymmetric dihydroxylation ligands were synthesized using a triazine spacer group in two, high yielding steps from cheap, readily available starting materials. The ligands, gave good enantioselectivities in the asymmetric dihydroxylation of alkenes and may provide a very economic alternative to current systems.
- McNamara, Catherine Anne,King, Frank,Bradley, Mark
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p. 8527 - 8529
(2007/10/03)
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- Enecarbamates as Selective Substrates in Oxidations: Chiral-Auxiliary-Controlled Mode Selectivity and Diastereoselectivity in the [2+2] Cycloaddition and Ene Reaction of Singlet Oxygen and in the Epoxidation by DMD and mCPBA
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The stereochemical course of the oxidation of chiral oxazolidinone-substituted enecarbamates has been studied for singlet oxygen (1O2), dimethyldioxirane (DMD), and m-chloroperbenzoic acid (mCPBA) by examining of the special structural and stereoelectronic features of the enecarbamates. Valuable mechanistic insight into these selective oxidations is gained. Whereas the R1 substituent on the chiral auxiliary is responsible for the steric shielding of the double bond and determines the sense of the π-facial diastereoselectivity, structural characteristic such as the Z/E configuration and the nature of the R 2 group on the double bond are responsible for the extent of the diastereoselectivity. Stereoelectronic steering by the vinylic nitrogen functionality controls the mode selectivity (ene reaction vs [2+2] cycloaddition) in the case of 1O2.
- Adam, Waldemar,Bosio, Sara G.,Turro, Nicholas J.,Wolff, Barbara T.
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p. 1704 - 1715
(2007/10/03)
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- New S,O-acetals from (1R)-(-)-myrtenal as chiral auxiliaries in nucleophilic additions
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Treatment of hydroxythiol 4 with α,α-diethoxyacetophenone at room temperature yielded a mixture of epimeric S,O-acetals 6 and 7 (1:4, 92% yield), which were efficiently separated by flash chromatography. The OTBS derivatives 8 and 9 were treated with several Grignard reagents to afford carbinols 10 and 13 respectively (85-99% yield, >95% dr). After successive hydrolysis and reduction of 10 and 13 it is possible to obtain either enantiomer of diols 16 in high optical purity (>95% er).
- Chacón-García, Luis,Lagunas-Rivera, Selene,Pérez-Estrada, Salvador,Vargas-Díaz, M. Elena,Joseph-Nathan, Pedro,Tamariz, Joaquín,Zepeda, L. Gerardo
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p. 2141 - 2145
(2007/10/03)
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- A trifunctional catalyst for one-pot synthesis of chiral diols via heck coupling-N-oxidation-asymmetric dihydroxylation: Application for the synthesis of diltiazem and taxol side chain
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A heterogeneous bifunctional catalyst composed of OsO42--WO42- and a trifunctional catalyst comprising PdCl42--OsO42-- WO42-, designed and prepared by an ion-exchange technique using layered double hydroxides (LDH) as an ion-exchanger and their homogeneous bifunctional analogue, K2OsO4-Na2WO4 and trifunctional analogue, Na2PdCl4-K2OsO4-K2 OSO4-NNa2WO4, devised for the first time are evaluated for the synthesis of chiral vicinal diols. These bifunctional and trifunctional catalysts perform asymmetric dihydroxylation-N-oxidation and Heck-asymmetric dihydroxylation-N-oxidation, respectively, in the presence of Sharpless chiral ligand, (DHQD)2PHAL in a single pot using H2O2 as a terminal oxidant to provide N-methylmorpholine oxide (NMO) in situ by the oxidation of N-methylmorpholine (NMM). The heterogeneous bifunctional catalyst supported on LDH (LDH-OsW) displays superior activity to afford diols with higher yields over the other heterogeneous catalysts developed by the ion exchange on quaternary ammonium salts covalently bound to resin (resin-OsW) and silica (silica-OsW) or homogeneous catalysts in the achiral dihydroxylation reactions. The LDH-OsW and its homogeneous analogue are found to be very efficient in performing a simultaneous asymmetric dihydroxylation (AD)-N-oxidation of a wide and varied range of aromatic, cyclic, and mono, di-, and trisubstituted olefins to obtain chiral vicinal diols with higher yields and ee's using H2O2. Further, the use of OsO42--WO42-- WO42- catalysts as such or in the supported form offers a simplified procedure for catalyst recycling, which shows consistent activity for a number of cycles. In this process, OsVI is recycled to OsVIII by a coupled electron transfer-mediator (ETM) system based on NMO-WO42- using H2O2, leading to a mild and selective electron transfer. The one-pot biomimic synthesis of chiral diols is mediated by a recyclable trifunctional heterogeneous catalyst (LDH-PdOsW) consisting of active palladium, tungsten, and osmium species embedded in a single matrix. This protocol, which provides prochiral olefins and NMO in situ by Heck coupling and N-oxidation of NMM, respectively, required for the AD, unfolds a low cost process. We extended the present method to the one-pot synthesis of trisubstituted chiral vicinal diols with moderate to excellent ee's by AD of trisubstituted olefins that are obtained by in situ Heck arylation of disubstituted olefins. The heterogeneous trifunctional catalysts offers chiral diols with unprecedented ee's and excellent yields in the AD of prochiral cinnamates, which are obtained in situ from acrylates and halobenzenes for the first time. The new variants such as LDH support and Et3N·HX inherently composed in the heterogeneous multicomponent system and slow addition of H202 facilitates the hydrolysis of osmium monogylcolate ester to subdue the formation of bisglycolate ester to achieve higher ee's. Without resorting to recrystallization, the chiral diols of cinnamates thus synthesized with 99% ee's and devoid of osmium contamination are directly put to use in the synthesis of diltiazem and Taxol side chain with an overall improved yield to demonstrate the synthetic utility of the trifunctional heterogeneous catalyst. The high binding ability of the heterogeneous osmium catalyst enables the use of equimolar ratio of ligand to osmium to give excellent ee's in AD in contrast to the homogeneous osmium system in which the excess molar quantities of the expensive chiral ligand to osmium are invariably used. Further, the XRD, FT-IR, UV-vis DRS, and XPS studies indicate the retention of the coordination geometries of the specific divalent anions anchored to LDH matrix in their monomeric form during the ion exchange and after the reaction.
- Choudary, Boyapati M.,Chowdari, Naidu S.,Madhi, Sateesh,Kantam, Mannepalli L.
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p. 1736 - 1746
(2007/10/03)
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- A new practical method for the osmium-catalyzed dihydroxylation of olefins using bleach as the terminal oxidant
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A general procedure for the osmium-catalyzed dihydroxylation of various olefins using bleach as oxidant is reported for the first time. Aromatic and aliphatic olefins yield the corresponding cis-1,2-diols in the presence of dihydroquinine or dihydroquinidine derivatives (Sharpless ligands) with good to excellent chemo- and enantioselectivities under optimized pH conditions. In the presence of a small excess of bleach as reoxidant fast dihydroxylation takes place even at 0°C. Under optimum reaction conditions it is possible to dihydroxylate terminal aliphatic and aromatic olefins as well as internal olefins. The low price of the oxidant and the simple handling of bleach make this dihydroxylation variant attractive for further applications.
- Mehltretter, Gerald M.,Bhor, Santosh,Klawonn, Markus,D?bler, Christian,Sundermeier, Uta,Eckert, Markus,Militzer, Hans-Christian,Beller, Matthias
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p. 295 - 301
(2007/10/03)
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- A soluble block copolymer-supported bis-cinchona alkaloid ligand for the asymmetric dihydroxylation of olefins
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A soluble block copolymer-supported ligand was prepared via polycondensation of a bis-cinchona alkaloid derivative, polyethylene glycol, and terephthaloyl chloride. Its application in the asymmetric dihydroxylation of olefins delivered very good enantioselectivity.
- Kuang, Yong-Qing,Zhang, Sheng-Yong,Wei, Ling-Ling
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p. 3545 - 3550
(2007/10/03)
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