- Wolff/Cope Approach to the AB Ring of the Sesterterpenoid Variecolin
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A stereoselective synthesis of the AB ring of the complex sesterterpenoid variecolin is presented. Our strategy features the development of a tandem Wolff/Cope rearrangement of α-diazo cyclobutyl ketones for the construction of fused, 8-membered carbocycles. Preliminary studies revealed a facile Wolff rearrangement but a difficult vinyl ketene cyclobutane Cope rearrangement. We have leveraged an efficient microwave-promoted tandem rearrangement to prepare the desired functionalized cyclooctadienones that we envision as potential key intermediates in the convergent synthesis of variecolin.
- Krout, Michael R.,Henry, Christopher E.,Jensen, Thomas,Wu, Kun-Liang,Virgil, Scott C.,Stoltz, Brian M.
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- Synthesis of (1S,4R)-(-)-40Hydroxy-2-cyclopentenyl Acetate by a Highly Enantioselective Enzyme-Catalyzed Transesterification in Organic Solvents
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(1S,4R)-(-)-4-Hydroxy-2-cyclopentenyl acetate (2), a versatile intermediate in prostaglandin syntheses, was readily prepared by an efficient enzyme-catalyzed enantioselective monoacetylation of cis-2-cyclopenten-1,4-diol (1) with 2,2,2-trichloroethyl acetate in the organic solvent system triethylamine/tetrahydrofuran.The chemical yield reached nearly 50percent.The enantiomeric excess of the crude product was 95percent.It could be raised to more than 99percent by a single recrystalization.Commercially available pancreatin, a crude enzyme preparation from porcine pancreas, was used as biocatalyst.
- Theil, Fritz,Ballschuh, Sibylle,Schick, Hans,Haupt, Monika,Haefner, Barbara,Schwarz, Sigfrid
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- Desymmetrization of meso-cyclopenten-cis-1,4-diol to 4-(R)- hydroxycyclopent-2-en-1-(S)-acetate by irreversible transesterification using Chirazyme
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The parameter optimization study for the desymmetrization of meso- cyclopenten-1,4-diol 1 through irreversible transesterification using an immobilized lipase from Mucor meihei, i.e., Lipozyme/Chirazyme is presented. The enzyme was studied for the transesterification of 1 in various organic solvents by varying reaction parameters such as the nature of acyl donor, temperature, enzyme quantity etc., to afford optically active 4-(R)- hydroxycyclopent-2-en-1-(S)-acetate 2 of >98% enantiomeric excess in >60% yield.
- Ghorpade, Sandeep R.,Kharul, Rajendra K.,Joshi, Rohini R.,Kalkote, Uttam R.,Ravindranathan
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- Total Synthesis of the Alleged Structure of Crenarchaeol Enables Structure Revision**
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Crenarchaeol is a glycerol dialkyl glycerol tetraether lipid produced exclusively in Archaea of the phylum Thaumarchaeota. This membrane-spanning lipid is undoubtedly the structurally most sophisticated of all known archaeal lipids and an iconic molecule in organic geochemistry. The 66-membered macrocycle possesses a unique chemical structure featuring 22 mostly remote stereocenters, and a cyclohexane ring connected by a single bond to a cyclopentane ring. Herein we report the first total synthesis of the proposed structure of crenarchaeol. Comparison with natural crenarchaeol allowed us to propose a revised structure of crenarchaeol, wherein one of the 22 stereocenters is inverted.
- Cunha, Ana V.,Havenith, Remco W. A.,Holzheimer, Mira,Minnaard, Adriaan J.,Schouten, Stefan,Sinninghe Damsté, Jaap S.
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supporting information
p. 17504 - 17513
(2021/07/06)
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- Acylative desymmetrization of cyclic meso-1,3-diols by chiral DMAP derivatives
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An efficient enantioselective acylative desymmetrization of cyclic meso-1,3-diols was developed by using a chiral DMAP derivative 1e having a 1,1¤-binaphthyl unit. The reactions required only 0.5mol% of the catalyst and showed good to excellent enantioselectivity. With this transformation, 5a, a key building block for the synthesis of natural products, was easily obtained in almost enantiomerically pure form after a single recrystallization. Control experiments revealed that tert-alcohol units on the catalyst were responsible for both the catalytic activity and enantioselectivity.
- Mandai, Hiroki,Hironaka, Tsubasa,Mitsudo, Koichi,Suga, Seiji
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supporting information
p. 471 - 474
(2021/03/15)
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- Pd-Catalyzed Asymmetric Allylic Substitution Annulation Using Enolizable Ketimines as Nucleophiles: An Alternative Approach to Chiral Tetrahydroindoles
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A synthesis of chiral tetrahydroindoles has been developed via a Pd-catalyzed asymmetric allylic substitution annulation using unstable enolizable ketimines as nucleophiles and our previously developed tBu-RuPHOX as a chiral ligand. The reaction proceeds via an asymmetric desymmetrization of the meso-diacetatecycloalkenes, providing the desired chiral tetrahydroindoles in moderate to good yields and with up to 96% ee. The annulation reaction could be performed on a gram-scale in high yields and the resulting products can be transformed to several types of N-hetereobicyclic derivatives. In addition, a chiral cis-perhydroindolic acid derivative was also readily synthesized starting from a prepared chiral tetrahydroindole. (Figure presented.).
- Xu, Kai,Ye, Jianxun,Liu, Hao,Shen, Jiefeng,Liu, Delong,Zhang, Wanbin
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supporting information
p. 2059 - 2069
(2020/04/29)
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- Preparation of (1R,4S)-4-hydroxycyclopent-2-en-1-yl acetate via Novozym-435 catalyzed desymmetrization of cis-3,5-Diacetoxy-1-cyclopentene
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Photooxidation of cyclopentadiene has been carried out in methanol using white light of LED lamp, rose bengal as photo initiator, and compressed air at 0 °C. Under conditions of [thiourea] ? [cyclopentadiene], the consumption of thiourea follows a pseudo-first-order reaction kinetics with half life of 75 ± 10 min; corr. coeff. r = 0.989. Slow addition of the monomer and maintaining excess thiourea concentration in reaction mass improves the yield. cis-3,5-Dihydroxy-1-cyclopentene is acetylated without isolation to obtain cis-3,5-Diacetoxy-1-cyclopentene of high purity (>99%) with overall isolated yield of 30%. Desymmetrization of the diacetate to (1R,4S)-4-hydroxycyclopent-2-en-1-yl acetate has been carried out via enzymatic transesterification with methanol in methyl tert-butyl ether (MTBE) at 5 °C using Novozym-435. The enantiomerically pure monoacetate (e.e. >99%) was obtained in 95% isolated yield. The recovered enzyme was reused for more than 10 times without loss in yield and selectivity. The entire protocol does not require purification of final product by chromatography.
- Putta, Shekhar,Reddy, Annem Mallikarjun,Sheelu, Gurrala,Reddy, B.V. Subba,Kumaraguru, Thenkrishnan
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p. 6673 - 6679
(2018/10/15)
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- Synthesis of Guanine α-Carboxy Nucleoside Phosphonate (G-α-CNP), a Direct Inhibitor of Multiple Viral DNA Polymerases
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The synthesis of guanine α-carboxy nucleoside phosphonate (G-α-CNP) is described. Two routes provide access to racemic G-α-CNP 9, one via base construction and the other utilizing Tsuji-Trost allylic substitution. The latter methodology was also applied to the enantiopure synthesis of both antipodes of G-α-CNP, each of which showing interesting antiviral DNA polymerase activity. Additionally, we report an improved multigram scale preparation of the cyclopentene building block 10, starting material for the preferred Tsuji-Trost route to 9.
- Maguire, Nuala M.,Ford, Alan,Balzarini, Jan,Maguire, Anita R.
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p. 10510 - 10517
(2018/09/06)
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- The construction of chiral fused azabicycles using a Pd-catalyzed allylic substitution cascade and asymmetric desymmetrization strategy
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A highly enantioselective Pd-catalyzed asymmetric allylic substitution cascade of cyclic N-sulfonylimines with an accompanying asymmetric desymmetrization has been developed for the construction of fused tetrahydroindole derivatives bearing two chiral centers. Mechanistic studies confirmed that the cascade reaction proceeds by initial allylic alkylation and subsequent allylic amination. The first alkylation is a chirality-control step and represents an asymmetric desymmetrization of ciscyclic allyl diacetates. The reaction has been performed on a gram scale, and the desired products can take part in several transformations.
- An, Qianjin,Liu, Delong,Shen, Jiefeng,Liu, Yangang,Zhang, Wanbin
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supporting information
p. 238 - 241
(2017/11/27)
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- Chemoenzymatic routes to cyclopentenols: The role of protecting groups on stereo- and enantioselectivity
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Enantiopure (R)-4-triisopropylsilyloxycyclopent-2-en-1-one was obtained through short sequences including either the enzymatic resolution of racemic cis-4-triisopropylsilyloxycyclopent-2-en-1-ol or the enzymatic desymmetrization of cis-cyclopent-2-en-1,3-diol. Alternatively, the enantiopure (S)-4-triisopropylsilyloxycyclopent-2-en-1-one was very efficiently obtained from diacetate of cis-cyclopent-2-en-1,3-diol using enzymatic desymmetrization with CAL-B. In these sequences, TIPS proved to be the best protecting group.
- Specklin, Simon,Dikova, Anna,Blanc, Aurélien,Weibel, Jean-Marc,Pale, Patrick
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p. 6987 - 6991
(2015/02/02)
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- Lipophilic oligopeptides for chemo- and enantioselective acyl transfer reactions onto alcohols
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Inspired by the extraordinary selectivities of acylases, we envisioned the use of lipophilic oligopeptidic organocatalysts for the acylative kinetic resolution/desymmetrization of rac- and meso-cycloalkane-1,2-diols. Here we describe in a full account the discovery and development process from the theoretical concept to the final catalyst, including scope and limitations. Competition experiments with various alcohols and electrophiles show the full potential of the employed oligopeptides. Additionally, we utilized NMR and IR-spectroscopic methods as well as computations to shed light on the factors responsible for the selectivity. The catalyst system can be readily modified to a multicatalyst by adding other catalytically active amino acids to the peptide backbone, enabling the stereoselective one-pot synthesis of complex molecules from simple starting materials.
- Mueller, Christian E.,Zell, Daniela,Hrdina, Radim,Wende, Raffael C.,Wanka, Lukas,Schuler, Soeren M. M.,Schreiner, Peter R.
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p. 8465 - 8484
(2013/09/24)
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- IMPROVED PROCESSES FOR PREPARING PURE (3AR,4S,6R,6AS)-6-AMINO-2,2-DIMETHYLTETRAHDRO-3AH-CYCLOPENTA[D] [1,3]-DIOXOL-4-OL AND ITS KEY STARTING MATERIAL
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Provided herein is an improved, commercially viable and industrially advantageous process for the preparation of a ticagrelor intermediate, (3aR,4S,6R,6aS)-6-amino-2,2- dimethyltetrahydro-3aH-cyclopenta[d][l,3]-dioxol-4-ol, which is useful for preparing ticagrelor or a pharmaceutically acceptable salt thereof in high yield and purity. The present invention further relates to an improved process for the preparation of (lS,4R)-cis-4-acetoxy- 2-cyclopenten-l-ol, which is a key starting material in the preparation of the ticagrelor intermediate.
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Page/Page column 24-25
(2012/05/31)
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- Studies toward the total synthesis of carba analogue of motif C of M. TB cell wall AG complex
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Herein we describe the synthesis of the carba analogue of motif C of arabinogalactan complex present in M. tuberculosis cell wall. Pd(0) catalyzed allylic alkylation and Fraser-Reid's glycosidation are the two key reactions that were employed for the synthesis of central glycosyl accepter unit and the glycosylation respectively.
- Gurjar, Mukund K.,Reddy, Challa Nageswar,Kalkote, Uttam R.,Chorghade, Mukund S.
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scheme or table
p. 909 - 925
(2010/10/20)
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- CYCLOPENTENE DIOL MONOACETATE DERIVATIVES
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A process for the preparation of organic compounds of formula (I), wherein R1is as described herein.
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Page/Page column 9; 11; 14
(2008/12/05)
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- Method for the Production of a Compound, Comprising a Free Hydroxyl Group and a Hydroxyl Group Which is Protected by an Ester Function by Enzymatic Reaction
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The invention relates to a method for the production of a compound comprising a free hydroxyl group and a hydroxyl group which is protected by an ester function by enzymatic reaction, using a lipase EC 3.1.1.3. The invention also relates to the use of the resultant compound as an intermediate for the production of medicaments and pharmaceutical products.
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Page/Page column 4-5
(2008/06/13)
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- Synthesis of enantiomerically pure cyclopentene building blocks
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An efficient synthesis of the enantiomerically pure cis-annulated cyclopentenes 2 and ent-2 was established by the use of an enzymatic transesterification and hydrolysis, respectively, followed by an S N2-type substitution with a benzyloxymethyl cuprate and a sigmatropic rearrangement. The advantage of this approach is the short sequence combined with an excellent overall yield and an enantiomeric excess of 99%. Georg Thieme Verlag Stuttgart.
- Tietze, Lutz F.,Stadler, Christian,B?hnke, Niels,Brasche, Gordon,Grube, Alexander
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p. 485 - 487
(2007/12/27)
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- Process for preparing enantiomerically enriched (1S,4R) 1-acetoxy-4-hydroxycyclopent-2-ene
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This invention relates to a process for the synthesis of enantiomerically enriched (1S,4R) 1-acetoxy-4-hydroxycyclopent-2-ene of Formula I, a compound useful as an intermediate in the synthesis of prostaglandins and prostanoids.
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Page/Page column 4-5
(2008/06/13)
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- Total synthesis of the epoxy isoprostane phospholipids PEIPC and PECPC
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(Chemical Equation Presented) A total synthesis of the naturally occurring hydroxy ketone PEIPC 1, a compound that plays a role in endothelial activation in atherosclerosis, has been completed via a triply convergent preparation of a protected EI derivative 13 from 3,5-diacetoxycyclopentene 7, pentane-1,5-diol, and vinyllithium, using Sharpless epoxidation and enzymatic resolution as key steps. Final coupling with lyso-PC 16 and silyl group deprotection gave PECPC 2 and PEIPC 1, which showed the same activity as natural PECPC and PEIPC.
- Jung, Michael E.,Berliner, Judith A.,Angst, Daniela,Yue, Dawei,Koroniak, Lukasz,Watson, Andrew D.,Li, Rongsong
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p. 3933 - 3935
(2007/10/03)
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- Biotransformations in low-boiling hydrofluorocarbon solvents
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Solvent solutions: Low-boiling hydrofluorocarbons (see examples) are excellent solvents for lipase-catalyzed reactions and ideal replacements for conventional organic solvents and supercritical fluids as media for nonaqueous biotransformations. Notably increased rates, yields, and enantioselectivities were observed with the model kinetic resolution of (±)-1-phenylethanol and the desymmetrization of weso-2-cyclopentene-1 ,4-diol.
- Saul, Simon,Corr, Stuart,Micklefield, Jason
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p. 5519 - 5523
(2007/10/03)
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- A novel approach to bis-isoxazolines using a latent form of cyclopentadienone
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The synthesis of a range of both racemic and homochiral 4-alkyl- and 4-aryl-8-hydroxy-2-oxa-3-azabicyclo[3.3.0]oct-3-en-6-ones (isoxazolines) from the 1,3-dipolar cycloaddition reactions between alky- and aryl-nitrile oxides and 4-alkoxycyclopent-2-enomes was described. Elimination of the 8-hydroxy group and subsequent additional cycloaddition reactions provided 5,9-disubstituted-3,11-dioxa-4,10-diazatricyclo[6.3.01,8.02 ,6]undeca-4,9-dien-7-ones formally derived fromcyclopentadienone. The results showed that in the structures studied the nonhydrogen atoms were included in geometric positions and given thermal parameters equivalent to 1.2 times those of the atoms to which they were attached.
- Basra, Sanjivanjit K.,Drew, Michael G.B.,Mann, John,Kane, Peter D.
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p. 3592 - 3598
(2007/10/03)
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- Conversion of allylic alcohols into allylic nitromethyl compounds via a palladium-catalyzed solvolysis: An enantioselective synthesis of an advanced carbocyclic nucleoside precursor
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A two-step reaction sequence to homoallylic nitro compounds from allylic alcohols is presented. Ethoxy carbonylation of the alcohols with ethyl chloroformate provides the corresponding allylic ethyl carbonates in high yields. Exposure of these substrates to catalytic palladium(0) in CH3NO2 initiates a reaction sequence, ionization-decarboxylation-nitromethylation, that culminates with the formation of nitroalkenes. The regio- and stereochemical outcomes of the nitromethyl allylation reaction can be explained by the behavior of the transient π-allylpalladium complexes. This methodology serves as a centerpiece for the synthesis of an important carbocyclic nucleoside intermediate.
- Deardorff, Donald R.,Savin, Kenneth A.,Justman, Craig J.,Karanjawala, Zarir E.,Sheppeck II, James E.,Hager, David C.,Aydin, Nebil
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p. 3616 - 3622
(2007/10/03)
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- 4-Hydroxycyclopent-2-en-1-one and derivatives as chiral synthetic equivalents of cyclopentadienone in asymmetric Diels-Alder reactions
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Endo-tricyclodecadienone 8a and related annelated-cyclopentenones (8b, 20, 21a-c and 22) are synthesized in good chemical yield by a Diels-Alder reaction of 4-hydroxycyclo-pent-2-en-1-one 12a and derivatives 12b-h with an appropriate diene. These additions are considerably accelerated by Lewis catalysts, high pressure and by using water as solvent. Due to opposing steric and electronic effects the diastereofacial selectivity of the asymmetric cycloadditions is moderate. By carefully choosing the substrate and reaction conditions an acceptable π-facial selectivity can be achieved.
- Dols,Klunder,Zwanenburg
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p. 8515 - 8538
(2007/10/02)
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- Chemoenzymatic Synthesis of 4-Substituted Riboses. S-(4'-Methyladenosyl)-L-homocysteine
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The synthesis of 4-C-methyl-D-ribose, 4-C-phenyl-D-ribose, D-ribose-4-d, and L-ribose derivatives as well as the title nucleoside by a chemoenzymatic strategy beginning from cyclopentadiene is described.
- Johnson, Carl R.,Esker, John L.,Zandt, Michael C. Van
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p. 5854 - 5855
(2007/10/02)
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- ACYLOXYLATION OF CYCLOPENTADIENE IN THE PRESENCE OF PALLADIUM COMPLEXES
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Cyclopentadiene reacts with PdCl4-2 in acetic acid to form a binuclear bridged complex, which probably has an asymmetric sandwich structure with one double bond being retained in the ring.The first acetoxy group is introduced almost instantaneously.This is followed by the attack of the second AcO- group or by the decomposition of the complex to form 3-acetoxycyclopentene.With using butyric acid, 3-butyroxycyclopentene is formed with higer selectivity.In the presence of the PdCl4-2-NaNO3-KIO3 system, the reaction becomes catalytic.
- Vekki, A. V.,Trushova, N. V.
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p. 394 - 396
(2007/10/02)
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- Enzymatic Asymmetrization of meso-2-Cycloalken-1,4-diols and Their Diacetates in Organic and Aqueous Media
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meso-2-Cycloalken-1,4-diols or the corresponding diacetates with five-, six-, and seven-membered rings were subjected to enzymatic asymmetrizations utilizing a recombinant version of lipase B from Candida antarctica (Novo SP-435) in organic or aqueous media.
- Johnson, Carl R.,Bis, Scott J.
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p. 7287 - 7290
(2007/10/02)
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- Facile synthesis of (+)-Brefeldin A
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(+)-Brefeldin A (1) was synthesized by using (+)-4-cyanomethylcyclopent-2-en-1-one (2) as a key compound. 4-Hydroxy-2-enoate functionality was built by the reaction of the aldehyde (7) with (S)-ethyl p-chlorophenylsulfinylacetate.
- Nokami,Ohkura,Dan-Oh,Sakamoto
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p. 2409 - 1412
(2007/10/02)
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- Enzymes in Organic Synthesis. 4. Investigation of the Pancreatin-Catalyzed Acylation of cis-Cyclopent-2-ene-1,4-diol with Various Trichloroethyl and Vinyl Alkanoates
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During the pancreatin-catalyzed acetylation of the meso-diol 1 with 2,2,2-trichloroethyl acetate (2a) in tetrahydrofuran/triethylamine, the enantiomeric monoacetates 3a and ent-3a are formed at nearly equal rates. ent-3a is rapidly acetylated in a second enzyme-catalyzed step, forming 4a, whereas 3a resists further enzymatic acetylation.Thus, the monoacetate 3a can be obtained in 48 percent yield with an enantiomeric excess (e.e.) of more than 99 percent. 2,2,2-Trichloroethyl propanoate and butanoate give the corresponding monoacylation products even in slightly better yields, whereas the octanoate affords the monoacylation product with a lower enantiomeric excess. 2,2,2-Trichloroethyl monochloroacetate provides the monoacylation product in a 40 percent yield with an e.e. of 90 percent.The dichloroacetate, however, affords the diacylation product exclusively in an enzyme-independent chemical reaction.With the 2,2,2-trichloroethyl esters of isobutyric, phenylacetic, and benzoic acid no transesterification could be achieved within 24 hours.The application of vinyl acetate, however, represents a significant improvement in the synthesis of enantiomerically pure monoacetate 3a from meso-diol 1.
- Theil, Fritz,Schick, Hans,Lapitskaya, Margarita A.,Pivnitsky, Kasimir K.
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p. 195 - 200
(2007/10/02)
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- Lipase-Catalyzed Transesterification of meso-Cyclopentane Diols
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The lipase-catalyzed transesterification of the meso-cyclopentane diols 1a - 6a with vinyl acetate in tetrahydrofuran/triethylamine in the presence of lipases of different origin has been investigated.Depending on the structure of the substrate and the origin of the lipase chiral cyclopentane derivatives with high enantiomeric excess could be obtained in good to excellent chemical yields. Key words: Lipase-catalyzed transesterifications; meso-cyclopentane diols; enantioselective acetylation; enzymes in organic solvents
- Theil, Fritz,Schick, Hans,Winter, Gabriele,Reck, Guenter
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p. 7569 - 7582
(2007/10/02)
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- Vitamin B12, a Catalyst in the Synthesis of Prostaglandins
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A prostaglandin F2α precursor containing all structural features from C6 to C20 with 8R,9S, 11R and 12R chirality is obtained by the one step formation of two C-C bonds in the B12-catalyzed radical cyclization-addition sequence starting from a chiral cyclopentene bromoacetal and 1-octyne-3-one.The B12-catalyzed radical cyclization-elimination sequence of a chiral cyclopentene precursor leads to (-)-(3aR,6aS)-3,3a,6,6a-tetrahydro-2H-cyclopentafuran-2-one.Its (+)-(3aS,6aR)-enantiomer is obtained via B12-catalyzed, enantioselective isomerization of cyclopentene oxide to (R)-2-cyclopentene-1-ol followed by the B12-catalyzed cyclization-elimination sequence of its bromoacetal.
- Busato, Stephan,Tinembart, Olivier,Zhang, Zhong-da,Scheffold, Rolf
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p. 3155 - 3166
(2007/10/02)
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- Process for the preparation of cyclopentanoids and novel intermediates produced thereby
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Cyclopentanoids (I) of the formula: STR1 including stereoisomers are described along with a process for the preparation of I. In particular the preparation of prostanoids of the formula: STR2 wherein R1 is a alkyl group containing 1 to 8 carbon atoms and R2 CO2 R3 is an alkenyl ester group, R2 contains 2 to 6 carbon atoms and R3 is a lower alkyl group containing 1 to 6 carbon atoms is described. A particular prostaglandin prepared by the process is PGE2. The prostanoids have been demonstrated to have pharmacological activity in animals and humans. Novel intermediates of (I) are also described.
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- ENANTIOSELECTIVE SYNTHESIS OF 3(S)-ACETOXY-5(R)-HYDROXYCYCLOPENT-1-ENE BY AN ENZYMATIC TRANSESTERIFICATION IN ORGANIC SOLVENTS
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3(S)-acetoxy-5(R)-hydroxycyclopent-1-ene has been obtained in 50percent yield with an enantiomeric excess >/= 99percent by porcine pancreatic lipase-catalysed transacetylation of cis-3,5-dihydroxycyclopent-1-ene in anhydrous pyridine.
- Jommi, Giancarlo,Orsini, Fulvia,Sisti, Massimo,Verotta, Luisella
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p. 863 - 864
(2007/10/02)
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- Liquid-phase 1,4-Diacetoxylation of Conjugated Dienes with Tellurium(IV) Oxide and Alkali Metal Halides
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Oxidation of buta-1,3-diene, isoprene, and 2,3-dimethylbuta-1,3-diene with tellurium(IV) oxide and lithium bromide in acetic acid affords an isomeric mixture of the corresponding diacetoxyalkenes (1,2- and 1,4-addition products).The product yield and selectivity for 1,4-isomers are high when an excess of LiBr is employed (LiBr/TeO2 = 5-10).The reaction also proceeds in the presence of NaBr, KBr, LiCl, HBr, or I2 in the place of LiBr, but both the selectivity for 1,4-isomers and the product yield are lower.The reaction hardly occurs using LiF, LiI, NaCl, Br2, and NH4Br as a halogen source.The reaction proceeds catalytically with respect to TeO2 to some extent when a re-oxidant such as H2O2 or t-BuOOH is used.In the cases of 2,5-dimethylhexa-2,4-diene, cyclopenta-1,3-diene, cyclohexa-1,3-diene, and cyclo-octa-1,3-diene the results are unsatisfactory in either the product yield or the selectivity for 1,4-isomers.Halogeno- and/or acetoxy-telluriation of a diene followed by acetolysis of the produced C-X (X = halogen) and C-Te bonds are proposed as one of the possible reaction pathways.
- Uemura, Sakae,Fukuzawa, Shin-ichi,Patil, Suresh R.,Okano, Masaya
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p. 499 - 504
(2007/10/02)
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- A PALLADIUM-CATALYZED ROUTE TO MONO- AND DIPROTECTED CIS-2-CYCLOPENTENE-1,4-DIOLS
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The ?-allylpalladium complex arising from cyclopentadiene monoepoxide has been shown to react with carboxylic acids and derivatives both as a nucleophile and an electrophile.This reaction represents an attractive synthetic route to protected versions of cis-2-cyclopentene-1,4-diol.
- Deardorff, Donald R.,Myles, David C.,MacFerrin, Kurtis D.
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p. 5615 - 5618
(2007/10/02)
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- Stereo-and Regioselective Palladium-Catalyzed 1,4-Diacetoxylation of 1,3-Dienes
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Palladium-catalyzed oxidation of 1,3-dienes in acetic acid using an oxidation system of MnO2 and catalytic amounts of p-benzoquinone selectively gives 1,4-diacetoxy-2-alkenes.The reaction proceeds with high stereo-and regioselectivity, and by ligand control the reaction can be made to take place with either cis or trans 1,4-diacetoxylation across the diene in cyclic systems.Also in an acyclic system the 1,4-relative stereochemistry can be controlled as shown by the stereoselective oxidation of (E,E)- and (E,Z)-2,4-hexadiene to their corresponding dl (>88percent dl) and meso (>95percent meso) diacetates 15 and 18, respectively.Evidence is provided that supports a mechanism involving a trans acetoxypalladation of the conjugated diene to give an intermediate (?-allyl)palladium complex, followed by either a cis or trans attack by acetate on the allyl group.The cis attack is best explained by a cis migration from a (?-allyl)palladium intermediate.The diacetoxylation reaction was applied to the preparation of a key intermediate for the synthesis of dl-shikimic acid.
- Baeckvall, Jan-E.,Bystroem, Styrbjoern E.,Nordberg, Ruth E.
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p. 4619 - 4631
(2007/10/02)
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- DIACETOXYLATION OF CONJUGATED DIENES WITH THALLIUM(III) ACETATE IN ACETIC ACID
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The reaction of conjugated dienes such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2,5-dimethyl-2,4-hexadiene, 1,3-cyclopentadiene, and 1,3-cyclohexadiene with thallium(III) acetate in acetic acid at 10-65 deg C for 0.5-15 hr affords an isomeric mixture of the corresponding diacetoxyalkenes (1,2- and 1,4-addition products) in 10-92 percent yields.The 1,2-addition products are predominantly formed in all cases examined except the case of 1,3-cyclopentadiene.The reaction is assumed to proceed through acetoxythallation and dethallation steps, the latter step being accompanied and/or followed by an attack of acetoxyl group.An initial attack of thallium moiety is proposed to occur mainly at C-1 and C-2 carbons in the cases of linear terminal dienes and cyclic dienes, respectively.
- Uemura, Sakae,Miyoshi, Haruo,Tabata, Akira,Okano, Masaya
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p. 291 - 295
(2007/10/02)
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- Process for the preparation of 1,4-diacetoxycyclopent-2-ene
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A process for the preparation of 1,4-diacetoxycyclopent-2-ene, which comprises contacting a solution of 1,4-dibromocyclopent-2-ene in an inert organic solvent which is slightly soluble or insoluble in water, with an aqueous solution or suspension of at least one metal salt of acetic acid which is at least partially water-soluble, in the presence of a cationic surface-active compound.
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