- A Method for preparing alpha-olefins from Biomass-derived fat and oil
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The present invention relates to a method for preparing alpha-olefins from biomass-derived fats and oils. According to the preparation method, all of the various saturated or unsaturated fatty acids in the biomass-derived fats and oils can be prepared into alpha-olefins, and a conventional problem that the saturated fatty acids do not participate in a reaction or a mixture is generated due to polyunsaturated fatty acids can be solved. Thus, the present invention can be advantageously used to prepare alpha-olefins from biomass.
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Paragraph 0145; 0153-0156
(2020/09/22)
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- Optimized Immobilization Strategy for Dirhodium(II) Carboxylate Catalysts for C?H Functionalization and Their Implementation in a Packed Bed Flow Reactor
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Herein we demonstrate a packed bed flow reactor capable of achieving highly regio- and stereoselective C?H functionalization reactions using a newly developed Rh2(S-2-Cl-5-CF3TPCP)4 catalyst. To optimize the immobilized dirhodium catalyst employed in the flow reactor, we systematically study both (i) the effects of ligand immobilization position, demonstrating the critical factor that the catalyst-support attachment location can have on the catalyst performance, and (ii) silica support mesopore length, demonstrating that decreasing diffusional limitations leads to increased accessibility of the active site and higher catalyst turnover frequency. We employ the immobilized dirhodium catalyst in a simple packed bed flow reactor achieving comparable yields and levels of enantioselectivity to the homogeneous catalyst employed in batch and maintain this performance over ten catalyst recycles.
- Davies, Huw M. L.,Hatridge, Taylor A.,Jones, Christopher W.,Liu, Wenbin,Yoo, Chun-Jae
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supporting information
p. 19525 - 19531
(2020/07/13)
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- Electrophilic Iron Catalyst Paired with a Lithium Cation Enables Selective Functionalization of Non-Activated Aliphatic C?H Bonds via Metallocarbene Intermediates
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Combining an electrophilic iron complex [Fe(Fpda)(THF)]2 (3) [Fpda=N,N′-bis(pentafluorophenyl)-o-phenylenediamide] with the pre-activation of α-alkyl-substituted α-diazoesters reagents by LiAl(ORF)4 [ORF=(OC(CF3)3] provides unprecedented access to selective iron-catalyzed intramolecular functionalization of strong alkyl C(sp3)?H bonds. Reactions occur at 25 °C via α-alkyl-metallocarbene intermediates, and with activity/selectivity levels similar to those of rhodium carboxylate catalysts. Mechanistic investigations reveal a crucial role of the lithium cation in the rate-determining formation of the electrophilic iron-carbene intermediate, which then proceeds by concerted insertion into the C?H bond.
- Hernán-Gómez, Alberto,Rodríguez, Mònica,Parella, Teodor,Costas, Miquel
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p. 13904 - 13911
(2019/08/30)
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- Control Mechanism for cis Double-Bond Formation by Polyunsaturated Fatty-Acid Synthases
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Polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA) are essential fatty acids for humans. Some microorganisms biosynthesize these PUFAs through PUFA synthases composed of four subunits with multiple catalytic domains. These PUFA synthases each create a specific PUFA without undesirable byproducts, even though the multiple catalytic domains in each large subunit are very similar. However, the detailed biosynthetic pathways and mechanisms for controlling final-product profiles are still obscure. In this study, the FabA-type dehydratase domain (DHFabA) in the C-subunit and the polyketide synthase-type dehydratase domain (DHPKS) in the B-subunit of ARA synthase were revealed to be essential for ARA biosynthesis by in vivo gene exchange assays. Furthermore, in vitro analysis with truncated recombinant enzymes and C4- to C8-acyl ACP substrates showed that ARA and EPA synthases utilized two types of DH domains, DHPKS and DHFabA, depending on the carbon-chain length, to introduce either saturation or cis double bonds to growing acyl chains.
- Hayashi, Shohei,Satoh, Yasuharu,Ogasawara, Yasushi,Maruyama, Chitose,Hamano, Yoshimitsu,Ujihara, Tetsuro,Dairi, Tohru
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p. 2326 - 2330
(2019/02/01)
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- Mechanochemical enzymatic resolution of N-benzylated-β3-amino esters
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The use of mechanochemistry to carry out enantioselective reactions has been explored in the last ten years with excellent results. Several chiral organocatalysts and even enzymes have proved to be resistant to milling conditions, which allows for rather efficient enantioselective transformations under ball-milling conditions. The present article reports the first example of a liquid-assisted grinding (LAG) mechanochemical enzymatic resolution of racemic β3-amino esters employing Candida antarctica lipase B (CALB) to afford highly valuable enantioenriched N-benzylated-β3-amino acids in good yields. Furthermore the present protocol is readily scalable.
- Pérez-Venegas, Mario,Reyes-Rangel, Gloria,Neri, Adrián,Escalante, Jaime,Juaristi, Eusebio
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supporting information
p. 1728 - 1734
(2017/09/27)
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- Polyhydroxyalkanoate-based 3-hydroxyoctanoic acid and its derivatives as a platform of bioactive compounds
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A library of 18 different compounds was synthesized starting from (R)-3-hydroxyoctanoic acid which is derived from the bacterial polymer polyhydroxyalkanoate (PHA). Ten derivatives, including halo and unsaturated methyl and benzyl esters, were synthesized and characterized for the first time. Given that (R)-3-hydroxyalkanoic acids are known to have biological activity, the new compounds were evaluated for antimicrobial activity and in vitro antiproliferative effect with mammalian cell lines. The presence of the carboxylic group was essential for the antimicrobial activity, with minimal inhibitory concentrations against a panel of bacteria (Gram-positive and Gram-negative) and fungi (Candida albicans and Microsporum gypseum) in the range 2.87.0 mM and 0.16.3 mM, respectively. 3-Halogenated octanoic acids exhibited the ability to inhibit C. albicans hyphae formation. In addition, (R)-3-hydroxyoctanoic and (E)-oct-2-enoic acids inhibited quorum sensing-regulated pyocyanin production in the opportunistic pathogen Pseudomonas aeruginosa PAO1. Generally, derivatives did not inhibit mammalian cell proliferation even at 3-mM concentrations, while only (E)-oct-2-enoic and 3-oxooctanoic acid had IC50 values of 1.7 and 1.6 mM with the human lung fibroblast cell line.
- Radivojevic, Jelena,Skaro, Sanja,Senerovic, Lidija,Vasiljevic, Branka,Guzik, Maciej,Kenny, Shane T.,Maslak, Veselin,Nikodinovic-Runic, Jasmina,OConnor, Kevin E.
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p. 161 - 172
(2016/01/09)
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- Characterization of FabG and FabI of the Streptomyces coelicolor dissociated fatty acid synthase
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Streptomyces coelicolor produces fatty acids for both primary metabolism and for biosynthesis of the secondary metabolite undecylprodiginine. The first and last reductive steps during the chain elongation cycle of fatty acid biosynthesis are catalyzed by FabG and FabI. The S. coelicolor genome sequence has one fabI gene (SCO1814) and three likely fabG genes (SCO1815, SCO1345, and SCO1846). We report the expression, purification, and characterization of the corresponding gene products. Kinetic analyses revealed that all three FabGs and FabI are capable of utilizing both straight and branched-chain β-ketoacyl-NAC and enoyl-NAC substrates, respectively. Furthermore, only SCO1345 differentiates between ACPs from both biosynthetic pathways. The data presented provide the first experimental evidence that SCO1815, SCO1346, and SCO1814 have the catalytic capability to process intermediates in both fatty acid and undecylprodiginine biosynthesis.
- Singh, Renu,Reynolds, Kevin A.
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p. 631 - 640
(2015/03/31)
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- A new stereocontrolled total synthesis of the mast cell inhibitory alkaloid, (+)-monanchorin, via the wittig reaction of a stabilized ylide with a cyclic guanidine hemiaminal
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An asymmetric total synthesis of the mast cell inhibitor (+)-monanchorin is reported in which a Sharpless AD on 11 and a cyclic sulfate ring opening with an azide feature as key steps. After further manipulation, a novel guanidine-controlled ester reduction provided the guanidine-hemiaminal 25 which underwent Wittig olefination to give 27. Hydrogenation and a second guanidine-controlled reduction of the ester in 28, to obtain aldehyde 29, then set up a trifluoroacetic acid mediated cyclization to give (+)-monanchorin TFA salt.
- Hale, Karl J.,Wang, Liping
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supporting information
p. 2154 - 2157
(2014/05/06)
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- Regio- and Stereocontrol in the Reactions of α-Halo-β,γ-enoates and α- O -Phosphono-β,γ-enenitriles with Organocuprates
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The reactions of (Z)- and (E)-ethyl 2-chloro-3-octenoate (4a and 17) and (E)- and (Z)-diethyl (1-cyano-2-heptenyl)phosphate (21a and 21b) with organocuprates were investigated as potential substrates for preparing γ-substituted α,β-enoates and enenitriles. In these copper-mediated allylic substitution reactions, the Z-isomer 4a displayed complete regio- and stereoselectivity (i.e., E:Z), while the regio- and stereoselectivity for E-isomer 17 varied as a function of solvent, cuprate reagent, transferable ligand, and cuprate counterion (e.g., Li+ vs MgX+). Excellent selectivities could be achieved with 17 and nBuCuCNLi in Et2O. Conditions for improved selectivities in the reactions of allylic cyanophosphates over those previously reported were found. A series of relative rate and competition experiments was performed, and the degree of regio- and stereoselectivity for each system was rationalized in the light of the current mechanistic understanding of cuprate-mediated allylic substitution reactions.
- Dieter, R. Karl,Picado, Alfredo
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p. 11125 - 11138
(2015/02/19)
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- Relay cross metathesis reactions of vinylphosphonates
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Dimethyl (β-substituted) vinylphosphonates do not readily undergo cross metathesis reactions with Grubbs catalyst and terminal alkenes. However, the corresponding mono- or diallyl vinylphosphonate esters undergo facile cross metathesis reactions. The improved reactivity is attributed to a relay step in the cross metathesis reaction mechanism.
- Malla, Raj K.,Ridenour, Jeremy N.,Spilling, Christopher D.
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p. 1933 - 1941
(2014/10/16)
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- Facile regio- and stereoselective hydrometalation of alkynes with a combination of carboxylic acids and group 10 transition metal complexes: Selective hydrogenation of alkynes with formic acid
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A facile, highly stereo- and regioselective hydrometalation of alkynes generating alkenylmetal complex is disclosed for the first time from a reaction of alkyne, carboxylic acid, and a zerovalent group 10 transition metal complex M(PEt3)4 (M = Ni, Pd, Pt). A mechanistic study showed that the hydrometalation does not proceed via the reaction of alkyne with a hydridometal generated by the protonation of a carboxylic acid with Pt(PEt 3)4, but proceeds via a reaction of an alkyne coordinate metal complex with the acid. This finding clarifies the long proposed reaction mechanism that operates via the generation of an alkenylpalladium intermediate and subsequent transformation of this complex in a variety of reactions catalyzed by a combination of Bronsted acid and Pd(0) complex. This finding also leads to the disclosure of an unprecedented reduction of alkynes with formic acid that can selectively produce cis-, trans-alkenes and alkanes by slightly tuning the conditions.
- Shen, Ruwei,Chen, Tieqiao,Zhao, Yalei,Qiu, Renhua,Zhou, Yongbo,Yin, Shuangfeng,Wang, Xiangbo,Goto, Midori,Han, Li-Biao
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supporting information; experimental part
p. 17037 - 17044
(2011/12/04)
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- Palladium(II)-catalyzed catalytic aminocarbonylation and alkoxycarbonylation of terminal alkynes: Regioselectivity controlled by the nucleophiles
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The aminocarbonylation and alkoxycarbonylation reactions of terminal alkynes took place smoothly and efficiently using a catalyst system Pd(OAc) 2-dppb-p-TsOH-CH3CN-CO under relatively mild experimental conditions. The catalytic system was tested and optimized using two different nucleophiles: alcohols and amines. Phenylacetylene (1a) was considered as an alkyne along with diisobutylamine (2b1) andmethanol (2c1) as nucleophiles. The results showed significant differences in the conversion of 1a and in the selectivity towards the gem or trans unsaturated esters or amides with these nucleophiles. The effects of the type of palladium catalysts, the type of ligands, the amount of dppb and the solvents were carefully studied. With diisobutylamine (2b1), excellent regioselectivity towards the 2-acrylamides (gem isomer, 3ab1) was almost always observed, while trans-α,β-unsaturated esters 4ac1 was the predominant product with methanol (2c1) as a nucleophile. This remarkable sensitivity in the selectivity of the reaction indicates two different possible mechanistic pathways for these carbonylation reactions. Copyright
- Suleiman, Rami,Tijani, Jimoh,El Ali, Bassam
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scheme or table
p. 38 - 46
(2010/10/02)
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- A supramolecular catalyst for the decarboxylative hydroformylation of α,β-unsaturated carboxylic acids
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(Chemical Equation Presented) Head 'em up, move 'em out, aldehyde! A catalytic transformation of α,β-unsaturated carboxylic acids into aldehydes through a hydroformylation-decarboxylation process has been developed (see scheme; Do = donor ligand, FG1 and FG2 = complementary functional groups). The reaction proceeds at mild conditions, tolerates many functional groups, and liberates CO2 as the only stoichiometric by-product.
- Smejkal, Tomas,Breit, Bernhard
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p. 3946 - 3949
(2008/12/23)
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- Wittig reactions in water media employing stabilized ylides with aldehydes. Synthesis of α,β-unsaturated esters from mixing aldehydes, α-bromoesters, and Ph3P in aqueous NaHCO3
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(Chemical Equation Presented) Water is demonstrated to be an effective medium for the Wittig reaction over a wide range of stabilized ylides and aldehydes. Despite sometimes poor solubility of the reactants, good chemical yields normally ranging from 80 to 98% and high E-selectivities (up to 99%) are achieved, and the rate of the reactions in water is unexpectedly accelerated. The efficiency of water as a medium in the Wittig reaction is compared to conventional organic solvents ranging from carbon tetrachloride to methanol. The aqueous Wittig reaction works best when large hydrophobic entities are present, such as aromatic, heterocyclic aromatic carboxaldehydes, and long-chain aliphatic aldehydes with triphenylphosphoranes. The E/Z-isomeric ratio of the Wittig products appears dependent on the electron-accepting/donating capacity and the location of the substituents present in the aromatic ring. The effect of additives, such as benzoic acid, LiCl, and sodium dodecyl sulfate (SDS), on the Wittig reaction has been explored. The Wittig reaction can also be conducted in the presence of acidic entities, such as phenols and carboxylic acids. In addition, large α-substituents in the aliphatic aldehydes do not jeopardize the reaction. It is also demonstrated that hydrates of aldehydes can be used directly in the aqueous Wittig reaction as substrates. The scope of the aqueous Wittig reaction is extended to 24 examples of one-pot mixtures of Ph3P, α-bromoesters, and aldehydes in sodium bicarbonate solution (at 20°C for 40 min to 3 h) to provide Wittig products of up to 99% yield and up to 98% E-selectivity. Since water is inexpensive, extremely easy to handle, and represents no environmental concerns, it should be considered a possible medium for new organic reactions.
- El-Batta, Amer,Jiang, Changchun,Zhao, Wen,Anness, Robert,Cooksy, Andrew L.,Bergdahl, Mikael
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p. 5244 - 5259
(2008/02/07)
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- Total structure and inhibition of tumor cell proliferation of laxaphycins
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From a mixed assemblage of Lyngbya majuscula rich marine cyanobacteria, we isolated a series of cell growth inhibitory cyclic peptides, The structures of the two major components, laxaphycins A (1) and B (2), and of two minor peptides, laxaphycins B2 (3) and B3 (4), were determined by spectroscopic methods and degradative analysis. Absolute configurations of natural and nonproteinogenic amino acids were determined by a combination of hydrolysis, synthesis of noncommercial residues, chemical derivatization, and HPLC analysis. The organism producing the laxaphycins was identified as the cyanobacterium Anabaena torulosa. The antiproliferative activity of laxaphycins was investigated on a panel of solid and lymphoblastic cancer cells. Our results demonstrate that in contrast to laxaphycin A, laxaphycin B inhibits the proliferation of sensitive and resistant human cancer cell lines and that this activity is strongly increased in the presence of laxaphycin A. This effect appears to be due to an unusual biological synergism.
- Bonnard, Isabelle,Rolland, Marc,Salmon, Jean-Marie,Debiton, Eric,Barthomeuf, Chantal,Banaigs, Bernard
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p. 1266 - 1279
(2007/10/03)
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- Stereoselective preparation of highly functionalized (Z)-3-copper enoates by an iodine-copper exchange reaction
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3-Iodoenoates are readily converted into the corresponding alkenylcopper species with complete retention of configuration of the double bond via an iodine-copper exchange reaction. Quenching reactions with various electrophiles provide highly functionalized enoates in good yields. Georg Thieme Verlag Stuttgart.
- Yang, Xiaoyin,Knochel, Paul
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p. 2167 - 2172
(2008/02/03)
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- A convenient one-pot PCC oxidation-Wittig reaction of alcohols
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A simple one-pot process for the PCC oxidation of alcohols followed by in situ trapping of the aldehyde with a Wittig reagent is described.
- Bressette, Andrew R.,Glover IV, Louis C.
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p. 738 - 740
(2007/10/03)
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- Ulongapeptin, a cytotoxic cyclic depsipeptide from a Palauan marine cyanobacterium Lyngbya sp.
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Ulongapeptin (1), a cyclic depsipeptide, was isolated from a Palauan marine cyanobacterium Lyngbya sp. The gross structure was elucidated through one-dimensional TOCSY experiments and other spectroscopic techniques. The absolute and relative stereochemistry of the β-amino acid, 3-amino-2-methyl-7-octynoic acid (AMO), in 1 was determined by synthesis of the saturated α-alkyl-β-amino acid and Marfey's analysis of the acid hydrolysate of tetrahydro-1. Ulongapeptin (1) was cytotoxic against KB cells at an IC50 value of 0.63 μM.
- Williams, Philip G.,Yoshida, Wesley Y.,Quon, Michael K.,Moore, Richard E.,Paul, Valerie J.
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p. 651 - 654
(2007/10/03)
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- A chemoselective reduction of alkynes to (E)-alkenes
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The trans reduction of all types of alkynes to give (E)-olefins is achieved through a two-stage trans hydrosilylation and protodesilylation. Reaction of an alkyne and a silane with the ruthenium catalyst [Cp*Ru(MeCN)3]PF6 results in
- Trost, Barry M.,Ball, Zachary T.,Joege, Thomas
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p. 7922 - 7923
(2007/10/03)
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- Copper-catalysed asymmetric 1,4-addition of organozinc compounds to linear aliphatic enones using 2,2′-dihydroxy 3,3′-dithioether derivatives of 1,1′-binaphthalene
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Directed ortho dilithiation of bis(diethylcarbamate) or bis(MOM)-protected (Sa)-1,1,′-bi(2-naphthol) followed by treatment with R2S2 [R = Me, Ph (X-ray structure)] or Me2Se2 cleanly affords the 3,3′ derivatives; the free naphthols are produced on deprotection. In the case of the bis(MOM) series, but not that of the bis(carbamates), some racemisation occurs. The ligand 2,2′-dihydroxy-3,3′-dimethylthio-1,1′-binaphthalene shows optimal performance in the addition of ZnEt2 to linear aliphatic enones (E)-R1C(O)CH=CHR2. Variation of the steric demands of R1 and R2 generates catalytic results consistent with binding of a zinc-based Lewis acid anti to the ene function and with the reactive conformation being s-cis. With enones containing the functions R2 = (CH2)nCH(OAlkyl)2 (n = 0-2), the ZnEt2 addition products undergo base-promoted cyclisation.
- Boerner, Christoph,Dennis, Michael R.,Sinn, Ekkehard,Woodward, Simon
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p. 2435 - 2446
(2007/10/03)
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- New approaches towards the synthesis of alkenes using the Horner-Wadsworth-Emmons (HWE) reaction as the key step
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Leading from our work in asymmetric alkene synthesis it was discovered that the alkenylatio of aldehydes with phosphonates proceeds smoothly at room temperature in the absence of Lewis acidusing triethylamine as the base if the reaction is carried out at a pressure of 8 kbar. Based on this protoco a new domino process was developed, combining the HWE reaction with a Heck coupling, thus allowing the one pot synthesis of trisubstituted alkenes.
- Bodman, Kerstin,Has-Becker, Shenay,Reiser, Oliver
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p. 173 - 176
(2007/10/03)
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- Highly cis-selective Horner-Wadsworth-Emmons (HWE) reaction of methyl bis(2,4-difluorophenyl) phosphonoacetate
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Of the previously reported Homer-Wadsworth-Emmons (HWE) reaction, the olefination of methyl bis(2,4-difluorophenyl)phosphonoacetate (1a) with various aldehydes gave unsaturated esters in the highest cis-selectivity.
- Kokin, Keisuke,Motoyoshiya, Jiro,Hayashi, Sadao,Aoyama, Hiromu
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p. 2387 - 2392
(2007/10/03)
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- STEREOSPECIFIC CROSS-COUPLING REACTIONS OF 3-ARYLSULFINYLPROPENOATES WITH ORGANOMETALLIC REAGENTS
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(E)- or (Z)-3-arylsulfinylpropenoates have been reacted with several organometallic reagents.Grignard reagents were found to promote only the complete substitution of the arylsulfinyl group in good yields (up to 92percent).The reaction followed a stereochemical course of retention of configuration with high values of stereospecificity (up to 99percent) in most cases.The observation made are discussed in the light of current views concerning nucleophilic substitution at a vinyl carbon atom.The addition-elimination pathway is considered valid, whereas a route involving the formation of a sulfurane as an intermediate, followed by a ligand coupling, is considered less likely.
- Cardellicchio, Cosimo,Cicciomessere, Angela Rosa,Naso, Francesco,Tortorella, Paolo
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p. 555 - 558
(2007/10/03)
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- Application of radical cyclisation/iodine atom transfer to the chiral synthesis of (-)-methylenolactocin
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Methylenolactocin, an antitumour antibiotic, has been synthesized through an efficient radical cyclisation process on a chiral iodo acetylene ester. Chiral iodohydrins may be formed by regioselective opening of a chiral epoxy ester, prepared by Sharpless epoxidation. C-2 opening is achieved with TMSCl/NaI and C-3 attack with MgI2. Subsequent esterification of the 2-iodo compound by reaction with substituted propynoyl triflates gives the key iodo acetylenic esters. This route is highly adaptable to the synthesis of analogues.
- Mawson, Simon D.,Weavers, Rex T.
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p. 11257 - 11270
(2007/10/02)
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- Formation of Unsaturated Esters in the Single Electron Transfer Reaction of Cyclopropanone Acetals with Quinones under Non-irradiated Conditions
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Unsaturated esters were formed from cyclopropanone aceytals in the reaction with DDQ or chloranil, where ring-opened C-C and C-O bonded adducts were the intermediates formed via a SET mechanism resulting in the ester formation.
- Abe, Manabu,Oku, Akira
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p. 3551 - 3554
(2007/10/02)
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- Electron Transfer Profile of Cyclopropanone Acetals in the Nonirradiated Reaction with Tetracyanoethylene, Chloranil, and Dicyanodichlorobenzoquinone
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The donor profiles of cyclopropanone acetals 1 and 2 were examined in the reactions with electron acceptors (TCNE, DDQ, chloranil, and 1-cyanonaphthalene).With TCNE under nonirradiating conditions, an exclusive 2 + 2 cycloaddition took place stereospecifically with monosubstituted acetals 1a-c but nonstereospecifically with disubstituted acetals 1d,e.With quinones, a ring-opening of the cyclopropane and its coupling with the quinone took place to give the C (cyclopropane)-O (quinone) adduct 9 (with chloranil) or 10 (with DDQ), the latter of which underwent the elimination of a phenol to produce unsaturated esters 5 and 6.In addition, the intervention of the C (cyclopropane)-C (quinone) adduct 14 (with chloranil) or 15 (with DDQ), both as the precursor of 5 and 6, was also postulated.With 1-cyanonaphthalene, under photolysis, the cis/trans isomerization of 1 and 2 occured.The results provided evidences that cyclopropanone acetals, in general, are prone to function as donors.The mechanism of the reaction with quinones, in particular, was investigated in detail.
- Oku, Akira,Abe, Manabu,Iwamoto, Masaharu
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p. 7445 - 7452
(2007/10/02)
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- New and efficient procedures for the synthesis of stereodefined 2-(hetero) aryl and 2-methyl substituted alkyl 2-alkenoates having very high stereoisomeric purity
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Stereodefined 2-(hetero)aryl and 2-methyl substituted alkyl 2-alkenoates of general formulai and2 have been synthesized with a high degree of stereoselectivity as well as in good overall yields starting from alkyl 2-alkynoates,4.
- Rossi, Renzo
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p. 4495 - 4498
(2007/10/02)
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- Total structure of hormothamnin A, a toxic cyclic undecapeptide from the tropical marine cyanobacterium hormothamnion enteromorphoides
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The tropical marine cyanobacterium Hormothamnion enteromorphoides produces a suite of cytotoxic and antimicrobial cyclic peptides. The structure of the most lipophilic of these, hormothamnin A, was determined by interpretation of physical data, principally high NMR and FAB MS, in combination with chemical derivitization and degradation schemes. Isolation of a key pentapeptide fragment DPHE-D-LEU-L-ILE-D-allo-ILE-L-LEU, obtained under partial hydrolysis conditions, was instrumental to the final structure determination. β-D-aminooctanoic acid (D-BAOA) was characterized as a per-ester derivative following complete acid hydrolysis and Z-didehydrohomoalanine (DHHA) was spectroscopically in the intact peptide. The remaining residues (HYPRO, 2 × HSER, GLY) were evident from amino acid and spectroscopic analysis. Sequencing of these residues made use of knowledge from fragments, high field NMR (NOESY and ROESY) and FAB MS analysis of the intact peptide. Absolute stereochemistries of the α-amino residues were determined by HPLC analysis of the acid liberated residues derivatized with Marfey's reagent. The absolute stereochemistry of the β-amino residue was shown by circular dichoroism analysis, HPLC analysis of the Marfey derivative, and chiral synthesis of a homolog. By these techniques, hormothamnin A was demonstrated to possess a cyclo-[D-PHE-D-LEU-L-ILE-D-allo-ILE-L-LEU-GLY-D-BAOA-L-HSER-DHHAL-HYPRO-L-HSER] structure.
- Gerwick, William H.,Jiang, Zhi D.,Agarwal, Santosh K.,Farmer, Bennett T.
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p. 2313 - 2324
(2007/10/02)
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- A convenient route for the homologation of saturated esters to α,β-unsaturated esters
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Methyl hexanoate (1a) is transformed to methyl 2-hydroxyheptanoate (5a) employing the following sequence of reactions (Scheme 1); (i) reaction with sodium hydride-dimethyl sulfoxide, (ii) Pummerer rearrangement with acetic anhydride-sodium acetate, (iii) alkaline hydrolysis and (iv) esterification with diazomethane.The α-hydroxy ester (5a) is converted into methyl 2E-heptenoate (7a) employing the following reactions (Scheme 2); (i) reaction with phosphorous tribromide and (ii) elimination using DBU.Thus, the sequence of reactions given in Schemes 1 and 2 provide aconvenient route for the one carbon homologation of saturated esters to α,β-unsaturated esters.
- Mohan, H Rama,Rao, A S
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p. 698 - 700
(2007/10/02)
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- New Stereoselective Snytheses of Stereodefined 2-Substituted Alkyl 2-Alkenoates and Their Applications
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Stereoisomerically pure alkyl (E)-2-tributylstannyl-2-alkenoates, (E)-8, which are easily prepared by palladium-catalyzed reaction between tributylstannane and alkyl 2-alkynoates, 15, have been employed as precursors to stereodefined 2-(hetero)aryl substituted alkyl 2-alkenoates of general formula 9 as well as alkyl (E)-2-methyl-2-alkenoates, (E)-10, having very high stereoisomeric purity.One of these esters, i.e. ethyl (Z)-4-(tert-butyldimethylsilyloxy)-2-phenyl-2-butenoate, (Z)-9d, has been employed in a very simple and efficient synthesis of3-phenyl-5(H)-2-furanone, 12, a metabolite of an hypnotic drug.On the other hand, the procedure employed to prepare esters (E)-10, which involves a configurational inversion, has been used to prepare the (S)-enantiomer of (E)-2,4-dimethyl-2-hexenoic acid, (E)-13, a caste-specific substance of male carpenter ants in the genus Camponotus, as well as 98percent optically pure (S)(E)-4,6-dimethyl-4-octen-3-one, (S)(E)-14, an alarm pheromone component of ants in the genus Manica.
- Rossi, Renzo,Carpita, Adriano,Cossi, Paolo
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p. 8801 - 8824
(2007/10/02)
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- Ethyl phenylsulfinyl fluoroacetate, a new and versatile reagent for the preparation of α-fluoro-α,β-unsaturated carboxylic acid esters
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The title compound 2 can be alkylated with a wide range of alkyl halides and Michael acceptors. Subsequent thermal elimination of phenyl sulfinic acid 3 leads to α-fluoro-α,β-unsaturated ethyl carboxylates 5 and 10, an important class of intermediates for fluorine containing biologically active compounds.
- Allmendinger, Thomas
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p. 4905 - 4914
(2007/10/02)
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- The First Example of a Catalytic Wittig-Type Reaction. Tri-n-butylarsine-Catalyzed Olefination in the Presence of Triphenyl Phosphite
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Tri-n-butylarsine-catalyzed olefination was achieved by the reaction of various aldehydes with methyl bromoacetate (or ω-bromoacetophenone) in the presence of triphenyl phosphite and potassium carbonate at room temperature in good yields with high E stereoselectivity.
- Shi, Lilan,Wang, Weibo,Wang, Yucheng,Huang, Yao-Zeng
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p. 2027 - 2028
(2007/10/02)
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- Synthesis of carbocycles from ω-substituted α,β-unsaturated esters via radical-induced cyclizations
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The intramolecular radical cyclization of ω-bromo α,β-unsaturated esters for the synthesis of carbocyclic compounds is described.The effect of carbon chain substituents, the bulk of the ester group, and the olefin geometry were examined.The highest level of stereoselectivity (trans/cis:9/1) was achieved with the Z ester via an exo cyclization.The sequential radical cyclization of a dihalodienoate to give a cis-fused bicyclic structure is also described.
- Hanessian, Stephen,Dhanoa, Daljit S.,Beaulieu, Pierre L.
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p. 1859 - 1866
(2007/10/02)
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- Enantioselective Diastereospecific Synthesis of anti-α-Alkyl-β-hydroxy Esters through Cuprate Opening of Glycidic Esters
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A diastereospecific chain elongation of the aldehydes 1 to anti-αalkyl-β-hydroxy esters 2 via the intermediates 4 - 7 is described.By means of the Sharpless epoxidation, 2 may be obtained with >90percent ee in either enantiomer.
- Mulzer, Johann,Lammer, Ortrud
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p. 2178 - 2190
(2007/10/02)
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- AN IMPROVED PROCEDURE FOR THE TWO CARBON HOMOLOGATION OF ESTERS TO α,β-UNSATURATED ESTERS
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Treatment of esters with diisobutylaluminium hydride (DIBAL) in the presence of lithio-trialkylphosphonoacetate results in improved yields of the homologated α,β-unsaturated esters.The problematic overreduction, which has previously observed in the half reduction of esters using DIBAL, is minimal (3percent) under these conditions.
- Takacs, James M.,Helle, Mark A.,Seely, Franklin L.
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p. 1257 - 1260
(2007/10/02)
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- ETUDE DE LA REACTION CHLOROCARBENE-ACETALS DE CETENES. II. STEREOSELECTIVITE DE LA REACTION.
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We have studied the stereoselectivity of the addition reaction of chloro and chloromethyl carbenoids with ketene alkylsilyl acetals.The best stereoselectivity was generally observed with the dimethyl tertiobutylsilyloxy group.With the chlorocarbenoid, using an E ketene acetal we obtained in majority (ca. 80percent) an E α,β-ethylenic ester and using a Z ketene acetal we obtained in majority (ca. 70percent) a Z α,β-ethylenic ester.In the case of the chloromethyl carbenoid the two ketene acetal isomers led to the same α-substituted α,β-ethylenic ester (ca. 88percent of selectivity).With the chlorophenylcarbenoid, formation of ca. 90percent of E α phenyl α,β-ethylenic ester is observed.
- Rousseau, G.,Slougui, N.
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p. 2653 - 2664
(2007/10/02)
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