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Tetrahedron Letters

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https://www.readbyqxmd.com/read/27713589/replacement-of-the-bryostatin-a-and-b-pyran-rings-with-phenyl-rings-leads-to-loss-of-high-affinity-binding-with-pkc
#1
Mark E Petersen, Noemi Kedei, Nancy E Lewin, Peter M Blumberg, Gary E Keck
We describe a convergent synthesis of a bryostatin analogue in which the natural A- and B-ring pyrans have been replaced by phenyl rings. The new analogue exhibited PMA like behavior in cell assays, but failed to maintain high affinity binding for PKC, despite retaining an unaltered C-ring 'binding domain'.
October 19, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/27713588/acceleration-of-metallacycle-mediated-alkyne-alkyne-cross-coupling-with-tmscl
#2
James S Cassidy, Haruki Mizoguchi, Glenn C Micalizio
Investigation of titanium-centered metallacycle-mediated cross-coupling between unsymmetrical internal alkynes has led to the discovery that TMSCl significantly accelerates the C-C bond forming event. We report a collection of results that compare the efficiency of this reaction employing Ti(Oi-Pr)4/2n-BuLi in PhMe with and without TMSCl, demonstrating in every case that the presence of TMSCl has a profound impact on efficiency. While relevant in the context of developing this fundamental bond-forming process as an entry to more complex organometallic transformations, these modified reaction conditions allow coupling processes to be run at > 10 times the concentrations previously possible [in 2...
August 24, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/27546917/two-step-enzymatic-synthesis-of-6-deoxy-l-psicose
#3
Liuqing Wen, Kenneth Huang, Yuan Zheng, Junqiang Fang, Shukkoor Muhammed Kondengaden, Peng George Wang
Rare sugars offer a plethora of applications in the pharmaceutical, medicinal, and industries, as well as in synthetic chemistry. However, studies of rare sugars have been hampered by their relative scarcity. In this work, we describe a two-step strategy to efficiently and conveniently prepare 6-deoxy-L-psicose from L-rhamnose. In the first reaction step, the isomerization of L-rhamnose (6-deoxy-L-mannose) to L-rhamnulose (6-deoxy-L-fructose) catalyzed by L-rhamnose isomerase (RhaI), and the epimerization of L-rhamnulose to 6-deoxy-L-psicose catalyzed by D-tagatose 3-epimerase (DTE) were coupled with selective phosphorylation reaction by fructose kinase from human (HK), which selectively phosphorylate 6-deoxy-L-psicose at C-1 position...
August 24, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/27795589/a-novel-stereoselective-8-2-double-cycloaddition-route-to-hydronaphthalene-ring-systems
#4
Weijiang Ying, Lei Zhang, Paul A Wiget, James W Herndon
Substituted hydronaphthalenes where each of the ten carbons of the two-ring system contains functionality were obtained through a tandem [8+2] cycloaddition and base-catalyzed rearrangement process using dienylfurans and electron-deficient alkynes. If the [8+2] process is conducted under solvent-free conditions the process could be conducted in a single reaction flask without isolation of the chromatographically sensitive [8+2] cycloadducts. A mechanism involving base catalysed alkene positional isomerization followed by disrotatory electrocyclic ring closure was proposed for the key reaction step that converts [8+2] cycloadducts to hydronaphthalenes...
July 6, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/27818534/an-enantioselective-synthesis-of-the-c3-c21-segment-of-the-macrolide-immunosuppressive-agent-fr252921
#5
Arun K Ghosh, Samuel Rodriguez
An enantioselective synthesis of the C3-C21 segment of the novel immunosuppressant FR252921 is described. The C12 and C13 stereogenic centers were constructed by a non-aldol process utilizing optically active 4-phenylbutyrolactone. The C18 stereogenic center was installed using Braun's highly diastereoselective acetate aldol reaction. Other key steps involved Curtius rearrangement and Horner-Wadsworth-Emmons olefination reactions.
June 29, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/27909348/rapid-cycloaddition-of-a-diazo-group-with-an-unstrained-dipolarophile
#6
Matthew R Aronoff, Brian Gold, Ronald T Raines
The cycloaddition of a diazoacetamide with ethyl 4,4,4-trifluorocrotonate proceeds with k = 0.1 M(-1)s(-1). This second-order rate constant rivals those of optimized strain-promoted azide- alkyne cycloadditions, even though the reaction does not release strain. The regioselectivity and a computational distortion/interaction analysis of the reaction energetics are consistent with the formation of an N-H…F-C hydrogen bond in the transition state and the electronic character of the trifluorocrotonate. Analogous reactions with an azidoacetamide dipole or with an acrylate or crotonate dipolarophile were much slower...
June 1, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/27182092/a-mild-and-efficient-approach-to-enantioenriched-%C3%AE-hydroxyethyl-%C3%AE-%C3%AE-unsaturated-%C3%AE-lactams
#7
Seo-Jung Han, Brian M Stoltz
A straightforward approach toward enantioenriched α-substituted α,β-unsaturated δ-lactams is described. Although a considerable number of approches toward α,β-unsaturated δ-lactams have been reported, there are relatively few examples of enantioenriched α,δ-disubstituted α,β-unsaturated δ-lactams formation. The δ-stereocenter was formed by addition of allylmagnesium bromide to an N-tert-butylsulfinyl imine. The α,β-unsaturated δ-lactam was furnished by ring-closing metathesis. Although Baylis-Hillman chemistry failed on this cyclic compound, introduction of the hydroxyethyl group prior to ring-closing metathesis was successful...
May 25, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/27274586/progress-in-kdo-glycoside-chemistry
#8
Paul Kosma
Glycosylation chemistry of 3-deoxy-D-manno-oct-2-ulosonic acid units has been considerably developed within the last decade. This review covers major achievements with respect to improved yields and anomeric selectivity as well as suppression of the elimination side reaction via selection of dedicated protecting groups and appropriate activation of the anomeric center.
May 18, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/27175039/unusual-hydroxyl-effect-on-fulvene-endoperoxide-decompositions
#9
Ihsan Erden, John Basada, Daniela Poli, Gabriel Cabrera, Fupei Xu, Scott Gronert
The thermal decomposition of fulvene endoperoxides ordinarily proceeds via an allene oxide intermediate affording oxepin-2(3H)-one derivatives. We have now uncovered new, unusual pathways in these decompositions where the presence of a hydroxyl group on the alkyl or aryl attached to the fulvene exocyclic double bond has a profound effect on the fate of the reactive intermediates derived from the unstable endoperoxides. Computational work supports the proposed mechanistic pathways.
May 18, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/27152055/an-alternative-synthesis-and-x-ray-crystallographic-confirmation-of-stepholidine
#10
Satishkumar V Gadhiya, Chunhua Hu, Wayne W Harding
A formal enantioselective synthesis of (-)-stepholidine that provides an alternative preparation of key lactone intermediate 2 is described. The stereostructure of (-)-stepholidine prepared via this method was confirmed by x-ray diffraction.
May 11, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/27152054/c-o-bond-formation-in-a-microfluidic-reactor-high-yield-snar-substitution-of-heteroaryl-chlorides
#11
Mohammad Parvez Alam, Barbara Jagodzinska, Jesus Campagna, Patricia Spilman, Varghese John
This study describes our development of a novel and efficient procedure for C-O bond formation under mild conditions, for coupling heteroaryl chlorides with phenols or primary aliphatic alcohols. We utilized a continuous-flow microfluidic reactor for C-O bond formation in electron-deficient pyrimidines and pyridines in a much more facile manner with a cleaner reaction profile, high yield, quick scalability and without the need for the transition metal catalyst. This approach can be of general utility to make C-O bond containing intermediates of industrial importance in a continuous and safe manner...
May 11, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/27182091/optimized-synthesis-of-a-pentafluoro-gem-diol-and-conversion-to-a-cf2br-glucopyranose-through-trifluoroacetate-release-and-halogenation
#12
Robert A Hazlitt, Jinu P John, Que-Lynn Tran, David A Colby
Pentafluoro-gem-diols are substrates that enable the synthesis of valuable difluoromethylene-containing organic molecules through the release of trifluoroacetate. Currently, only one synthetic strategy is available to assemble these important precursors. Herein, two new synthetic strategies to a complex pentafluoro-gem-diol are compared to the existing route, and an improved synthetic route has completed. Moreover, the first synthesis of a CF2Br-glucopyranose was finished by a tandem trifluoroacetate-release halogenation/cyclization protocol...
April 27, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/27110042/convenient-synthesis-of-phosphonohydrazines-from-arylamines
#13
Greggory T Kent, Daniel J Blackburn, Joseph R Gonzalez, Megan L Mayer, Weiming Wu
Phosphonohydrazines were prepared in good yield from corresponding arylamines by a one-pot reaction through diazotization with an organic nitrite and treatment with a trialkyl phosphite. The trialkyl phosphite is postulated to function as a nucleophile as well as a reducing agent.
April 11, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/27041776/synthesis-of-2-aryl-2h-tetrazoles-via-a-regioselective-3-2-cycloaddition-reaction
#14
Remi Patouret, Theodore M Kamenecka
A regioselective cycloaddition reaction of arenediazonium salts with trimethylsilyldiazomethane is reported. A series of 2-aryltetrazoles were obtained in good to moderate yields with wide functional group compatibility. Furthermore, this cycloaddition reaction opens the way to build up the versatile intermediate 2-aryl-5-bromotetrazole.
April 6, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/26955189/stereocontrolled-regeneration-of-olefins-from-epoxides
#15
Veronica S Wills, Xiang Zhou, Cheryl Allen, Sarah A Holstein, David F Wiemer
Through treatment with NaI and trifluoroacetic anhydride, which presumably forms trifluoroacetyl iodide in situ, epoxides can be converted to olefins. This reaction now has been shown to tolerate remote olefins without loss of their individual stereochemistry. A reaction sequence involving regiospecific epoxidation of an isoprenoid alcohol, conversion of the alcohol to an azide, and cycloaddition with an acetylene, followed by conversion of the epoxide back to the original olefin, has allowed stereocontrolled preparation of triazole bisphosphonates with a farnesyl or a geranylgeranyl substituent...
March 23, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/26989270/synthesis-of-extended-oxazoles-ii-reaction-manifold-of-2-halomethyl-4-5-diaryloxazoles
#16
Pravin C Patil, Frederick A Luzzio
2-(Halomethyl)-4,5-diphenyloxazoles are effective, reactive scaffolds which can be utilized for synthetic elaboration at the 2-position. Through substitution reactions, the chloromethyl analogue is used to prepare a number of 2-alkylamino-, 2-alkylthio- and 2-alkoxy-(methyl) oxazoles. The 2-bromomethyl analogue offers a more reactive alternative to the chloromethyl compounds and is useful in the C-alkylation of a stabilized (malonate) carbanion as exemplified by a concise synthesis of Oxaprozin.
February 17, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/26951759/reductive-debromination-of-1-2-dibromides-with-anisidines
#17
Kristen M McGraw, Jeannette T Bowler, Vy T Ly, Ihsan Erden, Weiming Wu
vic -Dibromides containing the α-bromocarbonyl or α-bromoaromatic moieties were reductively debrominated to furnish alkenes in high yield. o- and m-Anisidines but not p-anisidine were found to be effective debrominating agents. The reductive debrominations were found to be trans-stereospecific.
January 20, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/26783372/lanthanide-and-asymmetric-catalyzed-syntheses-of-sterically-hindered-4-isoxazolyl-1-4-dihydropyridines-and-4-isoxazolyl-quinolones
#18
Scott A Steiger, Chun Li, Charles F Campana, Nicholas R Natale
No abstract text is available yet for this article.
January 20, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/26744547/a-single-flask-synthesis-of-%C3%AE-alkylidene-and-%C3%AE-benzylidene-lactones-from-ethoxyacetylene-epoxides-oxetanes-and-carbonyl-compounds
#19
Kevin Ng, Vincent Tran, Thomas Minehan
Low temperature treatment of (ethoxyethynyl)lithium with epoxides or oxetanes in the presence of BF3•OEt2, followed by addition of aldehydes or ketones and warming to room temperature, affords structurally diverse five- and six-membered α-alkylidene and α-benzylidene lactones (5) in good to excellent yields. This one-pot process, in which three new carbon-carbon bonds and a ring are formed, affords substituted α,β-unsaturated lactones of predominantly Z-configuration. The reaction likely occurs via alkyne-carbonyl metathesis of a hydroxy-ynol ether intermediate, acid-promoted alkene E- to Z-isomerization, and lactonization...
January 20, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/26726272/first-ketene-cycloaddition-approach-to-%C3%A2-junionone
#20
Ihsan Erden, Samuel E Watson
Junionone is the first monocyclic cyclobutane monoterpenoid isolated from a plant. Of the existing four syntheses of this compound, none employs a ketene cycloaddition to construct the four-membered ring. Herein, we report the first total synthesis of junionone that features a ketene cycloaddition for the synthesis of this compound, starting from the commercially available 1,5-hexadiene. 2009 Elsevier Ltd. All rights reserved.
January 13, 2016: Tetrahedron Letters
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