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Tetrahedron Letters

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https://www.readbyqxmd.com/read/29332969/c12h12-interconversions-two-non-pyrolytic-syntheses-of-tricyclo-5-3-2-04-8-dodeca-2-5-9-11-tetraene
#1
Ihsan Erden, Cindy J Gleason
Herein, we describe two independent and non-pyrolytic syntheses of an important C12H12 hydrocarbon which had been prepared previously by gas phase thermolysis of compound 6. The first method is based on an unusual dipolar cycloaddition of dichloroketene onto bullvalene. After reductive dechlorination, a Shapiro-Heath reaction of the tosylhydrazone gave the title compound. Alternatively, compound 13 is also obtained from its isomer 6 by a Ag+ catalyzed reaction.
January 17, 2018: Tetrahedron Letters
https://www.readbyqxmd.com/read/29335658/highly-stereoselective-asymmetric-aldol-routes-to-tert-butyl-2-3-5-difluorophenyl-1-oxiran-2-yl-ethyl-carbamates-building-blocks-for-novel-protease-inhibitors
#2
Arun K Ghosh, Emilio L Cárdenas, Margherita Brindisi
Enantioselective syntheses of tert-butyl ((S)-2-(3,5-difluorophenyl)-1-((S)-oxiran-2-yl)ethyl)carbamate and ((S)-2-(3,5-difluorophenyl)-1-((R)-oxiran-2-yl)ethyl)carbamate are described. We utilized asymmetric syn- and anti-aldol reactions to set both stereogenic centers. We investigated ester-derived Ti-enolate aldol reactions as well as Evans' diastereoselective syn-aldol reaction for these syntheses. We have converted optically active ((S)-2-(3,5-difluorophenyl)-1-((S)-oxiran-2-yl)ethyl)carbamate to a potent β-secretase inhibitor...
October 25, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/29276314/stereochemistry-and-reactivity-of-the-hpa-imine-mannich-intermediate
#3
Daniel Polyak, Ngan Phung, Jian Liu, Robert Barrows, Thomas J Emge, Spencer Knapp
Homophthalic anhydride (HPA) typically reacts rapidly with benzalimines to afford the formal [4+2] adduct, a 1,2,3,4-tetrahydroisoquinolin-1-one-4-carboxylic acid. The stereochemical outcome of this reaction is consistent with an open transition state comprising an iminium species and enolized HPA, leading to a short-lived amino-anhydride intermediate. In the case of N-tert-butylbenzalimine, this Mannich-type intermediate, which would normally cyclize at low temperature to a single isomer of the delta-lactam, is intercepted by base treatment to afford beta-lactam products...
October 4, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/28966405/cis-%C3%AE-bromostyrene-derivatives-from-cinnamic-acids-via-a-tandem-substitutive-bromination-decarboxylation-sequence
#4
Khanh G Tang, Greggory T Kent, Ihsan Erden, Weiming Wu
cis-β-Bromostyrene derivatives were synthesized stereospecifically from cinnamic acids through β-lactone intermediates. The synthetic sequence did not require the purification of the β-lactone intermediates although they were found to be stable and readily purified in most cases.
October 4, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/29230073/selective-alkylation-oxidation-of-n-substituted-isoindolinone-derivatives-synthesis-of-n-phthaloylated-natural-and-unnatural-%C3%AE-amino-acid-analogues
#5
Pravin C Patil, Frederick A Luzzio, Jarrid M Ronnebaum
The interchangeability of the isoindolinone group as a nitrogen protecting group for amino acid intermediates is demonstrated by the preparation of several natural and unnatural α-amino acid derivatives using a two-carbon N-isoindolinone (phthalimidine) scaffold. Using a selective benzylic oxidation, the N-isoindolinone group is then converted to the N-phthaloyl group for convenient removal (65-98%). For preparation of the isoindolinone products which were to be the substrates for benzylic oxidation, a range of side chains were installed on the isoindolinone-protected glycine equivalent on deprotonation to demonstrate the utility of the N-protected isoindolinone synthon (51-93%)...
September 20, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/29249841/iodine-mediated-rearrangements-of-diallylsilanes
#6
Gregory W O'Neil, Elizabeth J Cummins
Diallylsilanes can be made to rearrange upon treatment with I2. Of the silanes tested, diallyldiphenylsilane showed the greatest propensity to undergo this intramolecular carbocation allylation process. After etherification of the initially formed iodosilane, the products from this transformation represent useful synthetic intermediates, suitable for alkylation and cross-metathesis/annulation reactions.
August 30, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/28867835/asymmetric-synthesis-of-all-carbon-quaternary-spirocycles-via-a-catalytic-enantioselective-allylic-alkylation-strategy
#7
Samantha E Shockley, J Caleb Hethcox, Brian M Stoltz
Rapid access to enantioenriched spirocycles possessing a 1,4-dicarbonyl moiety spanning an all-carbon quaternary stereogenic spirocenter was achieved using a masked bromomethyl vinyl ketone reagent. The developed protocol entails an enantioselective palladium-catalyzed allylic alkylation reaction followed by a one-pot unmasking/RCM sequence that provides access to the spirocyclic compounds in good yields and selectivities.
August 23, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/29200514/an-enantioselective-enzymatic-desymmetrization-route-to-hexahydro-4h-furopyranol-a-high-affinity-ligand-for-hiv-1-protease-inhibitors
#8
Arun K Ghosh, Anindya Sarkar
An enantioselective synthesis of (3aS,4S,7aR)-hexahydro-4H-furo[2,3-b]pyran-4-ol, a high-affinity nonpeptide ligand for a variety of potent HIV-1 protease inhibitors is described. The key steps involved a highly enantioselective enzymatic desymmetrization of meso-diacetate, an efficient transacetalization, and a highly diastereoselective reduction of a ketone. This route is amenable to large-scale synthesis using readily available starting materials.
August 16, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/28824209/efficient-synthesis-of-cn2097-using-in-situ-activation-of-sulfhydryl-group
#9
Shaban Darwish, Keykavous Parang, John Marshall, Dennis J Goebel, Rakesh Tiwari
CN2097 (R7Cs-sCYK[KTE(β-Ala)]V) is a rationally designed peptidomimetic that shows effectiveness in preclinical models for the treatment of neurological disorders, such as Angelman syndrome, traumatic brain injury (TBI) and stroke. Because of its therapeutic activity for the treatment of human CNS disorders, there was an urgent need to develop an efficient strategy for large-scale synthesis of CN2097. The synthesis of CN2097 was accomplished using Fmoc/tBu solid phase chemistry in multiple steps. Two different peptide fragments (activated polyarginine peptide Npys-sCR7 and CYK[KTE(β-Ala)]V) were synthesized, followed by solution phase coupling in water...
August 2, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/29230072/synthesis-of-cananodine-by-intramolecular-epoxide-opening
#10
Patrick Shelton, Toby J Ligon, Jennifer M Dell Née Meyer, Loagan Yarbrough, James R Vyvyan
Cananodine is a guaipyridine alkaloid with activity against liver cancer. Cananodine was synthesized using a remarkable intramolecular opening of a trisubstituted epoxide as the key step in construction of the seven-membered carbocycle of the target. The epoxide opening strategy allows all four stereoisomers of cananodine to be prepared.
August 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/29129945/solid-phase-synthesis-of-cyclic-hexapeptides-wollamides-a-b-and-desotamide-b
#11
Lissa S Tsutsumi, Ghee T Tan, Dianqing Sun
Solid-phase synthesis of antibacterial cyclohexapeptides including wollamides A, B and desotamide B has been developed. Briefly, the protected linear hexapeptides were assembled on 2-chlorotrityl chloride resin using standard Fmoc chemistry and diisopropylcarbodiimide/hydroxybenzotriazole coupling reagents, cleaved off-resin with hexafluoroisopropanol/dichloromethane to keep side-chain protecting groups intact, and cyclized in solution. Final global removal of all protecting groups using a cocktail of trifluoroacetic acid/triisopropylsilane/dichloromethane afforded the desired cyclic hexapeptides, which were characterized by (1)H, (13)C NMR, and HRMS...
July 5, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/29129944/verbenanone-an-octahydro-5h-chromen-5-one-from-a-hawaiian-plant-associated-fungus-ft431
#12
Chunshun Li, Ariel M Sarotti, James Turkson, Shugeng Cao
A new secondary metabolite verbenanone (1) with a unique (4aS,8aS)-octahydro-5H-chromen-5-one moiety has been obtained from the endophytic fungus FT431, which was isolated from the native Hawaiian plant Verbena sp. The structure of compound 1 was characterized based on NMR and MS spectroscopic analysis. The absolute configuration (AC) of compound 1 was determined by Mosher acids. Compound 1 was tested against A2780 and A2780cisR, but it was inactive.
June 7, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/29056780/asymmetric-solution-phase-mixture-aldol-reaction-using-oligomeric-ethylene-glycol-tagged-chiral-oxazolidinones
#13
Serhan Turkyilmaz, Craig S Wilcox
Sorting tags are oligomeric structures that can be used as protecting groups or chiral auxiliaries enabling solution-phase mixture syntheses of multiple tagged compounds in one pot and allowing for facile and predictable chromatographic separation of products at the end of synthetic sequences. Perfluorinated hydrocarbon and oligomeric ethylene glycol (OEG) derivatives are known classes of sorting tags. Herein we describe the preparation of OEGylated chiral oxazolidinones and their use in asymmetric solution-phase mixture aldol reactions...
May 24, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/28966404/competitive-substrate-dependent-reductive-debromination-dehydrobromination-of-1-2-dibromides-with-triethylamine
#14
Kristen M McGraw, Greggory T Kent, Joseph R Gonzalez, Ihsan Erden, Weiming Wu
The interaction of various 1,2-dibromides with NEt3 under various conditions (THF and DMF, respectively) at different temperatures was investigated. Our results from these reactions show that substrate dependent dehydrobrominations compete with reductive debrominations. A comprehensive discussion of these competitive pathways is offered.
May 17, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/29176914/efficient-route-to-pre-organized-and-linear-polyaminopolycarboxylates-cy-ttha-cy-dtpa-and-mono-di-reactive-tert-butyl-protected-ttha-cy-ttha
#15
Ali Mohamadi, Lawrence W Miller
Pre-organized polyaminopolycarboxylate chelators Cy-TTHA and Cy-DTPA were synthesized via modular five-step syntheses from commercially available starting materials in ~ 62% and 47% overall yields, respectively. Furthermore, strategies are reported for the efficient preparation of mono- and di-reactive, tert-butyl-protected TTHA/Cy-TTHA to selectively functionalize central chelators' carboxylic acids.
April 12, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/28413233/an-alternative-synthesis-of-vandetanib-caprelsa%C3%A2-via-a-microwave-accelerated-dimroth-rearrangement
#16
Kayleigh L Brocklesby, Jennifer S Waby, Chris Cawthorne, Graham Smith
Vandetanib is an orally available tyrosine kinase inhibitor used in the treatment of cancer. The current synthesis proceeds via an unstable 4-chloroquinazoline, using harsh reagents, in addition to requiring sequential protection and deprotection steps. In the present work, use of the Dimroth rearrangement in the key quinazoline forming step enabled the synthesis of Vandetanib in nine steps (compared to the previously reported 12-14).
April 12, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/28966403/synthesis-of-highly-substituted-benzene-ring-systems-through-three-component-coupling-of-enyne-imines-fischer-carbene-complexes-and-electron-deficient-alkynes
#17
Bishnu Dhakal, Lalith S R Gamage, Yanshi Zhang, James W Herndon
Three-component coupling of Fischer carbene complexes, enyne aldehyde hydrazones, and electron-deficient alkynes leads to simple benzoate derivatives in a process involving the formation of an N-aminopyrrole derivative, Diels-Alder reaction, and nitrene extrusion. The products are readily converted into isoquinolones through reaction with primary amines. The reaction proceeds best with highly substituted and electron-rich pyrroles even though these are the sterically least favorable substrates, and this reactivity trend is supported by a computational study...
April 5, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/28479613/synthesis-of-olefins-via-a-wittig-reaction-mediated-by-triphenylarsine
#18
Lun Li, Jared C Stimac, Laina M Geary
An arsine-mediated Wittig reaction for the synthesis of olefins is described. After heating triphenylarsine in the presence of an activated alkyl bromide for 30 minutes, the resulting arsonium salt condensed with aldehydes in as little as 5 minutes at room temperature, yielding the olefins in high yields. Aromatic, heteroaromatic, and alkyl aldehydes were all suitable substrates for this process.
April 5, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/28983131/a-simple-and-efficient-approach-for-the-synthesis-of-2-aminated-quinazoline-derivatives-via-metal-free-oxidative-annulation
#19
Amit N Pandya, Eric M Villa, E Jeffrey North
A simple and efficient approach for the synthesis of 2-aminoquinazoline derivatives in moderate to good yields. This reaction employs mild reaction conditions, is metal-free and utilizes readily available starting materials making it a more viable reaction for the scale up synthesis and ligand diversity. Notably, this methodology allows the synthesis of 2-aminoquinazolines using a free amine or cyclic amine enabling structural diversity and good atom economy.
March 29, 2017: Tetrahedron Letters
https://www.readbyqxmd.com/read/28970642/m-chloroperbenzoic-acid-oxchromium-vi-mediated-cleavage-of-2-4-5-trisubstituted-oxazoles
#20
Pravin C Patil, Frederick A Luzzio
An array of 2-substituted-4,5-diphenyloxazoles were found to be cleaved to triacylamines and diacylamines (imides) using a reagent system composed of 3-chloroperbenzoic acid (MCPBA) and 2,2'-bipyridinium chlorochromate (BPCC). The 2-alkyl-4,5-diphenyloxazoles give imides (38-60%) as the predominant cleavage product while the 2-aryl-4,5-diphenyloxazoles give triacylamines (44-71%). Two mechanisms involving intermediates such as cyclic endoperoxides or oxachromacycles were proposed. An application of the oxidative cleavage to the multi-step synthesis of (±)-phoracantholide I seco acid is detailed...
March 29, 2017: Tetrahedron Letters
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