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Catalyzed ring closure

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https://www.readbyqxmd.com/read/28530738/cobalt-carbonyl-catalyzed-carbonylation-of-functionalized-aziridines-to-versatile-%C3%AE-lactam-building-blocks
#1
Nicola Piens, Kristof Van Hecke, Dieter Vogt, Matthias D'hooghe
The Co2(CO)8-catalyzed carbonylation of different classes of non-activated aziridines with diverse substitution patterns was investigated. Special attention was devoted to selectivity issues and reaction optimization. This study resulted in the regio- and stereospecific synthesis of 24 novel β-lactam target structures in high yields on a multigram scale. The synthetic potential of the newly obtained azetidin-2-ones was illustrated via ring-expansion, ring-closure, and/or side chain-functionalization protocols to provide a straightforward entry to novel pyrrolidines, C-fused bi- and tricyclic β-lactams and monocyclic carbapenem analogs...
May 22, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28513654/rhodium-catalyzed-synthesis-of-1-2-dihydropyridine-by-a-tandem-reaction-of-4-1-acetoxyallyl-1-sulfonyl-1-2-3-triazole
#2
Haican Dai, Sisi Yu, Wanli Cheng, Ze-Feng Xu, Chuan-Ying Li
A tandem reaction of 4-(1-acetoxyallyl)-1-sulfonyl-1,2,3-triazole including formation of α-imino rhodium carbene, 1,2-migration of an acetoxy group and six electron electrocyclic ring closure was reported. The migration of the OAc group with excellent chemoselectivity was the crucial process, leading to the formation of 1,2-dihydropyridine specifically in up to 90% yield. Several transformations of the dihydropyridine product were also achieved illustrating the potential of the protocol in organic synthesis...
May 17, 2017: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/28420174/an-expedient-total-synthesis-of-triciribine
#3
Chen Hu, Zhizhong Ruan, Haixin Ding, Yirong Zhou, Qiang Xiao
In the present paper, we report an expedient total synthesis of triciribine, a tricyclic 7-deazapurine nucleoside and protein kinase B (AKT ) inhibitor, in 35% overall yield. Our synthesis route features a highly regioselective substitution of 1-N-Boc-2-methylhydrazine and a trifluoroacetic acid catalyzed one-pot transformation which combined the deprotection of the tert-butylcarbonyl (Boc) group and ring closure reaction together to give a tricyclic nucleobase motif.
April 17, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
https://www.readbyqxmd.com/read/28394400/the-missing-link-in-leguminous-pterocarpan-biosynthesis-is-a-dirigent-domain-containing-protein-with-isoflavanol-dehydratase-activity
#4
Kai Uchida, Tomoyoshi Akashi, Toshio Aoki
Pterocarpan forms the basic structure of leguminous phytoalexins, and most of the isoflavonoid pathway genes encoding the enzymes responsible for its biosynthesis have been identified. However, the last step of pterocarpan biosynthesis is a ring closure reaction, and the enzyme that catalyzes this step, 2'-hydroxyisoflavanol 4,2'-dehydratase or pterocarpan synthase (PTS), remains as an unidentified 'missing link'. This last ring formation is assumed to be the key step in determining the stereochemistry of pterocarpans, which plays a role in their antimicrobial activity...
February 1, 2017: Plant & Cell Physiology
https://www.readbyqxmd.com/read/28375013/regio-and-stereocontrolled-synthesis-of-3-substituted-1-2-diazetidines-by-asymmetric-allylic-amination-of-vinyl-epoxide
#5
Sundaram Rajkumar, Guy J Clarkson, Michael Shipman
Pd-catalyzed asymmetric allylic amination of rac-vinyl epoxide with unsymmetrical 1,2-hydrazines proceeds with excellent regio- and stereocontrol, which after further ring closure provides differentially protected 3-vinyl-1,2-diazetidines in good yields. The chirality at C-3 exerts stereocontrol over the nitrogen centers in the 1,2-diazetidine with all substituents orientating themselves trans to their neighbors. Efficient functionalization without rupture of the strained ring is demonstrated (e.g., by cross-metathesis), establishing the first general route to C-3-substituted 1,2-diazetidines in enantioenriched form...
April 4, 2017: Organic Letters
https://www.readbyqxmd.com/read/28296421/silver-catalyzed-regioselective-fluorination-of-carbonyl-directed-alkynes-synthesis-of-%C3%AE-fluoroketones
#6
Fang-Hui Li, Zhong-Jian Cai, Ling Yin, Jian Li, Shun-Yi Wang, Shun-Jun Ji
A novel silver-catalyzed fluorination reaction of carbonyl directed alkynes in the presence of N-fluorobenzenesulfonimide and water with high regioselectivities has been developed. The established protocol provides an alternative method for rapid assembly of α-fluoroketone derivatives under simple and mild reaction conditions. The reaction pathway involves a ring closure and opening process for the construction of new C-O and C-F bonds. In addition, a fluorine-containing indanone was observed through further N-heterocyclic carbene catalyzed intramolecular crossed-benzoin reaction of α-fluoroketone...
April 7, 2017: Organic Letters
https://www.readbyqxmd.com/read/28271894/altering-the-cyclization-modes-temperature-dependent-intramolecular-7-endo-dig-vs-6-endo-dig-electrophilic-ring-closures
#7
Maloy Nayak, Young Kee Kang, Ikyon Kim
In an attempt to construct 10-acyl-5H-benzo[e]pyrrolo[1,2-a]azepines via acid-catalyzed intramolecular alkyne carbonyl metathesis, two distinctive modes of cyclization were revealed to depend on the reaction temperatures. 5H-Benzo[e]pyrrolo[1,2-a]azepine-1-carbaldehydes with a substituent at the C11 position were obtained as major products at 90 °C as a result of intramolecular 7-endo-dig cyclization, while 6-endo-dig ring closure by electrophilic addition of nitrogen of the pyrrole to a vinyl cation generated under acidic medium followed by an unprecedented domino rearrangement process was observed at 40 °C in some cases, resulting in 5-aryl-11H-benzo[d]pyrrolo[1,2-a]azepine-1-carbaldehydes along with the former products...
March 8, 2017: Organic Letters
https://www.readbyqxmd.com/read/28244755/aromatic-metamorphosis-of-dibenzofurans-into-triphenylenes-starting-with-nickel-catalyzed-ring-opening-c-o-arylation
#8
Yuto Kurata, Shinya Otsuka, Norihito Fukui, Keisuke Nogi, Hideki Yorimitsu, Atsuhiro Osuka
A new class of aromatic metamorphosis has been developed in which dibenzofurans were converted into triphenylenes. This transformation is composed of three successive operations: (1) nickel-catalyzed ring-opening C-O bond arylation with arylmagnesium bromides, (2) trifluoromethanesulfonylation (triflation) of the resulting hydroxy moiety with Tf2O, and (3) palladium-catalyzed or photoinduced ring closure. In the last ring-closing step, the photoinduced process has proven to be more productive than the palladium-catalyzed one...
February 28, 2017: Organic Letters
https://www.readbyqxmd.com/read/28225267/efficient-enantioselective-syntheses-of-dalesconol-a-and-b
#9
Guoqing Zhao, Guangqing Xu, Chao Qian, Wenjun Tang
We herein report the first enantioselective syntheses of immunosuppressants (+)-dalesconol A and B in a highly efficient and concise manner, which features an efficient palladium-catalyzed enantioselective dearomative cyclization-kinetic resolution cascade to install the chiral all-carbon quaternary center, an effective sterically hindered Stille coupling, a powerful 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) oxidation to furnish all requisite unsaturation, and a tandem hydrolysis-ring closure sequence...
February 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28219006/ir-catalyzed-asymmetric-total-synthesis-of-communesin-f
#10
Xiao Liang, Tian-Yuan Zhang, Xue-Yi Zeng, Yu Zheng, Kun Wei, Yu-Rong Yang
The first catalytic asymmetric total synthesis of the heptacyclic alkaloid (-)-communesin F is described. A key step features an iridium-catalyzed asymmetric intermolecular cascade cyclization, constructing the lower N,N-aminal-containing CDEF tetracyclic core in one step. Another notable element is the closure of final ring system (A ring) via a facile reduction of a twisted amide and concomitant cyclization activated by mesylation of N,O-hemiaminal intermediate.
February 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28195725/theoretical-insight-into-the-conversion-mechanism-of-glucose-to-fructose-catalyzed-by-crcl2-in-imidazolium-chlorine-ionic-liquids
#11
Yaru Jing, Jun Gao, Chengbu Liu, Dongju Zhang
To better understand the efficient transformation of glucose to fructose catalyzed by chromium chlorides in imidazolium-based ionic liquids (ILs), density functional theory calculations have been carried out on a model system which describes the catalytic reaction by CrCl2 in 1,3-dimethylimidazolium chlorine (MMImCl) ionic liquid (IL). The reaction is shown to involve three fundamental processes: ring opening, 1,2-H migration, and ring closure. The reaction is calculated to exergonic by 3.8 kcal/mol with an overall barrier of 37...
February 22, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/27934470/northern-southern-route-to-synthetic-bacteriochlorins
#12
Yizhou Liu, Jonathan S Lindsey
A new route to bacteriochlorins via Northern-Southern (N-S) self-condensation of a dihydrodipyrrin-acetal complements a prior Eastern-Western (E-W) route. Each bacteriochlorin was prepared in five steps from an α-halopyrrole and a 2,2-dimethylpent-4-ynoic acid. The first three steps follow Jacobi's synthesis of dihydrodipyrrins: Pd-mediated coupling to form a lactone-pyrrole, Petasis reagent treatment for methenylation, and Paal-Knorr type ring closure to form the 1,2,2-trimethyl-substituted dihydrodipyrrin...
December 2, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27896336/cui-catalyzed-intramolecular-aminocyanation-of-terminal-alkynes-in-n-2-ethynylphenyl-n-sulfonylcyanamides-via-cu-vinylidene-intermediates
#13
Zhen-Yuan Liao, Pen-Yuan Liao, Tun-Cheng Chien
CuI-Catalyzed intramolecular aminocyanation of terminal alkynes in N-(2-ethynylphenyl)-N-sulfonylcyanamides was initiated by the formation of Cu-acetylide to trigger N-CN bond cleavage of the N-sulfonylcyanamide moiety followed by CN migration to form a β-cyano Cu-vinylidene intermediate. Subsequently, the indole ring closure furnished the corresponding 1-sulfonyl-3-cyanoindoles.
December 13, 2016: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/27875779/novel-pyrimidine-2-4-dione-1-2-3-triazole-and-furo-2-3-d-pyrimidine-2-one-1-2-3-triazole-hybrids-as-potential-anti-cancer-agents-synthesis-computational-and-x-ray-analysis-and-biological-evaluation
#14
Tomislav Gregorić, Mirela Sedić, Petra Grbčić, Andrea Tomljenović Paravić, Sandra Kraljević Pavelić, Mario Cetina, Robert Vianello, Silvana Raić-Malić
Regioselective 1,4-disubstituted 1,2,3-triazole tethered pyrimidine-2,4-dione derivatives (5-23) were successfully prepared by the copper(I)-catalyzed click chemistry. While known palladium/copper-cocatalyzed method based on Sonogashira cross-coupling followed by the intramolecular 5-endo-dig ring closure generated novel 6-alkylfuro[2,3-d]pyrimidine-2-one-1,2,3-triazole hybrids (24b-37b), a small library of their 5-alkylethynyl analogs (24a-37a) was synthesized and described for the first time by tandem terminal alkyne dimerization and subsequent 5-endo-trig cyclization, which was additionally corroborated with computational and X-ray crystal structure analyses...
January 5, 2017: European Journal of Medicinal Chemistry
https://www.readbyqxmd.com/read/27795589/a-novel-stereoselective-8-2-double-cycloaddition-route-to-hydronaphthalene-ring-systems
#15
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/27748978/the-br%C3%A3-nsted-acid-catalyzed-enantioselective-aza-diels-alder-reaction-for-the-direct-synthesis-of-chiral-piperidones
#16
Claudia Weilbeer, Marcel Sickert, Sergei Naumov, Christoph Schneider
We disclose herein the first enantioselective aza-Diels-Alder reaction of β-alkyl-substituted vinylketene silyl-O,O-acetals and imines furnishing a broad range of optically highly enriched 4-alkyl-substituted 2-piperidones. As a catalyst for this one-pot reaction we employed a chiral phosphoric acid which effects a vinylogous Mannich reaction directly followed by ring-closure to the lactam. Subsequent fully diastereoselective transformations including hydrogenation, enolate alkylation, and lactam alkylation/reduction processes converted the cycloadducts into various highly substituted piperidines of great utility for the synthesis of natural products and medicinally active compounds...
October 17, 2016: Chemistry: a European Journal
https://www.readbyqxmd.com/read/27744687/copper-catalyzed-cross-coupling-of-silicon-pronucleophiles-with-unactivated-alkyl-electrophiles-coupled-with-radical-cyclization
#17
Weichao Xue, Zheng-Wang Qu, Stefan Grimme, Martin Oestreich
A copper-catalyzed C(sp3)-Si cross-coupling of aliphatic C(sp3)-I electrophiles using an Si-B reagent as the silicon pronucleophile is reported. The reaction involves an alkyl radical intermediate that also engages in 5-exo-trig ring closures onto pendant alkenes prior to the terminating C(sp3)-Si bond formation. Several Ueno-Stork-type precursors cyclized with excellent diastereocontrol in good yields. The base-mediated release of the silicon nucleophile and the copper-catalyzed radical process are analyzed by quantum-chemical calculations, leading to a full mechanistic picture...
October 16, 2016: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/27605341/insights-into-n-heterocyclic-carbene-catalyzed-4-2-annulation-reaction-of-enals-with-nitroalkenes-mechanisms-origin-of-chemo-and-stereoselectivity-and-role-of-catalyst
#18
Linjie Zheng, Yang Wang, Donghui Wei, Yan Qiao
In this paper, density functional theory (DFT) calculations have been employed to investigate the detailed mechanisms, origin of chemo- and stereoselectivity, and role of catalyst for the reaction of enals with nitroalkenes catalyzed by N-heterocyclic carbenes (NHCs). The calculated results disclose that the reaction contains seven steps, that is, the nucleophilic attack on the α, β-unsaturated aldehyde by NHC, the [1, 2]-proton transfer for the formation of Breslow intermediate, the β-protonation for affording enolate intermediate, the nucleophilic addition on the Re/Si face of enolate by the nitroalkenes, the [1, 5] proton transfer, the ring-closure process, and the regeneration of NHC...
November 7, 2016: Chemistry, An Asian Journal
https://www.readbyqxmd.com/read/27554454/synthesis-properties-and-two-dimensional-adsorption-characteristics-of-6-hexahelicene-7-carboxylic-acid
#19
Maarten W van der Meijden, Tatyana Balandina, Oleksandr Ivasenko, Steven De Feyter, Klaus Wurst, Richard M Kellogg
A convergent synthesis of racemic [6]hexahelicene-7-carboxylic acid by cross-coupling of a bicyclic and a tricyclic component is described. A metal-catalyzed ring-closure is also a fundamental component of the synthetic approach. Scanning tunneling microscopy (STM) measurements of the racemate self-assembled on Au(111) at liquid-solid interface revealed the formation of ordered racemic 2D crystals.
October 4, 2016: Chemistry: a European Journal
https://www.readbyqxmd.com/read/27506796/oxidation-and-cyclization-of-casbene-in-the-biosynthesis-of-euphorbia-factors-from-mature-seeds-of-euphorbia-lathyris-l
#20
Dan Luo, Roberta Callari, Britta Hamberger, Sileshi Gizachew Wubshet, Morten T Nielsen, Johan Andersen-Ranberg, Björn M Hallström, Federico Cozzi, Harald Heider, Birger Lindberg Møller, Dan Staerk, Björn Hamberger
The seed oil of Euphorbia lathyris L. contains a series of macrocyclic diterpenoids known as Euphorbia factors. They are the current industrial source of ingenol mebutate, which is approved for the treatment of actinic keratosis, a precancerous skin condition. Here, we report an alcohol dehydrogenase-mediated cyclization step in the biosynthetic pathway of Euphorbia factors, illustrating the origin of the intramolecular carbon-carbon bonds present in lathyrane and ingenane diterpenoids. This unconventional cyclization describes the ring closure of the macrocyclic diterpene casbene...
August 23, 2016: Proceedings of the National Academy of Sciences of the United States of America
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