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Catalyzed ring closure

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https://www.readbyqxmd.com/read/29645401/phosphine-catalyzed-activation-of-vinylcyclopropanes-rearrangement-of-vinylcyclopropylketones-to-cycloheptenones
#1
Jun Wu, Yuhai Tang, Wen Wei, Yong Wu, Yang Li, Junjie Zhang, Yuansuo Zheng, Silong Xu
We report a phosphine-catalyzed activation of electron-deficient vinylcyclopropanes (VCPs) to generate an ambident C5 synthon that is poised to undergo consecutive reactions. The utility of the activation is demonstrated in a phosphine-catalyzed rearrangement of vinylcyclopropylketones to cycloheptenones in good yields with a broad substrate scope. Mechanistic investigations support a stepwise process comprising homoconjugate addition, water-involved hydrogen transfer, and 7-endo-trig SN2' ring closure.
April 12, 2018: Angewandte Chemie
https://www.readbyqxmd.com/read/29516590/efficient-light-induced-pka-modulation-coupled-to-base-catalyzed-photochromism
#2
Johannes Gurke, Simon Budzak, Bernd Schmidt, Denis Jacquemin, Stefan Hecht
Photoswitchable acid-base pairs, allowing for a reversible alteration of their pKa values, are attractive molecular tools to control chemical and biological processes by light. A significant, light-induced pKa change of three units in aqueous medium has been realized involving two thermally stable states, which can be interconverted using UV and green light. The light-induced pKa modulation is based on incorporating a 3-H-thiazol-2-one moiety into the framework of a diarylethene photoswitch, which upon photochemical ring-closure loses the heteroaromatic stabilization of the corresponding, negatively charged base and hence, becomes significantly less acidic...
March 7, 2018: Angewandte Chemie
https://www.readbyqxmd.com/read/29250949/dissecting-the-gold-i-catalyzed-carboaminations-of-n-allyl-tetrahydro-%C3%AE-carbolines-to-allenes
#3
Valérian Gobé, Maxime Dousset, Pascal Retailleau, Vincent Gandon, Xavier Guinchard
N-Allyl tetrahydro-β-carbolines undergo gold-catalyzed cyclizations that lead to tetracyclic compounds, resulting from both ring closure and the transfer of the allylic group from the nitrogen to the carbon backbone. The final skeleton obtained depends on the nature of both the R2 group of the allene and the R3 group of the allylic residue. Mechanistic studies and DFT calculations allowed the determination of all the mechanistic pathways involved in these processes, stemming from a common intermediate that evolves differently according to the substituents nature...
January 19, 2018: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/29239492/stereoselective-palladium-catalyzed-approach-to-vitamin-d-3-derivatives-in-protic-medium
#4
Diego Carballa, Rita Sigüeiro, Zaida Rodríguez-Docampo, Flavia Zacconi, Miguel A Maestro, Antonio Mouriño
We describe an efficient convergent synthesis of vitamin D3 metabolites and analogues. The synthetic strategy relies on a tandem Pd-catalyzed A-ring closure and Suzuki-Miyaura coupling to the CD-side chain component to set directly the vitamin D triene system under protic conditions. This strategy enables rapid access to vitamin D3 and 3-epi-vitamin D3 metabolites and analogues modified at the side chain for biological evaluation and structural and metabolic studies.
March 2, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29149572/au-i-catalyzed-dimerization-of-two-alkyne-units-interplay-between-butadienyl-and-cyclopropenylmethyl-cation-model-studies-and-trapping-experiments
#5
Mathis Kreuzahler, Sven Fabig, Gebhard Haberhauer, Rolf Gleiter
In recent years, Au(I)-catalyzed reactions proved to be a valuable tool for the synthesis of substituted cycles by cycloaromatization and cycloisomerization starting from alkynes. Despite the myriad of Au(I)-catalyzed reactions of alkynes, the mono Au(I)-catalyzed pendant to the radical dimerization of nonconjugated alkyne units has not been investigated by quantum chemical calculations. Herein, by means of quantum chemical calculations, we describe the mono Au(I)-catalyzed dimerization of two alkyne units as well as the transannular ring closure reaction of a nonconjugated diyne...
December 15, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/29140592/a-versatile-strategy-to-main-chain-sulfur-selenium-functionalized-polycarbonates-by-macro-ring-closure-of-diols-and-subsequent-ring-opening-polymerization
#6
Chao Wei, Yan Zhang, Bingkun Yan, Zhengzhen Du, Meidong Lang
Herein, a new class of main chain functionalized aliphatic polycarbonates with sulfur/selenium functional groups on the backbone is reported. Sulfur/selenium-containing cyclic carbonate monomers (MR ) are designed and synthesized by enzyme-catalyzed intermolecular macro-ring closure of related diols. The proposed synthetic strategy is tolerant of other functionalities such as N-substituted groups. The ring opening polymerization (ROP) of MR occurs readily as a versatile route to generate a new family of main chain sulfur/selenium substituted aliphatic polycarbonates (PR) with predictable molecular weights (MW), narrow molecular-weight distribution and controlled copolymer composition...
January 19, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28961328/fusing-carborane-carboxylic-acids-with-alkynes-3d-analogues-of-isocoumarins-via-regioselective-b-h-activation
#7
Furong Lin, Yunjun Shen, Yuanbin Zhang, Yuji Sun, Jiyong Liu, Simon Duttwyler
An iridium-catalyzed alkenylation/annulation sequence between monocarba-closo-dodecaborate carboxylic acids and diarylacetylenes is reported. Regioselective activation of the B2 position, followed by B-C bond formation and ring closure, affords 3D bora-analogues of isocoumarins. The reaction tolerates a variety of functional groups on the aromatic rings and can be extended to B12-substituted derivatives. Furthermore, subsequent alkenylation of the B4 vertex has been achieved in high yields.
January 12, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28800388/rapid-access-to-nanographenes-and-fused-heteroaromatics-by-palladium-catalyzed-annulative-%C3%AF-extension-reaction-of-unfunctionalized-aromatics-with-diiodobiaryls
#8
Wataru Matsuoka, Hideto Ito, Kenichiro Itami
Efficient and rapid access to nanographenes and π-extended fused heteroaromatics is important in materials science. Herein, we report a palladium-catalyzed efficient one-step annulative π-extension (APEX) reaction of polycyclic aromatic hydrocarbons (PAHs) and heteroaromatics, producing various π-extended aromatics. In the presence of a cationic Pd complex, triflic acid, silver pivalate, and diiodobiaryls, diverse unfunctionalized PAHs and heteroaromatics were directly transformed into larger PAHs, nanographenes, and π-extended fused heteroaromatics in a single step...
August 11, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28703584/synthesis-of-2-amino-3-hydroxy-3h-indoles-via-palladium-catalyzed-one-pot-reaction-of-isonitriles-oxygen-and-n-tosylhydrazones-derived-from-2-acylanilines
#9
Haoke Chu, Qiang Dai, Yan Jiang, Jiang Cheng
A cyanide-free one-pot procedure was developed to access 2-amino-3-hydroxy-3H-indoles, which involved: (1) in situ formation of ketenimines by the reaction of N'-(1-(2-aminophenyl)ethylidene)-p-tosylhydrazones with isonitriles; (2) the intramolecular nucleophilic attack of ketenimines by the amino in phenyl furnishing the ring closure leading to 2-aminoindoles; (3) the oxidation of 2-aminoindoles by O2 leading to 2-amino-3-hydroxy-3H-indoles. This strategy represents not only a key compliment to the sporadic synthetic methods toward 2-amino-3-hydroxy-3H-indoles but also progress in N-tosylhydrazone, isonitrile, and ketenimine chemistry...
July 25, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28679046/cp-co-iii-catalyzed-c-h-alkenylation-annulation-reactions-of-indoles-with-alkynes-a-dft-study
#10
Ken Sakata, Masami Eda, Yuri Kitaoka, Tatsuhiko Yoshino, Shigeki Matsunaga
The Cp*Co(III)-catalyzed C-H functionalization reaction of indoles with alkynes was examined using M06-level DFT calculations. The C≡C bond in the alkyne was inserted into the Co-C bond of an intermediate alkenyl-Co complex given by the acetate-assisted C-H bond activation step. Then the reaction pathway bifurcated into alkenylation and annulation pathways. In the case where AcOH, which was eliminated by ligand exchange for the alkyne, recoordinated to the Co atom, alkenylation proceeded via proton transfer...
July 11, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28593693/double-gold-activation-of-1-ethynyl-2-phenylethynyl-benzene-toward-5-exo-dig-and-6-endo-dig-cyclization-reactions
#11
Nery Villegas-Escobar, Mie Højer Larsen Née Vilhelmsen, Soledad Gutiérrez-Oliva, A Stephen K Hashmi, Alejandro Toro-Labbé
In this work, a detailed characterization was carried out of the ring-closure mechanism of EPB (1-ethynyl-2-(phenylethynyl)benzene) toward the 5-exo-dig and 6-endo-dig cyclization reactions, catalyzed by two Au-N-heterocyclic carbene (NHC) moieties. It was found that the 5-exo-dig cyclization takes place with a slightly lower activation barrier and larger exothermicity compared to that of the 6-endo-dig cyclization, in agreement with the available experimental data. A phenomenological partition (structural and electronic) for rate constants computed using transition-state theory and the reaction force analysis was used to shed light into the nature of the activation rate constant...
September 27, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28574261/pyreniporphyrins-porphyrin-analogues-that-incorporate-a-polycyclic-aromatic-hydrocarbon-subunit-within-the-macrocyclic-framework
#12
Ruixiao Gao, Deyaa I AbuSalim, Timothy D Lash
The first examples of porphyrin analogues incorporating pyrene units are reported. Acid-catalyzed condensation of a pyrene dialdehyde with a tripyrrane, followed by oxidation with DDQ, afforded a polycyclic aromatic hydrocarbon (PAH)-porphyrin hybrid in 38% yield. Pyreniporphyrin proved to be devoid of global aromatic character, but upon protonation aromatic mono- and dicationic species were generated. In the proton NMR spectrum for the dication, the internal CH was shifted upfield to approximately +3 ppm. NICS calculations and ACID plots confirmed the diatropic nature of these structures...
June 15, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28530738/cobalt-carbonyl-catalyzed-carbonylation-of-functionalized-aziridines-to-versatile-%C3%AE-lactam-building-blocks
#13
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...
June 7, 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
#14
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...
June 13, 2017: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/28420174/an-expedient-total-synthesis-of-triciribine
#15
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
#16
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
#17
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
#18
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
#19
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
#20
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
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