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PubMed Journals Articles About "Disrotatory Ring Opening Furans Gives Stereocontrol" RSS

20:09 EST 27th January 2020 | BioPortfolio

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Showing "Disrotatory Ring Opening Furans Gives Stereocontrol" PubMed Articles 1–25 of 1,800+

Disrotatory Ring-Opening of Furans Gives Stereocontrol.

The ring-opening of 2-methylfuran catalyzed by the Lewis acid catalyst tris(pentafluorophenyl)borane in the presence of hydrosilanes was studied by using quantum chemical methods. In a previous study, it was suggested that the stereoselective formation of the product is due to a nucleophilic vinylic substitution (SV) during the reaction. Our calculations show that the pathway involving the SV reaction is energetically not accessible. Instead, the intramolecular C-O bond cleavage is found to be much more fav...


Synthesis of Densely Functionalized -Alkenyl 2-Pyridones via Benzyne-Induced Ring Opening of Thiazolino-Fused 2-Pyridones.

We report the synthesis of 6-arylthio-substituted--alkenyl 2-pyridones by ring opening of bicyclic thiazolino-2-pyridones with arynes. Varied functionalization was used to investigate scope and substituent influences on reactivity. Selected conditions favor thioether ring opening over [4 + 2] cycloaddition and an unusual aryne incorporating ring expansion. Deuterium labeling was used to clarify observed reactivity. Using the knowledge, we produced drug-like molecules with complex substitution patterns and s...

Catalytic Desymmetric Cycloaddition of Diaziridines with Metalloenolcarbenes: the Special Role of Donor-Acceptor Cyclopropenes.

Chiral copper(I) catalysed reactions of symmetrical diaziridines with enoldiazo compounds undergo novel N-N bond ring opening with formal [3+3] cycloaddition to form four chiral centers with high stereocontrol. A broad spectrum of highly enantioenriched bridged bis-nitrogen heterocyclic compounds were obtained in high yield and diastereoselectivity using γ-substituted enoldiazoacetates, but their geometrical isomers gave different enantioselectivities. Donor-acceptor cyclopropenes formed from the geometric...


Mechanism of Photoinduced Dihydroazulene Ring-Opening Reaction.

The photoinduced ring-opening reaction is a key process in the functioning of dihydroazulene/vinylheptafulvene (DHA/VHF) photoswitches. Over the years, the mechanism of this reaction has been extensively debated. Herein, by means of nonadiabatic trajectory dynamics simulations and quantum chemistry calculations, we present the first detailed and comprehensive investigation on the mechanism of the photoinduced ring-opening reaction of DHA. The results show the crucial role of the excited-state ring planariza...

Ring-opening formal hetero-5+2 cycloaddition of 1-tosyl-2,3-dihydro-1H-pyrroles with terminal alkynes: entry to 1-tosyl-2,3-dihydro 2,3-dihydro-1H-azepines.

A new Lewis acid catalysed formal hetero-[5+2] cycloaddition of 2,3-dihydro-1H-pyrroles to terminal alkynes is described. By employing a FeCl3 and BF3·OEt2 co-catalytic strategy, the ring-opening of 1-tosyl-2,3-dihydro-1H-pyrroles by selective cleavage of the C(sp2)-N bond and subsequent annulation have been achieved to access 1-tosyl-2,3-dihydro-1H-azepines with excellent regioselectivity, offering a new avenue for cycloaddition through the ring-opening of non-strained-ring-based units.

Exposing the delocalized Cu-S π bonds on Au24Cu6(SPhtBu)22 nanocluster and its application in ring opening reaction.

Bimetallic nanomaterials are of major importance in catalysis. In this study, we synthesized a novel Au-Cu bimetallic nanocluster and found it effective to catalyze the epoxide ring opening reaction. The catalyst was analyzed by SCXRD and ESI-MS to be Au24Cu6(SPhtBu)22 (Au24Cu6 for short). Six copper atoms were found to exclusively occupy the surface positions in two groups with three atoms for each, and each group was bonded with three thiolate ligands to give a planar motif reminiscent of a benzene ring. ...

Domino Synthesis of Thioflavones and Thioflavothiones by Regioselective Ring Opening of Donor-Acceptor Cyclopropane Using In-Situ-Generated Thiolate Anions.

A copper-catalyzed intramolecular ring opening of donor-acceptor cyclopropane is developed for the synthesis of 3-alkyl-carbonated thioflavones and further extended to 3-alkyl-carbonated thioflavothione, using xanthate as a sulfur surrogate. This reaction proceeds through thiolate formation/ring opening/Krapcho decarboxylation, followed by hydrogen abstraction, to give thioflavanone, which is further oxidized by in-situ-generated iodine from waste byproduct KI. Experimental studies prove that the charge-tra...

Photo/N-Heterocyclic Carbene Co-catalyzed Ring Opening and γ-Alkylation of Cyclopropane Enal.

An unprecedented photo/NHC-co-catalyzed ring-opening C-C bond cleavage of cyclopropane enal and the following γ-alkylation with a halogenated compound via radicals were established, affording the corresponding γ-alkylated α,β-unsaturated esters in moderate to good yields.

Copper-Catalyzed Ring Opening of 1.1.1Propellane with Alkynes: Synthesis of Exocyclic Allenic Cyclobutanes.

Despite the long history and interesting properties of propellanes, these compounds still have tremendous potential to be exploited in synthetic organic chemistry. Herein we disclose an experimentally simple procedure to achieve cyclobutane-containing allenes and alkynes through a copper-catalyzed ring opening of [1.1.1]propellane and subsequent reaction with ethynes.

Copper-Catalyzed Enantioselective Ring-Opening of Cyclic Diaryliodoniums and -Alkylhydroxylamines.

A preparation of 2-hydroxyamino-2'-iodobiaryls via the Cu-catalyzed enantioselective ring-opening reaction of cyclic diaryliodonium salts with -alkylhydroxylamines is reported. 3,5-Di(-butyl)phenyl bis(oxazoline) was found to be the optimal ligand, and up to 99% ee values were achieved. The use of CaO as the base dramatically improved the yields and inhibited the side reactions. Finally, synthetic applications of these hydroxylamines were briefly demonstrated.

Architecture-Controlled Ring-Opening Polymerization for Dynamic Covalent Poly(disulfide)s.

A strategy is reported for controlling the architecture of poly(disulfide)s by ring-opening polymerization. Aryl thiol initiators shift the ring-chain equilibrium to yield cyclic polymers while alkyl thiols favor linear ones. Control over polymerization enables the synthesis of high polymers (630 kDa) and catalytic depolymerization of polymers to recycle monomers. This work provides a new avenue to create dynamic covalent polymers with controlled geometry and length, allowing better characterization of stru...

Ring-Opening Functionalization of Simple gem-Difluorocyclopropanes by Single Electron Oxidants.

It was reported for the first time that single electron oxidants such as CAN or KSO affected facile ring-opening of simple gem-difluorocyclopropanes to afford 1,3-dibromo-2,2-difluoropropanes in good yields by the action of KBr, and appro-priate choice of conditions allowed to incorporate not only second halogen atoms but also hydroxy or acetamido groups at the C position in the difluoropropane structures in a regiospecific fashion after initiation of the reaction by introduc-tion of the first bromine atom ...

Synthesis of water soluble and multi-responsive selenopolypeptides via ring-opening polymerization of N-carboxyanhydrides.

We report here the synthesis of water soluble selenopolypeptides via the ring-opening polymerization of N-carboxyanhydrides. The oligoethylene glycol-bearing selenopolypeptides are thermally responsive in aqueous solutions with tunable lower critical solution temperatures. The polymers can also undergo rapid and reversible helix-coil transitions upon responding to the added redox cycle.

Metal-Free Cyclopropanol Ring-Opening C(sp)-C(sp) Cross-Couplings with Aryl Sulfoxides.

A metal-free method for formal β-arylation/heteroarylation of ketones through efficient cyclopropanol ring-opening cross-couplings with aryl sulfoxides at room temperature has been developed. This protocol shows a broad substrate scope and promising scalability. In addition, the utility of the β-arylated ketones is further demonstrated through a variety of postcoupling transformations and synthetic applications.

Difunctionalization of Cyclopropyl Amines with -Iodosuccinimide (NIS) or in Situ Formed Cyanogen Iodide (ICN).

We report herein a 1,3-difunctionalization of cyclopropylamines that serve as a π nucleophile in a two-electron (2e) S2-like ring opening pathway. -Iodosuccinimide (NIS) or in situ generated cyanogen iodide (ICN) is employed as electrophilic iodinating reagents in conjunction with TMSCN or succinimide to furnish multiple pairs of functional groups disposed in a 1,3-manner. This 2e ring opening manifold overcomes the constraint of our previously reported 1e protocol as demonstrated by successful activation ...

Recent Advances in Metal-Mediated Stereoselective Ring-Opening Polymerization of Functional Cyclic Esters towards Well-defined Poly(hydroxy acid)s.

Poly(hydroxy acid)s are a family of biocompatible and (bio)degradable polyesters with various outcomes in different domains of application. To date, poly(hydroxy acid)s are best prepared by ring-opening polymerization (ROP) of the corresponding cyclic esters. Using racemic chiral monomers featuring side-chain groups enables to access, providing a stereoselective catalyst/initiator system is implemented, stereoregular functional polymers, thereby improving their physico-chemical properties and ultimately wid...

An Acid-Catalyzed Epoxide Ring-Opening/Transesterification Cascade Cyclization to Diastereoselective Syntheses of (±)-β-Noscapine and (±)-β-Hydrastine.

An acid-catalyzed stereoselective epoxide ring-opening/intramolecular transesterification cascade cyclization reaction and -Boc deprotection was found to be a successful strategy to construct the phthalide tetrahydroisoquinoline skeleton in one pot. Based on this strategy, the unified and highly diastereoselective routes for the total syntheses of (±)-β-Noscapine and (±)-β-Hydrastine were exploited.

High Glass-Transition Temperature Polymer Networks harnessing the Dynamic Ring Opening of Pinacol Boronates.

Differential scanning calorimetry of high molar mass poly(4-vinylphenylboronic acid, pinacol ester)s evidenced unusual reactive events above 120°C, resulting in a high glass-transition temperature of 220°C. We hypothesize a reversible ring-opening reactivity of pinacol boronates involving a nucleophilic attack on the sp2 boron and subsequent bridging between boron atoms by interconnected pinacol moieties to form a densely crosslinked network with high-Tg. FTIR, solid-state NMR investigations and rheology ...

Silylium-Ion-Promoted Ring-Opening Hydrosilylation and Disilylation of Unactivated Cyclopropanes.

A silylium-ion-promoted ring-opening hydrosilylation of unactivated cyclopropanes is reported. The reaction is facilitated by the γ-silicon effect, and the regioselectivity is influenced by various stabilizing effects on the carbenium-ion intermediates, including the β-silicon effect. The experimental observations are in accord with the computed reaction mechanism. The work also showcases the ability of silylium ions to isomerize cyclopropyl to allyl groups, and the resulting α-olefins engage in a silyli...

Cellulose-derived functional polyacetal by cationic ring-opening polymerization of levoglucosenyl methyl ether.

The unsaturated bicyclic acetal levoglucosenyl methyl ether is readily obtained from sustainable feedstock (cellulose) and polymerized by cationic ring-opening polymerization to produce a semi-crystalline thermoplastic, unsaturated polyacetal with relatively high apparent molar mass (up to ~36 kg mol -1 ) and decent dispersity (~1.4). The double bonds along the chain are prone to hydrogenation and thiol-ene chemistry as well as to crosslinking, making this polyacetal potentially interesting as a reactive fu...

Diastereoselective Desymmetrization of -Quinamines through Regioselective Ring Opening of Epoxides and Aziridines.

A highly diastereoselective desymmetrization of -quinamines via regioselective ring opening of epoxides and aziridines under mild conditions has been developed. A chairlike six-membered transition state with minimized 1,3-diaxial interactions explains the relative stereoselectivity of the cyclization reaction. This transition-metal free [3 + 3] annulation reaction provides rapid access to fused bicyclic morpholines and piperazines with a tetrasubstituted carbon center in high yields. In addition, it also al...

Mechanistic insights into ring cleavage of hydroquinone by PnpCD from quantum mechanical/molecular mechanical calculations.

PnpCD is a mononuclear non-heme iron(ii) dioxygenase containing an unusual 2His-1Glu-1Asn metal-binding motif. To gain insights into the catalytic mechanism of the ring opening of hydroquinone by PnpCD, hybrid quantum mechanics/molecular mechanics calculations have been performed by using two models with different protonation states of the substrate (nonionized and ionized forms of the Fe-bound hydroxyl group of hydroquinone). In both cases, the structure of the reactive Fe-O2 species reveals a trigonal bip...

A Spontaneous Ring Opening Reaction Leads to a Repair-Resistant T Oxidation Product in Genomic DNA.

The alphabet of modified DNA bases goes beyond the conventional four letters, with biological roles being found for many such modifications. Here we describe a novel observation for the thymine base that arises via spontaneous N₁-C₂ ring opening of its oxidation product 5-formyl uracil, after N₃-deprotonation. We first observed this phenomenon in silico though ab initio calculations, followed by in vitro experiments to verify its formation at a mononucleoside level and in a synthetic DNA oligonucleoti...

Alternating Sequence Control for Poly(ester amide)s by Organocatalyzed Ring-Opening Polymerization.

Sequence-controlled polymerization is the forefront of polymer chemistry. Herein, the feasibility of sequence regulation by using organocatalyzed ring-opening polymerization (ROP) is demonstrated. In particular, ring expansion strategy is employed to synthesize pre-organized monomers 1 and 2. ROP is conducted by using 1,5,7-triazabicyclo[4.4.0]dec-5-ene and benzyl alcohol as the catalyst and initiator, respectively. Poly(ester amide)s (PEAs) P1-P3 comprising glycolic acid, lactic acid, and 7-aminoheptanoic ...

Highly isoselective ring-opening polymerization of rac-O-carboxyanhydrides using a zinc alkoxide initiator.

The stereoselective ring-opening polymerization (ROP) of O-carboxyanhydrides (OCAs) remains a major challenge due to the easy epimerization of monomers. In this work, using a zinc alkoxide initiator, highly efficient ROP of enantiopure 5-methyl-1,3-dioxolane-2,4-dione (LacOCA), 5-benzyl-1,3-dioxolane-2,4-dione (PheOCA), and 5-(4-(benzyloxy)benzyl)-1,3-dioxolane-2,4-dione (Try(Bn)OCA) was achieved without obvious epimerization. Moreover, highly isoselective ROP of rac-LacOCA, rac-PheOCA, and rac-Try(Bn)OCA w...


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