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Siegfried Blechert - One of the best experts on this subject based on the ideXlab platform.
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Concise Total Syntheses of Dipiperidine Alkaloids Virgidivarine and Virgiboidine through Ru‐Mediated Ene‐Ene‐Yne Ring Rearrangement Metathesis (RRM)
European Journal of Organic Chemistry, 2013Co-Authors: Steffen Kress, Sabrina R. Schulz, Jochen Weckesser, Siegfried BlechertAbstract:Herein, we report on the first enantioselective synthesis of the sparteine-type alkaloids virgidivarine (1) and virgiboidine (2). The stereoselective construction of the challenging dipiperidine core within 1 and 2 was realized by applying an intramolecular ene-ene-yne Ring-Rearrangement metathesis (RRM) protocol. In combination with this sequence, an unprecedented tandem metathesis/oxidation reaction was established. Subsequent to the RRM event, the Ru-alkylidene species was converted into the highly potent dihydroxylation catalyst RuO4 by the addition of NaIO4. This transformation rendered five sequential reactions that include an ene-ene-yne RRM/dihydroxylation/glycol cleavage in a one-pot procedure. This approach provides practical and general access to dipiperidines and piperidino-quinolizidines. Despite their wide use in organic and organometallic chemistry as well as their occurrence in biologically active natural products, methods are still lacking for the stereoselective synthesis of these motifs.
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Ring-Rearrangement metathesis.
Chemistry an Asian journal, 2007Co-Authors: Nicole Holub, Siegfried BlechertAbstract:Ring-Rearrangement metathesis (RRM) refers to the combination of several metathesis transformations into a domino process, in which an endocyclic double bond of a cycloolefin reacts with an exocyclic alkene. RRM has proven to be a powerful method for the rapid construction of complex structures. The extension of the basic Ring-opening-Ring-closing metathesis process by further metathesis steps as well as an examination of the driving forces, limits, scope, recent advantages, and future perspectives of these domino sequences is presented with various examples, thus reflecting the high efficiency and utility of RRM in organic synthesis.
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Ring-Rearrangement metathesis.
Chemistry-an Asian Journal, 2007Co-Authors: Nicole Holub, Siegfried BlechertAbstract:Ring-Rearrangement metathesis (RRM) refers to the combination of several metathesis transformations into a domino process, in which an endocyclic double bond of a cycloolefin reacts with an exocyclic alkene. RRM has proven to be a powerful method for the rapid construction of complex structures. The extension of the basic Ring-opening–Ring-closing metathesis process by further metathesis steps as well as an examination of the driving forces, limits, scope, recent advantages, and future perspectives of these domino sequences is presented with various examples, thus reflecting the high efficiency and utility of RRM in organic synthesis. Ringumlagerungsmetathesen (RRM) haben sich als effektive und schnelle Methode fur die Darstellung von komplexen Strukturen erwiesen. Definitionsgemas handelt es sich bei diesen Prozessen um die Kombination von mehreren Metatheseschritten, bei denen die Doppelbindung eines Cycloolefins mit einer exocyclischen Doppelbindung in einer Ringoffnungs–Ringschluss-Metathese Sequenz (ROM–RCM) reagiert. Die Erweiterung dieses Konzeptes um zusatzliche Metatheseschritte, als auch die Betrachtung der Triebkrafte und der Grenzen dieser Reaktion werden in diesem Review an aktuellen Beispielen erlautert.
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Enantioselective Total Synthesis of (-)-trans-Dendrochrysine via a Ring-Rearrangement Metathesis Approach
Synlett, 2007Co-Authors: Maximilian Dochnahl, Sabrina R. Schulz, Siegfried BlechertAbstract:The enantioselective total synthesis of the dipyrrolidine alkaloid (-)- TRANS-dendrochrysine was accomplished in 18 steps starting from tropone. The key step was a Ring-Rearrangement -metathesis for the construction of the bisheterocyclic skeleton of the natural product in a single step.
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A concise synthesis of (-)-centrolobine via a diastereoselective Ring Rearrangement metathesis-isomerisation sequence.
Chemical communications (Cambridge England), 2006Co-Authors: Verena Böhrsch, Siegfried BlechertAbstract:A total synthesis of (−)-centrolobine (1) based on a diastereoselective Ring Rearrangement metathesis–double bond isomerisation sequence and a one-pot cross metathesis–hydrogenation procedure is described.
Sambasivarao Kotha - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of spiro-annulated cyclobutane derivatives through ketene [2+2] cycloaddition and Ring-Rearrangement metathesis
2020Co-Authors: Sambasivarao Kotha, Sunil PulletikurtiAbstract:Herein is reported a concise synthesis of spiro-annulated cyclobutane tetracyclic and pentacyclic derivatives by ketene addition, and Ring-Rearrangement metathesis (RRM) as key steps, starting with commercially available norbornadiene and dicyclopentadiene. The tetracyclic spiro-derivative contains a [5/5/4] core unit, which is the key building block to angular triquinanes synthesis. Whereas, the pentacyclic spiro-derivative contains a basic core skeleton of presilphiperfolanes, and other sesquiterpenoids.
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A new skeletal Rearrangement of 1,7-dimethyl Cookson's cage dione catalyzed by a Lewis acid
Organic & biomolecular chemistry, 2020Co-Authors: Sambasivarao Kotha, Subba Rao CheekatlaAbstract:A methyl-substituted polycyclic cage dione containing the PCUD framework has undergone an unprecedented Ring Rearrangement approach. Here, the PCUD framework with the aid of a Lewis acid such as BF3·MeOH gave unusual fragmentation products. Two new products were isolated via the skeletal Rearrangement process involving carbocation mediated intermediates. The substituents in the succinyl bond present in the strained PCUD skeleton produce a driving force for the Rearrangement in an unprecedented manner. Interestingly, the cyclobutane Ring was transformed to cyclopentane through the cleavage of the C1–C7 bond duRing the Ring-expansion process of PCUD via the carbocation intermediates. Unexpectedly, solvent (benzene) was captured duRing the Ring-homologation process due to the presence of methyl substituents placed at the cyclobutane Ring of the cage framework. It appears that this is the first report where an unexpected Ring-Rearrangement, Ring-homologation, and Ring-fragmentation occur with the aid of the BF3·MeOH complex.
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Application of Ring-Rearrangement metathesis in organic synthesis: A grand design
Tetrahedron Letters, 2019Co-Authors: Sambasivarao Kotha, Milind Meshram, Vikas R. AswarAbstract:Abstract In this report, we compiled various strategies involving a Ring-Rearrangement metathesis as a key step to assemble diverse molecules. Popular name reactions such as Grignard reaction, Overman Rearrangement, Fischer indolization, Beckmann Rearrangement and Diels–Alder reaction were used in combination with Ring-Rearrangement metathesis to construct complex targets. Additionally, C H activation and RRM strategy has been used to assemble azacycles. In some instances, the Ring-Rearrangement metathesis was expected to occur; however, Ring-opening metathesis products were realized. These methods were included in the miscellaneous section. We anticipate that the lessons learned here are useful in designing complex polycyclic and heterocyclic targets suitable for biological and material science applications. Beside our work, we have also included others work as a background information.
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Synthesis of cage [4.4.2]propellanes and $${D_{3}}$$ D 3
Journal of Chemical Sciences, 2018Co-Authors: Sambasivarao Kotha, Subba Rao CheekatlaAbstract:The synthesis of substituted cage [4.4.2]propellanes and $$D_{3}$$ D 3 -trishomocubanes beaRing spiro linkage have been assembled with the aid of Diels–Alder reaction and Ring-Rearrangement as key steps. Here, readily available 1,4-hydroquinone, isoprene, spiro[2.4]hepta-4,6-diene and spiro[4.4]nona-1,3-diene were used as starting materials. The unusual Rearrangement of cage propellanes with zinc/acetic acid produced $$D_{3}$$ D 3 -trishomocubanes in good yields. Graphical Abstract Several cage [4.4.2]propellanes and $$D_{3}$$ D 3 -trishomocubanes have been assembled by Diels–Alder reaction (DA), [2+2] photocycloaddition, and acid-promoted Rearrangement. Ring-Rearrangement was observed in cage [4.4.2]propellane framework duRing the acid catalyzed reaction. Rearrangement approach provide new opportunities to construct unusual polycycles.
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Synthesis of cage [4.4.2]propellanes and \({D_{3}}\)-trishomocubanes beaRing spiro linkage
Journal of Chemical Sciences, 2018Co-Authors: Sambasivarao Kotha, Subba Rao CheekatlaAbstract:The synthesis of substituted cage [4.4.2]propellanes and $$D_{3}$$ -trishomocubanes beaRing spiro linkage have been assembled with the aid of Diels–Alder reaction and Ring-Rearrangement as key steps. Here, readily available 1,4-hydroquinone, isoprene, spiro[2.4]hepta-4,6-diene and spiro[4.4]nona-1,3-diene were used as starting materials. The unusual Rearrangement of cage propellanes with zinc/acetic acid produced $$D_{3}$$ -trishomocubanes in good yields. Several cage [4.4.2]propellanes and $$D_{3}$$ -trishomocubanes have been assembled by Diels–Alder reaction (DA), [2+2] photocycloaddition, and acid-promoted Rearrangement. Ring-Rearrangement was observed in cage [4.4.2]propellane framework duRing the acid catalyzed reaction. Rearrangement approach provide new opportunities to construct unusual polycycles.
Ongolu Ravikumar - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of fused azacycle via Overman Rearrangement and Ring-Rearrangement metathesis as key steps
Tetrahedron Letters, 2016Co-Authors: Sambasivarao Kotha, Ongolu RavikumarAbstract:Abstract A simple and concise approach to fused tricyclic compound containing five stereogenic centers and one nitrogen atom is described starting with a readily available building block dicyclopentadiene. This route involves the Overman Rearrangement and ruthenium catalyzed Ring-Rearrangement metathesis as key steps.
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Design and synthesis of oxacycles from norbornene derivatives via Ring-opening metathesis and Ring-Rearrangement metathesis
Tetrahedron, 2016Co-Authors: Sambasivarao Kotha, Ongolu Ravikumar, Gaddamedi SreevaniAbstract:Abstract Norbornene derivatives containing oxygen atom(s) are found to undergo Ring-Rearrangement metathesis sequence to deliver cyclic ethers. Here, we have established a simple, efficient and an atom-economic process for the synthesis of fused and spiro-oxacyclic compounds starting with cyclopentadiene. Compounds prepared in this study are difficult to assemble by conventional retrosynthetic routes.
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synthesis of a tricyclic lactam via beckmann Rearrangement and Ring Rearrangement metathesis as key steps
Beilstein Journal of Organic Chemistry, 2015Co-Authors: Sambasivarao Kotha, Ongolu Ravikumar, Jadab MajhiAbstract:A tricyclic lactam is reported in a four step synthesis sequence via Beckmann Rearrangement and Ring-Rearrangement metathesis as key steps. Here, we used a simple starting material such as dicyclopentadiene.
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design and synthesis of fused polycycles via diels alder reaction and Ring Rearrangement metathesis as key steps
Beilstein Journal of Organic Chemistry, 2015Co-Authors: Sambasivarao Kotha, Ongolu RavikumarAbstract:Atom efficient processes such as the Diels–Alder reaction (DA) and the Ring-Rearrangement metathesis (RRM) have been used to design new polycycles. In this regard, ruthenium alkylidene catalysts are effective in realizing the RRM of bis-norbornene derivatives prepared by DA reaction and Grignard addition. Here, fused polycycles are assembled which are difficult to produce by conventional synthetic routes.
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Design and synthesis of fused polycycles via Diels–Alder reaction and Ring-Rearrangement metathesis as key steps
Beilstein journal of organic chemistry, 2015Co-Authors: Sambasivarao Kotha, Ongolu RavikumarAbstract:Atom efficient processes such as the Diels–Alder reaction (DA) and the Ring-Rearrangement metathesis (RRM) have been used to design new polycycles. In this regard, ruthenium alkylidene catalysts are effective in realizing the RRM of bis-norbornene derivatives prepared by DA reaction and Grignard addition. Here, fused polycycles are assembled which are difficult to produce by conventional synthetic routes.
Emanuela Erba - One of the best experts on this subject based on the ideXlab platform.
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Diastereoselective Synthesis of Pyrazolines by Metal-Free Rearrangement of Bicyclic Triazolines
Synthesis, 2020Co-Authors: Raffaella Bucci, Sara Pellegrino, Francesca Clerici, Emanuela ErbaAbstract:The metal-free preparation of diazoalkanes through the Ring Rearrangement of bicyclic triazolines is reported here. Their use in 1,3-dipolar cycloaddition reactions with electron-withdrawing alkenes was investigated. This synthetic procedure allows differently substituted pyrazolines to be obtained in few steps and with high atom economy.
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Asymmetric Modular Synthesis of a Semirigid Dipeptide Mimetic by Cascade Cycloaddition/Ring Rearrangement and Borohydride Reduction
The Journal of organic chemistry, 2014Co-Authors: Sara Pellegrino, Alessandro Contini, Maria Luisa Gelmi, Leonardo Lo Presti, Raffaella Soave, Emanuela ErbaAbstract:A new semirigid dipeptide mimetic was prepared on multigram scale, in good yield, and in a stereocontrolled way, starting from commercially available and unexpensive reagents, i.e., N-benzylpiperidone, tosyl azide, and proline methyl ester. The optimized multicomponent process consisted of a cascade click cycloaddition and a Ring Rearrangement reaction, followed by a reductive step. Theoretical calculations were performed to elucidate the reaction mechanism and support the stereochemical outcome of the reduction. Finally, the new scaffold was used for the preparation of model peptidomimetics, whose β turn conformation was confirmed by dynamic NMR experiments.
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asymmetric modular synthesis of a semirigid dipeptide mimetic by cascade cycloaddition Ring Rearrangement and borohydride reduction
Journal of Organic Chemistry, 2014Co-Authors: Sara Pellegrino, Alessandro Contini, Maria Luisa Gelmi, Leonardo Lo Presti, Raffaella Soave, Emanuela ErbaAbstract:A new semirigid dipeptide mimetic was prepared on multigram scale, in good yield, and in a stereocontrolled way, starting from commercially available and unexpensive reagents, i.e., N-benzylpiperidone, tosyl azide, and proline methyl ester. The optimized multicomponent process consisted of a cascade click cycloaddition and a Ring Rearrangement reaction, followed by a reductive step. Theoretical calculations were performed to elucidate the reaction mechanism and support the stereochemical outcome of the reduction. Finally, the new scaffold was used for the preparation of model peptidomimetics, whose β turn conformation was confirmed by dynamic NMR experiments.
Guillaume Vincent - One of the best experts on this subject based on the ideXlab platform.
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stereodivergent synthesis of piperidine alkaloids by Ring Rearrangement metathesis reductive lactam alkylation of nitroso diels alder cycloadducts
Chemistry: A European Journal, 2013Co-Authors: Guillaume Vincent, Delphine Karila, Georges Khalil, Pierre Sancibrao, Didier Gori, Cyrille KouklovskyAbstract:A general methodology for the stereoselective synthesis of 2-(2-hydroxyalkyl)piperidine alkaloids by Ring-Rearrangement metathesis of nitroso Diels–Alder cycloadducts is reported. The approach is illustrated by the formal synthesis of porantheridine and the total synthesis of andrachcinidine through a diastereodivergent allylation of an N-alkoxy bicyclic lactam. The asymmetric synthesis of the latter alkaloid provides new insights into the configurational stability of cycloadducts between chloronitroso reagents and cyclopentadiene.
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Stereodivergent Synthesis of Piperidine Alkaloids by Ring‐Rearrangement Metathesis/Reductive Lactam Alkylation of Nitroso Diels–Alder Cycloadducts
Chemistry: A European Journal, 2013Co-Authors: Guillaume Vincent, Delphine Karila, Georges Khalil, Pierre Sancibrao, Didier Gori, Cyrille KouklovskyAbstract:A general methodology for the stereoselective synthesis of 2-(2-hydroxyalkyl)piperidine alkaloids by Ring-Rearrangement metathesis of nitroso Diels–Alder cycloadducts is reported. The approach is illustrated by the formal synthesis of porantheridine and the total synthesis of andrachcinidine through a diastereodivergent allylation of an N-alkoxy bicyclic lactam. The asymmetric synthesis of the latter alkaloid provides new insights into the configurational stability of cycloadducts between chloronitroso reagents and cyclopentadiene.
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Ring Rearrangement metathesis of nitroso diels alder cycloadducts
ChemInform, 2011Co-Authors: Guillaume Vincent, Cyrille KouklovskyAbstract:The substrates are converted into valuable fused bicyclic heterocycles containing N—O bonds.
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Ring-Rearrangement Metathesis of Nitroso Diels—Alder Cycloadducts.
ChemInform, 2011Co-Authors: Guillaume Vincent, Cyrille KouklovskyAbstract:The substrates are converted into valuable fused bicyclic heterocycles containing N—O bonds.
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Ring Rearrangement metathesis of nitroso diels alder cycloadducts
Chemistry: A European Journal, 2011Co-Authors: Guillaume Vincent, Cyrille KouklovskyAbstract:Strained nitroso Diels-Alder bicyclo[2.2.1] or [2.2.2] adducts functionalized with alkene side chains of diverse length undergo a Ring-Rearrangement metathesis process with external alkenes and Grubbs II or Hoveyda-Grubbs II ruthenium catalysts, under microwave irradiation or classical heating, to deliver cis-fused bicycles of various Ring sizes, which contain a N-O bond. These scaffolds are of synthetic relevance for the generation of molecular diversity and to the total synthesis of alkaloids. The observation of unexpected reactions, such as epimerization or one-carbon homologation of the alkene side chain, is also reported.
