The Experts below are selected from a list of 3378 Experts worldwide ranked by ideXlab platform
Rambabu Chegondi - One of the best experts on this subject based on the ideXlab platform.
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Synthetic Strategy toward the Pentacyclic Core of Melodinus Alkaloids.
Journal of Organic Chemistry, 2018Co-Authors: Navya Goli, Shivakrishna Kallepu, Prathama S. Mainkar, Jerripothula K. Lakshmi, Rambabu Chegondi, Srivari ChandrasekharAbstract:The three-component Povarov reaction is efficiently utilized for construction of the pentacyclic framework of complex Melodinus alkaloids, which is amenable to expansion to other complex natural products. The key steps were Povarov reaction, one-pot Reductive Cyclization, and ring-closing metathesis (RCM) reaction.
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rhodium catalyzed highly regio and enantioselective Reductive Cyclization of alkyne tethered cyclohexadienones
ACS Catalysis, 2018Co-Authors: Krishna Kumar Gollapelli, Sangeetha Donikela, Nemali Manjula, Rambabu ChegondiAbstract:Rhodium-catalyzed asymmetric hydrogenation of alkyne-tethered cyclohexadienones enables highly regio- and enantioselective Reductive Cyclization to afford cis-hydrobenzofurans and cis-hydroindoles in high yields. Desymmetrization of 1,3-diyne-tethered cyclohexadienones was also explored, wherein the intramolecular coordination of a Rh complex with the cyclohexadienone ring induces exclusive regioselectivity. Mechanistic studies including hydrogen–deuterium crossover experiments suggested that hydrogen activation is the rate-determining step for tandem Reductive Cyclization. Moreover, this highly practical and atom-economical transformation has tolerance to many functional groups with a broad range of substrate scope, allowing further transformations to expand the structural complexity of the bicyclic scaffolds.
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Synthetic Strategy toward the Pentacyclic Core of Melodinus Alkaloids
2018Co-Authors: Navya Goli, Shivakrishna Kallepu, Prathama S. Mainkar, Jerripothula K. Lakshmi, Rambabu Chegondi, Srivari ChandrasekharAbstract:The three-component Povarov reaction is efficiently utilized for construction of the pentacyclic framework of complex Melodinus alkaloids, which is amenable to expansion to other complex natural products. The key steps were Povarov reaction, one-pot Reductive Cyclization, and ring-closing metathesis (RCM) reaction
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Rhodium-Catalyzed Highly Regio- and Enantioselective Reductive Cyclization of Alkyne-Tethered Cyclohexadienones
2018Co-Authors: Krishna Kumar Gollapelli, Sangeetha Donikela, Nemali Manjula, Rambabu ChegondiAbstract:Rhodium-catalyzed asymmetric hydrogenation of alkyne-tethered cyclohexadienones enables highly regio- and enantioselective Reductive Cyclization to afford cis-hydrobenzofurans and cis-hydroindoles in high yields. Desymmetrization of 1,3-diyne-tethered cyclohexadienones was also explored, wherein the intramolecular coordination of a Rh complex with the cyclohexadienone ring induces exclusive regioselectivity. Mechanistic studies including hydrogen–deuterium crossover experiments suggested that hydrogen activation is the rate-determining step for tandem Reductive Cyclization. Moreover, this highly practical and atom-economical transformation has tolerance to many functional groups with a broad range of substrate scope, allowing further transformations to expand the structural complexity of the bicyclic scaffolds
Jiong Yang - One of the best experts on this subject based on the ideXlab platform.
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iron catalyzed Reductive Cyclization of 1 6 enynes
ChemInform, 2014Co-Authors: Aijun Lin, Zhi-wei Zhang, Jiong YangAbstract:A FeCl2-catalyzed Cyclization of 1,6-enynes (I) and (III) is developed using a unique combination of Et2Zn and MgBr2·OEt2 as reagent for the in-situ-generation of the catalytically active species.
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Iron-catalyzed Reductive Cyclization of 1,6-enynes.
Organic letters, 2013Co-Authors: Aijun Lin, Zhi-wei Zhang, Jiong YangAbstract:A precatalyst of FeCl2 and iminopyridine was activated in situ by a combination of diethylzinc and magnesium bromide etherate; it catalyzed the Reductive Cyclization of 1,6-enynes to give pyrrolidine and tetrahydrofuran derivatives from N- and O-tethered 1,6-enynes. The scope of the transformation was explored.
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enantioselective synthesis of a diastereomer of iriomoteolide 1a what is the correct structure of the natural product
Organic Letters, 2010Co-Authors: Lijing Fang, Jiong Yang, Fei YangAbstract:An enantioselective approach to a diastereomer of iriomoteolide-1a is described. Highlighted is a SmI2-mediated intramolecular Reductive Cyclization approach to complex cyclic hemiketals. An acetylide−chloroformate coupling strategy is also featured. Our results show that the structures of iriomoteolide-1a−1c require careful reassessment.
Wenjun Tang - One of the best experts on this subject based on the ideXlab platform.
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optically active n alkyl aziridines via stereospecific Reductive Cyclization of α mesylated acetamides
Organic chemistry frontiers, 2018Co-Authors: Duanshuai Tian, Henian Peng, Ziyue Liu, Wenjun TangAbstract:An efficient method for the synthesis of optically active N-alkyl aziridines has been realized for the first time by stereospecific Reductive Cyclization of optically active α-mesylated acetamides. A series of optically active N-alkyl aziridines are prepared in moderate to good yields and excellent ees. The employment of (9-BBN)2 as the reagent is crucial for the success of the transformation.
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highly enantioselective nickel catalyzed intramolecular Reductive Cyclization of alkynones
ChemInform, 2015Co-Authors: Ming Nie, Aizhen Wang, Ziping Cao, Wenjun TangAbstract:The first asymmetric nickel-catalyzed intramolecular Reductive Cyclization of alkynones is reported.
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highly enantioselective nickel catalyzed intramolecular Reductive Cyclization of alkynones
Angewandte Chemie, 2015Co-Authors: Ming Nie, Aizhen Wang, Ziping Cao, Wenjun TangAbstract:The first asymmetric nickel-catalyzed intramolecular Reductive Cyclization of alkynones is reported. A P-chiral monophosphine and triethylsilane were used as the ligand and the reducing reagent, respectively, to form a series of tertiary allylic alcohols bearing furan/pyran rings in excellent yields and enantioselectivities. This reaction has a broad substrate scope and enabled the efficient synthesis of dehydroxycubebin and chiral dibenzocyclooctadiene skeletons.
Martin G. Banwell - One of the best experts on this subject based on the ideXlab platform.
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Palladium-Catalyzed Ullmann Cross-Coupling of β‑Iodoenones and β‑Iodoacrylates with o‑Halonitroarenes or o‑Iodobenzonitriles and Reductive Cyclization of the Resulting Products To Give Diverse Heterocyclic Systems
2018Co-Authors: Faiyaz Khan, Michael Dlugosch, Xin Liu, Marium Khan, Martin G. Banwell, Jas S. Ward, Paul D. CarrAbstract:The palladium-catalyzed Ullmann cross-coupling of β-iodoenones and β-iodoacrylates such as 5 (X = I) with o-halonitroarenes and o-iodobenzonitriles including 2 affords products such as compound 7. These can be engaged in a range of Reductive Cyclization reactions leading to heterocyclic frameworks such as 3,4-benzomorphan derivative 43
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Palladium-Catalyzed Ullmann Cross-Coupling/Tandem Reductive Cyclization Route to Key Members of the Uleine Alkaloid Family
2016Co-Authors: Fei Tang, Martin G. Banwell, Anthony C. WillisAbstract:The trisubstituted cyclohexenone 12, generated through a palladium-catalyzed Ullmann cross-coupling reaction between o-iodonitrobenzene and a 4,5-trans-disubstituted 2-iodo-2-cyclohexen-1-one, engaged in a tandem Reductive Cyclization process upon exposure to hydrogen gas in the presence of Raney cobalt. As a result, the 1,5-methanoazocino[4,3-b]indole 13 was obtained and this could be readily elaborated to the racemic modifications of the alkaloids uleine, dasycarpidone, noruleine, and nordasycarpidone (1–4, respectively)
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application of a raney cobalt mediated tandem Reductive Cyclization protocol to total syntheses of the aspidosperma alkaloids limaspermidine and 1 acetylaspidoalbidine
Organic Letters, 2012Co-Authors: Shen H Tan, Martin G. Banwell, Anthony C Willis, Tristan A ReekieAbstract:The racemic modification of the Aspidosperma alkaloid limaspermidine (1) has been prepared in ten steps including one involving a Raney-cobalt-mediated tandem Reductive Cyclization of nitrile 8 to give the tetracyclic system 9b. Compound (±)-1 has been converted over two steps into (±)-1-acetylaspidoalbidine [(±)-13].
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a pd 0 catalyzed ullmann cross coupling Reductive Cyclization approach to c 3 mono alkylated oxindoles and related compounds
ChemInform, 2011Co-Authors: Martin G. Banwell, Jayanta K Ray, Matthew T Jones, David T J Loong, David W Lupton, David M Pinkerton, Anthony C WillisAbstract:The Pd[0]-catalyzed Ullmann cross-coupling of o-nitrohaloarenes 1a–e with the brominated heterocycles 2a–f delivers the expected products 3a–j in good to excellent yields. The Reductive Cyclization of such products, as well as N-acyl derivatives 3k, l, and m, has been investigated and provided the C-3 mono-substituted oxindoles 5a–d, f, g, k, and m, the direct reduction products 4i and j or indole 5l.
Carina Weber - One of the best experts on this subject based on the ideXlab platform.
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an efficient and practical synthesis of 2 11c indole via superfast nucleophilic 11c cyanation and raney nickel catalyzed Reductive Cyclization
Organic and Biomolecular Chemistry, 2015Co-Authors: So Jeong Lee, Joanna S Fowler, David Alexoff, Michael J Schueller, Dohyun Kim, Alexander M Nauth, Carina WeberAbstract:A rapid method for the synthesis of carbon-11 radiolabeled indole was developed using a sub-nanomolar quantity of no-carrier-added [(11)C]cyanide as radio-precursor. Based upon a reported synthesis of 2-(2-nitrophenyl)acetonitrile (), a highly reactive substrate 2-nitrobenzyl bromide () was evaluated for nucleophilic [(11)C]cyanation. Additionally, related reaction conditions were explored with the goal of obtaining of highly reactive 2-(2-nitrophenyl)-[1-(11)C]acetonitrile () while inhibiting its rapid conversion to 2,3-bis(2-nitrophenyl)-[1-(11)C]propanenitrile (). Next, a RANEY® Nickel catalyzed Reductive Cyclization method was utilized for synthesizing the desired [2-(11)C]indole with hydrazinium monoformate as the active reducing agent. Extensive and iterative screening of basicity, temperature and stoichiometry was required to overcome the large stoichiometry bias that favored 2-nitrobenzylbromide () over [(11)C]cyanide, which both caused further alkylation of the desired nitrile and poisoned the RANEY® Nickel catalyst. The result is an efficient two-step, streamlined method to reliably synthesize [2-(11)C]indole with an entire radiochemical yield of 21 ± 2.2% (n = 5, ranging from 18-24%). The radiochemical purity of the final product was >98% and specific activity was 176 ± 24.8 GBq μmol(-1) (n = 5, ranging from 141-204 GBq μmol(-1)). The total radiosynthesis time including product purification by semi-preparative HPLC was 50-55 min from end of cyclotron bombardment.
