The Experts below are selected from a list of 183 Experts worldwide ranked by ideXlab platform
Neal J. Zondlo - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of a tetrasubstituted tetrahydronaphthalene scaffold for α-helix mimicry via a MgBr2-catalyzed Friedel-Crafts epoxide Cycloalkylation.
Organic letters, 2013Co-Authors: Devan Naduthambi, Santosh Bhor, Michael B. Elbaum, Neal J. ZondloAbstract:α-Helices are ubiquitous protein recognition elements that bind diverse biomolecular targets. The synthesis of a small molecule scaffold to present the side chains of an α-helix is described. The 1,3,5,7-tetrasubstituted 1,2,3,4-tetrahydronaphthalene scaffold, providing mimicry of the i, i+3, and i+4 positions of an α-helix, was synthesized using a novel MgBr2-catalyzed Friedel-Crafts epoxide Cycloalkylation as the key step. Each position may be differentiated via O-alkylation after scaffold synthesis, generating a diversity-oriented approach to readily synthesize proteomimetics for different targets.
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Synthesis of a Tetrasubstituted Tetrahydronaphthalene Scaffold for α‑Helix Mimicry via a MgBr2‑Catalyzed Friedel–Crafts Epoxide Cycloalkylation
2013Co-Authors: Devan Naduthambi, Santosh Bhor, Michael B. Elbaum, Neal J. ZondloAbstract:α-Helices are ubiquitous protein recognition elements that bind diverse biomolecular targets. The synthesis of a small molecule scaffold to present the side chains of an α-helix is described. The 1,3,5,7-tetrasubstituted 1,2,3,4-tetrahydronaphthalene scaffold, providing mimicry of the i, i+3, and i+4 positions of an α-helix, was synthesized using a novel MgBr2-catalyzed Friedel–Crafts epoxide Cycloalkylation as the key step. Each position may be differentiated via O-alkylation after scaffold synthesis, generating a diversity-oriented approach to readily synthesize proteomimetics for different targets
Dieter Hoppe - One of the best experts on this subject based on the ideXlab platform.
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asymmetric synthesis of 2 carbamoyloxy 1 alkenyl cyclopropanes by intramolecular Cycloalkylation
ChemInform, 2006Co-Authors: Sven Brandau, Dieter HoppeAbstract:Abstract Enantioenriched, diastereomerically pure (2-carbamoyloxy-1-alkenyl)cyclopropanes 22 are easily prepared via deprotonation of different allyl carbamates with n -butyllithium and (−)-sparteine ( 4 ). The mechanism of the cyclization reaction was determined and several substituted ( S )-configured vinylcyclopropanes 32 were synthesized by two different methods. The configurational stability of the intermediate lithiated allyl carbamates and the half-time of epimerization were investigated in a series of silylation experiments, achieving up to 90% ee in the kinetically controlled enantiotopos-differentiating deprotonation.
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Formation of 1-methylene-2-vinylcyclopropane by intramolecular -Cycloalkylation reaction
Tetrahedron Letters, 2005Co-Authors: Sven Brandau, Roland Fröhlich, Dieter HoppeAbstract:The synthesis of a substituted ( Z )-2-(2-methylenecyclopropyl)vinyl N , N -dialkylcarbamate is presented. Via α-deprotonation of a 4-chloromethyl-2,4-dienyl carbamate and succeeding intramolecular S E ′ -Cycloalkylation reaction, the diastereomerically pure cyclopropane is formed.
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total synthesis of α kainic acid by sparteine mediated asymmetric deprotonation Cycloalkylation
Organic Letters, 2004Co-Authors: Montserrat M Martinez, Dieter HoppeAbstract:We report a new enantioselective synthesis of (−)-α-kainic acid from d-serine methyl ester hydrochloride, based on a (−)-sparteine-mediated asymmetric deprotonation of an intermediate carbamate that, by stereospecific anti SN‘SE‘ intramolecular Cycloalkylation, leads to the pyrrolidine ring precursor of (−)-α-kainic acid, in high yield and diastereoselectivity. The intermediate pyrrolidine was further transformed to (−)-α-kainic acid in three steps.
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asymmetric synthesis of 2 alkenyl 1 cyclopentanols via tin lithium exchange and intramolecular Cycloalkylation
Organic Letters, 2002Co-Authors: Guido Christoph, Dieter HoppeAbstract:We report a method for the synthesis of chiral cyclopentanes using tin−lithium exchange and Cycloalkylation reactions. The sec-butyllithium/(−)-sparteine-mediated deprotonation of an alkyl carbamate and subsequent substitution furnishes a highly enantioenriched stannane as a stable carbanion equivalent. It was transformed into suitable cyclization precursors, which underwent tin−lithium exchange and stereoselective Cycloalkylation when reacted with n-butyllithium, giving highly enantioenriched cyclopentanes in very good yields. A kinetic resolution was observed with a higher substituted stannane.
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planar chiral 2e 7z and 2z 7e cyclonona 2 7 dien 1 yl carbamates by asymmetric bis allylic α α Cycloalkylation studies on their conformational stability
Chemistry: A European Journal, 2002Co-Authors: Alexander Deiters, Roland Fröhlich, Christian Mucklichtenfeld, Dieter HoppeAbstract:Enantiomerically enriched (>80 % ee) (M,1R,2Z,7E)- and (M,1R,2E,7Z)-cyclonona-2,7-dienyl carbamates have been synthesized by an intramolecular Cycloalkylation of the corresponding 1-lithio-9-chloronona-2,7-dienyl carbamates. The enantioenriched precursors were generated by asymmetric deprotonation of the dienyl carbamates by means of n-BuLi/(−)-sparteine. The primarily obtained cyclononadienes, each bearing one element of planar and centre chirality, were formed by an α,α′ coupling of both allylic moieties. These are the thermodynamically less favoured epimers, which arise from those allyllithiums bearing the carbamoyloxy residue in a 1-endo position. Both (M,R)-cyclononadienes epimerize slowly (t1/2 = 209 min and 328 min at 308 K) with inversion of the planar chirality to the corresponding, more stable (P)-epimers (ratios 3:97 and 30:70). The kinetics were measured by 1H NMR spectroscopy, the activation energies EA were found to be 26.4 and 27.5 kcal mol−1. From quantum-chemical calculations with the B3LYP density functional, the epimerization process was shown to consist of two coupled major conformational changes with high energy barriers. The calculated values match well with the observed ones.
Zivorad Cekovic - One of the best experts on this subject based on the ideXlab platform.
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annulation of the cyclohexane ring by tandem free radical alkylation of a nonactivated δ carbon atom intramolecular carbanion Cycloalkylation
Organic Letters, 2000Co-Authors: Goran Petrovic, Zivorad CekovicAbstract:Annulation of the cyclohexane ring by a combination of free radical and ionic reactions sequences was achieved. Free radical alkylation of the remote nonactivated δ-carbon atom involves addition of δ-carbon radicals, generated by 1,5-hydrogen transfer in alkoxy radical intermediates, to radicophilic olefins, while the polar sequence involves enolate anions as intermediates which undergo a Cycloalkylation reaction. Thus, the cyclohexane ring was constructed using diverse acyclic and cyclic structures as precursors of alkoxy radicals.
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annulation of the cyclohexane ring by tandem free radical alkylation of a nonactivated delta carbon atom intramolecular carbanion Cycloalkylation
Organic Letters, 2000Co-Authors: Goran Petrovic, Zivorad CekovicAbstract:Annulation of the cyclohexane ring by a combination of free radical and ionic reactions sequences was achieved. Free radical alkylation of the remote nonactivated δ-carbon atom involves addition of δ-carbon radicals, generated by 1,5-hydrogen transfer in alkoxy radical intermediates, to radicophilic olefins, while the polar sequence involves enolate anions as intermediates which undergo a Cycloalkylation reaction. Thus, the cyclohexane ring was constructed using diverse acyclic and cyclic structures as precursors of alkoxy radicals.
Pavel N. Gaponik - One of the best experts on this subject based on the ideXlab platform.
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facile synthesis of macrocyclic tetrazoles by regioselective Cycloalkylation of bistetrazoles with 2 5 dimethylhexane 2 5 diol in perchloric acid
Tetrahedron Letters, 2012Co-Authors: Sergei V. Voitekhovich, Alexander S. Lyakhov, Ludmila S. Ivashkevich, Pavel N. GaponikAbstract:Alkylation of 1,5-bis(tetrazol-5-yl)-3-oxapentane with 2,5-dimethylhexane-2,5-diol in 65% aqueous perchloric acid was found to proceed selectively on the N2 atoms of both tetrazole rings generating a 15-membered macrocycle with tetrazol-2,5-diyl moieties incorporated (yield ca. 80%). Under analogous alkylation conditions 1,5-bis(1-methyltetrazol-5-yl)-3-oxapentane undergoes quaternization resulting in a macrocyclic tetrazolium perchlorate containing two 1-methyltetrazolium-3,5-diyl units linked by 3-oxapentane-1,5-diyl and 2,5-dimethylhexane-2,5-diyl bridges. Crystal structures of the macrocyclic compounds obtained, determined by single crystal X-ray analysis, are described.
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Acid-mediated Cycloalkylation of C-aminoazoles with 2,5-dimethylhexane-2,5-diol
Tetrahedron Letters, 2012Co-Authors: Sergei V. Voitekhovich, Alexander S. Lyakhov, Ludmila S. Ivashkevich, Pavel N. GaponikAbstract:Abstract Alkylation of 5-aminotetrazole with 2,5-dimethylhexane-2,5-diol in perchloric acid was found to proceed on an endocyclic nitrogen atom as well as on the amino group, giving 5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-4H-tetrazolo[1,5-a][1,3]diazepine. Under analogous conditions, 3-amino-1,2,4-triazole undergoes Cycloalkylation of the neighboring N1 and N2 atoms of the heterocycle resulting in 1-amino-5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-[1,2,4]triazolo[1,2-a]pyridazinium perchlorate. The crystal structures of the products were determined by single crystal X-ray analysis.
Joseph Paul Jayachandran - One of the best experts on this subject based on the ideXlab platform.
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phase transfer catalyzed intramolecular Cycloalkylation of phenylacetonitrile with α ω dibromoalkanes in supercritical ethane
Journal of Supercritical Fluids, 2003Co-Authors: Joseph Paul Jayachandran, Christy Wheeler, Brandon C Eason, Charles L Liotta, Charles A EckertAbstract:Abstract An intramolecular Cycloalkylation of phenylacetonitrile (PAN) with different α,ω-dibromoalkanes in supercritical fluids under phase transfer catalysis (PTC) conditions is reported. In particular, the Cycloalkylation of PAN with an excess of 1,4-dibromobutane has been studied in the presence of tetrabutylammonium bromide and potassium carbonate as a base in supercritical ethane at 70 °C and 11.0 MPa. The reaction was complete in less than 6 h yielding selectively the desired cycloadduct in the presence of a PTC, but conversion in the absence of catalyst was low. A Cycloalkylation methodology has been developed using several dibromoalkanes, viz., 1,2-dibromoethane, 1,3-dibromopropane, 1,4-dibromobutane, 1,5-dibromopentane, 1,6-dibromohexane and 1,10-dibromodecane. When the Cycloalkylation was performed in the presence of supercritical CO 2, mono- and di-alkylated products were observed in addition to the cycloadduct. To compare the effect of SC ethane solvent, reactions were also carried out using different conventional solvents such as hexane, tert -butyl methyl ether, ethyl acetate and chlorobenzene. Use of SC ethane gave considerably better yields of products than the other solvents.
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phase transfer catalyzed alkylation of phenylacetonitrile in supercritical ethane
Industrial & Engineering Chemistry Research, 2002Co-Authors: Christy Wheeler, David R Lamb, Joseph Paul Jayachandran, And Charles L Liotta, Jason P Hallett, Charles A EckertAbstract:The first example of a phase-transfer-catalyzed alkylation reaction under supercritical fluid conditions is reported. The reaction is that of phenylacetonitrile and ethyl bromide in the presence of tetrabutylammonium bromide and potassium carbonate in supercritical ethane at 45, 60, and 75 °C and 138 bar. Results show that the reaction will go to completion in less than 24 h in the presence of the catalyst but that only a few percent conversion is achieved without it during the same period of time. The effects of catalyst concentration, temperature, and cosolvents are investigated. Catalyst solubility estimates and kinetic analyses suggest that the reaction takes place on the surface of the potassium carbonate particles. When the same reaction is attempted in supercritical carbon dioxide, both carboxylation and alkylation are observed. Cycloalkylation reactions between phenylacetonitrile and dibromoalkanes are also discussed.
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Cycloalkylation of phenylacetonitrile with 1 4 dibromobutane catalyzed by aqueous sodium hydroxide and a new phase transfer reagent dq br
Applied Catalysis A-general, 2000Co-Authors: Joseph Paul Jayachandran, Mawling WangAbstract:Abstract The kinetics of Cycloalkylation of phenylacetonitrile (PAN) with an excess of 1,4-dibromobutane has been studied under phase transfer catalysis (PTC) conditions using aqueous sodium hydroxide as the base and 2-benzilidine- N , N , N , N ′, N ′, N ′-hexaethylpropane-1,3-diammonium dibromide (Dq-Br) as a new phase transfer reagent. The reaction was carried out at 70°C under pseudo-first-order conditions by employing aqueous sodium hydroxide and chloroform in excess and was monitored by gas chromatography. The effect of various experimental parameters on the rate of the reaction has been studied; based on the experimental results, a suitable mechanism is proposed.
