- Stereoselectivity and kinetics of [4+2] cycloaddition reaction of cyclopentadiene to para-substituted E-2-arylnitroethenes
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In spite of diversified electrophilicity of E-2-arylnitroethenes, their [4+2] cycloaddition reactions with cyclopentadiene leads to the corresponding 6-endo-aryl-5-exo-nitronorbornenes and 6-exo-aryl-5-endo-nitronorbornenes as the only reaction products. Stereoselectivity, substituent and solvent effects, and activation parameters, suggest that these reactions occur via a synchronous concerted mechanism on both competing pathways. The experimental results obtained are consistent with the data from B3LYP/6-31G(d) calculations. Due to high electrophilicity of E-2-arylnitroethenes, the reactions studied should be considered as polar [4+2] cycloadditions. Copyright
- Jasinski, Radomir,Kwiatkowska, Magdalena,Baranski, Andrzej
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experimental part
p. 843 - 853
(2012/06/29)
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- Secondary α-deuterium kinetic isotope effects in [2+4] cycloaddition of (E)-2-phenylnitroethene to cyclopentadiene
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Secondary α-deuterium kinetic isotope effects confirm that [2+4] cycloaddition between (E)-2-phenylnitroethene and cyclopentadiene occurs in concerted manner, on both the pathway leading to 6-endo-phenyl-5-exo- nitronorbornene and the pathway leading to the corresponding 6-exo-phenyl-5-endo-nitro isomer. According to Hammond terminology the transition states on competitive pathways should be considered in terms of symmetrical early states.
- Kwiatkowska, Magdalena,Jasinski, Radomir,Mikulska, Maria,Baranski, Andrzej
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experimental part
p. 545 - 548
(2011/07/30)
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- 2-aminopyridinium ions activate nitroalkenes through hydrogen bonding
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2-Aminopyridinium ions were found to activate nitroalkenes toward conjugate addition of heteroaromatic compounds with low catalyst loadings and the Diels Alder reaction with the periselectivity opposite to that observed with metal Lewis acids, raising the
- Takenaka, Norito,Sarangthem, Robindro Singh,Seerla, Sreehari Kumar
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p. 2819 - 2822
(2008/02/07)
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- ω-Alkenyl α-Nitroalkyl Radicals. Part 3. Radical Chain Reactions of ω-Alkenyl α-Halogenonitroalkanes
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SRN1 reactions between 5-bromo-5-nitrohex-1-ene and the nitronate anions of 2-nitropropane and 5-nitrohex-1-ene failed to give cyclisation of the intermediate α-nitroalkyl radical onto the alkene.Reaction between exo-5-bromo-endo-5-nitro-exo-6-phenylbicyclohept-2-ene 1 and the anion of 2-nitropropane did not undergo an SRN1 reaction and Br+ abstraction gave 2-bromo-2-nitropropane and 5-endo-nitro-exo-6-phenylbicyclohept-2-ene.BNAH reduction of exo-5-bromo-endo-5-nitro-exo-6-phenylbicyclohept-2-ene 1, 6-bromo-6-nitrohept-1-ene, and 1-bromo-1-nitro-2-(prop-2-enyl)cyclohexane gave the corresponding nitroalkanes without any cyclosation of the intermediate α-nitroalkyl radicals.Initial results indicate that an iodine atom transfer methodology provides a possible general method for the cylisation of ω-alkenyl α-nitroalkyl radicals.Cyclisation of intermediate α-nitroalkyl radicals, generated by photolysis of 1-(bicyclohept-5-en-endo-2-yl)-2-iodo-2-nitropropane 5a, gave a good yield of two diastereomeric tricyclic iodonitro compounds 6a and 7a.Photolysis of 1-(bicyclohept-5-en-endo-2-yl)-2-iodo-2-nitroethane 5b and 2-(but-3-enyl)-1-iodo-1-nitrocyclohexane 11 also gave the expected products from 5-exo cyclisation of the intermediate α-nitroalkyl radicals.The tricyclic iodonitro compound 6a was synthesised from the corresponding endo-methanesulfonate 15, the structure of which was determined by X-ray crystallography.
- Bowman, W. Russell,Brown, David S.,Burns, Catherine A.,Crosby, David
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p. 2083 - 2090
(2007/10/02)
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- Oxidative Addition Reactions of ω-Alkenyl Nitronate Anions
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Anions are oxidatively added to nitronate anions to yield α-substituted nitroalkanes when potassium hexacyanoferrate(III) is used as oxidant.Oxidation of nitronate anions yields intermediate α-nitroalkyl radicals, which undergo addition by anions to give intermediate α-substituted nitroalkane radical anions, which are further oxidised to yield the α-substituted nitroalkanes.The nitronate anions used are derived from 5-nitrohex-1-ene, 6-nitrohept-1-ene, endo-5-nitro-exo-6-phenylbicyclohept-2-ene, and 1-(bicyclohept-5-en-endo-2-yl)-2-nitropropane.The intermediate α-nitroalkyl onto the ω-alkenes.The α-nitroalkyl radical derived from 1-(bicyclohept-5-en-endo-2-yl)-2-nitropropane underwent cyclisation when the oxidation was carried out in the absence of an added anion.The addition of anions (thiocyanate, benzenesulfinate, 4-chlorobenzenethiolate, and nitrite) to the α-nitroalkyl radicals derived from endo-5-nitro-exo-6-phenylbicyclohept-2-ene occurred stereoselectively from the less hindered exo face.Oxidative addition of 4-chlorobenzenethiolate to the nitronate from endo-5-nitro-exo-6-phenylbicyclohept-2-ene gave an unusual cyclisation via addition of a thiyl radical to the alkene.
- Bowman, W. Russell,Brown, David S.,Burns, Catherine A.,Crosby, David
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p. 2099 - 2106
(2007/10/02)
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- Reduction of Substituted Nitro Compounds with Tri-n-butyltin Hydride
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α-Substituted nitro compounds have been reduced with tri-n-butyltin hydride to give replacement of the α-substituent by hydrogen (2-bromo, 2-chloro- and 2-nitro-2-phenylsulphonylpropane to 2-nitropropane; p-nitrobenzyl chloride, bromide, iodide and thiocyanate to p-nitrotoluene; 5-nitrofurfuryl nitrate to 2-methyl-5-nitrofuran and 2-hydroxymethyl-5-nitrofuran; 2-(bromomethyl)-1-methyl-5-nitroimidazole to 1,2-dimethylimidazole). 2-Bromo-2-nitrohept-6-ene and 1-bromo-1-nitrohex-5-ene were reduced to 2-nitrohept-6-ene and 1-nitrohex-5-ene,5-bromo- and 5-phenylsulphonyl-5-nitro-6-phenyl-norborn-6-ene to 5-nitro-6-phenylnorborn-6-ene and 2-iodo-2-nitro-3-(endo-norborn-2-en-5-yl)propane to 2-nitro-3-(endo-norborn-2-en-5-yl)propane without cyclisation of the intermediate alkenyl α-nitroalkyl radicals. 2-Bromo-2-nitrohex-5-ene and 1-bromo-1-nitropent-4-ene were reduced to the respective nitroalkenes at high but at lower cyclisation to 1-methyl-1-nitrocyclopentane and 1-nitrocyclopentane took place.Inhibition studies of the reductions of 2-bromo-2-nitrohex-5-ene and p-nitrobenzyl bromide showed a radical chain mechanism.In some of the reductions at low , radical rearrangement of the intermediate α-nitroalkyl radicals gave the respective ketones.Mechanisms involving (a) addition/elimination and (b) dissociation of intermediate radical anions, are proposed.
- Bowman, W. Russell,Crosby, David,Westlake, Paul J.
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- STEREOSPECIFICITY OF 1,3-DIPOLAR CYCLOADDITIONS OF CYCLIC NITRONES TO (E) and (Z)-β-NITROSTYRENES
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3,4-Dihydroisoquinoline-N-oxide (1) reacted readily with (E)-β-nitrostyrene in a regiospecific reaction to give a mixture of 4-nitro-5-phenylisoxazolidines 3a and 4a resulting from endo and exo (with respect to the nitro group) transition states, respectively.This cycloaddition was found reversible under mild conditions.A careful study disclosed >= 99.89percent stereoselectivity thus narrowly circumscribing the possibility of stereochemical leakage over the cycloaddition and cycloreversion processes.Moreover, our experimental data showed that eventual loss of stereochemistry should be ascribed to base catalysed isomerizations in the adducts and/or educts.The reaction of 1 with (Z)-β-nitrostyrene (exo specific and regiospecific) turned out to be faster than that of the (E)-isomer.This is the first example of higher reactivity of a cis than a trans-alkene in 1,3-dipolar cycloadditions.The endo-trans adduct 3a cycloreverted faster than the exo-trans isomer 4a which in turn underwent fragmentation more readily than the exo-cis 6a.The cycloreversion rate was slightly enhanced by increased solvent polarity.This study was extended to the reaction of 5,5-dimethylpyrroline-N-oxide with both the cited dipolarophiles.
- Burdisso, Marina,Gamba, Anna,Gandolfi, Remo,Pevarello, Paolo
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p. 1835 - 1846
(2007/10/02)
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- Synthese d'aryl nitronorbornenes par cycloaddition de Diels-Alder entre les aryl-nitroethylenes et le cyclopentadiene. Justification de la stereochimie et de la reactivite relative observees par la methode CNDO/II. Obtention d'aryl aminonorbornenes
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Syntheses of numerous 2-aryl nitroethylenes (nitrostyrenes) have been optimized.The nitrostyrenes have been reacted with cyclopentadiene in Diels-Alder cycloadditions and the 3-aryl 2-nitronorbornenes obtained have been reduced into 3-aryl 2-aminonorbornenes.These compounds are potentially dopaminergic molecules.The stereochemistry of the adducts obtained in the Diels-Alder reaction has been determined by 1H nmr.The stereochemistry and the relative reactivity of the nitrostyrenes versus cyclopentadiene have been confirmed by theoretical calculations based on the CNDO/II method.
- Bourguignon, Jean,Le Nard, Gilles,Queguiner, Guy
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p. 2354 - 2361
(2007/10/02)
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- A Method for Determinig Absolute Configuration of Cycloalkanamines and Related Compounds by CD Spectra of Their 2,4-Dinitrophenyl Derivatives
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N-(2,4-Dinitrophenyl) derivatives of cycloalkanamines and related compounds having an amino and an aromatic groups in vicinal positions were prepared.Their CD spectra exhibited marked Cotton effect around 400nm, the sign of which was shown to coincide wit
- Kawai, Masao,Iwase, Teruhiko,Butsugan, Yasuo,Nagai, Ukon
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p. 304 - 308
(2007/10/02)
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