- Structure of the dimers arising from one-electron electrochemical reduction of pyridinium salts 3,5-disubstituted with electron-withdrawing groups
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One-electron electrochemical reduction of the salts 1-benzyl-3,5-bis(methylcarbamoyl)pyridinium bromide 3a and 1-benzyl-3,5-dicarbamoylpyridinium bromide 3b yields mixtures of four isomeric dimers, as shown by HPLC analysis and mass spectrometry. 1/
- Carelli, Vincenzo,Liberatore, Felice,Tortorella, Silvano,Di Rienzo, Barbara,Scipione, Luigi
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- Electron-deficient heteroarenium salts: An organocatalytic tool for activation of hydrogen peroxide in oxidations
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A series of monosubstituted pyrimidinium and pyrazinium triflates and 3,5-disubstituted pyridinium triflates were prepared and tested as simple catalysts of oxidations with hydrogen peroxide, using sulfoxidation as a model reaction. Their catalytic efficiency strongly depends on the type of substituent and is remarkable for derivatives with an electron-withdrawing group, showing reactivity comparable to that of flavinium salts which are the prominent organocatalysts for oxygenations. Because of their high stability and good accessibility, 4-(trifluoromethyl)pyrimidinium and 3,5-dinitropyridinium triflates are the catalysts of choice and were shown to catalyze oxidation of aliphatic and aromatic sulfides to sulfoxides, giving quantitative conversions, high preparative yields and excellent chemoselectivity. The high efficiency of electron-poor heteroarenium salts is rationalized by their ability to readily form adducts with nucleophiles, as documented by low pKR+ values (pKR+ red > -0.5 V). Hydrogen peroxide adducts formed in situ during catalytic oxidation act as substrate oxidizing agents. The Gibbs free energies of oxygen transfer from these heterocyclic hydroperoxides to thioanisole, obtained by calculations at the B3LYP/6-311++g(d,p) level, showed that they are much stronger oxidizing agents than alkyl hydroperoxides and in some cases are almost comparable to derivatives of flavin hydroperoxide acting as oxidizing agents in monooxygenases.
- ?turala, Ji?í,Bohá?ová, Soňa,Chudoba, Josef,Metelková, Radka,Cibulka, Radek
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p. 2676 - 2699
(2015/03/18)
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- Efficient synthesis of 3,5-dicarbamoyl-1,4-dihydropyridines from pyridinium salts: Key molecules in understanding NAD(P)+/NAD(P)H pathways
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3,5-Dicarbamoyl-1,4-dihydropyridines were prepared in high yields using a green protocol by reduction of the corresponding pyridinium salts in aqueous buffered sodium dithionite solutions. The pH value is a fundamental parameter for the reduction step and depends on the nature of substituent groups at positions 1, 3, and 5 of the pyridinium salts. These 3,5-dicarbamoyl dihydropyridines show a lower tendency towards oxidation and a higher stability than N-benzyl-3-carbamoyl-1,4-dihydropyridine at low pH values.
- Mellini, Paolo,De Vita, Daniela,Di Rienzo, Barbara,La Rosa, Salvatore,Padova, Alessandro,Scipione, Luigi,Tortorella, Silvano,Friggeri, Laura
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p. 221 - 226
(2015/01/30)
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- Synthesis of pyridine acrylates and acrylamides and their corresponding pyridinium ions as versatile cross-linkers for tunable hydrogels
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A small library of cross-linkers for hydrogels was synthesized. The cross-linkers consisted of 2,6- and 3,5-diacylpyridine or 2,4,6-triacylpyridine as the core unit, which were tethered via ethylene glycol, amino ethanol, and 1,n-diamine spacers to terminal acrylate or acrylamide moieties. Esterification and amide formation of the terminal acryl units were found to be dependent on the ratio of NH/O in the spacer, the constitution pattern of the pyridine ring, and the total number of acryl groups. Thus, esters generally gave higher yields than amides decreasing with increasing number of NH in the spacer and with increasing number of acryl units. In the case of 3,5-diacylpyridine derivatives, these trends were less prominent as compared to the 2,6-diacylpyridine series, indicating that steric hindrance and unfavorable hydrogen bonding interaction of the spacers might influence the observed reactivity differences. The 3,5-diacylpyridines were converted to the N-methylpyridinium salts and selected members of both neutral and cationic 3,5-diacylpyridinium derivatives were submitted to hydrogelations with synthetic polymer poly(1-glycidylpiperazine) via aza-Michael addition and thiolated natural hyaluronan via thio-Michael reaction, respectively. Rheological properties of the resulting hydrogels were studied, revealing that both spacer type as well as charge affected elastic moduli and degree of swelling. Georg Thieme Verlag Stuttgart New York.
- Mateescu, Markus,Nuss, Isabell,Southan, Alexander,Messenger, Hayley,Wegner, Seraphine V.,Kupka, Julia,Bach, Monika,Tovar, Guenter E. M.,Boehm, Heike,Laschat, Sabine
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supporting information
p. 1243 - 1253
(2014/05/06)
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- ANIONS AND DERIVED SALTS WITH HIGH DISSOCIATION IN NON-PROTOGENIC SOLVENTS
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Salts with formula X-M+ wherein M+ is Li, Na, K, an ammonium, a phosphonium, an imidazolium, a pyridinium, or a pyrazolium and X- is an anion formed from covalent linking of two negative moieties to a positive onium-type core are provided. Also provided are electrolytes and batteries produced from these salts.
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Page/Page column 6
(2013/06/05)
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