Synthesis of Anionic Hypervalent Cyclic Selenenate Esters: Relevance to the Hypervalent Intermediates in Nucleophilic Substitution Reactions at the Selenium(II) Center
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Title |
Synthesis of Anionic Hypervalent Cyclic Selenenate Esters: Relevance to the Hypervalent Intermediates in Nucleophilic Substitution Reactions at the Selenium(II) Center
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Creator |
SELVAKUMAR, K
SINGH, HB GOEL, N SINGH, UP BUTCHER, RJ |
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Subject |
cyclization
hypervalent compounds nucleophilic substitution selenenate esters selenium GLUTATHIONE-PEROXIDASE EXCHANGE-REACTIONS ATE COMPLEXES ANTIOXIDANT ACTIVITY LITHIUM-TELLURIUM CRYSTAL-STRUCTURE NMR-SPECTROSCOPY SULFENYL SULFUR DISELENIDES CHEMISTRY |
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Description |
The synthesis of a diaryl diselenide that contains 2,6-dicarboxylic acid groups, 2,2'-diselanediylbis(5-tert-butylisophthalic acid) (10), is described. Diselenide 10 undergoes intramolecular cyclization in methanol to form a cyclic selenenate ester, 5-tert-butyl-3-oxo-3H-benzo[c][1,2]oxaselenole-7-carboxylic acid (11). The cyclization reaction proceeds more rapidly in the presence of organic bases, such as pyridine, adenine, and 4,4'-bipyridine, to form pyridinium 5-tert-butyl-3-oxo-3H-benzo[c][1,2]oxaselenole-7-carboxylate (14), adeninium 5-tert-butyl-3-oxo-3H-benzo[c][1,2]oxaselenole-7-carboxylate (15), and 4,4'-bipyridiniumbis(5-tert-butyl-3-oxo-3H-benzo[c][1,2]oxaselenole-7-carboxylate) (16), respectively. However, 2,2'-diselanediyldibenzoic acid (22) does not undergo cyclization under similar conditions. Structural studies on cyclic selenenate esters 1416 revealed that the Se center dot center dot center dot O (COO-) secondary distances (2.170, 2.075, and 2.176 angstrom) were significantly shorter than the corresponding Se center dot center dot center dot O distances (2.465, 2.472, and 2.435 angstrom) observed for the selenenate esters stabilized by the neutral donors (CHO, COOH, and COOEt). 1H, 13C, and 77Se NMR spectroscopy of compounds 11 and 1416 reveal that the aryl protons of compound 11 and the organic cations of compounds 1416 exchange between the two carboxylate groups via a hypercoordinate intermediate. The corresponding hypercoordinate intermediate (14 b, pyridinium selenuranide) for compound 14 was detected at low temperatures using 77Se NMR spectroscopy. The presumed hypercoordinate intermediates in the carboxylate-exchange reactions at the selenium(II) center for a set of model reactions were optimized using DFT-B3LYP/6311+g(d) calculations and their structural features compared with the X-ray structure of anionic selenenate esters 1416.
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Publisher |
WILEY-V C H VERLAG GMBH
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Date |
2014-10-15T08:47:07Z
2014-10-15T08:47:07Z 2012 |
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Type |
Article
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Identifier |
CHEMISTRY-A EUROPEAN JOURNAL, 18(5)1444-1457
http://dx.doi.org/10.1002/chem.201003725 http://dspace.library.iitb.ac.in/jspui/handle/100/14720 |
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Language |
en
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