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Ravindra Pandey - One of the best experts on this subject based on the ideXlab platform.
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effect of meso substituents on the Osmium Tetraoxide reaction and pinacol pinacolone rearrangement of the corresponding vic dihydroxyporphyrins
Journal of Organic Chemistry, 2001Co-Authors: Yihui Chen, Craig J Medforth, Kevin M Smith, James L Alderfer, Thomas J Dougherty, Ravindra PandeyAbstract:To investigate the effects of electron-donating and electron-withdrawing substituents upon the reaction of porphyrins with Osmium Tetraoxide, and the pinacol−pinacolone rearrangement of the resulting diols, a series of meso-substituted porphyrins were prepared by total synthesis. Porphyrins with electron-donating substitutents at the meso-positions gave vic-dihydroxychlorins in which the adjacent pyrrole subunit was predominantly oxidized. No such selectivity was observed in a porphyrin containing a methoxycarbonyl as the electron-withdrawing group, whereas a formyl substituent again resulted in oxidation at the pyrrole unit adjacent to the meso-substituent. Under pinacol−pinacolone conditions, vic-dihydroxy chlorins containing 4-methoxyphenyl or 3,5-dimethoxyphenyl groups at the meso-position showed preferential migration of the ethyl group over the methyl group to give 8-ketochlorins, whereas the diol with an n-heptyl substituent under similar reaction conditions gave both 7- and 8-ketochlorins. In cont...
Craig J Medforth - One of the best experts on this subject based on the ideXlab platform.
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effect of meso substituents on the Osmium Tetraoxide reaction and pinacol pinacolone rearrangement of the corresponding vic dihydroxyporphyrins
Journal of Organic Chemistry, 2001Co-Authors: Yihui Chen, Craig J Medforth, Kevin M Smith, James L Alderfer, Thomas J Dougherty, Ravindra PandeyAbstract:To investigate the effects of electron-donating and electron-withdrawing substituents upon the reaction of porphyrins with Osmium Tetraoxide, and the pinacol−pinacolone rearrangement of the resulting diols, a series of meso-substituted porphyrins were prepared by total synthesis. Porphyrins with electron-donating substitutents at the meso-positions gave vic-dihydroxychlorins in which the adjacent pyrrole subunit was predominantly oxidized. No such selectivity was observed in a porphyrin containing a methoxycarbonyl as the electron-withdrawing group, whereas a formyl substituent again resulted in oxidation at the pyrrole unit adjacent to the meso-substituent. Under pinacol−pinacolone conditions, vic-dihydroxy chlorins containing 4-methoxyphenyl or 3,5-dimethoxyphenyl groups at the meso-position showed preferential migration of the ethyl group over the methyl group to give 8-ketochlorins, whereas the diol with an n-heptyl substituent under similar reaction conditions gave both 7- and 8-ketochlorins. In cont...
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pinacol pinacolone rearrangements in vic dihydroxychlorins and bacteriochlorins effect of substituents at the peripheral positions
Journal of Organic Chemistry, 1997Co-Authors: Ravindra K Pandey, Craig J Medforth, Meden Isaac Ian Macdonald, Mathias O Senge, And Thomas J Dougherty, K M SmithAbstract:Upon reaction with Osmium Tetraoxide a series of porphyrins and chlorins were converted into the corresponding vic-dihydroxychlorins and bacteriochlorins. The presence of an electron-withdrawing substituent at a peripheral position on the porphyrins or chlorins deactivated that particular pyrrole unit toward oxidation, and also directed the oxidation regioselectively to the pyrrole ring opposite to the one bearing the electronegative group. The vic-dihydroxychlorins and bacteriochlorins were converted into the corresponding oxochlorins and dioxobacteriochlorins under pinacol−pinacolone reaction conditions. The migratory behavior of the various substituents were found to be quite complex, since distant conjugated peripheral substituents were able to affect the stability of the carbocation intermediates during the process; the ability to rearrange was affected not only by the intrinsic nature of the migratory group but also by steric and electronic factors operative elsewhere on the porphyrin and chlorin ma...
Petr Mejzlik - One of the best experts on this subject based on the ideXlab platform.
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complexes between Osmium Tetraoxide bispyridine and dna a molecular mechanics study
Journal of Biomolecular Structure & Dynamics, 1994Co-Authors: Petr MejzlikAbstract:This study analyzes changes in conformation of five double-stranded DNA fragments related to binding of the single-strand selective probe Osmium Tetraoxide bispyridine (Os, py) to a thymine. Molecular mechanics was used to investigate four B-DNA and one A-DNA fragments including two structures containing a G.T mispair. The reactivity of a particular thymine was estimated by the difference in energies between interactions in a refined DNA fragment and the corresponding interactions in the transformed fragment with Os, py. Both calculations with and without counterions were performed and the results were in qualitative agreement with experiments. The energetically relaxed fragments with Os, py showed relatively minor global structural changes in comparison to the relaxed fragments without Os, py probe. The computed structures of fragments with Watson-Crick pairing that enable binding of Os, py had similar structural characteristics to geometries found in X-ray studies of single-base mismatches. The possible role of ions in binding Os, py to mispairs is also discussed.
Yihui Chen - One of the best experts on this subject based on the ideXlab platform.
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effect of meso substituents on the Osmium Tetraoxide reaction and pinacol pinacolone rearrangement of the corresponding vic dihydroxyporphyrins
Journal of Organic Chemistry, 2001Co-Authors: Yihui Chen, Craig J Medforth, Kevin M Smith, James L Alderfer, Thomas J Dougherty, Ravindra PandeyAbstract:To investigate the effects of electron-donating and electron-withdrawing substituents upon the reaction of porphyrins with Osmium Tetraoxide, and the pinacol−pinacolone rearrangement of the resulting diols, a series of meso-substituted porphyrins were prepared by total synthesis. Porphyrins with electron-donating substitutents at the meso-positions gave vic-dihydroxychlorins in which the adjacent pyrrole subunit was predominantly oxidized. No such selectivity was observed in a porphyrin containing a methoxycarbonyl as the electron-withdrawing group, whereas a formyl substituent again resulted in oxidation at the pyrrole unit adjacent to the meso-substituent. Under pinacol−pinacolone conditions, vic-dihydroxy chlorins containing 4-methoxyphenyl or 3,5-dimethoxyphenyl groups at the meso-position showed preferential migration of the ethyl group over the methyl group to give 8-ketochlorins, whereas the diol with an n-heptyl substituent under similar reaction conditions gave both 7- and 8-ketochlorins. In cont...
Steven M Weinreb - One of the best experts on this subject based on the ideXlab platform.
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a convenient mild method for oxidative cleavage of alkenes with jones reagent Osmium Tetraoxide
Journal of Organic Chemistry, 1993Co-Authors: James R Henry, Steven M WeinrebAbstract:Oxidative scission of alkenes is used for preparation of carboxylic acids and ketones. The authors present a method for cleavage of terminal olefins to yield a carboxylic acid based on the realization that a catalytic amount of Osmium Tetraoxide chromate should convert an olefin via a diol to an acid and/or ketone. The authors believe that and the Osmium is then reoxidized by the chromate, which also cleaves the 1,2-diol. 1 tab.