A molecular orbital study of diastereofacial selectivity in the Diels-Alder reaction and glycosidation via glycals and aryl(bisarylthio)sulfonium salts: Effect of nucleophile and aryl substitution on face selectivity.
Item
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Title
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A molecular orbital study of diastereofacial selectivity in the Diels-Alder reaction and glycosidation via glycals and aryl(bisarylthio)sulfonium salts: Effect of nucleophile and aryl substitution on face selectivity.
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Identifier
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AAI9119643
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identifier
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9119643
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Creator
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Kaila, Neelu.
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Contributor
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Adviser: Richard W. Franck
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Date
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1991
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Organic
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Abstract
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Part 1. The AM1 molecular orbital method is used to predict the face selectivity for six different Diels-Alder reactions of dienes bearing stereogenic allylic substituents. The predictions are based upon fully optimized and fully characterized transition states for each possible conformation of the 12 different transition states. The AM1 RHF method with complete geometrical optimization, is found to be adequate for predicting the face selectivities of reactions studied. Agreement with the available experimental literature is quite satisfactory. No single effect seems to dominate the predicted selectivities. They appear to result from a combination of electronic and steric interactions.;Part 2. Aryl(bisarylthio)sulfonium salts are found to be exceptionally useful reagents for glycosyl transfer of glucal to a variety of hydroxyl transfer donors. These are {dollar}\beta{dollar} selective reagents giving 2-arylthio substituted 2-deoxy-{dollar}\beta{dollar}-glucopyranosides. The method works for both phenols and acyloins (models for aureolic acid synthesis) as well as the more common primary and secondary sugar alcohols. The substituents on the phenyl ring of the aryl(bisarylthio)sulfonium salts are varied. The face selectivity depends on the nature of the nucleophile and the thiosulfonium reagent. The p-methylphenyl{dollar}\{lcub}{dollar}bis(p-methylphenyl)thio{dollar}\{rcub}{dollar}sulfonium salt is the most {dollar}\beta{dollar}-selective reagent. The sulfonium salt glycosidation procedure is used for the synthesis of the 2-deoxy-1-O-{dollar}\{lcub}{dollar}3{dollar}\sp\prime{dollar}-(2{dollar}\sp\prime{dollar}-deoxy-1{dollar}\sp \prime{dollar}-O-methyl)-{dollar}\beta{dollar}-D-rhamnopyranosyl{dollar}\{rcub}{dollar}-{dollar} \beta{dollar}-D-rhamnopyranoside, the C{dollar}\sp\prime{dollar}-D{dollar}\sp\prime{dollar} ring analog of aureolic acid.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
