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dc.contributor.authorPatwardhan, Neeraj Narendraen_US
dc.date.accessioned2014-03-14T21:11:05Z
dc.date.available2014-03-14T21:11:05Z
dc.date.issued2012-05-02en_US
dc.identifier.otheretd-05152012-225340en_US
dc.identifier.urihttp://hdl.handle.net/10919/37814
dc.description.abstractThe development of chiral organometallics for asymmetric synthesis is a topic of significant research in the recent past. The most studied in this class are the chiral organolithium reagents with many reported examples. The primary focus of our research is the development of Cα-chiral Grignard reagents, where the metal bearing α-carbon is the sole source of chirality. Examples of such Grignard reagents are rare owing to the problems associated with their synthesis, and their low configurational stability. We have studied these problems in three different modules of this project. Reactions of 1-magnesio-2,2-diphenyl-cyclopropylcarbonitrile with carbon electrophiles are first attempted in order to expand the utility of this configurationally stable Cα-chiral Grignard reagent in asymmetric synthesis. This reagent has been shown to be non-reactive towards carbon electrophiles at low temperatures. Consequently, we attempt to enhance the reactivity of this compound through two different approaches, Lewis-base activation and the â ate-complexâ generation. The Magnesium/Halogen (Mg/X) exchange reactions have been shown to be extremely useful in the synthesis of complex Aryl, alkenyl (sp2) and alkynyl (sp) Grignard reagents. Examples of Mg/X exchange reactions of Alkyl (sp3) halides are, however, rare. Even more rare are such examples with secondary and tertiary alkyl halides, justifying the relative paucity of chiral Grignard reagents. In this module of our project, we study the Mg/X exchange reactions on secondary alkyl halides possessing a γ-hydroxyl group, as an internal activator for such Mg/X exchange reactions. Enantiomerization pathways of chiral organolithium compounds have been widely studied. However, few such studies have been performed on chiral Grignard reagents. In this module of the project, we studied the solvent assisted enantiomerization mechanism of the Cα-chiral 1-magnesio-2,2-diphenyl-cyclopropylcarbonitrile. Rate constant for the enantiomerization of this compound was measured in three different ethereal solvents to study the effect of solvent on the configurational stability. Finally, the order of the enantiomerization process with respect to [Et2O] was studied in order to predict the mechanism of this process in Et2O solvent. Our kinetic studies on the enantiomerization process provided us with a definitive picture for the enantiomerization of the Cα-chiral 1-magnesio-2,2-diphenyl-cyclopropylcarbonitrile, where solvation of the Grignard reagent preceded an ion-pair separation step which eventually lead to enantiomerization of the Grignard species. However, the precise structure of all the involved solvated intermediates could not be determined as kinetics was not able to distinguish between these intermediates. We next performed computational calculations to study the effect of solvation on the analogous 1-magnesio-cyclopropylcarbonitrile in order to address the unanswered questions from our kinetic studies.en_US
dc.publisherVirginia Techen_US
dc.relation.haspartPatwardhan_NN_D_2012.pdfen_US
dc.rightsI hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Virginia Tech or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report.en_US
dc.subjectKeywords: enantiomerizationen_US
dc.subjectkineticsen_US
dc.subjectchiral Grignard reagentsen_US
dc.subjectsolvent effectsen_US
dc.subjectreaction orderen_US
dc.subjection-pair separationen_US
dc.subjectentropy of activationen_US
dc.subjectelectrostrictionen_US
dc.subjectDFT calculationsen_US
dc.titleStudy of synthesis, reactions and enantiomerization of Cα- chiral Grignard reagentsen_US
dc.typeDissertationen_US
dc.contributor.departmentChemistryen_US
thesis.degree.namePhDen_US
thesis.degree.leveldoctoralen_US
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen_US
dc.contributor.committeechairCarlier, Paul R.en_US
dc.contributor.committeememberSantos, Webster L.en_US
dc.contributor.committeememberTanko, James M.en_US
dc.contributor.committeememberKingston, David G. I.en_US
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-05152012-225340/en_US
dc.date.sdate2012-05-15en_US
dc.date.rdate2012-06-06
dc.date.adate2012-06-06en_US


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