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dc.contributor.advisorGregory C. Fu.en_US
dc.contributor.authorLiu, Shih-Yuan, 1975-en_US
dc.contributor.otherMassachusetts Institute of Technology. Dept. of Chemistry.en_US
dc.date.accessioned2006-03-24T18:16:11Z
dc.date.available2006-03-24T18:16:11Z
dc.date.copyright2003en_US
dc.date.issued2004en_US
dc.identifier.urihttp://hdl.handle.net/1721.1/30063
dc.descriptionThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, February 2004.en_US
dc.descriptionVita.en_US
dc.descriptionIncludes bibliographical references.en_US
dc.description.abstractBecause Lewis acids are very versatile mediators of a variety of stereoselective organic transformations, a great deal of effort has been devoted toward the development of chiral Lewis acids. This thesis describes the design, synthesis, and applications of 1,2-azaborolyl complexes as a novel family of planar-chiral Lewis acids that can perform a wide range of stereoselective transformations. The 1,2-azaborolyl ligand is a five-membered B-N bearing heterocycle that is isoelectronic and isostructural with the ubiquitous cyclopentadienyl ligand. In Part I of this dissertation, the feasibility of using boron-substituted 1,2-azaborolyls as tunable cyclopentadienyl surrogates is established. Thus, X-ray structural and spectroscopic studies demonstrate that 1,2-azaborolyls can serve as six-electron [pi]-ligands to a variety of transition metals and that the electronic nature of the boron substituent can modulate the properties of the resulting complexes. Building on the foundations of 1,2-azaborolyl ligand chemistry described in Part I, we establish in Part II that 1,2-azaborolyl complexes bearing good leaving groups on boron can serve indeed as planar-chiral Lewis acids. As a result, we have successfully synthesized a number of enantiomerically pure planar-chiral Lewis acids, and we show through structural and stereochemical correlation studies that these Lewis acids can activate substrates such as aldehydes and imines toward stereoselective nucleophilic attack in a predictable fashion. Specifically, we have investigated planar-chiral Lewis acid mediated nucleophilic attack of Grignard reagents to imines and Lewis acid mediated Mukaiyama aldol reaction of aldehydes with silyl ketene acetals.en_US
dc.description.abstract(cont.) Our studies indicate that unfavorable peri-interactions between the imine substrate and the Lewis acid may be the conformation-controlling element for nucleophilic additions to imines. On the other hand, detailed mechanistic studies of the Mukaiyama aldol reaction suggest a reaction pathway involving an intermediate with a coplanar aldehyde-Lewis acid conformation. These studies demonstrate the broad scope and the high efficiency with which the chiral information is transferred from the planar-chiral Lewis acid to its substrates. Consequently, the turnover step (regeneration of the active Lewis acid) represents the last hurdle to be addressed for achieving asymmetric Lewis acid catalysis. Part III of this thesis describes miscellaneous applications that have been discovered during the course of the development of 1,2-azaborolyl-based planar-chiral Lewis acids. In Chapter 7, we present a surprisingly mild and versatile method for palladium-catalyzed Suzuki cross-couplings of aryl chlorides in the presence of a triarylphosphine. With this catalytic system, both sterically demanding and electronically deactivated aryl chlorides can be efficiently coupled with a range of boronic acids in good yields, and coupling of activated aryl chlorides can be accomplished at room temperature. In Chapter 8, we report the synthesis and characterization of novel 1,2-azaborines and their potential as benzene surrogates.en_US
dc.description.statementofresponsibilityby Shih-Yuan Liu.en_US
dc.format.extent2 v. (245, A1-A83, 2, [B1]-B320 p.)en_US
dc.format.extent15447249 bytes
dc.format.extent15447046 bytes
dc.format.mimetypeapplication/pdf
dc.format.mimetypeapplication/pdf
dc.language.isoengen_US
dc.publisherMassachusetts Institute of Technologyen_US
dc.rightsM.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.en_US
dc.rights.urihttp://dspace.mit.edu/handle/1721.1/7582
dc.subjectChemistry.en_US
dc.titleApplications of novel boron-nitrogen containing heterocycles : design and synthesis o planar-chiral Lewis acids for stereoselective organic synthesisen_US
dc.typeThesisen_US
dc.description.degreePh.D.en_US
dc.contributor.departmentMassachusetts Institute of Technology. Dept. of Chemistry.en_US
dc.contributor.departmentMassachusetts Institute of Technology. Department of Chemistry
dc.identifier.oclc55628850en_US


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