Nazarov reaction : development of an organocatalytic asymmetric cyclopentannelation

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2010-12
Authors
Bow, William Frank
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[Honolulu] : [University of Hawaii at Manoa], [December 2010]
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Abstract
Five-membered carbocycles appear as subunits in many natural products of biological importance. The design and development of new chemical transformations to form five-membered rings is an important area of organic chemistry. The Nazarov reaction allows for the making of five-membered rings and is capable of installing multiple stereogenic centers through a single operation. This thesis describes some recent progress for this reaction. In Chapter 1, the Nazarov reaction is introduced. The mechanism of the traditional Nazarov cyclization will be described followed by a discussion of some of the recent advances in catalytic, asymmetric, and catalytic asymmetric cyclopentannelations. Some examples of Nazarov cyclizations used in the total syntheses of natural products are presented to illustrate the versatility and usefulness of this reaction. In Chapter 2, we discuss our progress towards an organocatalytic asymmetric Nazarov cyclization. Chiral nonracemic 1,2-diamines are investigated for reactivity with α-ketoenones to form products of the Nazarov cyclization. Although the process is not catalytic, a highly cooperative mechanism involving covalently bound intermediates is discovered. An asymmetric enamine-iminium ion mediated Nazarov cyclization is described. In the final chapter (Chapter 3), we demonstrate an organocatalytic asymmetric Nazarov cyclization. We hypothesize that a weaker, noncovalent catalyst along with a more reactive substrate could lead to a catalytic reaction. Bifunctional thiourea catalysts are shown to cyclize diketoester substrates with good to excellent enantioselectivities with nearly perfect diastereoselectivity. Enantioenriched cyclopentenones are formed with two new adjacent stereogenic centers, one of which is a quaternary center.
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M.S. University of Hawaii at Manoa 2010.
Includes bibliographical references.
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Nazarov cyclization
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Theses for the degree of Master of Science (University of Hawaii at Manoa). Chemistry.
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