Chemistry ETDs

Author

Aiguo Song

Publication Date

9-15-2014

Abstract

Facile construction of synthetically and medicinally significant optically active molecular architectures from simple and readily available materials via catalytic enantioselective cascade processes is the cental goal in organic synthesis. Toward this end, my Ph. D. work focuses on the development of novel organocatalytic asymmetric cascade reactions and their application in the synthesis of versatile molecular structures. A novel amine catalyzed decarboxylative enantioselective Diels—Alder reaction between aldehydes and readily available coumarin-3-carboxylic acids as dienophiles via dienamine catalysis has been realized. Notably, the decarboxylation facilitates the release of the catalyst in the Diels—Alder reaction adducts and achieves high reaction efficiency in terms of reaction time, yield and enantio- and diastereo-selectivity. Furthermore, the Diels—Alder adducts are smoothly transformed into optically active bridged tricyclic benzopyrans by a novel but unexpected 'one-pot' protocol of LiAlH4 or NaBH4 mediated reduction and subsequent acid (workup) catalyzed highly stereoselective cyclization. Moreover, the decarboxylative strategy is applied to the efficient 'one-pot' synthesis of aromatized xanthones by pyrrolidine catalyzed Diels—Alder reactions of enals and subsequent oxidation reaction using DDQ. In addition, we have designed and implemented an unprecedented amine-catalyzed [4+1] annulation reaction. The notable features of the process include a new conjugate addition-protonation-conjugate addition cascade sequence by employing readily available ynals and N-protected-2-aminophenols as reactants. The mild reaction protocol allows for a broad spectrum of ynals and 2-aminophenols to engage in the cascade sequence with high efficiency. Synthetically and biologically important benzoxazoles are created in one-pot operation. Finally, intermolecular enantioselective desymmetrization of p-quinols by urea catalyst mediated sulfa-Michael addition reactions has been developed to furnish the corresponding products in good yields and moderate to good enantioselectivities as single diastereomers.

Language

English

Keywords

Organocatalysis, Diels-Alder reaction, Decarboxylation, Bridged tricyclic benzopyran, Xanthone, Benzoxazole, [4+1] Annulation, Desymmetrization, Urea catalyst

Document Type

Dissertation

Degree Name

Chemistry

Level of Degree

Doctoral

Department Name

Department of Chemistry and Chemical Biology

First Advisor

Wang, Wei

First Committee Member (Chair)

Mariano, Patrick S.

Second Committee Member

Melancon, Charles

Third Committee Member

Feng, Changjian

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