Stereoselectivity studies of reactions between 2-(trimethylsilyloxy)-furan and acyclic N-acyl-N, O-Acetals /
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1992.
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| Subjects: | |
| Online Access: | Link to OAKTrust copy |
| Abstract: | A new, general method for the preparation of 5-aminoalkyl-furan-2(5H)-ones has been developed and the details of the reaction studied. 5-Aminoalkyl-furan-2(5H)-ones, which contain two chiral centers, were synthesized from 2-(trimethylsilyloxy)-furan and α-amidoalkylating reagents. The main emphasis of the study was to determine the controlling factors on diastereoselectivity and the possible mechanistic pathway which lead to the diastereomers. Results of the study show that the main controlling aspect of the newly developed reaction is the structure of the α-amidoalkylating reagent. α-Amidoalkylating reagents which contain bulky alkyl substituents, such as trichloromethyl and phenyl groups, display the largest diastereoselectivities, 80% and 70% de respectively. The threo isomer is preferred in these reactions. Alkyl substituents of lesser sterics, such as isobutyl and benzyl, produce diastereomers in approximately equal amounts (53:47). The isopropyl substituent favored formation of the erythro isomer in 35:65 ratio. The study revealed that diastereoselectivity of the reactions was independent of temperature, Lewis acid concentration, and Lewis acid type. Only one substrate showed exception to this finding. The diastereoselectivity of methyl substituted N,O-acetals protected as the Cbz carbamate varied with temperature. At the temperature of -78°C, the ratio of threo:erythro isomers was found to be 77:23. When the reaction was performed at -40°C, the ratio decreased to 58:42. High absolute stereochemical control was realized in one specific example. A chiral camphor auxiliary covalently attached to a trichloromethyl substituted N,O-acetal resulted in an enantiomerically enriched product (3:1:0:0). The product could be obtained in enantiomerically pure form upon one recrystallization. Other alkyl substituted chiral systems, however, were less successful. Cyclic acetal systems, limited in the number of possible conformations, were used as reaction pathway probes. By analysis of the stereochemistry of the products, the most plausible reaction pathway was determined to be a nucleophilic addition mechanism. This study disfavored a Diels-Alder reaction as a reaction pathway... |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Chemistry." |
| Physical Description: | xiii, 130 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |