Acyclic stereoselection in [alpha]-amidoalkylation reactions /
| Main Author: | |
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1989.
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| Subjects: | |
| Online Access: | Link to OAKTrust copy |
| Abstract: | The diastereoselectivity in reactions of chiral acyclic α-amidoalkylation reagents was investigated. The stereoselectivity for reaction of the α-hydroxyglycine derivative 65 with activated benzene rings and thiophene to give arylglycine derivatives was 72-79% ds. The reaction of 65 with 1-methoxynaphthalene was highly diastereoselective (% ds > 90%). The selectivity that was observed in reactions of α-hydroxyglycine derivative 66 was dependent upon the nucleophile. Thiophene and furan gave low selectivity (33% and 0% ds), while 1,4-dimethoxybenzene was fairly selective (74% ds), and anisole and thioanisole were highly selective (> 95% ds). The stereochemistry of the major diastereomer of the neopentyl auxiliary system was S. The stereochemistry of the major diastereomer of the sulfonamide auxiliary system was R. The stereochemistry was established by preparation of a sample from an amino acid of known configuration. The selectivity for reaction of 65 with allyltrimethylsilane was 3:1 (50% ds). The allylglycine derivative obtained from reaction of 66 with allyltrimethylsilane was a 1.6:1 mixture (23% ds) of diastereomers. The stereochemistry of the major product was not determined for the allylglycine derivatives 106 and 107. The selectivity of reactions of chiral acyclic α-amidoalkylation reagents with organometallic reagents was also investigated. The α-chloroglycine derivatives 67 and 68 were moderately diastereoselective in reactions with cuprate-BF3 complexes (38-50% ds). The use of other higher order cuprates or cuprate reagents without BF$ sb3$ resulted in lower selectivity. The stereochemistry of the major products for the neopentyl ether auxiliary was S in the reactions with cuprates, and the major products for the sulfonamide auxiliary had the R configuration. The diastereoselectivity of reaction of 67 and 68 with Grignard reagents was slightly higher than the selectivity observed with cuprate reagents (50-62% ds). The use of Grignard-BF3 complexes resulted in lower selectivity. The stereochemistry of the major products for the neopentyl ether auxiliary for reaction with Grignard reagents was S, and the stereochemistry of the major products for the sulfonamide auxiliary system was also S for reaction with Grignard reagents. The stereochemistry of the major products for the α-amidoalkylation of organometallic reagents were established by preparation of samples from amino acids of known configuration or single crystal X-ray analysis. The chiral auxiliary could be removed by a two step procedure involving a reduction/deprotonation sequence to give optically active oxazolidinones 126 and 128. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Chemistry." |
| Physical Description: | xi, 114 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |