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Chemistry and properties of perhydrobenzo[4.5.6]cholestanes
The investigations undertaken include an intramolecular Michael-aldol approach and a cycloaddition approach to the synthesis ofperhydrobe,nzo[4.5.6]cholestanes. A reaction sequence has been developed to obtain the 3 P-acetoxy-4cx.,5cx. - dihydrobenzo [ 4.5 .6] cholestan-5' (6'H)-one 85 in an optimis...
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| Format: | Thesis |
| Language: | English |
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Department of Chemistry
2023
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| _version_ | 1867613217842266112 |
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| access_status_str | Open Access |
| author | Mohamed, Camielah |
| author2 | Bull, James R |
| author_browse | Bull, James R Mohamed, Camielah |
| author_facet | Bull, James R Mohamed, Camielah |
| author_sort | Mohamed, Camielah |
| collection | Thesis |
| description | The investigations undertaken include an intramolecular Michael-aldol approach and a cycloaddition approach to the synthesis ofperhydrobe,nzo[4.5.6]cholestanes. A reaction sequence has been developed to obtain the 3 P-acetoxy-4cx.,5cx. - dihydrobenzo [ 4.5 .6] cholestan-5' (6'H)-one 85 in an optimised yield from the 3Pacetoacetoxy-i:4-6-ketone 71. The key steps in the transformation involved base-treatment of the 3P-acetoacetoxy enoneto give (2R)-2-(3P-hydroxy-6-oxo-5P-cholestan-4p-yl)-3- oxobutanoic acid 1,3'-lactone 79, which was followed by_lactone cleavage, decarboxylation and intramolecular aldol closure of the derived lactone to give 3P,6-dihydroxy4cx.,4',5P,6P-tetrahydrobenzo[4.5.6]cholestan-5'(6'H)-one 81. Treatment of 3P-acetoxy-6- hydroxy-4cx.,4',5P,6P-tetrahydrobenzo [4.5.6] cholestan-5'(6'H)-one 82 with HMPA and phosphoryl chloride gave the 3p-acetoxy-4cx.,4', sp,6-tetrahydrobenzo [ 4.5.6] cholest-6-en5'(6'H)-one 83 and the 4cx.,5cx. -i:4 '-isomer 85. The formation of 3p-hydroxy-4cx.,5cx. - dihydrobenzo [4.5.6] cholestan-5'(6'H)-one 80 when treating the lactone 79 with potassium hydroxide indicated an alternative reaction pathway to the 4cx.,5cx. -isomer. However, conditions were not established for the isolation of the 4cx.,5cx. -i: 4 '-isomer 80 in an appreciable yield. Access to the 4cx.,5P-isomer was achieved by treating the 3P-acetoxy-6p-hydroxy derivative 82 with BF3.OEt2 which gave the 4cx.,5p-i:6 -isomer 83 and 3P-acetoxy-4cx.,4',5P, 6-dihydrobenzo [4.5.6] cholestan-5'(6'H)-one 86. Thionyl choride-pyridine treatment of the 3 P-acetoxy-6p-hydroxy derivative 82 gave an inconclusive result including the formation of the expected 4cx.,5(3-i:6 -isomer 83. The expected thermodynamic relationship between the 4cx.,5cx. -isomer 85 and the 4P,5cx. -isomer was confirmed by base equilibration of the 4cx.,5cx. -isomer into the 4p,5cx. -isomer. Detailed 400 MHz 1 H and 13C NMR data of key pentacyclic cholestanes enabled interpretations about their structural ~d conformational properties and related thermodynamic stabilities. 2 The Diels-Alder cycloaddition of 6-methylenecholest-4-en-3p-ol 96 with acrolein and methyl vinyl ketone gave 6' a-acetyl-4P,4' ,5' p,6' -tetrahydrobenzo[ 4.5 .6]cholestan-3 Pyl acetate 97 and 3P,6'-epoxymethano-4P,4' ,5' ,6'-tetrahydrobenzo[4.5.6]cholestan-6' 1 P-yl acetate 98 respectively. The structures of these cycloaddition products were determined with 400 MHz 1H and 13C NMR data which included NOE spectra. The 6' -H orientation in the cycloadduct 98 could however not be established unambiguously. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/38573 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:32:38.580Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2023 |
| publishDateRange | 2023 |
| publishDateSort | 2023 |
| publisher | Department of Chemistry |
| publisherStr | Department of Chemistry |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/38573 Chemistry and properties of perhydrobenzo[4.5.6]cholestanes Mohamed, Camielah Bull, James R Gammon, David Chemistry The investigations undertaken include an intramolecular Michael-aldol approach and a cycloaddition approach to the synthesis ofperhydrobe,nzo[4.5.6]cholestanes. A reaction sequence has been developed to obtain the 3 P-acetoxy-4cx.,5cx. - dihydrobenzo [ 4.5 .6] cholestan-5' (6'H)-one 85 in an optimised yield from the 3Pacetoacetoxy-i:4-6-ketone 71. The key steps in the transformation involved base-treatment of the 3P-acetoacetoxy enoneto give (2R)-2-(3P-hydroxy-6-oxo-5P-cholestan-4p-yl)-3- oxobutanoic acid 1,3'-lactone 79, which was followed by_lactone cleavage, decarboxylation and intramolecular aldol closure of the derived lactone to give 3P,6-dihydroxy4cx.,4',5P,6P-tetrahydrobenzo[4.5.6]cholestan-5'(6'H)-one 81. Treatment of 3P-acetoxy-6- hydroxy-4cx.,4',5P,6P-tetrahydrobenzo [4.5.6] cholestan-5'(6'H)-one 82 with HMPA and phosphoryl chloride gave the 3p-acetoxy-4cx.,4', sp,6-tetrahydrobenzo [ 4.5.6] cholest-6-en5'(6'H)-one 83 and the 4cx.,5cx. -i:4 '-isomer 85. The formation of 3p-hydroxy-4cx.,5cx. - dihydrobenzo [4.5.6] cholestan-5'(6'H)-one 80 when treating the lactone 79 with potassium hydroxide indicated an alternative reaction pathway to the 4cx.,5cx. -isomer. However, conditions were not established for the isolation of the 4cx.,5cx. -i: 4 '-isomer 80 in an appreciable yield. Access to the 4cx.,5P-isomer was achieved by treating the 3P-acetoxy-6p-hydroxy derivative 82 with BF3.OEt2 which gave the 4cx.,5p-i:6 -isomer 83 and 3P-acetoxy-4cx.,4',5P, 6-dihydrobenzo [4.5.6] cholestan-5'(6'H)-one 86. Thionyl choride-pyridine treatment of the 3 P-acetoxy-6p-hydroxy derivative 82 gave an inconclusive result including the formation of the expected 4cx.,5(3-i:6 -isomer 83. The expected thermodynamic relationship between the 4cx.,5cx. -isomer 85 and the 4P,5cx. -isomer was confirmed by base equilibration of the 4cx.,5cx. -isomer into the 4p,5cx. -isomer. Detailed 400 MHz 1 H and 13C NMR data of key pentacyclic cholestanes enabled interpretations about their structural ~d conformational properties and related thermodynamic stabilities. 2 The Diels-Alder cycloaddition of 6-methylenecholest-4-en-3p-ol 96 with acrolein and methyl vinyl ketone gave 6' a-acetyl-4P,4' ,5' p,6' -tetrahydrobenzo[ 4.5 .6]cholestan-3 Pyl acetate 97 and 3P,6'-epoxymethano-4P,4' ,5' ,6'-tetrahydrobenzo[4.5.6]cholestan-6' 1 P-yl acetate 98 respectively. The structures of these cycloaddition products were determined with 400 MHz 1H and 13C NMR data which included NOE spectra. The 6' -H orientation in the cycloadduct 98 could however not be established unambiguously. 2023-09-13T07:55:03Z 2023-09-13T07:55:03Z 1997 2023-09-13T07:28:03Z Master Thesis Masters MSc http://hdl.handle.net/11427/38573 eng application/pdf Department of Chemistry Faculty of Science |
| spellingShingle | Chemistry Mohamed, Camielah Chemistry and properties of perhydrobenzo[4.5.6]cholestanes |
| thesis_degree_str | Master's |
| title | Chemistry and properties of perhydrobenzo[4.5.6]cholestanes |
| title_full | Chemistry and properties of perhydrobenzo[4.5.6]cholestanes |
| title_fullStr | Chemistry and properties of perhydrobenzo[4.5.6]cholestanes |
| title_full_unstemmed | Chemistry and properties of perhydrobenzo[4.5.6]cholestanes |
| title_short | Chemistry and properties of perhydrobenzo[4.5.6]cholestanes |
| title_sort | chemistry and properties of perhydrobenzo 4 5 6 cholestanes |
| topic | Chemistry |
| url | http://hdl.handle.net/11427/38573 |
| work_keys_str_mv | AT mohamedcamielah chemistryandpropertiesofperhydrobenzo456cholestanes |