{"id":{"repo_id":"cape-town","oai_identifier":"oai:open.uct.ac.za:11427/38573"},"canonical_url":"https://search.dev.ndltd.org/etd/cape-town/oai:open.uct.ac.za:11427/38573","repository":{"repo_id":"cape-town","name":"University of Cape Town","base_url":"https://open.uct.ac.za/oai/request"},"display":{"title":"Chemistry and properties of perhydrobenzo[4.5.6]cholestanes","abstract":"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.","abstract_html":"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.","abstract_has_math":false,"creators":["Mohamed, Camielah"],"institution":"Department of Chemistry","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Bull, James R","Gammon, David"],"committee_chairs":[],"committee_members":[],"year":1997,"date_issued":"1997","date_published":"1997","updated_at":"2026-07-22T22:22:57Z","subjects":["Chemistry"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/11427/38573","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Bull, James R","Gammon, David"]},{"key":"dc:creator","label":"Author","values":["Mohamed, Camielah"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2023-09-13T07:55:03Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2023-09-13T07:55:03Z"]},{"key":"dc:date.issued","label":"Date","values":["1997"]},{"key":"dc:publisher.department","label":"Dc Publisher Department","values":["Department of Chemistry"]},{"key":"dc:type","label":"Dc Type","values":["Master Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Masters","MSc"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Chemistry"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/11427/38573"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["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."]},{"key":"dc:title","label":"Title","values":["Chemistry and properties of perhydrobenzo[4.5.6]cholestanes"]}]}],"canonical_facts":{"dc:contributor.advisor":["Bull, James R","Gammon, David"],"dc:creator":["Mohamed, Camielah"],"dc:date.accessioned":["2023-09-13T07:55:03Z"],"dc:date.available":["2023-09-13T07:55:03Z"],"dc:date.issued":["1997"],"dc:description.abstract":["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."],"dc:identifier.uri":["http://hdl.handle.net/11427/38573"],"dc:publisher.department":["Department of Chemistry"],"dc:subject":["Chemistry"],"dc:title":["Chemistry and properties of perhydrobenzo[4.5.6]cholestanes"],"dc:type":["Master Thesis"],"dc:type.qualificationlevel":["Masters","MSc"]},"updated_at":"2026-07-22T22:22:57Z"}