Chemistry and properties of perhydrobenzo[4.5.6]cholestanes

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dc.contributor.advisorBull, James R
dc.contributor.advisorGammon, David
dc.contributor.authorMohamed, Camielah
dc.date.accessioned2023-09-13T07:55:03Z
dc.date.available2023-09-13T07:55:03Z
dc.date.issued1997
dc.date.updated2023-09-13T07:28:03Z
dc.description.abstractThe 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.apacitationMohamed, C. (1997). <i>Chemistry and properties of perhydrobenzo[4.5.6]cholestanes</i>. (). ,Faculty of Science ,Department of Chemistry. Retrieved from http://hdl.handle.net/11427/38573en_ZA
dc.identifier.chicagocitationMohamed, Camielah. <i>"Chemistry and properties of perhydrobenzo[4.5.6]cholestanes."</i> ., ,Faculty of Science ,Department of Chemistry, 1997. http://hdl.handle.net/11427/38573en_ZA
dc.identifier.citationMohamed, C. 1997. Chemistry and properties of perhydrobenzo[4.5.6]cholestanes. . ,Faculty of Science ,Department of Chemistry. http://hdl.handle.net/11427/38573en_ZA
dc.identifier.ris TY - Master Thesis AU - Mohamed, Camielah AB - 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. DA - 1997 DB - OpenUCT DP - University of Cape Town KW - Chemistry LK - https://open.uct.ac.za PY - 1997 T1 - Chemistry and properties of perhydrobenzo[4.5.6]cholestanes TI - Chemistry and properties of perhydrobenzo[4.5.6]cholestanes UR - http://hdl.handle.net/11427/38573 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/38573
dc.identifier.vancouvercitationMohamed C. Chemistry and properties of perhydrobenzo[4.5.6]cholestanes. []. ,Faculty of Science ,Department of Chemistry, 1997 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/38573en_ZA
dc.language.rfc3066eng
dc.publisher.departmentDepartment of Chemistry
dc.publisher.facultyFaculty of Science
dc.subjectChemistry
dc.titleChemistry and properties of perhydrobenzo[4.5.6]cholestanes
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationlevelMSc
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