{"id":{"repo_id":"cape-town","oai_identifier":"oai:open.uct.ac.za:11427/22136"},"canonical_url":"https://search.dev.ndltd.org/etd/cape-town/oai:open.uct.ac.za:11427/22136","repository":{"repo_id":"cape-town","name":"University of Cape Town","base_url":"https://open.uct.ac.za/oai/request"},"display":{"title":"Stereoselective reactions of 16-Methylene 19-Norsteroids","abstract":"The influence of the 17-substituent upon epoxidation of 3-methoxy-16-methylene-estra- 1,3,5(10)-trien-17-one and the derived 17β-hydroxy and 17β-acetoxy compounds was investigated. Alkaline hydrogen peroxide epoxidation of 3-methoxy-16-methyleneestra- 1,3,5(10)-trien-17-one occurred in good yields, but poor stereoselectivity was obtained due to mechanistic considerations. Poor stereoselectivity was also obtained for the peracid epoxidation of 3-methoxy-16-methylene-estra-1,3,5(10)-trien-17β-ol, due to the pseudo-equatorial position of the 17β-hydroxyl group. However, excellent stereoselectivity was obtained using Sharpless conditions (vanadium catalyst), which gave only the epoxide syn to the hydroxyl group, in good yields. Surprisingly, peracid epoxidation of 3-methoxy-16-methylene-estra-1,3,5(10)-trien-17β-yl acetate favoured equatorial attack resulting in a 2:1 ratio of the (16R)- and (16S)-epoxide isomers, instead of the expected axial approach by the peracid.","abstract_html":"The influence of the 17-substituent upon epoxidation of 3-methoxy-16-methylene-estra- 1,3,5(10)-trien-17-one and the derived 17β-hydroxy and 17β-acetoxy compounds was investigated. Alkaline hydrogen peroxide epoxidation of 3-methoxy-16-methyleneestra- 1,3,5(10)-trien-17-one occurred in good yields, but poor stereoselectivity was obtained due to mechanistic considerations. Poor stereoselectivity was also obtained for the peracid epoxidation of 3-methoxy-16-methylene-estra-1,3,5(10)-trien-17β-ol, due to the pseudo-equatorial position of the 17β-hydroxyl group. However, excellent stereoselectivity was obtained using Sharpless conditions (vanadium catalyst), which gave only the epoxide syn to the hydroxyl group, in good yields. Surprisingly, peracid epoxidation of 3-methoxy-16-methylene-estra-1,3,5(10)-trien-17β-yl acetate favoured equatorial attack resulting in a 2:1 ratio of the (16R)- and (16S)-epoxide isomers, instead of the expected axial approach by the peracid.","abstract_has_math":false,"creators":["Kaiser, Delene Anne"],"institution":"Department of Chemistry","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Bull, James R"],"committee_chairs":[],"committee_members":[],"year":1991,"date_issued":"1991","date_published":"1991","updated_at":"2026-07-22T22:22:55Z","subjects":[],"languages":["eng"],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/11427/22136","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"]},{"key":"dc:creator","label":"Author","values":["Kaiser, Delene Anne"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2016-10-14T06:27:22Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2016-10-14T06:27:22Z"]},{"key":"dc:date.issued","label":"Date","values":["1991"]},{"key":"dc:publisher.department","label":"Dc Publisher Department","values":["Department of Chemistry"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cape Town"]},{"key":"dc:type","label":"Dc Type","values":["Master Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Masters"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["MSc"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["eng"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/11427/22136"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["The influence of the 17-substituent upon epoxidation of 3-methoxy-16-methylene-estra- 1,3,5(10)-trien-17-one and the derived 17β-hydroxy and 17β-acetoxy compounds was investigated. Alkaline hydrogen peroxide epoxidation of 3-methoxy-16-methyleneestra- 1,3,5(10)-trien-17-one occurred in good yields, but poor stereoselectivity was obtained due to mechanistic considerations. Poor stereoselectivity was also obtained for the peracid epoxidation of 3-methoxy-16-methylene-estra-1,3,5(10)-trien-17β-ol, due to the pseudo-equatorial position of the 17β-hydroxyl group. However, excellent stereoselectivity was obtained using Sharpless conditions (vanadium catalyst), which gave only the epoxide syn to the hydroxyl group, in good yields. Surprisingly, peracid epoxidation of 3-methoxy-16-methylene-estra-1,3,5(10)-trien-17β-yl acetate favoured equatorial attack resulting in a 2:1 ratio of the (16R)- and (16S)-epoxide isomers, instead of the expected axial approach by the peracid."]},{"key":"dc:title","label":"Title","values":["Stereoselective reactions of 16-Methylene 19-Norsteroids"]}]}],"canonical_facts":{"dc:contributor.advisor":["Bull, James R"],"dc:creator":["Kaiser, Delene Anne"],"dc:date.accessioned":["2016-10-14T06:27:22Z"],"dc:date.available":["2016-10-14T06:27:22Z"],"dc:date.issued":["1991"],"dc:description.abstract":["The influence of the 17-substituent upon epoxidation of 3-methoxy-16-methylene-estra- 1,3,5(10)-trien-17-one and the derived 17β-hydroxy and 17β-acetoxy compounds was investigated. Alkaline hydrogen peroxide epoxidation of 3-methoxy-16-methyleneestra- 1,3,5(10)-trien-17-one occurred in good yields, but poor stereoselectivity was obtained due to mechanistic considerations. Poor stereoselectivity was also obtained for the peracid epoxidation of 3-methoxy-16-methylene-estra-1,3,5(10)-trien-17β-ol, due to the pseudo-equatorial position of the 17β-hydroxyl group. However, excellent stereoselectivity was obtained using Sharpless conditions (vanadium catalyst), which gave only the epoxide syn to the hydroxyl group, in good yields. Surprisingly, peracid epoxidation of 3-methoxy-16-methylene-estra-1,3,5(10)-trien-17β-yl acetate favoured equatorial attack resulting in a 2:1 ratio of the (16R)- and (16S)-epoxide isomers, instead of the expected axial approach by the peracid."],"dc:identifier.uri":["http://hdl.handle.net/11427/22136"],"dc:language.iso":["eng"],"dc:publisher.department":["Department of Chemistry"],"dc:publisher.institution":["University of Cape Town"],"dc:title":["Stereoselective reactions of 16-Methylene 19-Norsteroids"],"dc:type":["Master Thesis"],"dc:type.qualificationlevel":["Masters"],"dc:type.qualificationname":["MSc"]},"updated_at":"2026-07-22T22:22:55Z"}