Catalytic transformations via metallocarbenes
<p>This thesis describes a new catalytic activity of a commonly used metathesis catalyst and demonstrates the viability of directly coupling two powerful C-C bond forming strategies: cross-metathesis and ylide transformations, both proceeding <em>via</em> metal-catalysed carbene t...
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| Format: | Thesis |
| Language: | English |
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2007
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| _version_ | 1797098966179905536 |
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| author | Angrish, D Angrish, Deepshikha |
| author2 | Hodgson, D |
| author_facet | Hodgson, D Angrish, D Angrish, Deepshikha |
| author_sort | Angrish, D |
| collection | OXFORD |
| description | <p>This thesis describes a new catalytic activity of a commonly used metathesis catalyst and demonstrates the viability of directly coupling two powerful C-C bond forming strategies: cross-metathesis and ylide transformations, both proceeding <em>via</em> metal-catalysed carbene transfer. Catalytic C-C bond formation reactions are highly significant; my studies focus on such transformations involving metallocarbenes. Grubbs' 2<sup>nd</sup> generation Ru catalyst is the most commonly used catalyst in olefin metathesis to generate thermodynamically preferred <em>trans</em>-olefms. During the course of my studies, I established that Grubbs 2<sup>nd</sup> generation catalyst (0.5 mol%) can also dimerise diazoacetates to give <em>cis</em>-enediesters (maleates) in good to excellent yields (74-99%) with high stereoselectivity (<em>Z</em>:<em>E</em>>95:5). The reaction between two different diazoacetates, catalysed by Grubbs catalyst gave access to unsymmetrical <em>cis</em>-enediesters with high stereoselectivity (<em>Z</em>:<em>E</em>>95:5, generally 99:1).</p> <p>The catalyst was found to retain its alkene metathetical activity during diazo coupling; building on this latter observation a novel route to access dienyl dilactones by <em>head</em>-to-<em>head</em> dimerisation of unsaturated diazoacetates was developed.</p> <p>Cross-metathesis was found to be chemoselective in the presence of diazo functionality (when flanked by two carbonyl groups), allowing the functionalisation of tethered olefin. The elaborated diazocarbonyl olefms were subjected to Rh<sub>2</sub>(OAc)<sub>4</sub> catalysed ylide formation and subsequent transformations. Significantly, one-pot cross-metathesis/ylide transformations (1,3-dipolar cycloaddition and [2,3]-simgatropic rearrangement) also proved to be viable, establishing that the spent Ru catalyst following metathesis does not affect the subsequent Rh(II)-catalysed transformation.</p> |
| first_indexed | 2024-03-07T05:17:04Z |
| format | Thesis |
| id | oxford-uuid:dd93e21b-7e8a-44dc-b2f5-49fc670e065c |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T05:17:04Z |
| publishDate | 2007 |
| record_format | dspace |
| spelling | oxford-uuid:dd93e21b-7e8a-44dc-b2f5-49fc670e065c2022-03-27T09:25:59ZCatalytic transformations via metallocarbenesThesishttp://purl.org/coar/resource_type/c_db06uuid:dd93e21b-7e8a-44dc-b2f5-49fc670e065cMetathesis (Chemistry)Carbenes (Methylene compounds)EnglishPolonsky Theses Digitisation Project2007Angrish, DAngrish, DeepshikhaHodgson, DHodgson, D<p>This thesis describes a new catalytic activity of a commonly used metathesis catalyst and demonstrates the viability of directly coupling two powerful C-C bond forming strategies: cross-metathesis and ylide transformations, both proceeding <em>via</em> metal-catalysed carbene transfer. Catalytic C-C bond formation reactions are highly significant; my studies focus on such transformations involving metallocarbenes. Grubbs' 2<sup>nd</sup> generation Ru catalyst is the most commonly used catalyst in olefin metathesis to generate thermodynamically preferred <em>trans</em>-olefms. During the course of my studies, I established that Grubbs 2<sup>nd</sup> generation catalyst (0.5 mol%) can also dimerise diazoacetates to give <em>cis</em>-enediesters (maleates) in good to excellent yields (74-99%) with high stereoselectivity (<em>Z</em>:<em>E</em>>95:5). The reaction between two different diazoacetates, catalysed by Grubbs catalyst gave access to unsymmetrical <em>cis</em>-enediesters with high stereoselectivity (<em>Z</em>:<em>E</em>>95:5, generally 99:1).</p> <p>The catalyst was found to retain its alkene metathetical activity during diazo coupling; building on this latter observation a novel route to access dienyl dilactones by <em>head</em>-to-<em>head</em> dimerisation of unsaturated diazoacetates was developed.</p> <p>Cross-metathesis was found to be chemoselective in the presence of diazo functionality (when flanked by two carbonyl groups), allowing the functionalisation of tethered olefin. The elaborated diazocarbonyl olefms were subjected to Rh<sub>2</sub>(OAc)<sub>4</sub> catalysed ylide formation and subsequent transformations. Significantly, one-pot cross-metathesis/ylide transformations (1,3-dipolar cycloaddition and [2,3]-simgatropic rearrangement) also proved to be viable, establishing that the spent Ru catalyst following metathesis does not affect the subsequent Rh(II)-catalysed transformation.</p> |
| spellingShingle | Metathesis (Chemistry) Carbenes (Methylene compounds) Angrish, D Angrish, Deepshikha Catalytic transformations via metallocarbenes |
| title | Catalytic transformations via metallocarbenes |
| title_full | Catalytic transformations via metallocarbenes |
| title_fullStr | Catalytic transformations via metallocarbenes |
| title_full_unstemmed | Catalytic transformations via metallocarbenes |
| title_short | Catalytic transformations via metallocarbenes |
| title_sort | catalytic transformations via metallocarbenes |
| topic | Metathesis (Chemistry) Carbenes (Methylene compounds) |
| work_keys_str_mv | AT angrishd catalytictransformationsviametallocarbenes AT angrishdeepshikha catalytictransformationsviametallocarbenes |