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Title: Catalytic transformations via metallocarbenes
Author: Angrish, Deepshikha
ISNI:       0000 0001 3424 7464
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2007
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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 via metal-catalysed carbene transfer. Catalytic C-C bond formation reactions are highly significant; my studies focus on such transformations involving metallocarbenes. Grubbs' 2nd generation Ru catalyst is the most commonly used catalyst in olefin metathesis to generate thermodynamically preferred trans-olefms. During the course of my studies, I established that Grubbs 2nd generation catalyst (0.5 mol%) can also dimerise diazoacetates to give cis-enediesters (maleates) in good to excellent yields (74-99%) with high stereoselectivity (Z:E>95:5). The reaction between two different diazoacetates, catalysed by Grubbs catalyst gave access to unsymmetrical cis-enediesters with high stereoselectivity (Z:E>95:5, generally 99:1). 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 head-to-head dimerisation of unsaturated diazoacetates was developed. 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 Rh2(OAc)4 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.
Supervisor: Hodgson, David M. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Metathesis (Chemistry) ; Carbenes (Methylene compounds)