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Title: Studies towards the nucleophilic dearomatisation of electron-deficient heteroaromatics and hydrogen borrowing reactions of methanol
Author: Poole, Darren L.
ISNI:       0000 0004 5366 8434
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2014
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Introduction – Dearomatisation of Heteroaromatic Compounds The introduction provides a survey of dearomatisation reaction of heteroaromatics, with a particular focus on pyridines/pyridinium salts and furans. The mechanism, scope, and limitations of various approaches are covered, along with the goals of this project. Results and Discussion – Dearomatisation of Electron-Deficient Heteroaromatics This chapter initially explores the asymmetric addition of organometallic nucleophiles to pyridinium salts bearing a chiral counterion. Unfortunately, this approach ultimately proved unsuccessful, due to low observed enantioselectivities, and the low solubility of such salts. The second part of this chapter concerns the attempted asymmetric addition of dicarbonyl nucleophiles to electron-deficient furans, under conditions of chiral phase-transfer catalysts, affording bicyclic products in moderate enantioselectivity. Various alternative routes were also explored for the dearomatisation of furans and benzenoid systems. Introduction – Hydrogen Borrowing Alkylation Reactions with Alcohols The introduction surveys the range of methods available for the alkylation of various nucleophiles with alcohols under transition metal-catalysed conditions. Related methodologies are also explored, along with methods for the dehydrogenation of methanol. Results and Discussion - Rhodium-catalysed Methylation of Ketones Using Methanol This chapter describes the development of a novel ketone α-methylation using methanol. The development of reaction conditions is explored, followed by expansion of the substrate scope, including limitations of the methylation reaction. Mechanistic investigations support a methanol oxidation, aldol reaction/elimination, conjugate reduction pathway. Investigations into the role of O2 in the methylation reaction proved inconclusive. The utility of the reaction was also expanded via one-pot dialkylation reactions (work by Di Shen), Baeyer-Villiger oxidation of the products, and an attempted asymmetric transfer-hydrogenation. Results and Discussion - Interrupted Hydrogen Borrowing Reactions of Methanol This chapter looks to intercept intermediates from the α-methylation reaction. The selective methylenation of ketones is described, and a range of nucleophiles are screened for further functionalisation of ketones. Finally, a number of nucleophiles, including nitroalkanes, amines, peroxides and boronic acids are applied to one pot methylenation/conjugate addition protocols, affording complex products after two steps in one reaction vessel. Experimental Full experimental procedures and spectroscopic characterisation of compounds are provided.
Supervisor: Donohoe, Timothy J. Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Organic synthesis ; Organic chemistry ; Heterocyclic chemistry ; Catalysis ; Asymmetric catalysis ; chemistry ; chiral counterions ; phase-transfer catalysis ; transition metal chemistry ; transition metal catalysis ; hydrogen borrowing ; hydrogen autotransfer