Browsing by Author "Msutu, Ath'enkosi"

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    New CO₂ chemistry for fine chemical synthesis
    (2011) Msutu, Ath'enkosi; Hunter, Roger
    There is a great need in the chemical industry for developing CO2 as a C1 building block as an important step towards "green chemistry". CO2 is also attractive as a chemical feedstock because it is readily available, inexpensive, nontoxic and it can replace toxic building blocks such as phosgene and CO. Industrially, megatons of CO2 are used each year for the production of urea, inorganic carbonates, salicylic acid, and polycarbonates, yet this is still miniscule compared to the immense potential that is still yet to be harnessed in using this versatile building block. This thesis discusses how a novel methodology was developed for synthesising a benzotriazole (Bt) urea directly from CO2 in a two-step, one-pot synthesis. The procedure involves trapping CO2 with a primary or secondary amine in the presence of DBU, and reaction of the resultant carbamate salt with triphenylphosphine and chlorobenzotriazole (BtCl) to produce Bt ureas in moderate to high yields. The Bt group may serve as a leaving group in nucleophilic substitution reactions, therefore it is also shown here how the Bt urea presents itself as a precursor for an array of useful organic intermediates. These intermediates include ureas, amides, S-thiocarbamates and sulfonylureas.
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    New methodology for the organocatalysed α-Amination reaction
    (2015) Msutu, Ath'enkosi; Hunter, Roger
    Research into organocatalyzed asymmetric reactions has been a rapidly growing and competitive field in recent times, wherein amino catalysis is widely used for the asymmetric functionalisation of carbonyl compounds. Since its simultaneous publication by List and Jørgensen, the organocatalysed α-amination reaction has become a key method for asymmetric heteroatom functionalisation of carbonyl compounds. Herein we report the first application of this methodology to acetals, with the ultimate goal of applying the methodology to the asymmetric desymmetrisation of bis-acetals as a novel contribution to this growing field. Following extensive optimisation, acidic reaction conditions for the reaction were established in which dibenzyl azodicarboxylate (DBAD) was used as the aminating agent and (S)-(-)-5-(2-pyrrolidinyl)-1H-tetrazole as the preferred organocatalyst. The desired aminated products were obtained in high yields and enantioselectivities. The reaction showed broad substrates cope in its application to ketals, dioxolanes and lactols. A hydrazide N-N bond cleavage methodology was also developed for the aminated products in oxazolidinone form. This methodology is based on Magnus' alkylation / E1CB strategy. The novel contribution here is using ditheyl bromoacetate as an alkylating agent and as a better elimination partner. A range of bis-acetals were synthesised via three synthetic routes using malonate-, sulfone and cyclopentene-based synthesis strategies. The acetal reaction was used for the desymmetrisation of two of these bisacetals as a proof of concept. This is a feat not achieved with the more reactive dicarbonyl analogue.