Dearomatising Addition of Organolithiums to 2-Aryloxazolines: A Route to Amino-carbasugar Analogues

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Abstract

2-Aryl-4,5-anti-diphenyloxazolines undergo nucleophilic dearomatising addition to the 2-aryl group when treated with secondary organolithiums at -78 °C in the presence of the deaggregating co-solvent DMPU. Quenching the reaction with methyl iodide gives a highly substituted conjugated diene. Quenching the reaction with a proton source gives a substituted unconjugated 1,4-diene. The stereochemistry of the anti-diphenyl oxazoline controls the diastereoselectivity of the nucleophilic addition; only one diastereoisomeric product is observed. Importantly these conditions allow the dearomatisation of phenyl rings; this moiety has proven resistant to nucleophilic dearomatisation in all but the harshest conditions. This thesis presents the application of this dearomatising reaction. First the scope of this method was explored towards the dearomatisation of phenyl rings with fluorine substituents, as precursors for fluorinated carbasugar analogues. Secondly amino-carbasugar analogues were synthesised. The dearomatisation of a 4-methoxy phenyl ring was used to construct a dearomatised carbocyclic skeleton, which was functionalised through a series of reactions to give fully substituted cyclohexanoid amino-carbasugar analogues. These amino carbasugars were synthesised without the use of protecting groups, in order to do this a number of chemoselective conditions were studied and chemoselective reactions were developed.

Keyword(s)

Carbasugar; Dearomatisation; Organic Chemistry; Organolithium

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