New stereoselective approaches to highly substituted pyrrolidines.
Williams, Sian Margaret.
In studies towards the synthesis of substituted pyrroles, the Knight group have adapted an aldol reaction, originally developed by Kazmaier, as a highly diastereoselective method for the synthesis of the cyclisation precursors. Both acetylenic and a,b-unsaturated aldehydes have been successfully utilised in this reaction to afford a variety of b-hydioxy-a-amino ester precursors. This project centred around establishing the optimum conditions for the iodocyclisations of these precursors, and highly substituted pyrrolidines were obtained in the majority of cases. Also it was noted that these aldol adducts were structurally similar to Sphingosine, and via a series of selective reductions, a formal diastereoselective synthesis of Sphingosine was accomplished. In addition, silver-nitrate catalysed 5-endo-dig cyclisations were also applied towards the total synthesis of both Preussin and Codonopsinine. Finally, studies were conducted to establish the selectivity of 5-exo-trig cyclisations in the synthesis of iodo-lactones, and using this methodology, the piperidine core of Pseudodistomin was successfully synthesised.
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