University of Tasmania
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New methods for the synthesis of nitrogen containing, biologically relevant small molecules

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posted on 2023-05-27, 10:10 authored by Howard, JK
The following thesis consists of two independent parts, both linked by a common theme of developing new methods for the synthesis of small nitrogen containing molecules. The first part is titled the oxidative dearomatisation of pyrrole, while the second part is titled the strain driven rearrangement of cyclopropenyl trichloroacetimidates. The oxidation of pyrrole typically leads to uncontrolled polymerisation and decomposition, however it was postulated that under appropriate reaction conditions the controlled oxidation of pyrrole to 2-pyrrolinone would be possible. Thus, the controlled oxidation of electron rich pyrroles was achieved in good to excellent yields with the hypervalent iodine oxidant Dess‚Äöv†v¿Martin periodinane, and also its synthetic precursor 2-iodoxybenzoic acid (IBX). The sensitized photo-oxidation of pyrrole was also examined by utilizing the narrow spectrum light emission from LEDs. This led to an optimised method for the photo-oxidation of a range of pyrroles to produce 2-pyrrolinones in good to high yields; a result that was only possible due to limiting the absorbance of light by pyrrole and selectively exciting the dye sensitizer for the oxidation. The products from the methods of controlled pyrrole oxidation have been used in an initial study towards the total synthesis of pyrrolidine alkaloid natural products including preussin, codonopsinine and crispine A. Nitrogen-substituted benzylidene cyclopropanes were prepared by a strain-driven Overman rearrangement of cyclopropenyl trichloroacetimidates in good to excellent yields. This methodology demonstrates the first rearrangement of a cyclopropene to an alkylidenecyclopropane with a nitrogen atom participant. The product benzylidene cyclopropanes were used as precursors to biologically relevant cyclopropyl ureas and saturated cyclopropanes.


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