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Title: Synthesis of aziridines and the functionalisation of the intact ring
Author: Boultwood, Tom
ISNI:       0000 0004 6423 1385
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2015
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Aziridines continue to offer synthetic interest, whilst providing important intermediates in the preparation of a variety of biologically active targets. This thesis describes the preparation of novel functionalised aziridines that offer new complementary reactivity in aziridine functionalisation chemistry. The development of divergent stereospecific methodology to functionalise these aziridines will also be explored, keeping the ring intact during this process. The first preparation of an iodo-aziridine is detailed, achieved via the use of LiCHI2 and imines in a diastereoselective addition-cyclisation protocol. Both aromatic and alkyl iodoaziridines can be accessed in good yields, exclusively as their cis-diastereoisomers. These bench stable functionalised aziridines provide scaffolds for further derivatisation of the intact ring via formation of aziridinyl anions, aziridinyl radicals and aziridinyl metal species. Stereospecific lithiation of alkyl and aryl N-Ts iodoaziridines at low temperature generates an unstabilized aziridinyl lithium species which can be subsequently trapped with a range of carbon and heteroatom electrophiles allowing the exclusive formation of cis-substituted aziridines. Furthermore, aziridinyl radicals can be generated from the N-Ts iodoaziridine via single electron transfer in a radical substitution. The resulting aziridines are accessed predominately as their trans-diastereoisomer, with the reaction proceeding via a planar aziridinyl radical intermediate. The use of transition metal catalysis has also enabled the first cross-coupling of an iodoaziridine, with excellent diastereoselectivity observed in the coupling protocol. The stereochemical outcome at each stage of functionalisation will be fully discussed.
Supervisor: Bull, James Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral