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Title: Regio and stereocontrolled palladium-catalysed allylation of organozincs
Author: Slater, Mark
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2008
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Abstract:
Although allylic alkylation reactions under palladium catalysis have been extensively reported in the literature, the majority of publications have focused on the use of soft nucleophiles. We have investigated the use of hard nucleophiles in the allylic alkylation ' reaction. In particular, we wished to investigate if nucleophilic attack upon 1,3-nonsymmetrically disubstituted 1t-allyl palladium intermediates could be achieved with high levels of regioselectivity, a major challenge in allylic alkylation chemistry (Scheme 1). Excellent levels of regioselectivity in the nucleophilic attack of organ6zinc nucleophiles upon 1,3-disubstituted 1t-allyl intermediates has been observed, with the presence of aromatic functionality at one of the allylic termini found to be crucial in directing nucleophilic attack. The choice of ligand in the catalytic system has also been found to be important in determining the observed regioselectivity of the reaction. A range of substituted aromatic organozinc reagents bearing electron-donating and withdrawing groups have been successfully incorporated as the nucleophile. In addition, a range of substituted aromatic electrophiles have displayed excellent levels of regiocontrol. Excellent stereochemical fidelity in the reactions of enantioenriched substrates supports the proposed mechanism of internal delivery of the nucleophile via palladium. The excellent regioselectivity and stereochemical fidelity of the reaction has resulted in the development of a novel synthesis of 1,3-disubstituted allylsilanes, products which are of enormous utility in organic synthesis. In addition, a novel synthesis of secondary benzylic stereocentres which contain only carbon substituents, a motif found in many interesting natural products and pharmaceutical targets, has been achieved.
Supervisor: Not available Sponsor: Not available
Qualification Name: University of Leeds, 2008 Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.485638  DOI: Not available
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