Multiple Kinetic Resolution of Tetrathia[7]helicenes. Towards the Study of Two Photon Circular Dichroism.

Doulcet, Julien (2014) Multiple Kinetic Resolution of Tetrathia[7]helicenes. Towards the Study of Two Photon Circular Dichroism. Doctoral thesis, University of East Anglia.

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Abstract

This doctoral thesis had as its aim the asymmetric synthesis of tetrathia[7]helicene
derivatives using a newly developed multiple kinetic resolution (multi-KR) approach. The
derivatives obtained (formyl- and diformylhelicene) should also be useful intermediates for
the synthesis of chiral push-pull systems.
The first part of the project was devoted to the synthesis of 7,8-dipropyltetrathia[7]helicene
reported by Licandro and Maiorana. A key intermediate in this synthesis is the benzo[1,2-
b:4,3-b']thiophene building block, previously obtained via a photochemical reaction, and
for which we developed an alternative chemical synthesis1.
The second part of the project focused on the kinetic resolution, designed to obtain formyland
diformylhelicene. Two strategies were identified to obtain the desired aldehydes: direct
asymmetric formylation using novel chiral formamide reagents and/or asymmetric
lithiation using (–)-sparteine followed by a DMF quench. The chiral auxiliaries were first
examined in single kinetic resolution experiments in order to identify the most suitable
conditions and auxiliaries. Asymmetric lithiation proceeded in up to 84% e.e. and the
asymmetric formylation using a chiral formamide gave at best 42% e.e. The most
successful examples were chosen to design several multi-KR approaches using a suitable
combination of matched and/or mismatched steps. These strategies have allowed us to
synthesise very highly enantioenriched helicene derivatives that can be recrystallized to
enantiopurity.
Finally, the synthesis of (electron donor)-(chiral-)-(electron acceptor) [D-(chiral-)-A]
and (electron acceptor)-(chiral-)-(electron acceptor) [A-(chiral-)-A] chiral push-pull
systems was examined. Racemic A-(chiral-)-A structures were readily obtained, and
although one racemic D-(chiral-)-A target was synthesised; the synthesis of this latter
class of compound has proved to be more challenging because of issues with the stability
of the synthetic intermediates. Both D-(chiral-)-A and A-(chiral-)-A structures are to be
examined in photophysics experiments by Pr. T. Verbiest at the University of Leuven.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Chemistry
Depositing User: Mia Reeves
Date Deposited: 09 Jul 2014 13:50
Last Modified: 09 Jul 2014 13:50
URI: https://ueaeprints.uea.ac.uk/id/eprint/49484
DOI:

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