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

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.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2014

Author dc:creator

• Doulcet, Julien

Language dc:language

en