Synthesis of Tetrathia-[7]-helicenes as chiral pi systems for non linear optics

Helicenes are C2 symetric molecules which possess the particular feature of presenting a chiral conjugated pi system. The first report of helicenes was made by Cook in 1933[1], and the first helicene to be obtained in nonracemic form was hexahelicene in 1955[2]. Since then several types of helicenes have been synthesised, and studied for their chiroptical properties[3]. Amongst those, tetrathia-[7]-helicenes are candidates of choice to try to study the predicted but so far not observed Two Photon Circular Dichroism (TPCD).The long term objective of this project is the synthesis of enantiomerically pure tetrathia-[7]-helicenes in order to study two photon circular dichroism. • The first step is then to develop a route providing easy access to racemic helicene in reasonably large scale. Scheme 1:Racemic mixture of Tetrathia-[7]-Helicenes Objectives Synthesis • The racemic helicenes should undergo a double kinetic resolution providing enantiomerically pure helicene. •Introduction of electron donor group (D) at one end and electron acceptor group (A) at the other of the helicene providing a unique D-(chiral p)-A system used to observe TPCD.