Stereoselective Synthesis of Bioactive Compounds
(Track)
Helicoidal chiral molecules: Synthesis, chiroptical properties and applications
Béchir Ben Hassine
Laboratoire de Synthèse Organique Asymétrique et Catalyse Homogène, Faculté des Sciences de Monastir, avenue de l'Environnement, 5019 Monastir, Tunisia
Abstract:
Helicenes constitute a class of molecules characterized by aromaticity, chirality, capability of self-assembling in columnar solid state architectures and ability to behave as organic electrical conductors. These organic molecules present left- and right-handed chiral helical structures of M and P configuration, respectively1. Starting from the synthesis reported by Newman in 19552, a great deal of work was carried out both on carbohelicenes and on helicenes containing selected heteroatoms (aza- or thiahelicenes).
These rigid structures are particularly attractive owing to their potential as chiral ligands3, catalysts4 and auxiliaries5. When helicenes are substituted with various organic functional groups; the helical shape is maintained, but the physical properties change.. Another physical property salient in the family of molecules is their incredible ability to rotate plane-polarized light. The chirality of many helicenes is on the order of [a]D20~ 30006. The inherent chirality of helicenes is often the basis of many applications, such as photo-optical switches7, enantioselective fluorescence detectors8, molecular ratchets9 and nanoelectronic technology10.
Trying to ensure a continuation of our research program focusing on the synthesis and applications of compounds which owe their asymmetry to intramolecular overcrowding, we wish to report in this conference a synthetic sequence relying on Mozoroki-Heck couplings11 followed by classical photocyclodehydrogenation which have been applied to various functionalized penta-12, hexa-13 and heptahelicenes11,14.
Enantiomeric resolution of homodentate helical phenols I, II13a, prepared according to this alternative synthetic approach, has been performed either by chiral HPLC or by means of (S)-camphanic acid chloride. The same strategy has been suitably applied to the synthesis of an heptahelicene derivative bearing a diphenylphosphine function III. Resolution of the monodentate helical phosphine was achieved by means of the ortho-metalled (R)-1-(naphthyl)ethylamine-palladium complex14. The diphenylphosphine III was used as ligand with rhodium complex to catalyze the hydrogenation of dehydroaminoacids giving a chemical yield of 87%.
