Design, Preparation and Chirality Aspects of New Mono-functionalized Helicenes

M. VAN DER MEIJDEN; E. GELENS; T. BALANDINA; SHENGBIN LEI; S. DE FEYTER; M. LINGENFELDER; H. ASCOLANI; R. KELLOG

Liverpool

Simposio; 23rd INTERNATIONAL SYMPOSIUM ON CHIRAL DISCRIMINATION (ISCD 23); 2011

University of Liverpool Liverpool

In our ongoing investigation in the field of racemizable conglomerates1, we turned our focus to the synthesis and characterization of mono-functionalized helicenes. To the best of ourknowledge all helicenes described thus far in the literature2,3 crystallize as conglomerates. We desired a helicene that contained a functional group that could be readily manipulated. Using a much improved and shorter synthetic route (not shown) we were able to prepare 5-aminohexahelicene 1 and investigate its chiral properties. Compound 1 was prepared in 5% overall yield in 12 steps. The pure enantiomers were obtained enantiomerically pure by preparative chiral HPLC. This helicene underwent complete thermally induced racemisationwithin 2-3 h at ~210°C. We hoped we could combine conglomerate crystallization with thermal racemization to deploy attrition enhanced deracemization1. However, SecondHarmonic Generation (SHG) analysis revealed to our surprise that 1 is a racemic compound rather than a conglomerate. STM-experiments show that compound 1 can be trapped in a cage on a graphite surface. Investigation is ongoing to see whether the enantiomers bindselectively. Absorbtion on copper surface is under investigation.The position of the functional group clearly influences the crystallization behaviour. To assess the influence the position of substitution (as well as nature of substituent) on the helicene system has, acid 2 is currently under preparation. The synthesis is in an advancedstage.