Preferential crystallization of a helicene-viologen hybrid - An efficient method to resolve [5]helquat enantiomers on a 20 g scale

Abstract

The bistriflate salt of racemic [5]helquat 1 was found to form a conglomerate. Based on this finding, the preferential crystallization of this chiral helicene-viologen hybrid was developed to deliver pure enantiomers on a 20 g scale (10.5 g of each enantiomer). To the best of our knowledge, this is the largest amount of nonracemic helicene-like compound obtained by preferential crystallization to date. The absolute configuration of the P enantiomer was confirmed by X-ray crystal structure analysis. The chromatography-free synthesis of racemic 1 on a multigram scale (30 g) is also presented as an entry point to this resolution study. The bistriflate salt of a racemic [5]helquat was found to form a conglomerate, and the preferential crystallization of this chiral helicene-viologen hybrid was developed to deliver pure enantiomers on a 20 g scale. The chromatography-free synthesis of racemic [5]helquat on a multigram scale (30 g) is also presented. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.