Search for Conglomerate in Set of [7]Helquat Salts: Multigram Resolution of Helicene–Viologen Hybrid by Preferential Crystallization

Investigation of a set of 12 [7]­helquat salts by X-ray crystal diffraction led to identification of conglomerate behavior in bis­(trifluoroacetate) salt [2]­[CF3CO2]2. This is to demonstrate that a systematic search for conglomerates can be performed for a given helicenoid enabling straightforward multigram resolution via preferential crystallization. Subsequently, preferential crystallization of this chiral helicene–viologen hybrid has been established to obtain pure P and M enantiomers on a multigram scale, 5 g each. Furthermore, preparation of nonracemic samples of [7]­helquat 2 via diastereomeric (R,R)-dibenzoyltartrate salts is described, and determination of absolute configuration and racemization barrier is also reported.