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.