Synthesis, Characterization, and Solid-State Structure of [8]Cycloparaphenylenes with Inherent Chirality

We report here the
synthesis of two [8]­cycloparaphenylenes ([8]­CPP)
derivatives, 1 and 2, bearing a monosubstituted
benzene moiety. The presence of the substituent implies a planar chirality
for the monosubstituted [8]­CPP 1 and 2,
whose configuration is here described by applying the chirality descriptors
pR and pS. Experimental evidence
of this planar chirality has been obtained through 1H VT
NMR studies and by addition of Pirkle’s reagent. This was confirmed
by the X-ray crystal structure of 2, which represents
an interesting example of solid-state structure of a monosubstituted
[8]­CPP derivative. Derivative 2 crystallizes in two monoclinic
crystal forms (α and β), which show a herringbone motif.
The [8]­CPP ring of the α form encapsulates two dichloromethane
molecules, held through C–H···π interactions,
while in the β form, open channels are partially filled by highly
disordered solvent molecules.