Self-Assembly of Conformationally Rigid Dialcohols (Bis-Benzocyclobutenols): Supramolecular Cyclophanes and Arrays

Bis-benzocyclobutenols
are synthetically important intermediates,
and their structures have been established for the first time. These
unique molecular systems allow investigation of the hydrogen bond-mediated
aggregation of diols with rigid disposition of the hydroxyl groups
on both sides of a flat arene core, namely bis-benzocyclobutene. The syn-diols 1a and 2a were found
to assemble via O–H···O hydrogen bonds between
the hydroxyl groups into dimers, which may be termed “supramolecular
cyclophanes”. However, the analogous diols that are sterically
encumbered by ethyl and phenyl groups were found to aggregate via
adoption of tetrameric (syn-2c) or water-expanded
dimeric (syn-2b) supramolecular synthons.
The sterically unhindered anti diols were found to
self-assemble via helical supramolecular synthon in contrast to the
sterically encumbered ones; the latter were found to display preference
to undergo cyclic tetrameric aggregation. The results thus point to
intriguing possibilities in the adoption of supramolecular synthons
when a given diol is constrained by the obligation to exploit two
or more functional groups of the same kind.