Regiocontrolled Synthesis and Optical Resolution of Mono‑, Di‑, and Trisubstituted Tribenzotriquinacene Derivatives: Key Building Blocks for Further Assembly into Molecular Squares and Cubes

The regiocontrolled
syntheses of four chiral C1- or C3-symmetrical tribenzotriquinacene
(TBTQ) derivatives bearing methoxy or hydroxy groups at the peripheral
positions [(2,6-(OMe)2, (±)-18 and (±)-20; 2,6-(OH)2, (±)-19; and 2,6,10-(OMe)3, (±)-21] by two different synthesis protocols
are reported. Compounds (±)-19, (±)-20, and (±)-21 and two (already-known) monosubstituted C1-symmetrical TBTQ analogues [2-OH (±)-23 and 2-OMe (±)-24] were readily resolved
by chiral HPLC, and their absolute configurations were determined
by X-ray crystallography and/or circular dichroism (CD) studies. Optical
resolution of three closely related TBTQ derivatives [2,6-(OMe)2, (±)-18; 2-OMe, (±)-22; and 2-OH, (±)-25] containing the same peripheral
substituents but other bridgehead residues failed. Enantiopure TBTQ
derivatives of this sort are considered promising structural motifs
toward the construction of molecular squares and cubes.