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[3+3] Cyclocondensation of Disubstituted Biphenyl Dialdehydes: Access to Inherently Luminescent and Optically Active Hexa-substituted <i>C</i><sub>3</sub>‑Symmetric and Asymmetric Trianglimine Macrocycles
A general
synthetic route to inherently luminescent and optically
active 6-fold substituted C<sub>3</sub>-symmetric and asymmetric biphenyl-based
trianglimines has been developed. The synthesis of these hexa-substituted
triangular macrocycles takes advantage of a convenient method for
the synthesis of symmetrically and asymmetrically difunctionalized
biphenyl dialdehydes through a convergent two-step aromatic nucleophilic
substitution-one-pot Suzuki-coupling reaction protocol. A modular
[3+3] diamine-dialdehyde cyclocondensation reaction between both the
symmetrically and asymmetrically difunctionalized-4,4′-biphenyldialdehydes
with enantiomerically pure (1<i>R</i>,2<i>R</i>)-1,2-diaminocyclohexane was employed to construct the hexa-substituted
triangular macrocycles. B97-D/6-311GÂ(2d,p) density functional theory
determined structures and X-ray crystallographic analysis reveal that
the six substituents appended to the biphenyl legs of the trianglimine
macrocycles adopt an alternating conformation not unlike the 1,3,5-alternate
conformation observed for calix[6]Âarenes. Reduction of the imine bonds
using NaBH<sub>4</sub> afforded the corresponding 6-fold substituted
trianglamine without the need to alkylate the amine nitrogen atoms
which could hinder their later use as metal coordination sites and
without having to introduce asymmetric carbons