Combining Stereoselective Enzyme Catalysis with Chirality-Assisted Synthesis in Tribenzotriquinacene Chemistry

A Triptycene-Based Enantiopure Bis(Diazadibenzoanthracene) by a Chirality-Assisted Synthesis Approach

By applying a chirality-assisted synthesis (CAS) approach enantiopure diaminodibromotriptycenes were converted to rigid chiral helical diazadibenzoanthracenes, which show besides pronounced Cotton effects in circular dichroism spectra higher photoluminescence quantum yields as comparable carbacyclic analogues. For the enantiopure building blocks, a protocol was developed allowing the large scale synthesis without the necessity of separation via HPLC.

Chiral Derivatives of 2-Aminotribenzotriquinacene: Synthesis and Optical Resolution

Starting from a hitherto unknown 2-aminotribenzotriquinacene, several 2-amino-3-X-substituted TBTQ derivatives, all bearing a single ortho-difunctionalized indane wing, were synthesized as rigid and chiral building blocks for the potential construction of complex supramolecular architectures. Efficient access to two pairs of enantiomeric TBTQ derivatives, namely, the peripheral ortho-nitroaniline (X = NO₂) and the related anthranilic acid (X = CO₂H), was developed using chiral auxiliaries as the resolving reagents. The structure of the intermediate diastereomers was confirmed by ¹H and ¹³C NMR spectroscopy, high-resolution mass spectroscopy (HRMS), and polarimetry. The absolute configuration of the optically active derivatives was confirmed by quantum chemical time-dependent density functional theory (TD-DFT) calculations of the theoretical electronic circular dichroism (ECD) spectra and by single-crystal X-ray structure analysis of a synthesis intermediate.

Solvent-Controlled Racemic Resolution of C3-Symmetric Trihydroxytribenzotriquinacenes

A racemic C₃-symmetric trihydroxytribenzotriquinacene was resolved on a large scale by fractional crystallization of the corresponding (1S)-camphanic esters, achieving both enantiopure enantiomers (>99% ee) in 35% and 32% yields. The method relies on a distinct solvent-controlled discrimination process between the diastereomers. The enantiopure trihydroxytribenzotriquinacenes were converted into four other enantiopure building blocks, which are valuable precursors for supramolecular and materials chemistry to illustrate the utility of the synthesized compounds.

Stereoselective synthesis of enantiomerically pure bowl-shaped hydroxytribenzotriquinacenes

A bowl-shaped (M)-2-hydroxytribenzotriquinacene was obtained in enantiomerically pure form by stereoselective enzyme-catalysed ester hydrolysis of the racemic TBTQ-based aryl acetate.