1. Enantiomerically Pure Tribenzotriquinacenes through Stereoselective Synthesis
Wilko Greschner, Beate Neumann, Hans-Georg Stammler, Harald Gröger, Dietmar Kuck Angew Chem Int Ed Engl. 2015 Nov 9;54(46):13764-8. doi: 10.1002/anie.201506906. Epub 2015 Sep 25.
Inherently chiral acetophenones and benzaldehydes bearing the large, bowl-shaped framework of tribenzotriquinacene (TBTQ) were synthesized in enantiomerically pure form employing enzyme catalysis. Five-step sequences involving lipase CAL-B lead to the (M)-enantiomers, (+)-2-acetyl-TBTQ (M)-5 and (+)-2-formyl-TBTQ (M)-6, whereas use of lipase PS leads to the (P)-enantiomers, (-)-2-acetyl-TBTQ (P)-5 and (-)-2-formyl-TBTQ (P)-6, with at least 99% ee in each case. The absolute configuration of these rigid 3D building blocks was determined by X-ray diffraction analysis of the ketones 5 and by comparison of their chiroptical properties with those of the aldehydes 6.
2. Stereoselective synthesis of enantiomerically pure bowl-shaped hydroxytribenzotriquinacenes
Philipp Rommelmann, Beate Nachtigall, Tim Guntelmann, Harald Gröger, Dietmar Kuck Org Biomol Chem. 2018 Aug 8;16(31):5635-5642. doi: 10.1039/c8ob01425f.
Enzyme-catalysed hydrolysis of the inherently chiral aryl acetate rac-11 bearing the bowl-shaped tribenzotriquinacene (TBTQ) core enables the stereoselective synthesis of the enantiomerically pure (M)-2-hydroxytribenzotriquinacene (M)-12. Starting from rac-11, for which two independent routes are described, the use of immobilised lipase CAL-A in buffered biphasic solution at pH 7 led to the TBTQ-phenol (M)-12 in 33% yield and with >99% ee on a preparative scale. Extended enzyme screening revealed that the use of CAL-B gives the same enantioselectivity. Furthermore, the chiroptical properties of the enantiomerically pure TBTQ-acetates (M)-11 and (P)-11, TBTQ-phenols (M)-12 and (P)-12 and the corresponding 2-hydroxy-3-iodotribenzotriquinacenes (M)-13 and (P)-13 are reported.
3. C3-symmetrical tribenzotriquinacene derivatives: optical resolution through cryptophane synthesis and supramolecular self-assembly into nanotubes
Tao Wang, Yu-Fei Zhang, Qin-Qing Hou, Wen-Rong Xu, Xiao-Ping Cao, Hak-Fun Chow, Dietmar Kuck J Org Chem. 2013 Feb 1;78(3):1062-9. doi: 10.1021/jo302470v. Epub 2013 Jan 23.
Based on a regioselective tris-formylation of a tribenzotriquinacene (TBTQ) hydrocarbon, the racemic C(3)-symmetrical TBTQ-trialdehyde and the corresponding TBTQ-trimethanol were synthesized along with their C(1)-isomers. Conversion of the C(3)-trialdehyde to three diastereomeric TBTQ-based cryptophanes occurring in high yield enabled the preparation of the optically pure C(3)-symmetrical TBTQ-trialdehydes and the determination of their absolute configuration. The racemic C(3)-symmetrical TBTQ-trimethanol was found to form several stable nanotubular aggregates in the solid state.
