Tribenzotriquinacenes based on regioselective bis-formylation: Optical resolution and absolute configuration of inherently chiral derivatives and synthesis of the first cyclophane-type tribenzotriquinacene dimers

摘要

Enantiomerically pure tribenzotriquinacenes (TBTQs) bearing two monofunctionalized aromatic nuclei were synthesized for the first time and their optical properties and absolute configuration determined. A remarkably regioselective bis-formylation of the fully bridgehead methylated parent TBTQ hydrocarbon with MeOCHCl_2/TiCl_4 afforded a mixture of two C_s-symmetrical (achiral) difunctionalized derivatives together with one C_1-symmetrical (chiral) isomer. Reduction and subsequent column chromatography furnished the three respective benzylic TBTQ dialcohols. Optical resolution of the racemic 2,6-bis(hydroxymethyl) derivative was achieved via the diastereomeric (R)-1,1′-bi-2-naphthol ethers and the absolute configuration of the enantiomers was determined by CD exciton model analysis. The electronic circular dichroism (ECD) spectra and the specific rotation of the enantiomers were found to agree with the results of DFT calculations. Among the C_s-symmetrical isomers, the "proximal" 2,11-dialdehyde and the corresponding benzylic dialcohol were identified by 2D NMR spectroscopy and X-ray crystallographic analysis, respectively, and used as the starting point for the synthesis of several novel dithiametacyclophanes. These include the first "dimeric" tribenzotriquinacene-based cyclophanes bearing the bowls of the two TBTQ units attached to each other in a syn (concave-concave) or anti (convex-concave) configuration. The usefulness of such thiacyclophanes as fluorescent chemosensors for different metal ions is also demonstrated. Get versatile! Based on a remarkably regioselective bis-formylation of tribenzotriquinacene 1, enantiomerically pure difunctionalized tribenzotriquinacene (TBTQ) derivatives, such as (-)-2 and (+)-2 were synthesized for the first time and their optical properties and absolute configuration were determined. The corresponding C_s-symmetrical isomers, led to several novel TBTQ-dithiacyclophanes, including the first "dimeric" TBTQ-based cyclophane.