Synthesis, Structures, and Photophysical Properties of Optically Stable 1,16-Diphenyl-3,14-diaryl-Substituted Tetrahydrobenzo[5]helicenediol Derivatives: Enantioselective Recognition toward Tryptophan Methyl Esters.

Starting from commercially available 7-methoxytetralone, 1,16-diphenyl-3,14-dibromotetrahydrobenzo[5]helicenediol (Br-H[5]HOL) was conveniently prepared, which underwent efficient resolution to give the optically stable enantiomeric diols in gram scale by HPLC with semipreparative chiral columns. The absolute configurations of the diols were determined by the circular dichroism (CD) spectra and X-ray crystal structure. By Suzuki-Miyaura cross-coupling reactions, a series of enantiopure π-extended 1,16-diphenyl-3,14-diaryltetrahydrobenzo[5]helicenediol derivatives (Ar-H[5]HOL) were further synthesized in high yields. The enantiomeric Ar-H[5]HOL exhibited almost identical absorption and emission spectra but showed mirror-image CD spectra and mirror-image circularly polarized luminescence properties. Moreover, it was also found that aryl substituents at the 3,14-positions could extend the chiral environment of the helical skeletons, which led to efficient enantioselective recognition of the enantiomers of tryptophan methyl esters.