Enantio- and Diastereoselective Synthesis and Spiral-Stair-Like Single Helix Assembly of Figure-Eight Cyclophenylenes

Abstract

Helix assemblies of chiral molecules can transfer microscopic unimolecular chirality to macroscopic supramolecular chirality, enhancing various chiral properties. In addition to the commonly observed spiral-column-like helix assembly, a small number of spiral-stair-like helix assemblies have also been reported in aromatic nanocarbons with multiple chirality-related irregularities. However, they require separation of diastereomers and/or enantiomers or do not have stable chirality. Here, we report the enantio- and diastereoselective synthesis of figure-eight [10]cyclophenylenes with stable helical chirality by the rhodium-catalyzed four consecutive intramolecular [2 + 2 + 2] cycloadditions of dodecaynes with two flexible biphenyl units. The chiral figure-eight [10]cyclophenylene with ethyl and methyl side chains exhibits the spiral-stair-like single helix assembly in the crystal due to CH–π and CH–O interactions and good CPL properties in solution. Experimental verification of the enantio- and diastereodetermining steps of four consecutive [2 + 2 + 2] cycloadditions is also reported.