A Route to Enantiopure (<i>O</i>‑Methyl)₆‑2,6-Helic[6]arenes: Synthesis of Hexabromo-Substituted 2,6-Helic[6]arene Derivatives and Their Suzuki–Miyaura Coupling Reactions

A route to enantiopure (O-methyl)6-2,6-helic­[6]­arenes (+)-P-2 and (−)-M-2 has been provided. By the reaction of enantiopure triptycene precursors (+)-1 and (−)-1 in refluxed o-DCB for 12 h in the presence of catalytic amount of FeCl3, and then followed by treatment of the obtained oligomers under the same conditions, (+)-P-2 and (−)-M-2 could be obtained in 51% and 53% total yield, respectively. It was also found that racemic and enantiopure (O-methyl)6-2,6-helic­[6]­arenes could be easily brominated by Br2 to give the corresponding hexabromo-substituted helic[6]­arene derivatives rac-4, (+)-P-4, and (−)-M-4 in high yields. The crystal structure of (+)-P-4 further confirmed the absolute configuration of the helic[6]­arenes and their derivatives. Moreover, a series of hexaaryl-substituted helic[6]­arene derivatives 5a–f with deepened cavities could be conveniently synthesized in 55–71% yield by Suzuki–Miyaura coupling reactions of 4 and arylboronic acids. rac-5a could encapsulate chloroform and exhibit self-sorting stacking in solid state. Enantiopure (+)-P-5a–f and (−)-M-5a–f showed mirror images in their CD spectra.