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

Abstract

A route to enantiopure (O-methyl)6-2,6-helic[6]arenes (+)-P-2 and (â?)-M-2 has been provided. By the reaction of enantiopure triptycene precursors (+)-1 and (â?)-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 (â?)-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 (â?)-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 (â?)-M-5a-f showed mirror images in their CD spectra.