Selective Preparation of Isomeric Tetrahydroxypillar[5]arenes and Pillar[3]arene[2]quinones

The isomeric tetrahydroxylated pillar[5]arenes were synthesized through partial oxidation of 1,4-dimethoxypillar[5]arene or 1,4-dimethoxypillar[4]arene[1] quinone by (NH4)(2)-[Ce(NO3)(6)] and then reduction by Na2S2O4. The intermediate 1,4-dimethoxypillar[3]arene[2]quinones have two constitutional isomers. The yield of the 1,3-isomer 1 can reach 42%, and was far higher than that of the 1,2-isomer 2 (formed in trace amounts). The approach provides an efficient way to prepare constitutional-isomeric selectively functionalized pillar[5]arenes 3 and 4. Furthermore, the host-guest complexation of 3 and 4 with a bis(imidazolium) salt was investigated.