Synthesis Of Bispillar[5]arenas

Calixarenes are macrocyclic compounds which are generally formed by condensation of aldehydes and substituted phenols. Because calixarenes have a calix-shape, hydrophobic cavity and several reactable positions, they have attracted considerable attentions. They are broadly used as building blocks to construct well preorganized host molecules which have widely potential applications in the field of molecular recognition, enzyme mimics, etc. Therefore they are considered as the third host molecule after crown ethers and cyclodextrins in supramolecular chemistry.Tradictional calixarenes were connected by methylene groups in meta position. T. Ogoshi first reported a new calixar[5]arene named 1,4-dimethoxypillar[5]arene, which was synthesized by a Lewis acid-catalyzed reaction using 1,4-dimethoxybenzene and formaldehyde in the presence of BF3·Et2O. The methylene groups were in para position. They also got pillar[5]arenes by demethylation of 1,4-dimethoxypillar[5]arenes. But the yeilds were poor. Our research group found a simple method for the synthesis of pillar[5]arene. 2,5-Bis(ethoxymethyl)-1,4-dialkoxybenzene was treated with catalytic amount of p-toluenesulfonic acid in boiling dichloromethane to give 1,4-dialkoxypillar[5]arenes in high yield. Recent research on pillar[5]arenes included molecular recognition, spectral properties, nonsymmetric pillar[5]arene, conformation analyses.In this article, we applied our synthetic method to synthesize bispillar[5]arene. 4-Methoxyphenol reacted with dihalo-compounds to form a dimer; then chloromethylation and methoxylation of the dimer gave the intermediate with four methoxymethyl groups. The intermediate was treated with catalytic amount of p-toluenesulfonic acid. However, bispillar[5]arene was not found. We have tried many mehtods, but failed.1,4-Alkoxylpillar[5]arenes reacted with NBS to give bis(4-bromo-2,5-dialkoxyphenyl)methane, undergoing ring opening reaction, ipso substituted reaction. Nitration of 1,4-methylpillar[5]arenes with nitric acid gave bis(4-nitro-2,5-dimethoxyphenyl)methane. This synthetic method for preparation of such a compound has some advantages, such as mild reaction conditions, simple operation, high selectivity and good yield.