Synthesis And Structure Analyssi Of Pillararenes

Calixarenes and their derivatives have attracted considerable attention over the past two decades. This can be attributed to their applications in areas as diverse as gas adsorption, nanotubes, catalysis, DNA recognition and fullerene chemistry. With the development of calixarene chemistry, many new calixarene analogues have been developed in supramolecular chemistry, such as calixpyrrole, thiacalixarenes, and homooxacalixarene.In contrast to the vast literature about the meta-bridged calixarene, their para-bridged analogues which are called pillar[n]arenes are very little known,. The first two members of this series were reported by Ogoshi in 2008. In the Lewis acid catalyzed condensation of 1,4-dimethoxybenzene and paraformaldehyde, they found a novel meta-bridged cyclic pentamer called DMpillar[5]arene. Ether cleavage with BBr3 afforded the pillar[5]arene with free hydroxy groups which exhibited very interesting host-guest properties. However, the yield of pillar[5]arene was low.In the acid-catalyzed reaction of benzyl ether, we found a facile and effcient preparation of pillararenes. In order to know the details of the reaction, we studied the influence of acids, solvent, reaction time, reaction temperature on the reaction. p-Toluenesulfonic acid in CH2Cl2 proved to be the best catalyst. Under the optimal condition, we chose some alkoxy-substituent reagents and side chain ether-substituent reagents as the materials to research the reaction. With a detailed study, some pillar[5]arenes, the first pillar[6]arene 26a, the first pillar[7]arene 27b and pillar[10]arene 210b were prepared. Their structures were characterized with NMR and MS, and partly confirmed by X-ray crystallography. From the X-ray crystallography, acetonitrile molecule was found in the cavity. When pillar[5]arenes was treated with (NH₄)₂Ce(NO₃)₆, the first electron-deficient pillar[5]quinone 95 was yielded.From the experimental results we found: (1) with increasing length of the alkoxy-substituent, the yield of pillar[5]arene derivatives decreased and the yield of pillar[6]arene derivatives increased, Reaction time needed longer, but the reagent utilization ratio was nearly 100%. (2) with increasing length and steric hindrance of the side chains, the yields of pillar[5]arenes decreased obviously, and pillar[6]arene derivatives increased; higher temperature (reflux) and longer reaction time were needed.. The reagent utilization ratio was also very high. In the synthesis of pillararenes, the highest yield was pentamer.An improved synthesis of pillararene was developed. When 1,4-dialkoxybenzene and paraformaldehyde reacted in CH2Cl2 with p-toluenesulfonic acid as the catalyst, the yield of pillararene was high.Eight nonsymmetric pillar[5]arenes 13⁵a, 13⁵b, 13⁵c, 13⁵d and 14⁵a, 14⁵b, 14⁵c, 14⁵d were got and their structures were characterized. From the X-ray crystallography of 13⁵b- 13⁵d, pillararenes inclusion effect of solvent molecules was also found. The total yield of all four nonsymmetric pillar[5]arenes was high. Short ethoxy-methoxy substituent asymmetric Pillar[5]arenes only have one structure showed benzene ring torsion occurred.The radical cation mechanism of pillararene formation was presented, which was compared with related literature. The host-guest properties between alkoxy-substituent pillararenes and butylamine hydrochloride, between pillar[5]quinone 95 and pyridine hydroquinone as well as p-phenylenediamine were preliminary studied.