Title : Application of catalytic hydrogenation in the synthesis of hydroxylated Pillar(5)arenebased Amphiphiles
Abstract:
A new approach was employed for the synthesis of Hydroxylated pillar[5]arene-based amphiphiles by a co-cyclization strategy followed by catalytic hydrogenation to remove the pillar[5]arene-bearing benzyl group(s). Conformational mobilities of the units and host–guest complexation with n-octyltrimethylammonium hexa?uorophosphate of the synthesized perbenzylated pillar[5]arenes were studied. Di?erent cavity sizes of amphiphilic pillararenes have been reported based on pillar[5]arenes, pillar[6]arenes, pillar[7] arenes, and pillar[10]arenes. They are divided into three main categories, cationic, neutral, and anionic amphiphiles. Nonsymmetrical amphiphilic pillararenes with di?erent hydrophilic and hydrophobic groups were synthesized. For example, sugar-functionalized amphiphilic pillar[5]arenes have been applied in bacterial cell agglutination and hydrophilic lysin head group amphiphilic pillar[5]arenes were self-assembled into bimolecular micelles in water and used to stabilize gold nanoparticles by reducing HAuCl4 with ascorbic acid. Many of these amphiphilic pillar[5]arenes were synthesized based on bromo or propargyl derivatives, however, recently we reported the synthesis of mono-, di- and penta-hydroxylated pillar[5]arenes by introducing benzyl groups followed by selective removal via catalytic hydrogenation. This approach provides a platform to access pillararenes with countless structural variations.
We report the synthesis of perbenzylated-pillar [5]arenes through the condensation of hydroquinone derivatives of 1,4-dibenzyloxybenzene. Co-cyclization with 1,4-dibenzyloxybenzene and hydroquinone derivatives with mono- or di-octyl group(s) followed by selective removal using catalytic hydrogenation resulted in the formation of amphiphilic pillar[5]arenes. Host–guest complexation with n-octyltrimethyl ammonium hexafluorophosphate (OMA) was investigated by 1H nuclear magnetic resonance (NMR) titration and mass spectroscopy. The conformational mobilities of the units were studied by variable 1H NMR. The use of easily and selectively removable benzyl protecting groups enables a wide range of structural manipulations of the pillararene system. Amphiphilic hydroxylated-functionalized pillar[5]arenes reported in this study were synthesized by co-cyclization of hydroquinone derivatives followed by catalytic hydrogenation over palladium in charcoal using anhydrous ethyl acetate as a solvent. Further studies, modification, application and self-assemblies of these amphiphilic hydroxylated-functionalized pillar[5]arenes are underway in our laboratories.
