Title : Application of catalytic hydrogenation in the synthesis of hydroxylated Pillar(5)arenebased Amphiphiles
A new approach was employed for the synthesis of Hydroxylated pillararene-based amphiphiles by a co-cyclization strategy followed by catalytic hydrogenation to remove the pillararene-bearing benzyl group(s). Conformational mobilities of the units and host–guest complexation with n-octyltrimethylammonium hexa?uorophosphate of the synthesized perbenzylated pillararenes were studied. Di?erent cavity sizes of amphiphilic pillararenes have been reported based on pillararenes, pillararenes, pillar arenes, and pillararenes. 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 pillararenes have been applied in bacterial cell agglutination and hydrophilic lysin head group amphiphilic pillararenes were self-assembled into bimolecular micelles in water and used to stabilize gold nanoparticles by reducing HAuCl4 with ascorbic acid. Many of these amphiphilic pillararenes were synthesized based on bromo or propargyl derivatives, however, recently we reported the synthesis of mono-, di- and penta-hydroxylated pillararenes 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 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 pillararenes. 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 pillararenes 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 pillararenes are underway in our laboratories.