Templated Synthesis of Glycoluril Oligomers and Monofunctionalized Cucurbituril Derivatives
Isaacs, Lyle D
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The molecular recognition properties exhibited by molecular containers have inspired supramolecular chemists to generate diverse and specialized macrocycles. The family of hosts known as cucurbiturils (CB[n]) have become a popular platform for molecular recognition due to their high binding affinities and selectivity in water. As CB[n] branch into increasingly complex applications it becomes important to find efficient pathways to prepare monofunctionalized CB[n] derivatives bearing reactive functional groups. Chapter 1 presents a literature review of the synthesis, properties, mechanism of formation, and applications of the CB[n] family. We use this background information to explain our key hypothesis, that templated reactions offer potential routes to obtain glycoluril oligomer building blocks that allow the preparation of monofunctionalized CB[n] compounds. Chapter 2 describes the templated synthesis of glycoluril hexamer (<bold>6C</bold>) in a one step synthetic procedure on the gram scale using the <italic>p</italic>-xylylenediammonium ion (<bold>II-11</bold>). Hexamer <bold>6C</bold> undergos cyclization with (substituted) phthalaldehdyes <bold>II-12</bold>, <bold>II-14</bold>, <bold>II-15</bold>, <bold>II-18</bold> under acidic conditions at room temperature to deliver monofunctionalized CB derivatives <bold>II-13</bold>, <bold>II-15</bold>, <bold>II-16</bold>, and <bold>II-19</bold>. Furthermore, the reaction kinetics for CB cyclization between hexamer and formaldehyde or phthalaldehyde is influenced by the size and shape of ammonium ion templates. The larger size of the <italic>p</italic>- xylylenediammonium ion (<bold>II-11</bold>) allows it to act as a negative template by discouraging transformation of hexamer and paraformaldehyde to form CB. However, <bold>II-11</bold> and hexanediammonium ion (<bold>II-20</bold>) act as positive templates during the reaction of <bold>6C</bold> and phthalaldehyde <bold>II-12</bold> by giving (±)-<bold>II-21</bold> as an intermediate along the mechanistic pathway to CB derivative <bold>II-13</bold>. Finally, a fluorescence turn-on assay was investigated using the fluorophore and metal-ion binding (e.g., Eu3+) of naphthalene- CB derivative <bold>II-19</bold>. The synthesis of monofunctionalized CB derivatives in high yields has broad implications toward tailor-made approaches to CB[n] derived functional systems in the future. Chapter 3 describes the high yield synthesis of glycoluril pentamer (<bold>5C</bold>) by the 3,5- dimethylphenol induced fragmentation of bis-ns-CB under acid conditions. The access to large quantities of 5C and 6C and previously reported tetramer <bold>III-4</bold> allowed for a comparison of host-guest recognition properties of acyclic CB[n]-type receptors toward alkaneammonium ions in water.