Synthesis, NMR spectroscopy, and crystal structure of [9](N6,9)-6-aminopurinophane

[9](N6,9)-6-Aminopurinophane, 9, was synthesized by Mitsunobu coupling of 9-azidononanol, 5, and 6-chloropurine, 6. Reduction of the azide allowed for intramolecular nucleophilic displacement of chloride by the resultant amine and cyclization to the cyclophane. Variable temperature proton NMR showed the presence of two conformers below −25 °C separated by an activation barrier having a ΔG c ≠ = 50.2 ± 2.5 kJ mol −1 . The conformers arose from …