We attribute this broad resonance to the O-H proton of a t-BuOH molecule which reversibly protonates the methine carbon of 1, resulting in the equilibrium depicted in Scheme 3. A closer inspection of the 1 H-NMR spectrum revealed a singlet at δ = 1.35 ppm, partially obfuscated by the dipp methyl resonances, which could potentially be attributed to the t-Bu protons of the exchanging t-BuOH. Extensive (freeze-)drying of the compound did not lead to a decrease of the amount of exchanging t-BuOH, suggesting that in the solid state the equilibrium lies to the side of the non-dearomatized ligand (Scheme 3, right). Interestingly, addition of an extra equiv of 18-c-6 did not result in the change of speciation, suggesting that one K + ion is tightly bound in the naphthyridine pocket as depicted in Scheme 3.