Hydrogen Bonding-Induced Aromatic Oligoamide Foldamers as Spherand Analogues to Accelerate the Hydrolysis of Nitro-Substituted Anisole in Aqueous Media

Four intramolecular hydrogen bonding-driven aromatic amide foldamers 2−5 have been designed and
synthesized in which a 2-methoxy-3-nitrobenzamide unit was incorporated at the end of the backbone.
Kinetic studies in dioxane−water (4:1, v/v) at 60−90 °C have revealed that the folded backbone of the
oligomers was, like the rigidified spherand, able to complex Li+, Na+, and K+ and, consequently,
accelerated the hydrolysis of the nitro-appended anisole unit of the foldamers. Generally, longer foldamers
displayed an increased accelerating effect, and LiOH displayed the highest reactivity probably due to the
most efficient complexation by the folded oligomers. Addition of excessive potassium chloride substantially
reduced the complexing interaction, and the hydrolysis of the longer oligomers became slower than that
of the shorter ones due to an increased steric effect. The results indicate that, even in a hot aqueous
medium of high polarity, intramolecular hydrogen bonding is still able to induce structurally matched
oligomers to generate a preorganized rigidified conformation.