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.

四种由分子内氢键驱动的芳香酰胺折叠聚合物2-5已被设计和合成，其中在主链末端引入了2-甲氧基-3-硝基苯甲酰胺单元。在二氧六环-水（体积比4:1）的溶液中，于60-90°C进行的动力学研究表明，这些寡聚物的折叠主链，类似于刚化的球形聚合物，能够与Li+、Na+和K+形成复合物，从而加速了折叠聚合物上硝基取代的苯甲醇单元的水解。通常，较长的折叠聚合物表现出更强的催化作用，而LiOH显示出最高的反应活性，这可能是由于折叠寡聚物与其形成最有效的复合作用。过量添加氯化钾显著降低了复合作用，并且由于空间位阻效应的增加，较长寡聚物的水解速度比较短者慢。这些结果表明，即使在高极性的热水介质中，分子内氢键仍然能够诱导结构匹配的寡聚物生成预先组织的刚化构象。