Two series of competitive acylation experiments with a polar and an apolar alcohol substrate, imitating two parts of amphiphilic diols, examined the influence of bases of varying strength on the substrate selectivity. While weakly basic 2,4,6-collidine only mildly accelerates the acylation of the polar substrate without affecting that of the apolar one, the acylation of both substrates is drastically hastened by strongly basic DBU. In both cases there is a notable, though not overwhelming, shift of the substrate selectivity towards the polar substrate, compared to the base-free acylation, which favors that of the apolar one. The extraordinarily strong change in the substrate selectivity in favor of the polar substrate was induced, however, by aliphatic tertiary amine bases, DIPEA and Et3N, of ‘Goldilocks’ moderate base strength, which strongly accelerate the acylation of the polar substrate, while almost not affecting that of the apolar one. These effects of the bases on the substrate selectivity are reflected in the site-selectivity trends observed in the acylation of a model diol amphiphile.

中文翻译：

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两亲性二醇酰化中碱强度对位点选择性的金发效应

使用极性和非极性醇底物进行的两个系列竞争性酰化实验，模拟两亲性二醇的两部分，研究了不同强度的碱对底物选择性的影响。虽然弱碱性 2,4,6-可力丁仅轻微加速极性底物的酰化而不影响非极性底物的酰化，但强碱性 DBU 大大加速了两种底物的酰化。在这两种情况下，与无碱酰化相比，底物选择性向极性底物发生了显着的但不是压倒性的转变，后者有利于非极性的酰化。然而，由具有中等碱强度的“金发姑娘”的脂肪族叔胺碱 DIPEA 和 Et3N 诱导了底物选择性的异常强烈变化，有利于极性底物，强烈加速极性底物的酰化，同时几乎不影响非极性底物的酰化。碱基对底物选择性的这些影响反映在模型二醇两亲物酰化中观察到的位点选择性趋势中。