Several protic ionic liquids were tested as potential mediators for pinacol rearrangements employing microwave irradiation. Using hydrobenzoin as a model substrate, the optimal conditions were found to be heating at 80 °C for 5 min using H2SO4:triethylamine as the ionic liquid. A key feature of this reaction was to keep the microwave power low (20 W) to avoid ionic liquid degradation. Application of these conditions to triphenylethylene glycol gave rearrangement products in high yield and purity, while phenylethylene glycol and styrene oxide gave pinacol products that underwent a cascade aldol condensation. These conditions represent an efficient means by which pinacol rearrangements can be carried out while avoiding the use of strong Brønsted acids, high temperatures and extended reaction times.
几种质子型
离子液体被测试为运用微波辐射进行片呐醇重排反应的潜在介质。使用氢氧化苯偶姻作为模型底物,发现最佳条件是采用H2SO4:
三乙胺作为
离子液体,在80°C下加热5分钟。该反应的关键特征是保持微波功率低(20瓦)以避免
离子液体降解。将这些条件应用于
三苯乙烯二醇,得到了高产率和高纯度的重排产物,而
苯乙烯二醇和
苯乙烯氧化物则得到了进行级联醛醇缩合的片呐醇产物。这些条件提供了一种高效手段,可以在避免使用强布朗斯台德酸、高温和长时间反应的同时进行片呐醇重排反应。