前言 用正丁基锂和芳卤进行锂卤交换反应时,一般都需要干冰丙酮浴之类的低温条件,这与锂化中间体的稳定性以及副反应控制有关。 对于很多实验室而言,低温锂化反应的放大是很难实现的,一般只能多批次堆料。 这种低温锂卤交换反应,用格氏试剂代替锂试剂是常用的放大解决策略,后续推文中会介绍相关案例。 但如果格氏试剂反应不好,锂试剂又需要低温,该怎么放大呢? 兼具锂试剂活性和格氏试剂稳定性的镁锂试剂
2,6-二溴吡啶,拔溴锂化,和DMF反应合成醛。
实验操作: Dry toluene (45.3kg) and n-BuLi (1.63 M in hexane, 45.8 kg, 109 mol) were charged to a 800 L reactor and cooled to -10 °C. n-BuMgCl (1.95 M in THF, 26.9 kg, 54.6 mol) was added over 30 min, while maintaining the temperature at -10 to 0 °C, and the mixture was stirred at -10 °C for 30 min. A solution of 2,6-dibromopyridine (34.92 kg, 144.8 mol) in toluene (228 kg, KF = 69 ppm) was added dropwise over a period of 1 h while keeping the temperature of the mixture below -5 °C. The resulting suspension was stirred at -10 °C for 2.5 h. The mixture was transferred via cannula to a cooled solution (-10 °C) of DMF (14 kg, 188.9 mol) in toluene (43.2 kg) while maintaining the temperature below 10 °C. The solution was allowed to stand at -5 to -10 °C for 30 min and then transferred via a Teflon cannula to an aqueous citric acid solution (56.6 kg in 105 L of water) while maintaining the temperature of the mixture below 20 °C. After stirring the mixture below 20 °C for 10 min, the organic layer was separated and washed with water (105 L). The organic layer was concentrated to ca. 130 L, in vacuo, and was used in the next step. HPLC analysis showed that the desired product was obtained in 91% assay yield (25.0 kg)参考文献 JOC.2001,66,6775 |
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