Thiazolium-functionalized polystyrene monolithic microreactors for continuous-flow umpolung catalysis
作者:Olga Bortolini、Alberto Cavazzini、Paolo Dambruoso、Pier Paolo Giovannini、Lorenzo Caciolli、Alessandro Massi、Salvatore Pacifico、Daniele Ragno
DOI:10.1039/c3gc41284a
日期:——
Thiazolium salt pre-catalysts have been immobilized on silica and monolithic polystyrene and their activity was tested under batch conditions in three model umpolung reactions, namely the benzoin condensation of benzaldehyde, the acyloin-type condensation of biacetyl, and the Stetter reaction of biacetyl with trans-chalcone. A prerequisite of the study has been the utilization of environmentally benign water and ethanol solvents. After having established the higher performance of polystyrene monolithic thiazolium carbene catalysts, their effectiveness has been tested under the flow regime by fabricating the corresponding monolithic microreactors (pressure-resistant stainless-steel columns). Importantly, it has been demonstrated by a brief substrate scope study that the polymeric matrix and the continuous flow regime synergistically contribute to preserve the activity of the carbene catalysts over time, thus permitting the long-term operation (up to 7 days) of the prepared monolithic reactors for the production of valuable compounds via the umpolung strategy.
噻唑盐预催化剂已被固定在硅胶和单一聚苯乙烯上,并在批处理条件下测试了它们在三种模型反应中的活性,包括苯甲醛的苯基醇缩合反应、生物酮的酰亚胺型缩合反应,以及生物酮与反式查尔酮的斯特特反应。该研究的前提是使用环保的水和乙醇溶剂。在确立了聚苯乙烯单体噻唑碳烯催化剂的高性能后,通过制作相应的单体微反应器(耐压不锈钢柱)在流动条件下测试了它们的有效性。重要的是,通过简要的底物范围研究,已经证明聚合物基质和连续流动模式协同作用,有助于在一段时间内保持碳烯催化剂的活性,从而允许制备的单体反应器在通过反转策略生产有价值化合物方面进行长期操作(长达7天)。