Expanding the Toolbox of Heterogeneous Asymmetric Organocatalysts: Bifunctional Cyclopropenimine Superbases for Enantioselective Catalysis in Batch and Continuous Flow,Advanced Synthesis & Catalysis

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Expanding the Toolbox of Heterogeneous Asymmetric Organocatalysts: Bifunctional Cyclopropenimine Superbases for Enantioselective Catalysis in Batch and Continuous Flow
Advanced Synthesis & Catalysis ( IF 4.4 ) Pub Date : 2021-09-15 , DOI: 10.1002/adsc.202100757
Costanza Leonardi ₁ , Arianna Brandolese ₁ , Lorenzo Preti ₁ , Olga Bortolini ₁ , Eleonora Polo ₂ , Paolo Dambruoso ₂ , Daniele Ragno ₁ , Graziano Di Carmine ₃ , Alessandro Massi ₁

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A strategy for the immobilization of chiral 2,3-bisaminocyclopropenium salt (pre-catalyst) onto polystyrene and silica supports is presented together with a suitable procedure for the conversion into the corresponding cyclopropenimine superbase catalysts. The activity and recyclability of polystyrene- and silica-supported cyclopropenimines were initially tested under batch conditions in a model Michael addition detecting comparable efficiencies but a superior stability of the latter heterogeneous catalyst (5 cycles, accumulated TON of 27.1). The preferred silica-supported cyclopropenimine behaved very similarly to the soluble counterpart in the reaction of glycine imine with different Michael acceptors (48–92% yield; 60–98% ee) and it could be utilized as packing material for the fabrication of fixed-bed mesoreactors (pressure-resistant stainless-steel columns). Continuous-flow experiments were performed with satisfactory long-term stability (24 h on stream) with unaltered conversion efficiency and enantioselectivity.

中文翻译：

扩展多相不对称有机催化剂的工具箱：用于间歇和连续流对映选择性催化的双功能环丙烯亚胺超碱

将手性 2,3-双氨基环丙烯盐（预催化剂）固定在聚苯乙烯和二氧化硅载体上的策略以及用于转化为相应环丙烯亚胺超强碱催化剂的合适程序。聚苯乙烯和二氧化硅负载的环丙烯亚胺的活性和可回收性最初是在分批条件下在迈克尔加成模型中测试的，检测出可比较的效率，但后者多相催化剂具有优异的稳定性（5 个循环，累积 TON 为 27.1）。在甘氨酸亚胺与不同迈克尔受体的反应中，优选的二氧化硅负载的环丙烯亚胺的表现与可溶性对应物非常相似（48-92% 产率；60-98% ee)，它可以用作制造固定床中反应器（耐压不锈钢柱）的填充材料。连续流实验具有令人满意的长期稳定性（运行 24 小时），转换效率和对映选择性不变。

更新日期：2021-09-15

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