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

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.