Organocatalysis with externally applied electric fields under organic synthesis conditions in microfluidic capacitors is explored for aldol reactions using Jørgenson–Hayashi type prolinol ether catalysts. For one of the most explored organocatalysis reactions, the electric field could triple microfluidic yields from 29% to 90%. Under the developed conditions, no detectable current is flowing in response to applied voltage up to 40 V. We propose that in toluene, in response to applied fields, protons transfer from Brønsted acid co‐catalysts to prolinol ethers to generate charges, which are separated and driven to the respective plate electrodes. There, they assemble into electric double layers that serve as supramolecular electrodes to generate the high effective electric fields required for catalysis. This mechanism and its fundamental difference from proline‐based electric‐field catalysis (EFC) in polyarginine double layers show that scalable EFC in microfluidic capacitors operates not merely like a general oriented polar solvent but with unique supramolecular chemistry waiting to be explored. Ion‐pair separation and the templated assembly of charged monomers into organocatalytic supramolecular 2D polymers emerge as central EFC principles that are distinct from mechanisms in stirred solution and will serve as guidelines for the discovery of organic synthesis at high voltage.
Guo et al. (Wed,) studied this question.