To establish this new concept, we selected as model reaction Jacobsen's HKR 9 providing valuable chiral 1,2-diols from racemic epoxides [Fig. ]. Indeed, this transformation should be a good candidate reaction due to the lower polarity of the epoxides compared to their corresponding diols. Membrane with selective permeability To evaluate the feasibility of such a process, the selective permeability of PDMS membrane was first studied. Each compartment of the reactor was filled with each opposite enantiomer of styrene oxide 1a [Fig. ]. The enantiomeric excess of styrene oxide 1a was then monitored over time depending on several pivotal parameters: the nature of the solvent, the thickness of the membrane and the temperature. Enantiomeric excess of the chiral substrate is thus used as a probe to measure its rate of transfer between two compartments in the absence of concentration gradient, which has never been achieved before to the best of our knowledge.