This report shows how the net supramolecular chirality that emerged by spontaneous mirror-symmetry breaking (SMSB) at the mesoscale level can be transferred towards asymmetric solution chemistry. The J-aggregates obtained by self-assembly of an achiral porphyrin act as chiral counteranions in an iminium-promoted Diels-Alder reaction, leading to enantiomeric imbalances in the final adducts.