HAL Id:hal-03396644 Two-dimensional molecular assemblies on surfaces have opened a way to design and control chirality, featuring promising electronic and chemical properties that depend on the local handedness of the layer. Yet, the mechanisms leading to spontaneous chiral resolution are not fully understood at every reaction stage. Here, starting from achiral 10-bromoanthracene-9-boronic acid as a molecular precursor, we demonstrate enantiomeric induction in products during the stage of covalent bonding, stemming from the competing point symmetries of the Ag(001)-supporting surface and the reaction products. Upon dehalogenation and dehydration of precursors, hexagonal boroxine rings linked by organometallic anthracene dimers are formed, which undergo a strong interaction with a fourfold symmetric substrate. The prochiral structural character of the resulting oligomer and its impact over the spatial distribution of the electronic molecular states are revealed by high-resolution scanning tunneling microscopy and spectroscopy. Financial support was provided by the European Union through Interreg-POCTEFA (Grant TNSI/EFA194/16) program, including EFRD funds, as well as by the Spanish Plan Nacional de I + D + i (MAT2016-78293-C6 and PID2019-107338RB-C6). We also acknowledge funding from Gobierno de Aragón (grupo de referencia E13_20R “NANOMIDAS”) and Xunta de Galicia (Centro singular de investigación de Galicia, accreditation 2019-2022, ED431G 2019/03). Peer reviewed