Several nucleophilic reactions on bicyclobutanes activated at the bridgehead carbon by electron withdrawing groups (SO2Ph, CO2Me, COPh, and CN) were performed in MeOH. In all cases, the less stable 1, 3-disubstituted cyclobutanes isomer was preferentially obtained (compared to the equilibrium ratio). The results for the two charge localizing groups CN and SO2Ph oppose the existing knowledge regarding the protonation stereochemistry of such ...