A transition-metal-free ring opening of bicyclo[1.1.0]butanes (BCBs) using hydroperoxides as nucleophiles in hexafluoroisopropanol (HFIP) resulting in the diastereoselective synthesis of peroxycyclobutanes under mild conditions with a broad scope is demonstrated. Preliminary mechanistic experiments, including density functional theory studies, provide insight into the mechanism and stereochemical outcome of the reaction, thus underscoring the unique role of HFIP in activating BCB for facile nucleophilic addition.