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The spin-orbit entangled (SOE) Jeff-state has been a fertile ground to study novel quantum phenomena. Contrary the conventional weakly correlated Jeff=1/2 state of 4d and 5d transition metal compounds, CuAl2O4 hosts with strong correlation Coulomb U. Here, we report that surprisingly Cu2+ ions overcome otherwise usually Jahn-Teller distortion instead stabilize SOE state, although cuprate relatively small coupling. From x-ray absorption spectroscopy high-pressure diffraction studies, obtained definite evidence cubic lattice at ambient pressure. We also found pressure-induced structural compressed tetragonal consisting spin-only S=1/2 for pressure higher than Pc=8 GPa. This phase from Mott insulating states is unique phenomenon not reported before. Our offers rare example under electron its state.