Dehydro-Diels–Alder (DDA) reaction is a textbook reaction for preparing six-membered rings in solution but is scarcely seen in solid-state synthesis. In this work, using multiple characterization techniques, we demonstrate that the bowl-shaped clusters C₁₈Te₃Br₄(Bu-O)₆ might experience a DDA reaction at room temperature and high pressure between 5.5 and 7.4 GPa. Above 17.0 GPa, it is found that the bonding conversion from the intramolecular sp² to the intermolecular sp³ occurred, in the form of pressure-induced diamondization. The recovered samples from 20.0 and 36.1 GPa showed incomplete reversibility, while the decompression-induced graphitization of glassy carbon was observed during decompression from 46.5 GPa. The electrochemical impedance spectroscopy results indicated that the transport properties changed from grain boundary dominant to grain dominant due to the DDA reaction and the grain boundary effect disappeared as the intermolecular sp³ bonding building-up and carrier transmission channel formation above 17.0 GPa. The results in this study open a new route to construct the crystalline carbon materials with different transport properties.