We report a solvent-directed and regioselective carbon-carbon bond cleavage of aryl ketones by azido-1,3,5-triazines (ATs), which is typically completed within 10 min in DMSO at room temperature, without using transition metal catalysts. The cleavage is driven by the steric hindrance in the adducts of aryl ketones and ATs, which is substantiated by DFT calculation. Our recent results showed that ATs present high reactivity in solution and high stability in solid state. This "stability-reactivity paradox" has been explained in light of the molecular and crystal structures of ATs.