Using BrC(Br)(Br)Br, CC(C)(C)OC(=O)n1cc(C=O)c2ccccc21 to produce CC(C)(C)OC(=O)n1cc(C=C(Br)Br)c2ccccc21, please predict the agent for this reaction in SMILES notation in \boxed{$SMILES1, SMILES2, ...} format.