Using COC(=O)C1=NN(c2ccccc2Cl)C(c2ccc(Br)cc2F)C1 to produce O=C(O)C1=NN(c2ccccc2Cl)C(c2ccc(Br)cc2F)C1, please predict the agent for this reaction in SMILES notation in \boxed{$SMILES1, SMILES2, ...} format.