Using COC(=O)C1=Cc2cc(C(=O)c3cccc(Cl)c3)c(O)cc21 to produce O=C(O)C1=Cc2cc(C(=O)c3cccc(Cl)c3)c(O)cc21, please predict the agent for this reaction in SMILES notation in \boxed{$SMILES1, SMILES2, ...} format.