Using BrCCCBr, CCOC(=O)Cn1c(C(=O)OCC)c(O)c(O)c1C(=O)OCC to produce CCOC(=O)Cn1c(C(=O)OCC)c2c(c1C(=O)OCC)OCCCO2, please predict the agent for this reaction in SMILES notation in \boxed{$SMILES1, SMILES2, ...} format.