Using CCOCC, CCCC1Cc2c(c(C)c(C)c3oc(C(=O)O)cc23)C1=O to produce CCCC1Cc2c(c(C)c(C)c3oc(C(=O)OCC)cc23)C1=O, please predict the agent for this reaction in SMILES notation in \boxed{$SMILES1, SMILES2, ...} format.