[{"from": "human", "value": "Synthesize a molecule that matches the given characteristics. The molecule is a butan-4-olide having a 1-[(methylsulfonyl)oxy]ethyl group at the 3-position and two methyl substituents at the 5-position. It is a butan-4-olide and a methanesulfonate ester."}, {"from": "gpt", "value": "[C][C][Branch1][#C][C][C][C][Branch1][=Branch1][O][C][Ring1][Branch1][=O][Branch1][C][C][C][O][S][=Branch1][C][=O][=Branch1][C][=O][C]"}]