Spiro[1H-​indene-​1,​9'-​[9H]​xanthene]​-​6-​carboxylic acid, 3',​6'-​bis(1-​azetidinyl)​-​2-​diazo-​2,​3-​dihydro-​3-​oxo-​, 2,​5-​dioxo-​1-​pyrrolidinyl ester