[CH2:1]=[CH:2][CH:3]=[CH2:4].[N+](=[CH:7][C:8]([O:10][CH2:11][CH3:12])=[O:9])=[N-]>C(OCC)C.CCCCC.CC([O-])=O.CC([O-])=O.CC([O-])=O.CC([O-])=O.[Rh+2].[Rh+2]>[CH:2]([CH:3]1[CH2:4][CH:7]1[C:8]([O:10][CH2:11][CH3:12])=[O:9])=[CH2:1]Butadiene (200 ml , Aldrich) condensed at -70° was transferred to a glass lined autoclave vessel and ethyl diazoacetate (20 g, 0.175 mol, Aldrich) and rhodium acetate dimer (0.3 g, Aldrich) added. The suspension was stirred in a sealed autoclave for 24 hours at ambient temperature. The contents were diluted with 2% diethyl ether in pentane and passed through a silica pad (50 g). The pad was washed with a little ethanol and further ether-pentane. The eluant containing ethanol was treated separately. The organic phases were concentrated at reduced pressure (<5°) and subjected to short path bulb to bulb disillation (90-105° at 12 mm) to give the product as a colourless liquid (14.6 g).
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