1,3-Butadiene → Cyclopropanecarboxylic acid, 2-ethenyl-, ethyl ester

Butadiene (200 ml, Aldrich) condensed at -700 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).