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

Butadiene (200 mL) was liquified at -70° C. and added to ethyl diazoacetate (20 g, 175 mmol) in a pressure vessel. The catalyst, rhodium (II) acetate dimer (300 mg, 0.7 mmol), was added and the reaction vessel sealed. The reaction mixture was allowed to warm to ambient temperature and the reaction vessel was shaken for 24 h at ambient temperature. The reaction mixture and the ethanol rinse of the reaction vessel were combined and this blue solution was filtered through 50 g of silica gel. The silica gel was washed with 2% diethyl ether in pentane until the blue color was eluted. The blue solution was then concentrated in vacuo at 0° C. and filtered through CeliteR filter aid to remove any remaining catalyst. The filtrate was distilled under reduced pressure (approximately 15 mm) to yield 18.6 g (76% yield) of ethyl 2-ethenylcyclopropane carboxylate as a clear colorless liquid, b.p. 22°-26° C.