3-ethylpent-4-enoic acid

3-ethylpent-4-enoic acid can be prepared by reacting 4-Vinyloxetan-2-one with Ethylmagnesium bromide in the presence of Cuprous iodide reagent.^[1] 

[1] Toshio Sato. “A convenient method for the synthesis of (E)-3-alkenoic acids by a regio- and stereoselective reaction of β-vinyl-β-propiolactone with organocopper reagents.”Tetrahedron Letters 22 19 (1981): Pages 1817-1820.