Treatment of methyl 2, 3-pentadlenoate, 3, with bromine in carbon tetrachloride affords a complex mixture, whose main products are methyl (E)-and (Z)-3, 4-dlbromo-2-pentenoate, 9 and 10, and 4-bromo-5-methyl-5H-furan-2-one, 4. The mechanism of formation of these and other minor compounds is discussed. Hydrolysis of the crude mixture in the presence of barium hydroxide affords lactone 4 in 30% overall yield.
