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The stoichiometric reaction of sodium salts of 3-butenoic acid, 3-pentenoic acid, 4-pentenoic acid, and 4-hexenoic acid with lithium tetrachloropalladate(II) affords 2-buten-4-olide, 4-methyl-2-buten-4-olide (2b), 2b, and 4-ethyl-2-buten-4-olide respectively. Similarly, the reaction of 2-styrylbenzoic acid with palladium(II) salt leads to the formation of 3-phenylisocoumarin.
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Kasahara et al. (1977) studied this question.
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