Cationic Palladium Complex-Catalyzed Carbonylation of 2,3-Dien-1-ols to 1,3-Diene-2-carboxylic Acids and Esters under Mild Conditions.

A cationic palladium complex, [Pd(PPh3)2(MeCN)2](BF4)2, catalyzed the carbonylation of 2,3-dien-1-ols under mild conditions. The dienols bearing two or more alkyl substituents on the diene part afforded 1,3-diene-2-carboxylic acids successfully in tetrahydrofuran (THF), while those possessing one or no alkyl substituent gave polymers of the products exclusively. The former afforded the corresponding methyl esters in good yields when the reactions were carried out in methanol, while the latter afforded mainly the Diels–Alder reaction products of the resulting esters. An alkylidene group-substituted π-allylpalladium species has been presumed to be an intermediate. Copyright © 2000 John Wiley & Sons, Ltd.