Palladium-catalyzed oxidation of 1,3-dienes in acetic acid using an oxidation system of Mn02 and catalytic amounts of p-benzoquinone selectively gives l,4-diacetoxy-2-alkenes. The reaction proceeds with high stereoand regioselectivity, and by ligand control the reaction can be made to take place with either cis or trans 1,4-diacetoxylation across the diene in cyclic systems. Also in an acyclic system the 1,4-relative stereochemistry can be controlled as shown by the stereoselective oxidation of (EE)-and (£rZ)-2,4-hexadiene to their corresponding dl (>88% di) and meso (>95% meso) diacetates 15 and 18, respectively. Evidence is provided that supports a mechanism involving a trans acetoxypalladation of the conjugated diene to give an intermediate (ir-allyl)palladium complex, followed by either a cis or trans attack by acetate on the allyl group. The cis attack is best explained

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Formation of 4-methoxycyclohex-2-enyl acetate (3) from the n-allylpalladium complex (2) shows that the acetate has attacked the 7r-ally1 ligand from the same side as the metal (cis-addition).THE stereochemistry of nucleophilic addition to n-allyl-and 7r-olefin-palladium complexes has been investigated extensively during the last decade.l-* The two principal modes of addition to n-ally1 complexes are shown in Scheme 1.Recently Trost et al.2*3 found that Pd(PPh,), catalyses the cis-trans isomerization of substituted cyclohexen-3-yl acetates. They rationalized the isomerization by assuming the formation of a n-allylpalladium intermediate, which may give both trans-and cis-acetate addition (paths A and B, ieipectively). A comparison of