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
Sodium 2-thienyltellurolate, generated in catalytic amounts from sodium borohydride and bis(2-thienyl) ditelluride, was found to efficiently debrominate l,4-dibromo-2-olefins to 1,3-dienes under very mild reaction conditions. The required 1,4-dibromo-2-olefins were usually synthesized by allylic , '-bromination of olefins.Terminal olefins yielded, via allylic rearrangement, a mixture of 1,4-dibromo-2-olefins and l,2-dibromo-3-olefins.Both these isomers were converted to 1,3-dienes (E/Z = 9/1) by the tellurolate reagent. The synthetic utility of the tellurolate-induced debromination reaction was demonstrated in a two-step synthesis of the main component
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