Palladium0-catalyzed isomerization of (Z)-1-functionalized-4-acetoxy-2-butenes: Solvent and substituent effects

The Pd(PPh3)4-catalyzed isomerization of (Z)-1,4-diacetoxy-2-butene, (Z)-1-(t-butyldimethylsilyloxy)-4-acetoxy-2-butene and (Z)-1-(t-butyldiphenylsilyloxy)-4-acetoxy-2-butene affords the corresponding (E)-isomers and 1,2-difunctionalized-3-butenes. In THF, the formation of the (E)-isomers is mainly due to reaction from an η1-allylpalladium intermediate while an η3-allylpalladium is the main key intermediate in DMF. The time to reach equilibrium between the products and their respective concentrations depend on the nature of the substituents and the solvent.