Allylic Oxidation of Ester-Substituted 1,4-Dienes.

The cobalt-catalyzed hydrovinylation reaction and the Alder-ene reaction generate acyclic 1,4-dienes, which were investigated in the selenium dioxide oxidation to afford further functionalized dienes prone for follow-up reactions. The chemoselective allylic oxidation of ester-functionalized 1,4-dienes occurs at the most electron-rich double bond. The steric demand of the electron-rich, alkyl-substituted double bond determines the reaction pathway, whether the double bond transposition toward the conjugated 1,3-diene or the allylic oxidation is faster. As reaction products, 2,4-diene-6-ols or divinyl ketones were obtained.