The palladium-catalyzed intramolecular cyclization of alkadienyl-substituted 1,3-diketones

Hydroxydeca-3,7,9-triene-2-one (prepared by metallation of acetylacetone followed by treatment with 1-bromopenta-2,4-diene) undergoes intramolecular cyclization in the presence of a [Pd(iPr2PC2H4PiPr2)] catalyst to give a mixture of cyclohexanone and cycloheptenone derivatives. The cyclohexanone 2-(1-hydroxyethyliden)-3-vinylcyclohexanone isomerizes in the presence of palladium to give the palladium-alkene complex (η2-2-acetyal-3-ethylcyclohex-2-enone)Pd(iPr2PC2H4PiPr2) whose crystal structure has been established by X-ray diffraction. A related cyclization reaction involving the disubstituted 1,3-diketone 9-hydroxy-1,3,7,12,14-pentaene-7-one leads to the formation of a mixture of spiro compounds (mainly 5,11-divinyl-spiro[5.5]undeca-1,7-dione) whose structures have been elucidated with the help of 1H- and 13C-NMR spectroscopies using 2D-NMR techniques