THE PALLADIUM-CATALYZED INTRAMOLECULAR CYCLIZATION OF ALKADIENYL-SUBSTITUTED 1,3-DIKETONES

Abstract 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( i Pr 2 PC 2 H 4 P i Pr 2 )] 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 (η 2 -2- acetyl -3- ethylcyclohex -2- enone ) Pd ( i Pr 2 PC 2 H 4 P i Pr 2 ) 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 1 H- and 13 C-NMR spectroscopies using 2 D-NMR techniques.