SYNTHESIS OF 2-PHENYL-2-CYCLOALKENONES VIA PALLADIUM-CATALYZED TANDEMEPOXIDE ISOMERIZATION-INTRAMOLECULAR ALDOL CONDENSATION

We have extended the scope of our palladium-catalyzed tandem epoxide i somerization/aldol condensation reaction to encompass intramolecular c ondensations, which provide facile access to conjugated cycloalkenones from epoxy aldehydes or diepoxides, For example, reaction of 5,6-epox y-6-phenylhexanal with Pd(OAc)(2)-PBu3 catalyst in the presence of NaH CO3 and 3 degrees molecular sieves forms 2-phenyl-2-cyclopentenone (80 %). Similarly, 1,2;5,6-diepoxy-1-phenylhexane affords 3-methyl-2-pheny l-2-cyclopentenone (72%). The observation of dicarbonyl intermediates (e.g., 1-phenyl-2,5-hexanedione in the latter case) demonstrates that the reaction proceeds via Pd-catalyzed isomerization of the diepoxide to the diketone, followed by base-catalyzed aldol condensation. (C) 19 98 Elsevier Science Ltd. All rights reserved.