PALLADIUM-CATALYZED REDUCTIVE COUPLING OF ACID-CHLORIDES WITH BETA-STANNYL ENONES - SYNTHESIS OF 1,4-DIKETONES AND MECHANISTIC ASPECTS

The palladium-catalyzed coupling of acid chlorides with (E)-1,2-bis(tri-n-butylstannyl)ethene or beta-stannyl enones gives butane-1,4-diones directly by reduction of the intermediate enedicarbonyl intermediate. The double bond conjugated with a single carbonyl group was not significantly reduced. The generality of the method is illustrated by two syntheses of the 1,4-diketone ipomeanine. By performing the reaction at lower temperatures, alpha,beta-unsaturated 1,4-diketones can also be prepared. The reduction of the intermediate alpha,beta-unsaturated 1,4-diketones probably proceeds by insertion of a palladium hydride, formed in situ by reaction of a Pd(II) complex with Bu(3)SnCl, followed by hydrolysis of the intermediate palladium enolate.