Palladium-catalyzed alkylation of unactivated olefins
Ross A. Widenhoefer
P.M. Gross Chemical Laboratory, Duke University, Durham,
NC 27708-0346, USA
Abstract: The reaction of a 3-butenyl β-diketone with a
catalytic amount of PdCl2(CH3CN)2 in
dioxane at room temperature led to olefin hydroalkylation and formation
of the corresponding 2-acylcyclohexanone in good yield as a single regioisomer.
Deuterium-labeling experiments for the hydroalkylation of 7-octene-2,4-dione
were in accord with a mechanism involving outer-sphere attack of the
pendant enol on a palladium-complexed olefin to form a palladium cyclohexyl
species, followed by palladium migration via iterative β-hydride
elimination/addition and protonolysis from a palladium enolate complex.
In comparison to a 3-butenyl β-diketone, reaction of a 4-pentenyl
β-diketone with a catalytic amount of PdCl2(CH3CN)2
in the presence of CuCl2 led to oxidative alkylation and
formation of the corresponding 2-acyl-3-methyl-2-cyclohexenone in good
yield as a single isomer. Unactivated olefins tethered to less reactive
carbon nucleophiles such as β-keto esters, α-aryl ketones,
and even dialkyl ketones underwent palladium-catalyzed hydroalkylation
in the presence of Me3SiCl or HCl to form the corresponding cyclohexanones
in moderate-to-good yield with high regioselectivity.
*Plenary and invited lectures presented at the 12th
International Symposium on Organometallic Chemistry Directed Towards
Organic Synthesis (OMCOS-12), Toronto, Ontario, Canada, 6-10 July 2003.
Other lectures are published in this issue, pp.
453-695.
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