Treatment of 1-methyl-2-(4-pentenyl)indole (5) with a catalytic amount of [PdCl₂(MeCN)₂] (2; 5 mol %) and a stoichiometric amount of CuCl₂ (3 equiv) in methanol under CO (1 atm) at room temperature for 30 min gives methyl (9-methyl-2,3,4,9-tetrahydro-4-carbazolyl)acetate (6), which was isolated in 83 % yield. A number of 2- and 3-alkenyl indoles undergo a similar palladium-catalyzed cyclization/carboalkoxylation to give the corresponding polycyclic indole derivatives in moderate to excellent yields with excellent regio- and diastereoselectivity. Under similar conditions, vinyl arenes undergo intermolecular arylation/carboalkoxylation with indoles to give 3-(1-aryl-2-carbomethoxyethyl) indoles in moderate yield with high regioselectivity. Stereochemical analyses of the palladium-catalyzed cyclization/carboalkoxylation of both 2- and 3-alkenyl indoles are in agreement with mechanisms involving outer-sphere attack of the indole on a palladium–olefin complex followed by α-migratory insertion of CO and methanolysis of the resulting acyl palladium intermediate. CuCl₂ functions as the terminal oxidant in this palladium-catalyzed cyclization/carboalkoxylation of alkenyl indoles and also significantly increases the rate of reaction of 2 with the alkenyl indole to form the corresponding acyl palladium complex. Spectroscopic studies are in agreement with the intermediacy of a heterobimetallic Pd/Cu complex as the active catalyst in this reaction.

Reaction of 8-nonene-2,4-dione with a catalytic amount of [PdCl₂(CH₃CN)₂] (2; 5 mol %) and a stoichiometric amount of CuCl₂ (2.5 equiv) at room temperature for 3 h led to oxidative alkylation and formation of 2-acetyl-3-methyl-2-cyclohexenone in 80 % isolated yield. The oxidative alkylation of 4-pentenyl β-diketones tolerated a number of terminal acyl groups and substitution at the C1 and C3 carbon atoms of the 4-pentenyl chain. Likewise, 4-pentenyl β-keto esters that possessed geminal disubstitution at the C1, C2, or C3 carbon atom of the 4-pentenyl chain cyclized to form 2-carboalkoxy-2-cyclohexenones in moderate to good yield as the exclusive cyclized product. Deuterium-labeling experiments provided information regarding the mechanism of the palladium-catalyzed oxidative alkylation of 4-pentenyl β-dicarbonyl compounds.

Reaction of 3-butenyl β-keto esters or 3-butenyl α-aryl ketones with a catalytic amount of [PdCl₂(CH₃CN)₂] (2) and a stoichiometric amount of Me₃SiCl or Me₃SiCl/CuCl₂ in dioxane at 25–70 °C formed 2-substituted cyclohexanones in good yield with high regioselectivity. This protocol tolerated a number of ester and aryl groups and tolerated substitution at the allylic, enolic, and cis and trans terminal olefinic positions. In situ NMR experiments indicated that the chlorosilane was not directly involved in palladium-catalyzed hydroalkylation, but rather served as a source of HCl, which presumably catalyzes enolization of the ketone. Identification of HCl as the active promoter of palladium-catalyzed hydroalkylation led to the development of an effective protocol for the hydroalkylation of alkyl 3-butenyl ketones that employed sub-stoichiometric amounts of 2, HCl, and CuCl₂ in a sealed tube at 70 °C.