Palladium-Catalyzed Allylation of Cyclopropyl Acetylenes

Palladium-Catalyzed Allylation of Cyclopropyl Acetylenes

Author: European Journal of Organic Chemistry

Conjugated 1,3-dienes are useful building blocks, e.g., for medicinal chemistry and natural product synthesis. Thus, efficient and atom-economical methods to access them are useful.

Chuan-Jun Lu, Qing-Bao Song, Zhejiang University of Technology, China, and colleagues have developed a palladium-catalyzed allylic alkylation of oxindoles with cyclopropyl acetylenes which gives 1,3-dienes (pictured). The team used Pd(dba)2 (bis(dibenzylideneacetone)palladium(0)) as a catalyst, PPh3 as a ligand, 3‐chlorobenzoic acid as an additive, and 1,4-dioxane as the solvent. The reaction gives good to excellent yields of the desired diene products.

The products feature a quaternary stereocenter and are formed with high regio- and stereoselectivities and good atom economy. The reaction could be compatible with enantioselective catalysis. The mechanism proposed by the researchers involves a vinyl palladium intermediate, which undergoes a β‐C elimination to form an alkylpalladium(II) intermediate. This is converted to a vinyl allene by β‐H elimination. A hydropalladation of the vinyl allene gives a π‐allylpalladium species, which isomerizes and is captured by the oxindole to give the final product.




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