Kumada Coupling

The Kumada cross-coupling is the transition metal-catalyzed carbon-carbon bond-forming reaction of alkenyl or aryl halides and organomagnesium or organolithium reagents.

General features: 1. The coupling is stereoselective, and the stereochemistry of the starting vinyl halides is preserved. 2. The reaction can be catalyzed by Ni and Pd catalysts. The Pd-catalyzed process is more chemo- and stereoselective and has a much broader scope. 3. The coupling takes place with aryl bromides and iodides, but not with aryl chlorides when Pd catalysts are employed. 4. Organomagnesium and organolithium reagents are used most often. 5. Base-sensitive functional groups are not tolerated because of the polar nature of the organomagnesium and organolithium compounds. 6. Possible side-reactions include homocoupled and reduction products. 7. The reaction is often carried out in tetrahydrofuran or diethyl ether, which are the typical solvents for generating the Grignard reagent. 8. As in many coupling reactions, the palladium catalyst is often air-sensitive, requiring an inert reaction environment.