What Is Kumada Cross-Coupling Reaction?
The coupling of organomagnesium reagents with alkyl halides by Corriu and Kamada independently, both in 1972, marks the birth of cross-coupling chemistry. This process, which has come to be known as the Kumada cross-coupling or Kumada-Corriu cross-coupling, is usually carried out in diethyl ether over the nickel catalyst NiCl2(dppb). Alkyl, vinyl, and aryl halides are tolerated (except for the competing direct reaction of Grignard reagents with alkyl halides). Its advantages are that it is an easy reaction, and that it works even at low temperatures. It also allows the direct use of Grignard reagents without having to be converted to other organometallic reagents. The main disadvantage is that Grignard reagents, with their basic and strong nucleophilic nature, are not selective enough and often react with many functional groups. It is therefore not suitable for alkyl halides that are unstable in the presence of Grignard reagents.
The Kumada coupling, the first Pd- or Ni-catalyzed cross-coupling reaction, has been applied in the industrial-scale production of styrene derivatives, due to its convenience of directly using simple and economical Grignard reagents, and still remains the first choice, economic and convenient method for the synthesis of asymmetric biaryls.
- Reagents:
a) Catalyst: Typically nickel-based (e.g., Ni(II) complexes like Ni(dppp)Cl2) or palladium-based complexes.
b) Solvent: Etheric solvents, most commonly tetrahydrofuran (THF) or diethyl ether. - Reactants: An organohalide (aryl, vinyl, or alkyl halide; R–X). An organomagnesium halide (Grignard reagent; R'–MgX).
- Products: A coupled organic compound (R–R') with a new carbon-carbon bond. Magnesium halide salt (MgX2) as a by-product.
- Reaction Type: Transition metal-catalyzed cross-coupling reaction.
- Related Reactions: Suzuki-Miyaura coupling, Negishi coupling, Stille coupling, Heck reaction.
- Experimental Tips:
a) By varying the ligand and leveraging the synergistic effect of the Ni-Mg bimetallic reaction, researchers have developed Kumada-Corriu couplings involving inactive chloroalkanes, fluoroalkanes, and nonactivated p-toluenesulfonates, respectively, broadening the applicability of the reaction.
b) In the presence of appropriate phosphine ligands, functionalized Knochel-type Grignard reagents can be cross-coupled with arylbenzenes at low temperatures. Notably, the air-stable PinP(O)H can be used as a ligand precursor.
Fig 1. Kumada reaction and its mechanism. [1]
Mechanism of Kumada Reaction
The canonical Pd(0)/Ni(0) cycle comprises three principal steps:
- Oxidative addition — R–X (aryl/vinyl/alkyl halide or pseudohalide) adds to low-valent Pd(0) or Ni(0) to form R–M(II)–X (M = Pd, Ni). Rate/order: I > Br > Cl for oxidative addition; nickel is often better at activating less reactive halides.
- Transmetalation — the organomagnesium reagent transfers its R group to the metal center, displacing X (or via ligand-assisted pathways), forming R–M(II)–R'.
- Reductive elimination — formation of the C–C bond R–R' and regeneration of M(0).
Application Examples of Kumada Reaction
- Example 1: Pan-Pan Chen et al. used a combined computational and experimental approach to elucidate the stereospecificity and chemoselectivity of nickel-catalyzed Kumada and cross-electrophile coupling reactions of benzyl ethers. [2]
- Example 2: Xin Linghu et al. synthesized pyridone 1, a key intermediate of the ERK inhibitor GDC-0994, via a cross-coupling/hydrolysis sequence. The C–C bond formation was achieved via an efficient palladium-catalyzed Kumada–Corriu cross-coupling reaction. [3]
Fig 2. Synthetic examples via Kumada reaction.
Related Products
References
- Jie Jack Li. Name Reactions-A Collection of Detailed Mechanisms and Synthetic Applications, Sixth Edition, 2021, 310-313.
- Chen, Pan-Pan, et al. Journal of the American Chemical Society 141.14 (2019): 5835-5855.
- Linghu, Xin, et al. Organic Process Research & Development 21.9 (2017): 1320-1325.
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