Nickel complexes Grignard coupling

Sugimura, H. Takei, H. Synthesis of 6-Alkylpurine Derivatives by Nickel Complex Catalyzed Coupling Reaction of 6-(Meth-ylthio)purine derivatives with Grignard Reagents. Bull. Chem. Soc. Jpn. 1985, 58, 664-666. 

K. Tamao, S. Kodama, I. Nakajima, M. Kumada, A. Minato, and K. Suzuki, Nickel-phosphine complex-catalyzed Grignard coupling — II Grignard coupling of heterocyclic compounds, Tetrahedron, 38 3347-3354, 1982. 

The cross-coupling route to allylsilanes is effective with either aromatic or aliphatic a-silylated Grignard reagents16, and palladium catalysts are more reactive and stereoselective than the corresponding nickel complexes. Unsubstituted or i+monosubstituted alkenyl bromides work well but the Z-substituted bromides give lower yields and an inferior enantiomeric excess. The enantiomeric excess increases quite markedly with decreasing temperature, and optimum results are obtained at 0 C or below. 

Asymmetric Grignard Cross-Coupling Catalyzed by Chiral Phosphine-Nickel Complexes 73)... 

Hayashi et al.74 described a process of kinetic resolution in the coupling of Grignard reagents R Mgx (having a chiral center at the point of attachment to the metal) with various alkenyl halides under the influence of chiral phosphine-nickel complexes. Chiral amino acid derivatives (35) were used as ligands. 

B. Cross-coupling Reactions of Grignard Reagents in the Presence of Nickel Complexes... 

New syntheses of ( )-ar-turmerone (79) and ( )-nuciferal (80) have been reported (Schemes 10 and 11 ) whereas Meyers and Smith have used the (+)-oxazoline (81) to good effect in an asymmetrically induced synthesis of (+)-ar-turmerone (82) (Scheme 12). A neat one-pot synthesis of /3-curcumene (83) has been developed which involves only two steps (Scheme 13). In a synthesis of the aromatic analogue, (-)-a-curcumene (84), Kumada et al. have used an asymmetrically induced cross-coupling Grignard reaction in the presence of a nickel complex of (85) to produce (84) in 66% enantiomeric excess (Scheme 14). A Vilsmeier-Haack-Arnold formylation of (-f-)-limonene has been used as... 

The reaction gives good yields with primary, secondary, and tertiary alcohols, and with alkyl and arylhthium reagents. Allylic alcohols also couple with certain Grignard reagents in the presence of a nickel complex to give both normal products and the products of allylic rearrangement. 

A further advantage is the possible in situ generation of catalysts from simple metal salts or complexes (e. g., Ni(OR)2, PdCU) and azolium salts. The nickel-catalyzed Grignard cross-coupling of aryl chlorides at room temperature [123] and the activation of aryl fluorides [136] are convincing examples. 

Tamao, K., Sumitani, K., Kiso, Y., Zembayashi, M., Fujioka, A., Kodama, S., Nakajima, I., Minato, A., Kumada, M. Nickel-phosphine complex-catalyzed Grignard coupling. I. Cross-coupling of alkyl, aryl, and alkenyl Grignard reagents with aryl and alkenyl halides general scope and limitations. Bull. Chem. Soc. Jpn. 1976, 49, 1958-1969. 

Couplings between alkenyl chlorides and alkyl Grignard reagents are catalyzed best by nickel complexes,as exemplified by the synthesis of terminal alkenes, disubstituted alkenes, cyclic alkenes and a silylmethyldiene (equations 5-8),2 while Pd(PPh3)4 has also been claimed to be useful for a few... 

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