Abstract
A cross-coupling reaction of allylic aryl ethers with arylmagnesium reagents was investigated using β-aminoketonato- and β-diketiminato-based pincer-type nickel(II) complexes as catalysts. An β-aminoketonato nickel(II) complex bearing a diphenylphosphino group as a third donor effectively catalyzed the reaction to afford the target cross-coupled products, allylbenzene derivatives, in high yield. The regioselective reaction of a variety of substituted cinnamyl ethers proceeded to give the corresponding linear products. In contrast, α- and γ-alkyl substituted allylic ethers afforded a mixture of the linear and branched products. These results indicated that the coupling reaction proceeded via a π-allyl nickel intermediate.
Highlights
Transition metal-catalyzed cross-coupling reactions are efficient and widely utilized synthetic protocols for constructing carbon–carbon bonds [1]
The choice of the metal catalyst is critical for linear and branched selectivity. Precious metals such as Pd and Ir have been extensively explored in selective allylic substitution reactions [2,3,4], recent efforts have focused on first-row late transition-metals such as Cu, Co, Fe, and Ni, whose complexes act as highly active catalysts
To evaluate the catalytic activity of nickel(II) complexes 1a–d, we carried out the reaction between
Summary
Transition metal-catalyzed cross-coupling reactions are efficient and widely utilized synthetic protocols for constructing carbon–carbon bonds [1]. Allylic electrophiles with efficient leaving groups, such as allylic halides, acetates, and phosphates, are commonly used in these reactions [2,3,4,5,6]. In contrast to these allylic electrophiles, allylic ethers have been considered less-reactive electrophiles in cross-coupling reactions, whereas these electrophiles are accessible, cheap, and easy to handle. The choice of the metal catalyst is critical for linear and branched selectivity Precious metals such as Pd and Ir have been extensively explored in selective allylic substitution reactions [2,3,4], recent efforts have focused on first-row late transition-metals such as Cu, Co, Fe, and Ni, whose complexes act as highly active catalysts. Feringa reported the asymmetric allylic alkylation of acyclic allylic ethers with organolithium reagents using a
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