Reactivity of mixed organozinc and mixed organocopper reagents: 14. Phosphine-nickel catalyzed aryl-allyl coupling of (n-butyl)(aryl)zincs. Ligand and substrate control on the group selectivity and regioselectivity

The group selectivity and regioselectivity in the allylation of mixed (n-butyl)(aryl) zinc reagents in THF depends on the nickel catalyst type and also on nature of the allylic substrate. Allylation of (n-butyl)(phenyl) zinc reagent with alkyl substituted primary allylic chlorides and acetates in the presence of NiCl2(dppf) catalysis affords the phenyl coupling product with gamma-selectivity. However, allylation with aryl substituted primary allylic substrates results in both phenyl-and alkyl-coupling products with medium alpha-selectivity in the presence of NiCl2(dppf) catalysis whereas phenyl coupling product is formed with alpha-selectivity in the presence of NiCl2(Ph3P)(2) catalysis. This new NiCl2(dppf) catalyzed protocol for gamma-selective aryl allylation of (n-butyl)(aryl) zinc reagents with alkyl substituted primary allylic chlorides in THF at room temperature provides an atom economic alternative to allylation of (aryl)(2)Zn reagents. A mechanism for the dependence of group selectivity and regioselectivity of Ni catalyzed allylation of (n-butyl)(aryl)zinc reagents on the catalyst ligand and the substrate was proposed. (C) 2016 Elsevier B.V. All rights reserved.