NICKEL-CATALYZED COUPLING OF ALLYLAMINES AND BORONIC ACIDS

Allylamines function as substrates for cross-coupling with boronic acids in the presence of nickel(o) catalysts rather than palladium(o) catalysts. Aryl,- vinyl- and methyl-boronic acids function well. With vinyl derivatives, E-isomers couple more efficiently than Z-isomers and both fully retain the geometrical integrity. Methylations preferably employ the boronic esters like 2-methyl-1,3,2-benzodioxaborole or 2-methyl-1,3,2-dioxaborolane rather than methylboronic acid. The stereochemistry of the reaction involves a net inversion with respect to the allylamine. The regioselectivity is a function of ligand. Generally, sterically bulky donor phosphines promote new C-C bond formation at the less substituted position. Bidentate ligands, notably 1,1'-binaphthyl-2,2'-ylbis(diphenylphosphinite) (BINAPO), promote new C-C bond formation at the more substituted allyl terminus. The amines appear to be the preferred partner compared to allyl alcohols and esters with the boronic acids and give higher stereospecificity.