Reactivity of mixed organozinc and mixed organocopper reagents. Part 4: a kinetic study of group transfer selectivity in C-C coupling of mixed diorganocuprates

The competitive rate data and Taft relationships for the coupling of bromomagnesium n-butyl (substituted phenyl) cuprates with alkyl bromides show that selective n-butyl transfer can be explained by an oxidative addition mechanism. Taft reaction constants also show that the residual group FG-C6H4 in the mixed cuprate n-Bu(FG-C6H4)CuMgBr changes the ability of the copper nucleophile to react with the electrophile RBr. These results provide support for the commonly accepted hypothesis regarding the dependence of the R-1 group transfer ability on the strength of R-2-Cu bond in reactions of (RRCuMgBr)-R-1-Cu-2 reagents. Copyright (C) 2009 John Wiley & Sons, Ltd.