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

Abstract

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-C 6 H 4 in the mixed cuprate n-Bu(FG-C 6 H 4 )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 R 1 R 2 CuMgBr reagents.

Reactivity of mixed organozinc and mixed organocopper reagents: 5-A kinetic insight to compare the transfer ability of the same group in copper catalyzed alkylation of mixed and homozincates

“…We were surprised to see that the selective transfer of n-Bu group in the alkylation of stoichiometric bromomagnesium n-butylphenylcuprate, n-BuPhCuMgBr at room temperature [42] gets reversed in the CuI catalyzed alkylation of bromomagnesium zincate n-BuPh 2 ZnMgBr 1ab 2 at reflux temperature and also a preference for transfer of Ph group over n-Bu group is observed in the CuI catalyzed alkylation of bromomagnesium zincate n-Bu 2 PhZnMgBr 1a 2 b. Before discussing the formation and reaction of active organocopper intermediates in the reactions of copper catalyzed zincates, we made a literature survey on the structure of triorganozincates.…”

“…We reported that selective n-butyl transfer takes place in the alkyl coupling of bromomagnesium n-butyl-phenylcuprate, n-BuPhCuMgBr in THF [42]. In addition, our kinetic work on the coupling of n-BuRCuMgBr (R ¼ substituted phenyl) with alkyl bromides showed that selective n-butyl transfer can be explained by an oxidative mechanism and the residual group changes the ability of the copper nucleophile to react with the electrophile.…”

Reactivities of mixed organozinc and mixed organocopper reagents. Part 13 Kinetic study for phosphine‐catalyzed acylation of alkylarylzincs and effect of residual group on the transfer rate of alkyl group

“…In their systematic work, Erdik and coworkers observed that the group selectivities of mixed diorganocuprates, R 1 R 2 CuM (MMgBr), ZnI, diorganozincs, R 1 R 2 Zn, and Cu‐catalyzed mixed triorganozincates, R 1 (R 2 ) 2 ZnMgBr, depend on the reaction parameters, that is, the electrophilic substrate, the solvent, and the temperature as well as the transition metal catalyst and organocatalyst, and reported that the group selectivity of mixed organocopper and organozinc reagents can be controlled by changing the reaction parameters. They also developed new atom‐economic synthetic procedures for CC, C‐acyl, and CN coupling employing mixed arylzinc reagents. However, probing the origin of group selectivity in the mixed organocopper and organozinc reagents still seems a problem.…”

“…In connection with my recent studies on the control of group selectivity in acylation of n ‐alkylphenylzinc reagents and kinetics of acylation of iodozinc alkylarylcuprates, I focused my interest on the acylation of n ‐alkylarylzinc reagents with the objectives of kinetics and mechanism of phosphine‐catalyzed acylation of diorganozincs and providing another kinetic support for Erdik's hypothesis regarding the dependence of R T group transfer ability on R R group in reactions of R R R T Zn reagents. According to the best of my knowledge, there is a limited number of reported work on the kinetics of reactions of uncatalyzed and Cu(I)‐ and Ni(II)‐catalyzed reactions of monoorganozincs and diorganozincs. A theoretical study for transfer ability in mixed diorganozincs has been also published .…”

Minimization of Organocuprate Complexity through Self‐Organization: Remarkable Orientation Effect in Mixed Cuprate π Complexes

“…Apparently, the presence of a moiety capable of chelating Li ions destabilized the mixed cuprate p complex and promoted the metathesis reaction. [20] The observation of small cis and large trans two-bond coupling across Cu in the NMR spectra of cuprate-thiocarbonyl complexes suggests a pseudo square planar arrangement of ligands, [15,21] which in turn implies a significant degree of Cu III character. [18] The second major factor that influences the structures of mixed cuprates with dummy ligands such as cyano, alkynyl, and thiolato was identified as a structural trans effect ("trans influence").…”