Reactivity of mixed organozinc and mixed organocopper reagents: 10 Comparison of the transferability of the same group in acylation of mixed and homo halozinc diorganocuprates with benzoyl chloride. A kinetic study

• In mixed cuprates, RRRTCuM (M = Li, MgX, ZnX), RT is transferable group and RT is residual group.
• The accepted hypothesis is that the group forming a stronger Cu—C bond acts as RR.
• Our hypothesis is that the reaction rate of RT depends on RR in mixed cuprates, RRRTCuM.
• We offered a mechanism for acylation of n-alkyl groups of halozinc n-alkylarylcuprates.
• This study supports our hypothesis providing an explanation for the accepted hypothesis.

A detailed kinetic study has been carried out for the acylation of iodozinc n-butyl (substituted phenyl) cuprates, n-Bu(FG-C6H4)CuZnI and iodozinc din-butylcuprate, n-Bu2CuZnI with benzoyl chloride in THF at 15–(−15)°C. Third order reaction was found which is first order in benzoyl chloride and second order in cuprate. We offered a reaction mechanism for the acylation of halozinc diorganocuprates depending on the kinetic data and activation parameters. Lower reaction rate of transferable group, n-Bu in mixed cuprate, n-Bu(PhCuZnI than that of homocuprate, n-Bu2CuZnI and Hammett correlation of the reaction rate of transferable group, n-Bu in n-Bu(FG-C6H4)CuZnI reagents with the substituent constants of residual group, FG-C6H4 with a positive reaction constant (relative reactivity of FG: 4-Br > 3-MeO > H > 3-Me > 4-Me > 4-MeO) are in accordance with the proposed mechanism. These findings support our hypothesis that the reaction rate of transferable group, RT changes depending on the residual group, RR in mixed cuprates. RRRTCuM (M = Li, MgX, ZnX) and also provide a kinetic explanation for the commonly accepted hypothesis regarding the dependence of the RT group transfer ability on the strength of the RR–Cu bond in mixed cuprates, RRRTCuLi.

The kinetic results provide a support for our hypothesis that the reaction rate of transferable group, RT changes depending on the residual group, RR in mixed cuprates, RRRTCuM (M = Li, MgX, ZnX).Figure optionsDownload as PowerPoint slide