Relative reactivities of bromine-substituted substrates toward bromophilic attack by a carbanion

Halophilic attack on carbon-halogen bond by nucleophiles has recently become a sub-ject of interest and intensive study.A wide variety of substrates and nucleophiles has beenexamined.But no quantitative measurements on the reactivities of substrates have ever beenreported.The present work is a first attempt to evaluate the relative reactivities of perfluoro-bromoalkanes（R-Br）and some bromo organic compounds（R-Br）by intermolecular compe-tition kinetics.A large excess of ClCCFCFCl（1）,a chlorine-containing substrate withconvenient reactivity toward halophilic attack,and R-Br is used to compete for a small amountof the enolate anion of mesityl isopropyl ketone（E-）in dimethyl formamide（DMF）at 20℃in their reactions to form α-chloroisopropyl mesityl ketone（A）and α-bromoisopropylmesityl ketone（B）as products（eq 1）