Aromatic Reactivity. Part XXVI. Relative Reactivities of Some Aryl-Lithium Compounds in Couplings with Ethyldimethylsilane and Its Chloro- and Ethoxy-Derivatives

摘要

A competition method was used to measure the relative reactivities of some aryl-lithium compounds, X.C6H4.Li (where X = p-Me, m-Me, H, or m-CF3), towards ethyldimethylsilane and its chloro- and ethoxy-derivatives in ether. Towards the chloride, all appear to be equally reactive, but towards the ethoxide and the parent the order is p-tolyl > Ph, m-tolyl > m-trifluoromethylphenyl. That electron-release in the substituent X facilitates, and electron-withdrawal hinders, reaction is consistent with regarding cleavage of the aryl-lithium bond as an electrophilic aromatic substitution. Contrary to a possible implication of earlier experiments, p-dimethyl-aminophenyl-lithium is little, if any, less reactive than phenyl-lithium. The reactivity of o-tolyl-lithium could not be measured because of unexpected side reactions. (Author)