Lithium Dialkylcuprates Lithium dialkylcuprates are useful synthetic reagents. They are prepared from alkyllithiums and a copper(I) halide. 2RLi + CuX R2CuLi + LiX [customary solvents are diethyl ether and tetrahydrofuran (THF)]
R Li R Cu Cu I How? the alkyllithium first reacts with the copper(I) halide Li+ I–
R Li R Cu Cu I R R Li R Cu R Cu How? the alkyllithium first reacts with the copper(I) halide Li+ I– then a second molecule of the alkyllithium reacts with the alkylcopper species formed in the first step Li+ –
Reactions of Organocuprates • To form a ketone from a carboxylic acid derivative, a less reactive organometallic reagent—namely an organocuprate—is needed. • Acid chlorides, which have the best leaving group (Cl¯) of the carboxylic acid derivatives, react with R’2CuLi to give a ketone as the product. • Esters, which contain a poorer leaving group (¯OR), do not react with R’2CuLi.