The organolithium reagents, characterized by a C-Li bond, are important in organic synthesis as organomagnesium halides. Lithium is less electronegative than carbon, and the C-Li bond is polarized as in organomagnesium halide. The organolithium reagents are more reactive than organomagnesium halides and are expected to behave both as a nucleophile and a base.

The reaction of lithium metal at low temperature with an alkyl halide in a hydrocarbon solvent gives alkyl lithium. The reaction proceeds smoothly in the presence of above 0.02% of sodium and the reactivity of the alkyl halides is RI > RBr > RCl.

Scheme 1

Another route to the preparation of the organolithium compounds is the use of metal halogen exchange reactions. This method is useful for the preparation of organolithium reagents that cannot be obtained from alkyl halide and metal directly. In this method organic halide is treated with alkyl lithium. This process is best suited for the preparation of aryl lithium derivatives (Scheme 2).

Scheme 2

In addition, compounds containing acidic hydrogen can be easily converted into organolithium compound by treatment with a suitable organolithium compound (Scheme 3).

Scheme 3

The replacement of a hydrogen by a lithium (known as lithiation) can also be used to generate organolithium species. This reaction is essentially an acid base reaction. However, in the case, where there is activation by a coordinating group, the reaction occurs with considerable ease. This type of activation is particularly helpful in introducing an ortho substituent to a preexisting   coordinating group (Scheme 4).

Scheme 4