• Another very useful method for the preparation of the organolithium reagents is the hydrogen-lithium exchange or metalation process (Scheme 4). The directing effect of the substituents and the acidity of the available hydrogens in the substrates influence the position of the lithiation.
Scheme 4
• The preparation of organolithium reagents can also be followed using a metal-metal exchange process involving an alkyl lithium and an organometallic compound (Scheme 5). This process leads to the formation of the organometallic derivative with the more stable carbanion bound to the electropositive metal.
Scheme 5
3.3.2 Reactions with Carbonyl Compounds
The reactions of organolithium reagents with aldehydes and ketones give alcohols (Scheme 6).
Scheme 6
In comparison to organomagnesium compounds, organolithium reagents are less susceptible to steric factors. For example, the sterically hindered ketone can be reacted with tert -BuLi to afford tertiary alcohol in good yield (Scheme 7).
Scheme 7
Furthermore, the reaction of carboxylic acids with organolithium reagents is very useful protocol for the synthesis of ketones (Scheme 8). This reaction is less effective with organomagenesium reagents.
Scheme 8
Ketones can also be prepared via the reaction of organolithium compounds with acid anhydrides, acyl chlorides and N-methoxyamides.