Nitrogen lithium tetramethylpiperidide LiTMP

With heterocycles containing an sp--nitrogen atom, a totally different problem can occur, namely nucleophilic addition of the base to the azo-methine (C=N) bond. The use of very sterically hindered bases such as lithium tetramethylpiperidide (LiTMP) can prevent this type of addition in certain cases, but bases of this sort tend to be expensive and not suitable for general use. However, two different approaches to overcoming the problem of azomethine addition have been developed over the years, both relying on the fact that the addition is temperature dependent, and that by enabling metalation reactions to be performed at low temperatures, the desired carbanion formation can often be achieved. 

Secondary amines can be acylated with acyl groups bearing no a-hydrogens. Deprotonation next to the nitrogen atom and introduction of electrophiles allow the oxidation of that position. Eaiiy work showed that these anions underwent self-condensation. For example, A(,lV-dimethylbenzainide can be deproton-ated with lithium 2,2,6,6-tetramethylpiperidide (LITMP) to give Af-methyl-lV-phenacylbenzamide in 60% yield. It is clear that lithium ion is crucial to the success of this reaction. Ctown ethers prevent the reaction,and recent kinetic studies show intermediate lithium complex formation. ... 

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