Heterocyclic Chemistry at a Glance

Diazines 53

Lithiodiazines are also accessible via halogen exchange with alkyllithiums. The examples show how 5-bromopyrimidine
can be converted into 5-substituted derivatives using either a very low temperature, or by adding the electrophile before
then-butyllithium so that the 5-lithiopyrimidine is trapped as soon as it is formed.

Diazine Grignard reagents can be obtained and used without the need for very low temperatures; diazine zinc compounds
can be obtained by exchange of lithium compounds (see next section).

Palladium(0)-catalysed reactions

Boronic acids (or boronate esters) and stannanes of all the parent diazines and at all positions are known, pyrimidine-2-
and -5-boronic acids, and pyridazine-4-boronic acids fi nding particular use. 2,4,6-Trichloropyrimidine can be used
as a substrate for clean sequential Suzuki couplings: C-4, then C-6, then C-2. Some typical examples are given below.