56 Diazines
N-Alkylation of O-silylated derivatives is an important method for unambiguous N-alkylation, especially for ribosyla-
tion of uracils.
N-Arylation can be achieved either using base with a reactive aryl halide or by copper-catalysed reaction with either a
boronic acid or (unactivated) aryl halide.
Replacement of oxygen
The diazinones are the best sources of the synthetically versatile halo-diazines, by reaction with thionyl choride or
phosphoric trichloride (POCl 3 ). Thiones can also be prepared by direct replacement of oxygen using phosphorus
sulfi des.
Nucleophilic addition
An interesting and useful example involving nucleophilic addition to the uracil ring is the reaction of 1,3-dimethyluracil
with double nucleophiles such as guanidines, which results in replacement of three ring atoms (N-CO-N).