6-Aminouracils are very useful intermediates for building different categories of heterocyclic compounds. 6-Aminouracils are electron rich compounds due to the presence of free amino group which can initiate interactions with electron deficient centres or activate the nearby C-5 position to start the reaction followed by cyclization in most cases. The present review summarizes the different reactions developed for the synthesis of substituted and annulated pyrimidines. A diversity of substituted pyrimidines was prepared directly from reactions of 6-aminouracils with some electrophilic reagents, meanwhile formation of fused pyrimidines were achieved by reaction of 6-aminouracils with a variety of reagents such as aromatic and aliphatic aldehydes, acyclic and cyclic methylene ketones, cyclic enols, alkynes, iminium salts and a diversity of other reagents.