The concept of nucleophilic aromatic substitution in halogenheterocycles has been successfully used for the derivatisation of a number of azaaromatics in numerous publications. Due to the fact, that 5-halopyrimidins are not very susceptible to nucleophilic substitution these compounds have been rarely used in organic synthesis. This work describes the reactivity of some 5-halogen-2-methylsulfonylpyrimidin-4-carboxylic acid derivatives towards nucleophiles. Especially the intramolecular nucleophilic cyclizations were studied. The method for preparation of hitherto unknown 2-amino-5-halogen- und 2-amino-5-methylsulfonylpyrimidin-4-carboxylic acids was worked out. The interaction of ethyl 2-alkylmercapto-4-chlor-5-pyrimidincarboxylates with 2-azahetarylacetonitriles was investigated. That results in the synthesis of hitherto unknown Pyridopyrimidins. In some cases the intermediates of these interactions were isolated. Although the cyclization rate of obtained carboxylates depends of both the basicity of heterocyclic fragment and steric surrounding of the heterocyclic nitrogen atom, it was shown, that this intramolecular acylation turns out to be more sensitive to basicity factor. The first representatives of eight new heterocyclic systems were synthesized.