ELECTROPHYLIC HETEROCYCLIZATION OF 5-METHYL-6-TIOXOPYRAZOLO[3,4-d]PYRIMIDINE-4-ON

Derivatives of pyrazolo[3,4-d]pyrimidine have valuable biological activity. The structural fragment of pyrazolopyrimidines is widely used to develop new effective pharmaceuticals. A new promising direction in the construction of polycyclic systems based on pyrazolopyrimidine is the method of electrophilic intramolecular heterocyclicization.The halogenation of 5-methyl-6-thioxopyrazolo[3,4-d]pyrimidin-4-one was carried out in acetic acid medium at room temperature with twice the excess of halogen. It was found that halogenation (with bromine and iodine) of 5-methyl-6-thioxopirazolo[3,4-d]pyrimidin-4-one results the annelation of the thiazolinic cycle with the formation of linear polynuclear systems of a salt-like structure. 7-Halogenomethyl-7-methyl-1,4,6,7-tetrahydropyrazolo[3,4-d][1,3]thiazolo[3,2-a]pyrimidin-4-one was obtained via the action of sodium sulfite in the DMSO-water medium.To study the effect of the nature of the electrophilic reagent on the direction of the electrophilic intramolecular cyclization of 5-methyl-6-thioxopyrazolo[3,4-d]pyrimidin-4-one the p-methoxyphenyltetrachloride was used (tested). Electrophilic heterocyclization take place under similar conditions (room temperature, glacial acetic acid medium), with the formation of the tricyclic system with an exocyclic aryltellurium moiety – 7-(dichloro-(4-methoxyphenyl) telluromethyl)-7-methyl-1,4,6,7-tetrahydropyrazolo[3,4-d][1,3]thiazolo[3,2-a]pyrimidin-4-one. Thus, the direction of electrophilic intramolecular cyclization of 5-methyl-6-thioxopyrazolo[3,4-d]pyrimidine-4-one using as electrophilic agents of halogens (bromine, iodine) and p-methoxyphenyltetrachloride does not depend on the nature of the electrophile and takes place with the participation of the exocyclic sulfur atom in the second position of the pyrimidine and lead to the formation of a condensed system of linear structure – halogenomethyl or aryl telluromethyl derivatives of pyrazolo[3,4-d][1,3]thiazolo[3,2-a]pyrimidin-4-one. The composition and structure of all synthesized compounds were proved by elemental analysis and 1H-NMR spectra.