Slivka N. Chemo- and regioselectivity in reaction of halogenocyclization of 2-alkenylthiosubstituted benzimidazoles, pyrimidin-6(1H)-ones, 1,2,4-thiazin-5(2H)-ones

It was shown that the effective methods for preparation of thiazolo (thiazino) benzimidazolium, pyrimidinium, thiazinium bromides and iodides are based on electrophilic intermolecular cyclization, and the appropriate recipes were elaborated. The regioselectivity of ring closure in these systems is governed by the nature and positioning of the substituents in alkenyl group at sulphur atom and proceeds in accordance with Markovnikov's rule. The chemo selectivity in these reactions is determined by the basicity of nitrogen atoms in the heterocycles. It is stated that halogenocyclization of 3-alkeniltio-4-amino-1,2,4-thiazin-5(2H)-ones that contains amino-group at N(4) atom proceeds on N(2) center, the basiсity of the latter is greater than this nitrogen atom in NH2 group. The method for oxidation of 2-alkenylthiosubstituted benzimidazoles, 2,3-dihydrothiazolobenzimidazoles and 2,3,4-trihydrothiazinobenzimidazoles by hydrogen peroxide for preparation of the approprate sulphons was elaborated.