РЕГІО- ТА СТЕРЕОСЕЛЕКТИВНІСТЬ ТЕЛУРОІНДУКОВАНОЇ ЦИКЛІЗАЦІЇ 6-МЕТИЛ-2-ПРОПАРГІЛТІОПІРИМІДИН-4(3H)-OНУ п-АЛКОКСИФЕНІЛТЕЛУРТРИХЛОРИДАМИ

Abstract

Aryltellurium trihalides are used as reagents for electrophilic cyclization of alkenyl and alkynyl substances with an additional O-nucleophilic center, the products of cyclization exhibit high biological activity. On the other hand, the information on the tellur-inducted cyclization of N, S-unsaturated pyrimidinone derivatives is limited only by the usege of alkenylfunctionalized heterocycles. Therefore, the purpose of this work is to investigate the regio- and stereoselectivity of the tellurocyclization of S-alkynyl pyrimidine. The 6-methyl-2-propargylthiopyrimidin-4(3H)-one was obtained by alkylation of 6-methyl-2- thioxopyrimidin-4-one and it was selected as the object of study. Synthetically available p-methoxyand p-ethoxyphenyltellurium trichlorides were used as tellurium-containing electrophilic reagents. Propargyl pyrimidinone has several nucleophilic centers for the attack of electrophilic reagents - the triple carbon-carbon bond of the alkynyl substituent, the endocyclic nitrogen atoms in the first and third positions of the pyrimidine cycle. This makes it a convenient system for the study of the regioand stereoselectivity of aryltellurochlorination. The telluroheterocyclization of alkenyl derivatives of heterocycles occurs through the stage of formation of a telluronium cation followed by an intramolecular nucleophilic attack of an additional nucleophilic center (N, S, or O). Therefore, for the propargyl pyrimidinone, two competing cyclization directions with the involvement of N (1) - or N (3) -pyrimidine atoms are possible. The reaction of 6-methyl-2-propargylthiopyrimidin-4-one with p-alkoxyphenyltellurium trichlorides was carried out in acetic acid at room temperature. After 8 hours of stirring the reagents, thiazolinopyrimidine complexes with p-alkoxyphenyltellurium trichlorides formed and irrespective of the ratio of the reagents were isolated and spectrally identified. NMR and IR spectra proved the annulation of the thiazole cycle with the involvement of the N(3)-atom and the formation of the complex. It should be noted that aryltelluromethylidenthiazolinopyrimidine is formed as one configuration isomer with the Z-configuration. The advantage of the formation of the Z-isomer is explained by the possibility of intramolecular coordination of the carbonyl oxygen atom to the tellurium atom of the exocyclic telluromethylidene group. Therefore, the tellurium-induced cyclization of 6-methyl-2-propargylthiopyrimidin-4(3H)-one occurs regioselectively with the formation of complex of hydrochloride 7-methyl-3-{[dichloro (4- alkoxyphenyl)-telluro]methylidene}-2,3-dihydro-5H-[1,3]thiazolo[3,2-a]pyrimidin-5-one with palkoxyphenyltellurium trichlorides. Aryltellurochlorination proceeds stereoselectively with the formation of the single Z-configuration isomer.