Fused pyrimidine derivatives R 0515 Novel Alkylations of Cyclic Thioureas by α-Halocarboxylic Acids and Their Esters. Part 4. Alkylation of 1-Methyltetrahydropyrimidine-2(1H)-thione. -Alkylation of the cyclic thiourea (I) with α-chloroor bromoacetic acids or esters affords chloro or bromo salts of type (III). The chloro salts are readily hydrolyzed to the open-chain ammonium salt of type (IV) whereas the bromo salts are considerably more stable towards hydrolysis. -(KUSHAKOVA, P. M.; BASAN, Y. V.; YULISOVA, A. I.; LIFONTOVA, V. V.; RAMSH, S. M.; GARABADGIU, A. V.; BELOBRZECKAJA COSTA, L. N.; Chem. Heterocycl.

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dione hydrochloride while the second is more stable towards hydrolysis such that the corresponding hydrobromide is not separated. A paradoxical trend in the extent of the hydrolysis decreasing with the content of the water in the alcoholic solution comes to a complete stop in water. A possible explanation of this phenomenon is given.Keywords: 1-methyltetrahydropyrimidine-2(1H)-thione (N-methylpropylenethiourea), alkylation with chloro and bromoacetic acids and their esters.The reaction of tetrahydropyrimidine-2(1H)-thione (propylenethiourea) with α-halocarboxylic acids gives only the bicyclic thiazolo[3,2-a]pyrimidine hydrohalide structures [2][3][4][5]. As a result of alkylation with ethylbromo or ethylchloroacetate under "mild" conditions (room temperature in anhydrous acetone) it was possible to prepare "open" S-carbethoxymethyl propylenethiourea hydrohalide derivatives [5]. It was expected that the presence of an N-methyl substituent in the 1-methyltetrahydropyrimidine-2(1H)-thione molecule (1) would hinder the cyclization of the isothiouronium salts 2a-h which were formed when alkylating with α-halocarboxylic acids and their esters. However, it was found that these salts are labile under the indicated "mild" conditions and are readily cyclized to the corresponding 6,5-bicyclic compounds 3a-c.Holding compound 1 with chloroacetic acid or its esters in anhydrous acetone at room temperature for from several hours to several days gave either a crystalline precipitate or an oil which crystallized on standing in vacuo over P 2 O 5 or was self generating after several days (in the case of the butyl ester after 5 months). According to 1 H NMR and mass spectrometric data one and the same substance having the bicyclic structure 8-methyl-3-oxo-2,3,6,7-tetrahydro-5H-[1,3]thiazolo[3,2-a]pyrimidin-8-ium chloride (3a) was formed in all _______ * For Communication 3 see [1]. __________________________________________________________________________________________