We have recently shown that N-aryl-3-oxobutanethioamides react with such 2-aminoazoles (azines) as 3-amino-5-R-1,2,4-triazoles [1], 2-amino-5-R-pyridines [2], 2-amino-4-R-5-R 1 -thiazoles [3], and 5-aminotetrazole [4] via a [3+3] cycloaddition scheme to form two groups of compounds (pyrimidine-4-thione and 4-(arylamino)pyrimidine derivatives) the ratio of which depends on the basicity of the heterocyclic 1,3-dinucleopile and the acidity of the solvent [1][2][3][4].The aim of this work is to continue our investigation [1-4] and study of the regioselectivity of the cyclization of the N-aryl-3-oxobutanethioamides 1a-d with such 1,3-dinucleophiles as the 5-amino-3-R-4-R 1 -pyrazoles, viz 5-amino-3-methylpyrazole (2a), 5-amino-4-cyanopyrazole (2b), and 3-amino-2H-pyrazolo-[3,4-b]pyridine (2c) in the absence and the presence of a proton donor solvent. Such a course should prove an addition to the general results of preceding work [1][2][3][4], in particular the observation of the effect of the nucleophilicity of the 2-aminoazole and the acidity of the solvent on the regioselectivity of the process.Since the [3+3] cyclocondensation can occur at three reaction centers in the N-aryl-3-oxobutanethioamides 1a-d and at two in the 5-amino-3-R-4-R 1 -pyrazoles 2a-c the reaction products can be four groups of compounds i.e. 2(4)-methyl-7-R-8-R 1 -1,4(1,2)-dihydropyrazolo[1,5-a]pyrimidine-4(2)-thiones and 4(2)-arylamino-2(4)-methyl-7-R-8-R 1 -pyrazolo[1,5-a]pyrimidines.It was shown that two groups of compounds are the result of the reaction, i.e. the pyrimidine thiones 3a,b and the 4-(arylamino)pyrazolo[1,5-a]pyrimidines 4a-f. The structure of the dihydropyrazolo[1,5-a]pyrimidine thiones 3a,b was proved by thionation of the 2,7-dimethyl-1,4-dihydropyrazolo-[1,5-a]pyrimidin-4-one 5 (the structure of which had been proved using X-ray analysis [5]) to give the 2,7-dimethyl-1,4-dihydropyrazolo-[1,5-a]pyrimidine-4-thione (3a). Since the 5-amino-3-R-4-R 1 -pyrazoles are isoelectronic with 3-amino-__________________________________________________________________________________________
