Reduced 3,4′-bipyrazoles carrying thiophene and thiazole substituents: structures of two intermediates and two products

Abstract

Cycloaddition reactions between 3-(5-aryloxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)-1-(thiophen-2-yl)prop-2-en-1-ones and thiosemicarbazide leads to the formation of reduced 3,4′-bipyrazole-2-carbothioamides. Further cycloaddition of these intermediates with either diethyl acetylenedicarboxylate or 4-bromophenacyl bromide leads to reduced 3,4′-bipyrazoles carrying oxothiazole or thiazole substituents, respectively. The structures of two representative intermediates and two representative products established unambiguously the regiochemistry of the cycloaddition reactions. The molecules of 3′-methyl-5′-(2-methylphenoxy)-1′-phenyl-5-(thiophen-2-yl)-3,4-dihydro-1′H,2H-3,4′-bipyrazole-2-carbothioamide, C25H23N5OS2 (Ia), are linked by N—H...N hydrogen bonds to form simple C(8) chains. The analogous compound 5′-(2,4-dichlorophenoxy)-3′-methyl-1′-phenyl-5-(thiophen-2-yl)-3,4-dihydro-1′H,2H-3,4′-bipyrazole-2-carbothioamide hemihydrate crystallizes as a hemihydrate, C24H19Cl2N5OS2·0.5H2O (Ib), and the independent components are linked into a chain of spiro-fused R44(20) rings by a combination of O—H...N and N—H...O hydrogen bonds. In the structure of ethyl (Z)-2-{2-[3′-methyl-1′-phenyl-5-(thiophen-2-yl)-5′-(2-methylphenoxy)-3,4-dihydro-1′H,2H-3,4′-bipyrazole-2-yl]-4-oxo-4,5-dihydrothiazol-5-ylidene}acetate, C31H27N5O4S2 (II), inversion-related pairs of molecules are linked by paired C—H...π(arene) hydrogen bonds to form cyclic centrosymmetric dimers, but there are no direction-specific intermolecular interactions in 4-(4-bromophenyl)-2-[5′-(2,4-dichlorophenoxy)-3′-methyl-1′-phenyl-5-(thiophen-2-yl)-3,4-dihydro-1′H,2H-3,4′-bipyrazole-2-yl]-4-thiazole, C32H22BrCl2N5OS2 (III). Comparisons are made with the structures of some related compounds.

Keywords

• heterocyclic compounds
• reduced bipyrazoles
• synthesis
• crystal structure
• regiochemistry
• hydrogen bonding
• supramolecular assembly