Crystal structures of (5RS)-(Z)-4-[5-(furan-2-yl)-3-phenyl-4,5-di­hydro-1H-pyrazol-1-yl]-4-oxobut-2-enoic acid and (5RS)-(Z)-4-[5-(furan-2-yl)-3-(thio­phen-2-yl)-4,5-di­hydro-1H-pyrazol-1-yl]-4-oxobut-2-enoic acid

The title compounds, C(17)H(14)N(2)O(4) (I) and C(15)H(12)N(2)O(4)S (II), possess very similar mol­ecular geometries. In both mol­ecules, the central 1,3,5-tris­ubstituted di­hydro­pyrazole ring adopts an envelope conformation. The oxobutenoic acid fragment has an almost planar Z conformation [r.m.s. deviations of 0.049 and 0.022 Å, respectively, for (I) and (II)] which is determined by the both bond conjugation and the strong intra­molecular O—H⋯O hydrogen bond. The substituents in positions 1 and 3 of the di­hydro­pyrazole ring [oxobutenoic acid and phenyl in (I) and oxobutenoic acid and thienyl in (II)] are nearly coplanar with its basal plane [the corresponding dihedral angles are 6.14 (9) and 2.22 (11)° in (I) and 6.27 (12) and 3.91 (11)° in (II)]. The furyl ring plane is twisted relative to the basal plane of the di­hydro­pyrazole ring by 85.51 (8) and 88.30 (7)° in (I) and (II), respectively. In the crystal of (I), mol­ecules form zigzag hydrogen-bonded chains along [001] by C—H⋯O hydrogen bonds, which are further packed in stacks along [100]. Unlike (I), the crystal of (II) contains centrosymmetric hydrogen-bonded dimers formed by pairs of C—H⋯S hydrogen bonds, which are further linked by weak C—H⋯O hydrogen bonds into a three-dimensional framework.