Methyl (2Z)-2-{(2Z)-3-[(cyclopentylidene)amino]-4-oxo-2-phenylimino-1,3-thiazolidin-5-ylidene}acetate

In the title compound, C17H17N3O3S, the thiazole ring is nearly planar [maximum deviation = 0.015 (1) Å for the ring N atom] and the cyclopentane ring has a twist conformation. The molecular conformation is stabilized by a hypervalent interaction between the S atom and the ester group carbonyl O atom, with an S⋯O distance of 2.7931 (10) Å. In the crystal, C—H⋯O interactions generate chains of molecules propagating along [110] and π–π stacking interactions [centroid–centroid distance = 3.4677 (7) Å] between the thiazole rings organize these chains into (001) layers.


Comment
Diversity in the biological response profile of thiazolidinone and analogous scaffolds has attracted much attention to the exploration of this skeleton for a variety of therapeutic applications. Thus, the successful pharmaceutical applications of pioglitazone as a hypoglycemic agent (Pfützner et al., 2007;Schianca et al., 2012), thiazolidomycin activity against streptomyces species (Jain et al., 2012), etozoline as an antihypertensive (Lant, 1986), and ralitoline as a potent anticonvulsant (Rock et al., 1991) have established the wide spectrum potential of the thiazolidinone moiety. As part of our ongoing program of drug design and discovery, we report the synthesis and crystal structure of the title compound.

Experimental
A solution of 1 mmol (233 mg) 2-cyclopentylidene-N-phenylhydrazinecarbothioamide in 15 ml ethanol was added dropwise to a solution of 1 mmol (142 mg) dimethyl but-2-ynedioate in 10 ml ethanol. The reaction mixture was stirred and refluxed at 351 K. The reaction progress was monitored by TLC until completion. On cooling a solid yellow product was precipitated, filtered off under vacuum and recrystallized from ethanol to furnish block-shaped yellow crystals (m.p. 541-543 K).

Refinement
All H atoms were positioned geometrically and treated as riding atoms, with C-H = 0.95 Å (aromatic H), 0.98 Å (methyl H) and 0.99 Å (methylene H), with U iso (H) = 1.5 U iso (C) for methyl H atoms and U iso (H) = 1.2 U iso (C) for the others. The components of the displacement parameters in the direction of the bond between non-hydrogen atoms were restrained to be equal within an effective standard deviation of 0.01 (DELU instruction).

Figure 1
Perspective view of the title compound with 50% probability displacement ellipsoids.

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq S1 0.49073 (