Ethyl 5-hydroxy-6-oxo-4-phenyl-5,6-dihydro-4H-cyclopenta[b]thiophene-5-carboxylate

In the title molecule, C16H14O4S, the dihydrocyclopentathiophenone ring system is almost planar, with an r.m.s. deviation of 0.060 Å from the best fit plane through all nine non-H atoms. The cyclopentanone ring adopts a severely flattened envelope conformation with the C atom carrying the OH and ethylcarboxylate substituents at the flap. This atom lies only 0.185 (3) Å from the plane through the other four C atoms. The phenyl substituent is inclined at 43.37 (5)° to the dihydrocyclopentathiophenone mean plane. In the crystal, molecules are linked by pairs of O—H⋯O hydrogen bonds, forming inversion dimers with R 2 2(10) ring motifs. Weak C—H⋯O hydrogen bonds also link molecules into chains along c, while an approximately orthogonal set of C—H⋯O contacts form chains along b, resulting in layers lying parallel to (100). Inversion dimers also form through weaker R 2 2(12) C—H⋯S contacts, which combine with C—H⋯O contacts to form stacks along b.

In the title molecule, C 16 H 14 O 4 S, the dihydrocyclopentathiophenone ring system is almost planar, with an r.m.s. deviation of 0.060 Å from the best fit plane through all nine non-H atoms. The cyclopentanone ring adopts a severely flattened envelope conformation with the C atom carrying the OH and ethylcarboxylate substituents at the flap. This atom lies only 0.185 (3) Å from the plane through the other four C atoms. The phenyl substituent is inclined at 43.37 (5) to the dihydrocyclopentathiophenone mean plane. In the crystal, molecules are linked by pairs of O-HÁ Á ÁO hydrogen bonds, forming inversion dimers with R 2 2 (10) ring motifs. Weak C-HÁ Á ÁO hydrogen bonds also link molecules into chains along c, while an approximately orthogonal set of C-HÁ Á ÁO contacts form chains along b, resulting in layers lying parallel to (100). Inversion dimers also form through weaker R 2 2 (12) C-HÁ Á ÁS contacts, which combine with C-HÁ Á ÁO contacts to form stacks along b.

Comment
There is currently much interest in research into conducting thiophene polymers (Anquetil et al., 2003). Our interest in molecular actuators based on this chemistry led to the isolation of the previously unreported title compound.
In the molecular structure of the title molecule ( Fig. 1), the flap atom of the severely flattened C3···C7 ring carries both hydroxy and ethylcarboxylate substituents. Atom C6 lies 0.185 (3) Å from the mean plane through atoms (C3-C5,C7) and this plane is inclined at 4.43 (8) ° to the thiophene ring (S1,C1-C4) mean plane. As a result the dihydrocyclopenta-thiopheneone ring system is also reasonably planar with a r.m.s. deviation of only 0.060 Å from the plane through all 9 non-hydrogen atoms. The C7 atom of the cyclopentane ring carries a phenyl substituent that subtends a dihedral angle of 43.37 (5) ° to the dihydrocyclopentathiophene plane. The Cambridge Crystal Structure Database (CSD, Version 5.32, last update Aug. 2011; Allen, 2002) reveals only three structures involving dihydrocyclopenta-thiophene-one ring systems (Bonini et al., 2004;Chang et al., 2004). In the title molecule the bond distances are normal (Allen et al., 1987) and similar to those reported for these similar molecules.
X-ray quality crystals were obtained from a CH 2 Cl 2 solution of the title compound layered with hexane. M.p 404 K. HRMS (+ve ESI) m/z calc for C 16 H 13 O 4 SNa 324.0427, found 325.1152. Spectroscopic data for the title compound are available in the archived CIF.

Refinement
The H atom of the OH group was located in a difference Fourier map and its coordinates were refined with U iso = 1.5U eq (O).
All C-bound H atoms were included in calulated positions and refined using a riding model: d(C-H) = 0.95, 1.00, 0.99 supplementary materials sup-2 and 0.98 Å, for aromatic, methine, methylene and methyl H-atoms, respectively, with U iso = k × U eq (C), where k = 1.5 for methyl H atoms, and k = 1.2 for all other H atoms. Fig. 1. The molecular structure of the title molecule, with numbering scheme and dispacement ellipsoids drawn at the 50% probability level.   Ethyl 5-hydroxy-6-oxo-4-phenyl-5,6-dihydro-4H-cyclopenta[b]thiophene-5-carboxylate Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness 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 threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) 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.