6-Chloro-3-[(dimethylamino)methylidene]thiochroman-4-one

The asymmetric unit of the title compound, C12H12ClNOS, contains three independent molecules, with the thiochroman ring adopting a sofa conformation in each one. The crystal structure features C—H⋯O interactions; one of the O atoms accepts three such bonds. Together, the hydrogen bonds give rise to a molecular tape propagating in [010].


Comment
Thiochromanones belong to an important class of oxygen containing heterocycles; many of their derivatives have been reported to possess important biological activities including antifungal activity (Wang et al.,2010). They also serve as the starting material for the synthesis of novel heterocyclic systems (Sosnovskikh, 2003).
There are three crystallographically independent molecules (A, B and C) in an asymmetric unit of the title compond ( Fig. 1) wherein 6-chloro-thiochroman moiety is substituted with the dimethylaminomethylene group at C2. The dimethylamino group is oriented trans with respect to the oxo group of the thiochroman moiety which is described by the torsion angles N1-C3A-C2A -C4A, N2-C3B-C2B-C4B and N3-C3C-C2C- C4C [172.25 (3), -173.45 (2) and -171.53 (3)°] for the molecules A, B and C, respectively. The thiochroman rings in the three molecules are significantly puckered and adopt sofa conformations. A mean-planes calculation shows that the atoms S1A, S1B and S1C deviate from the mean planes of the remaining ring atoms by 0.7536 (1), -0.7360 (1) and -0.6753 (1) Å, respectively. The bond distances and angles in the three molecules of the title compound agree very well with the corresponding bond distances and angles reported in a closely related compound (Butt et al., 1988).
The crystal structure is stabilized by C-H···O type intermolecular interactions (Tab. 1 & Fig. 2); three such interactions form trifurcated bonds from three donors C1A, C11A and C12A to the same acceptor O1B, linking the molecules in a tape like structure. Whereas, another C-H···O interaction results in a one dimensional chain along the b-axis.

Experimental
A mixture of 6-chloro -thiochroman-4-one (0.01 mol) and dimethylformamide-dimethylacetal (DMF-DMA) (2 mL) was heated under reflux for 10 h. The reaction mixture was triturated with ethanol to give a solid product that was collected by filtration and crystallized from ethanol to give the title compound as deep yellow crystals, melting point 379-381 K. Yield 78%.

Refinement
The H atoms were placed at calculated positions in the riding model approximation with C-H = 0.97° A, 0.93 Å and 0.96 Å for aromatic, heterocyclic and methyl H-atoms respectively, with U iso (H) = 1.5U eq (C) for methyl H atoms and U iso (H) = 1.2U eq (N/C). Since the crystals contained racemic twins, an absolute structure could not be established and therefore, 2865 Friedel pairs of reflections were merged.

Computing details
Data collection: SMART (Bruker, 1998); cell refinement: SAINT-Plus (Bruker, 1998); data reduction: SAINT-Plus     where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.20 e Å −3 Δρ min = −0.32 e Å −3 Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes. 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 > 2σ(F 2 ) is used only for calculating R-factors(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.