trans-1,2-Bis(3,5-dimethoxyphenyl)ethene

The title compound, C18H20O4, was prepared in high yield from 3,5-dimethoxystyrene via a Ru-catalysed homo-olefin metathesis. Exclusive formation of the E-configurated isomer was observed. Interestingly, one symmetric unit contains two molecules adopting an s-syn-anti and and an all-s-anti conformation.

The title compound, C 18 H 20 O 4 , was prepared in high yield from 3,5-dimethoxystyrene via a Ru-catalysed homo-olefin metathesis. Exclusive formation of the E-configurated isomer was observed. Interestingly, one symmetric unit contains two molecules adopting an s-syn-anti and and an all-s-anti conformation.

Related literature
For the preparation of differently substituted stilbenes using a Ru-catalysed metathesis strategy, see: Velder et al. (2006). Alternative methodologies for the synthesis of oxy-functionalized stilbenes using Wittig-type olefinations or Heck couplings have been described by Kim et al. (2002), Lion et al. (2005), Botella & Nayera (2004) and Reetz et al. (1998). For the bioactivity of various stilbenes with a focus on their anticancer activity, see: Aggarwal et al.

Comment
In recent years, polyhydroxylated stilbenes such as resveratrol have gained a tremendous importance especially due to their potential for the prevention and therapy of cancer (Aggarwal et al. (2004), Wolter et al. (2002), Fremont (2000, Jang et al. (1997)). In the course of our own research in the field of bioactive stilbenes (Wieder et al. (2001)) we were able to develop a highly efficient synthetic route towards symmetrically as well as unsymmetrically substituted E-stilbenes applying a Ru-catalyzed metathesis strategy (Velder et al. (2006)). Alternative strategies for the synthesis of stilbenes are based on One of the compounds prepared was the title compound trans-1,2-bis-(3,5-dimethoxyphenyl)ethene. The asymmetric unit contains two molecules, A and B, both of which exhibit a center of symmetry (figure 1). The 3,5-dimethoxy groups of molecule B all adopt a s-anti configuration, whereas in molecule A, a s-syn as well as a s-anti conformation is found on both sides. Zhang and co-workers reported the same observation on a related structure (Yin et al., 2002). The torsion angles between the benzene ring planes in molecule A are 0.2 (3)° (C1a-C1-C2-C3), which gives the molecule a planar shape.
The molecules form slightly twisted pseudo-layers which are arranged along the b axis (Fig. 2). In figure 3, two of those pseudo-layers are shown from the top view (with the front layer being displayed in dark and the retral layer in light green).

Experimental
In a glove-box (Labmaster 130, mBraun), the catalyst (Grubbs-II, 2 mol %) was weighted into a 25 ml Schlenk tube, which was then sealed with a rubber septum. This was then taken out of the box, connected to an Ar-vacuum double manifold and equipped with a reflux condenser under argon. A solution of 3,5-dimethoxy-styrene (1 mmol) in CH 2 Cl 2 (10 ml) was then added via syringe and the resulting solution was refluxed for 1.5 h under argon. After allowing the reaction mixture to cool to room temperature, the solvent was evaporated in vacuo and the crude product was purified by flash chromatography (SiO 2 , cyclohexane/ ethyl acetate = 10:1) to give 138 mg (0.46 mmol; 92%) of the homo metathesis product (1). mp. 142°C   Fig. 1. A view of (1). Displacement ellipsoids are drawn at the 50% probability level.