Diethyl 1,8-diphenyl-11-oxatricyclo[6.2.1.02,7]undeca-2,4,6-triene-9,10-dicarboxylate

The title compound, C28H26O5, is the Diels–Alder adduct from 1,3-diphenylbenzo[c]furan and diethyl maleate. The molecule comprises of a fused tricyclic system containing two five-membered rings, which are in envelope conformations with the O atom at the flap, and a six-membered ring adopting a boat conformation. The dihedral angle between phenyl substituents in the 1,8-positions is 55.1 (1)°. The ethyl groups are disordered over two sets of sites, with occupancy ratios of 0.648 (9):0.352 (9) and 0.816 (1):0.184 (1). In the crystal, pairs of C—H⋯π interactions link the molecules into inversion dimers.

The title compound, C 28 H 26 O 5 , is the Diels-Alder adduct from 1,3-diphenylbenzo[c]furan and diethyl maleate. The molecule comprises of a fused tricyclic system containing two fivemembered rings, which are in envelope conformations with the O atom at the flap, and a six-membered ring adopting a boat conformation. The dihedral angle between phenyl substituents in the 1,8-positions is 55.1 (1) . The ethyl groups are disordered over two sets of sites, with occupancy ratios of 0.648 (9):0.352 (9) and 0.816 (1):0.184 (1). In the crystal, pairs of C-HÁ Á Á interactions link the molecules into inversion dimers.
Cg1 and Cg2 are the centroids of the C2-C7and C9-C14 rings respectively. including the synthesis of discrete molecular architectures such as molecular gears (Stevens & Richards 1997). The title compound, C 28 H 26 O 5 , comprises a fused tricyclic system and two phenyl rings attached with this system (Fig. 1). The tricyclic system consists of two 5-membered rings and one aromatic ring. In addition, two ethyl carboxylate units are attached to the tricyclic system. Geometrical parameters agree well with reported structures (Doboszewski et al. 2010;Toze et al. 2011;Bailey et al. 1995;Ohwada et al. 2001;Takahashi et al. 2003). The five membered ring C 1 \C 2 \C 7 \C 8 \O 1 adopts an envelope conformation with O 1 displaced by -0.752 Å from the mean plane of the other ring atoms C 1 \C 2 \C 7 \C 8 .
Atoms C24 and C28 of the ester groups are disordered over two sites with occupancy ratios of 0.648 (9)

Experimental
1, 3-diphenylisobenzofuran (1.00 g, 2.26 mmole) was dissolved in toluene (25 ml) and treated with 2 equivalents of diethyl maleate (0.78 g, 4.52 mmole). The reaction mixture was refluxed and the reaction was monitored by TLC. After 8 h, the mixture was cooled to room temperature. The solvent was removed and the residue was purified by column chromatography (Silica gel, 10%, ethyl acetate/hexane) to give the adduct as a white solid. Yield: 1.42 g (87%). This adduct was crystallized from CHCl 3 /CH 3 OH (3:1) by slow evaporation of tzhe solvent.

Refinement
All H atoms were positioned geometrically and allowed to ride on their parent atoms, with (C-H= 0.93-0.96 Å), and U iso (H) = 1.5 U eq (C) for methyl H atoms and 1.2 U eq (C) for other H atoms. The carbon atoms of ester groups are disordered over two sites with occupancy ratio of 0.648 (9): 0.352 (9) and 0.816 (1): 0.184 (1).   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 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.