(4Z,6Z)-4,6-Bis(4-methoxybenzylidene)-2,2-dimethyl-1,3-dioxan-5-one

The title compound, C22H22O5, crystallizes with two independent molecules in the asymmetric unit, both of which possess pseudo-C s symmetry. The central 1,3-dioxanone rings have envelope conformations, with the C atom bearing the two methyl groups at the flap. The benzene rings of the methoxybenzylidene units, attached in the 4- and 6-positions on the central 1,3-dioxanone rings, are tilted in the same direction with dihedral angles varying between 8.2 (1) and 18.1 (1)°. The crystal packing is influenced by π-stacking interactions of the parallel displaced type [centroid–centroid distance of 3.723 (1) Å for molecule 1 and 3.884 (1) Å for molecule 2, with ring slippages of 1.432 and 1.613 Å, respectively] and the T-shaped type, with the long molecular axes all aligned along [010].

The title compound, C 22 H 22 O 5 , crystallizes with two independent molecules in the asymmetric unit, both of which possess pseudo-C s symmetry. The central 1,3-dioxanone rings have envelope conformations, with the C atom bearing the two methyl groups at the flap. The benzene rings of the methoxybenzylidene units, attached in the 4-and 6-positions on the central 1,3-dioxanone rings, are tilted in the same direction with dihedral angles varying between 8.2 (1) and 18.1 (1) . The crystal packing is influenced by -stacking interactions of the parallel displaced type [centroid-centroid distance of 3.723 (1) Å for molecule 1 and 3.884 (1) Å for molecule 2, with ring slippages of 1.432 and 1.613 Å , respectively] and the T-shaped type, with the long molecular axes all aligned along [010].  Table 1 Hydrogen-bond geometry (Å , ).

Comment
In the course of our investigations on the synthesis of bisarylidenes of hetero-and homo-cyclic ketones (Abaee et al., 2008a,b), we herein report on the synthesis and crystal structure of the title compound.
The asymmetric unit of the title compound contains two crystallographically independent molecules (1 and 2, Fig. 1), both having pseudo-C s symmetry. The bond distances and angles are close to those observed in similar compounds (Abaee et al., 2012;Nesterov et al., 2011;Shahani et al., 2010).
The crystal packing is influenced by π-stacking interactions (Hunter & Sanders, 1990) in a parallel displaced way concerning benzene ring II (C8-C13) and its symmetry equivalent in both independent molecules [symmetry center: -x, -y, -z+1 for molecule 1, and -x+1, -y+2, -z+2 for molecule 2]. The centroid-centroid distances are 3.723 (1) Å for molecule 1, and 3.884 (1) Å for molecule 2, with ring slippages of 1.432 and 1.613 Å, respectively. In addition, a T-shaped π-stacking contact is observed, involving the same benzene ring, II of molecule 1, via a C-H···π interaction with an equivalent benzene ring II of molecule 2 (Table 1). These interactions result in a mutually perpendicular orientation of molecules 1 and 2, and a parallel orientation of the benzene rings II of all molecules of type 1 to each other and all molecules of type 2 to each other.
All the long axes of both molecules are oriented parallel to the [010] direction (Fig. 2).

Experimental
A mixture of 2,2-dimethyl-1,3-dioxan-5-one (2 mmol), 4-methoxybenzaldehyde (4 mmol), diethylamine (8 mmol), and MgBr 2 .OEt 2 (0.2 mmol, 10 mol%) was stirred at room temperature under an atmosphere of argon for 2 h. The progress of the reaction was checked by TLC using a 1:4 mixture of EtOAc/hexane. At the end of the reaction, the mixture was diluted by CH 2 Cl 2 and washed with brine. The organic layer was dried using Na 2 SO 4 and concentrated under reduced pressure.
The product was isolated (83%) by column chromatography over silicagel using a 1:4 mixture of EtOAc/hexane. The solid product was recrystallized from EtOAc, giving yellow plate-like crystals of the title compound.