2,3,5,6-Tetramethoxypiperazine-1,4-dicarbaldehyde

The asymmetric unit of the title compound, C10H18N2O6, contains two halves of two independent centrosymmetric molecules with almost identical conformations. Weak intermolecular C—H⋯O hydrogen bonds consolidate the crystal packing.

The asymmetric unit of the title compound, C 10 H 18 N 2 O 6 , contains two halves of two independent centrosymmetric molecules with almost identical conformations. Weak intermolecular C-HÁ Á ÁO hydrogen bonds consolidate the crystal packing.

Comment
The molecule of 1,4-diformyl-2,3,5,6-tetra-methoxypiperazine (Ferguson,1968a, b) (I), contains two formamyl groups in the two contrary-sides of the six-membered ring and four methoxy groups in the same axial situations. There are four asymmetric carbon atoms, S, S and R, R configuration which are mirror images of each other and diastereoisomer. The skeleton is symmetric by a central symmetry. The crystal contains two halves of two independent centrosymmetric molecules with almost identical conformations, which are comparable with similar molecule with acetyl substitutions (Vedachalam et al., 1991).
Despite the presence of six O and two N atoms carrying lone-pair electrons potentially are available for hydrogen-bond formation, there are, in fact, no powerful intramolecular C-H···N or C-H···O hydrogen bonds, rather some week C-H···O intermolecular interactions are observed (Table 1, Fig. 2).
The Properties of the anomeric effect in the infected system, n O →σ* C-N interactions are recognizable (Reed & Schleyer, 1988), The O-C bond is shorter than the C-N bond and the stability of gauche (axial) forms is definitely more than anti (equatorial) ones ( Figure 1). This electron transfer results in lengthening the exocyclic anomeric C-O bonds, in the endocyclic contraction of the C-N bonds by increasing its double-bond character in the opening of the O-C-N angle as compared with its normal tetrahedral value. It can be considered that aa, ag and gg conformations of the C-O-C-N-C moieties, where a = anti (antiperiplanar) and g = gauche (synclinal) which aa and ag refer to equatorial and gg to axial. All of the Methoxy groups are in the gg conformations, comparable with gg in glycoside conformations that are more stable than aa, equatorial conformations (Schleifer et al., 1990). The acetyl groups as substitutions select axial positions than equatorials (Vedachalam et al., 1991).
In (I) via resonation of N-lone-pairs with pi-electrons of the carbonyl double-bond, N-pyramidalities (about 360°) are larger than natural forms (about 320°) at the same of molecule with acetyl substitutions (Vedachalam et al., 1991).
Experimental 1,4-Diformyltetrachloropiperazine (7.04 g,0.04 mol) (Ferguson, 1968a,b) were mixed with barium carbonate (78 g) and absolute methanol (32 ml, 0.79 mol) were added to the mixture and heated at 313 K for 3 h with stirring. The barium carbonate was filtered off and the methanol solution evaporated. The solid residue was extracted by 20 ml of hot chloroform and the extract evaporated to give white precipitation and washed with a little cold water and dried in oven by 303 K of temperature affording 1.83 g (70% yield) of (I). This solid was crystallized by hot mixture of methanol and benzene (m.p. supplementary materials sup-2 Refinement All H atoms were geometrically positioned (C-H 0.93 -0.98 Å) and refined as riding, with U iso (H) = 1.2-1.5 U eq (C). Fig. 1. Two independent molecules of (I) showing the atomic numbering and 50% probability displacement ellipsoids [symmetry codes: (A) 1 -x, 1 -y , 1 -z; (B) 2 -x , 1 -y , 1 -z]. H atoms omitted for clarity.