Dimethyl 2-(aminomethylene)malonate

In the title compound, C6H9NO4, which is an example of a push–pull alkene, N—H⋯O interactions stabilize the crystal structure.

In the title compound, C 6 H 9 NO 4 , which is an example of a push-pull alkene, N-HÁ Á ÁO interactions stabilize the crystal structure.
Mainly enamines (X = NH, NR 1 ) are frequently used as reactants or intermediates in chemical syntheses of drugs, polymers and dyes (Bouzard et al., 1990, Cook et al., 1969. But also alkoxymethylenes (X = O) are often used in organic synthesis (Freeman et al., 1981).
Due to the opposite character of the substituents, the olefinic C=C double bond order is reduced and accompanied by increased bond orders of bonds between the olefinic carbon atoms and their electron donor and electron acceptor groups.
This leads to the substantial decrease of the rotational barrier about the C=C double bond and to the increase of an analogues barrier about the adjacent bonds. These changes are connected with the separation of positive and negative charges and electron delocalization within the π-electron system. Such compounds belong to the most developed structures in the search for new compounds with non-linear optics responses (Nalwa et al., 1997, Chemla et al., 1987. The study of a similar compound, dimethyl-(dimethylaminomethylene)-malonate, has been done (Shmueli et al., 1973).
This study revealed that dimethyl-(dimethylaminomethylene)-malonate exists in solid phase as ZE conformer (Z denotes towards to C=C double bond orientation of the carbonyl oxygen in trans position; E denotes away from C=C double bond orientation of the carbonyl oxygen in cis position). The study of aminomethylene-malonic acid dimethyl ester revealed that this compound exists in solid phase as EZ conformer. The =C-N bond length of 1.301 (4)Å in the title compound is somewhat shorter than in the case of dimethyl-(dimethylaminomethylene)-malonate (1.337 Å). The C=C bond length of 1.385 (5)Å is slightly longer than in the case of dimethyl-(dimethylaminomethylene)-malonate (1.380 Å). The =C-C trans and cis bond lengths are 1.470 (4)/1.456 (5)Å, respectively in the title compound and 1.442/1.488 Å in dimethyl-(dimethylaminomethylene)-malonate.

Experimental
To dimethyl 3-methoxymethylenemalonate (1.74 g, 10 mmol) in methanol (10 ml), an aqueous solution of ammonia (12 mmol) was added dropwise (amount according to concentration and density) over a period of 30 min with stirring. The slightly warmed mixture was stirred overnight at room temperature. The reaction mixture was then briefly heated to reflux (ca. 20 min). After ensuring that no starting derivative remained (thin-layer chromatography; Silufol 254, Kavalier Czechoslovakia; eluent chloroform-methanol 10:1 v/v, detection UV light 254 nm), the reaction mixture was evaporated on a vacuum evaporator and chromatographed on silica gel (eluent dichloromethane-methanol 10:1 v/v). Obtained product was recrystallized from minimal amount of chloroform and n-hexane mixture in refrigerator.
supplementary materials sup-2 The solid phase mid-IR vibrational spectrum was recorded with a Nicolet model NEXUS 470 FTIR spectrometer at room temperature. The measurement was performed after mixing the powdered sample with KBr into a pellet.

Refinement
All H atoms were positioned geometrically and allowed to ride on their corresponding parent atoms at distances of C methyl -H = 0.96Å, C aromatic -H = 0.93Å and N-H =0.86 Å, with U iso (H) = 1.2U eq (C,N) or U iso (H) = 1.5U eq (C methyl ). Methyl groups were allowed to rotate but not to tip. Fig. 1. The atom-numbering scheme of aminomethylene-malonic acid dimethyl ester. Displacement ellipsoids are drawn at the 50% probability level.  Rotation method data acquisition using ω and φ scans θ min = 4.2º 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 Rfactors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq