Diethyl 3,8-di­methyl-4,7-di­aza­deca-2,8-dienedioate

The title compound, C₁₄H₂₄N₂O₄, consists of two symmetric moieties related through a twofold axis. The whole mol­ecule has a cis conformation. Both the ionic enol form and the non-ionic keto form make comparable contributions to the structure. In the crystal structure, infinite supramolecular chains are formed through N—H...O hydrogen bonds.

S1. Comment

β-Enaminoesters represent an important class of functionalized synthetic blocks (Bartoli et al., 2004). Recently, the title compound, (I), has been synthesized for the first time in our laboratory. According to a model of synergetic mutual reinforcement of hydrogen bonding and π-delocalization within a heterodienic system (Gilli et al., 1989, 1993; Bertolasi et al., 1991), (I) may be regarded as containing both the ionic enolic and non-ionic keto forms (see scheme). The structure of (I) has been established by ¹H and ¹³C NMR and IR spectroscopies, and has been fully confirmed by an X-ray structural analysis. \sch

As shown in Fig. 1, compound (I) is built up from two asymmetric units related through a twofold axis. The whole molecule is arranged in a cis conformation with respect to the C6—C6(1 − x, y, 3/2 − z) bond. The C3═O1 bond [1.221 (2) Å] is shorter than a normal single C—O bond (ca 1.40 Å; Reference?), but longer than the double C═O bonds found in some esters, such as in an Amadori compound [1.189 (5) Å; Kojić-Prodić et al., 1995], a benzoate [1.200 (4) Å; Huertas et al., 1997] and a glycine derivative [1.186 (2) Å; Zhao et al., 2002]. The N═C5 bond in (I) [1.344 (2) Å] is longer than a typical double C═N bond (ca 1.269 Å; Reference?) but shorter than the C—N single bond [N—C6 1.443 (4) Å]. The C3—C4 bond length [1.425 (2) Å] is intermediate between a single C—C bond (ca 1.50 Å; Reference?) and a C═C double bond (ca 1.34 Å; Reference?). These features of the bond lengths in (I) indicate that both the ionic enolic and the non-ionic keto forms make comparable contributions to the structure. Please provide a reference for the standard bond lengths used in the above comparisons.

The ¹H and ¹³C NMR spectra show the olefinic resonances of atom C4 and its attached H atom at noticeably higher magnetic fields, 4.93 and 83.83 p.p.m., respectively. This indicates the contribution of the non-ionic keto form, which undertakes π-delocalization. On the other hand, the NH signal appears at a much lower magnetic field (8.64 p.p.m.) in the ¹HNMR spectrum and this is indicative of the contribution of the ionic enolic form. These two forms are also observed in the related compound with an ethylenediimine (Özkara et al., 2004), which shows almost the same deviations of the corresponding signals in the NMR spectra.

The IR spectroscopic data of (I) are consistent with the crystal structure. The absorption band centred at around 3297 cm⁻¹ is readily ascribed to the NH group. The absorption band of C═O stretching at 1604 cm⁻¹ appears to be lower than that for a typical C═O group (1712–1708 cm⁻¹; Reference?) and is indicative of the ionic enolic form of the molecule.

The asymmetric unit of (I) is almost planar, with mean and maximum deviations of 0.0014 and 0.1330 Å, respectively, as the π-delocalization is reinforced by an N—H···O1 hydrogen bond. The sum of the angles around the N atom is close to 360°, indicating that the N atom is involved in the ionic enolic form. In the solid state, the two halves of (I) are skewed, with a dihedral angle of 46.3° between them. In the structure, an infinite zigzag chain of molecules of (I) running along the [001] direction (Fig. 2) is built up via an N—H···O1(1 − x, 1 − y, 1 − z) hydrogen bond. These intermolecular hydrogen bonds form a ring which may be described as graph set R₂²(4) (Etter, 1990). This ring is embedded in the chain. There are no hydrogen bonds between separate chains. Duplication of the chain forms layers of (I) parallel to the (010) plane.

S2. Experimental

Ethyl acetoacetate and ethylenediamine, in a molar ratio of 2:1, were mixed together and refluxed with stirring for 2 h. Crystals of (I) were formed by recrystallization of the resulting solid from ethanol, with a yield of approximately 65% based on ethyl-acetoacetate. Spectroscopic analysis: IR (KBr, ν, cm⁻¹): 3297, 2984, 2953, 2898, 1604 (br), 1509, 1438, 1390, 1288, 1259, 1224, 1167 (br), 1115, 1092, 1067, 1021, 980, 784, 726, 566; ¹H NMR (CDCl₃, δ, p.p.m.): 8.64 (1H, NH), 4.48 (1H, s, C4—H), 4.07 (2H, q, C2—H₂), 3.35 (2H, s, C6—H₂), 1.90 (3H, s, C7—H₃), 1.23 (3H, t, C1j^aH₃); ¹³C NMR (CDCl₃, δ, p.p.m.): 170.86 (C5), 161.55 (C3), 83.83 (C4), 58.72 (CH₂), 44.07 (CH₂), 19.49 (CH₃), 14.85 (CH₃).

S3. Refinement

All H atoms were positioned geometrically and allowed to ride on their parent atoms, with an N—H distance of 0.86 Å and C—H distances in the range 0.93–0.97 Å, and with U_iso(H) = 1.5U_eq(C) for methyl H atoms and 1.2U_eq(C,N) for others. Please check amended text.

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SMART; data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXTL (Bruker, 2000); program(s) used to refine structure: SHELXTL; molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The formula unit of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii. Hydrogen bonds are illustrated by dashed lines.
	Fig. 2. Part of the crystal structure of (I), showing the infinite hydrogen-bonded chains running along the [001] direction. H atoms have been omitted for clarity, except those involved in hydrogen bonds. Hydrogen bonds are illustrated by dashed lines.

Diethyl 3,8-dimethyl-4,7-diazadec-2,8-dienedioate

Crystal data

C14H24N2O4	F(000) = 616
Mr = 284.35	Dx = 1.220 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 850 reflections
a = 11.734 (3) Å	θ = 2.7–20.2°
b = 10.566 (2) Å	µ = 0.09 mm^−1
c = 13.418 (3) Å	T = 293 K
β = 111.44 (1)°	Prism, colourless
V = 1548.5 (6) Å^3	0.25 × 0.15 × 0.15 mm
Z = 4

Data collection

Bruker SMART Apex CCD area-detector diffractometer	1520 independent reflections
Radiation source: fine-focus sealed tube	946 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.071
ϕ and ω scans	θmax = 26.0°, θmin = 2.7°
Absorption correction: multi-scan (SADABS; Bruker, 2000)	h = −14→14
Tmin = 0.98, Tmax = 0.99	k = −12→8
4031 measured reflections	l = −16→14

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.047	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.112	H-atom parameters constrained
S = 0.91	w = 1/[σ^2(Fo^2) + (0.0455P)^2] where P = (Fo^2 + 2Fc^2)/3
1520 reflections	(Δ/σ)max < 0.001
93 parameters	Δρmax = 0.11 e Å^−3
0 restraints	Δρmin = −0.15 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² 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 (Ų)

	x	y	z	Uiso*/Ueq
C1	0.63346 (19)	0.99298 (19)	0.38556 (14)	0.0799 (7)
H1A	0.5979	1.0627	0.4098	0.120*
H1B	0.6141	1.0003	0.3098	0.120*
H1C	0.7207	0.9941	0.4220	0.120*
C2	0.58367 (19)	0.87270 (18)	0.40878 (14)	0.0722 (6)
H2A	0.4950	0.8730	0.3763	0.087*
H2B	0.6143	0.8020	0.3798	0.087*
C3	0.59892 (15)	0.74921 (19)	0.56145 (14)	0.0559 (5)
C4	0.64768 (14)	0.74732 (17)	0.67556 (13)	0.0543 (5)
H4	0.6858	0.8204	0.7108	0.065*
C5	0.64255 (15)	0.64664 (17)	0.73649 (13)	0.0516 (5)
C6	0.56509 (14)	0.43002 (17)	0.75074 (13)	0.0531 (5)
H6A	0.6219	0.4318	0.8244	0.064*
H6B	0.5790	0.3522	0.7185	0.064*
C7	0.70155 (17)	0.65551 (18)	0.85594 (12)	0.0661 (6)
H7A	0.6397	0.6510	0.8869	0.099*
H7B	0.7445	0.7345	0.8751	0.099*
H7C	0.7581	0.5868	0.8823	0.099*
N	0.58968 (12)	0.53648 (14)	0.69409 (10)	0.0536 (4)
H	0.5682	0.5285	0.6259	0.064*
O1	0.54318 (12)	0.66427 (13)	0.50176 (9)	0.0680 (4)
O2	0.62179 (11)	0.86080 (12)	0.52292 (9)	0.0667 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0989 (16)	0.0766 (16)	0.0645 (13)	−0.0110 (12)	0.0303 (12)	0.0107 (11)
C2	0.0907 (14)	0.0717 (15)	0.0516 (12)	−0.0127 (11)	0.0228 (10)	0.0043 (10)
C3	0.0626 (11)	0.0541 (12)	0.0554 (12)	−0.0057 (9)	0.0265 (9)	−0.0007 (10)
C4	0.0587 (11)	0.0551 (12)	0.0503 (10)	−0.0089 (9)	0.0214 (8)	−0.0062 (9)
C5	0.0536 (10)	0.0556 (12)	0.0486 (10)	−0.0050 (9)	0.0223 (8)	−0.0066 (9)
C6	0.0628 (10)	0.0487 (11)	0.0496 (10)	0.0032 (8)	0.0227 (8)	−0.0003 (8)
C7	0.0736 (12)	0.0700 (14)	0.0492 (11)	−0.0074 (10)	0.0158 (9)	−0.0031 (9)
N	0.0667 (9)	0.0553 (10)	0.0424 (8)	−0.0074 (7)	0.0241 (7)	−0.0048 (7)
O1	0.0880 (9)	0.0632 (9)	0.0513 (8)	−0.0215 (7)	0.0237 (6)	−0.0062 (7)
O2	0.0905 (9)	0.0578 (9)	0.0509 (8)	−0.0148 (7)	0.0249 (6)	0.0011 (6)

Geometric parameters (Å, º)

C1—C2	1.479 (2)	C4—H4	0.9300
C1—H1A	0.9600	C5—N	1.344 (2)
C1—H1B	0.9600	C5—C7	1.499 (2)
C1—H1C	0.9600	C6—N	1.445 (2)
C2—O2	1.436 (2)	C6—C6^i	1.520 (3)
C2—H2A	0.9700	C6—H6A	0.9700
C2—H2B	0.9700	C6—H6B	0.9700
C3—O1	1.221 (2)	C7—H7A	0.9600
C3—O2	1.353 (2)	C7—H7B	0.9600
C3—C4	1.425 (2)	C7—H7C	0.9600
C4—C5	1.356 (2)	N—H	0.8600
C2—C1—H1A	109.5	N—C5—C7	117.93 (16)
C2—C1—H1B	109.5	C4—C5—C7	119.38 (16)
H1A—C1—H1B	109.5	N—C6—C6^i	112.71 (11)
C2—C1—H1C	109.5	N—C6—H6A	109.0
H1A—C1—H1C	109.5	C6^i—C6—H6A	109.0
H1B—C1—H1C	109.5	N—C6—H6B	109.0
O2—C2—C1	107.88 (15)	C6^i—C6—H6B	109.0
O2—C2—H2A	110.1	H6A—C6—H6B	107.8
C1—C2—H2A	110.1	C5—C7—H7A	109.5
O2—C2—H2B	110.1	C5—C7—H7B	109.5
C1—C2—H2B	110.1	H7A—C7—H7B	109.5
H2A—C2—H2B	108.4	C5—C7—H7C	109.5
O1—C3—O2	121.54 (16)	H7A—C7—H7C	109.5
O1—C3—C4	127.05 (17)	H7B—C7—H7C	109.5
O2—C3—C4	111.40 (16)	C5—N—C6	127.00 (14)
C5—C4—C3	124.73 (17)	C5—N—H	116.5
C5—C4—H4	117.6	C6—N—H	116.5
C3—C4—H4	117.6	C3—O2—C2	117.13 (13)
N—C5—C4	122.65 (15)
O1—C3—C4—C5	2.2 (3)	C7—C5—N—C6	10.9 (2)
O2—C3—C4—C5	−177.66 (16)	C6^i—C6—N—C5	96.2 (2)
C3—C4—C5—N	−0.1 (3)	O1—C3—O2—C2	−3.3 (3)
C3—C4—C5—C7	177.78 (15)	C4—C3—O2—C2	176.53 (14)
C4—C5—N—C6	−171.27 (16)	C1—C2—O2—C3	−171.74 (16)

Symmetry code: (i) −x+1, y, −z+3/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N—H···O1	0.86	2.14	2.7841 (18)	132
N—H···O1^ii	0.86	2.67	3.292 (2)	130

Symmetry code: (ii) −x+1, −y+1, −z+1.