Potassium (1-methoxy­carbonyl-2-methyl­prop-2-en-2-yl­idene)azinate

Cédric Reuter; Jörg M Neudörfl; Hans-Günther Schmalz

doi:10.1107/S1600536810010159

. 2010 Mar 27;66(Pt 4):m461. doi: 10.1107/S1600536810010159

Potassium (1-methoxycarbonyl-2-methylprop-2-en-2-ylidene)azinate

Cédric Reuter ^a, Jörg M Neudörfl ^a, Hans-Günther Schmalz ^a,^*

PMCID: PMC2984059 PMID: 21580546

Abstract

In the title compound, K⁺·C₆H₈NO₄ ⁻, the K⁺ cations have a coordination number of seven and are surrounded by four bidentate azinate anions. The methylene groups of the anions are always directed towards the coordinated potassium cations. The N—C—C—C torsion angle is 101.2 (2)°. The orthogonal non-conjugated nature of the salt confirms the supposed geometry and reactivity of this compound.

Related literature

For a short overview of peptidomimetics, see: Grauer et al. (2009 ▶); Vagner et al. (2008 ▶); Wu et al. (2008 ▶). For the synthesis of peptidomimetics, amino-acid-based building blocks play a key role in the assembly of these structures, see: Kemp, Boyd & Muendel (1991 ▶); Kemp, Curran et al. (1991 ▶); Beal et al. (2000 ▶); Kühne et al. (2008 ▶). A known deprotonation/protonation sequence (Bouveault & Wahl, 1901 ▶) was used in the synthesis of the title compound. The protonation of the title compound occurs exclusively at the α-position and no protonation of the methylene group was observed (Baldwin et al., 1977 ▶).

Experimental

Crystal data

K⁺·C₆H₈NO₄ ⁻
M _r = 197.23
Monoclinic,
a = 23.9269 (13) Å
b = 5.2909 (2) Å
c = 14.2510 (7) Å
β = 113.361 (2)°
V = 1656.21 (14) Å³
Z = 8
Mo Kα radiation
μ = 0.62 mm⁻¹
T = 100 K
0.20 × 0.15 × 0.03 mm

Data collection

Nonius KappaCCD diffractometer
6264 measured reflections
1810 independent reflections
1416 reflections with I > 2σ(I)
R _int = 0.041

Refinement

R[F ² > 2σ(F ²)] = 0.028
wR(F ²) = 0.061
S = 1.01
1810 reflections
111 parameters
H-atom parameters constrained
Δρ_max = 0.31 e Å⁻³
Δρ_min = −0.27 e Å⁻³

Data collection: COLLECT (Hooft, 1998 ▶); cell refinement: DENZO (Otwinowski & Minor, 1997 ▶); data reduction: DENZO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: SCHAKAL99 (Keller, 1999 ▶); software used to prepare material for publication: PLATON (Spek, 2009 ▶), publCIF (Westrip, 2010 ▶) and ORTEP (Davenport et al., 1999 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536810010159/jj2024sup1.cif

e-66-0m461-sup1.cif^{(23KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810010159/jj2024Isup2.hkl

e-66-0m461-Isup2.hkl^{(89.3KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected bond lengths (Å).

K1—O1ⁱ	2.7036 (10)
K1—O2ⁱⁱ	2.7539 (11)
K1—O3ⁱ	2.7988 (11)
K1—O1	2.7994 (11)
K1—O2	2.8896 (10)
K1—O3ⁱⁱⁱ	2.8970 (12)
K1—O1ⁱⁱⁱ	2.9080 (11)

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) .

Acknowledgments

This work was supported by the Deutsche Forschungsgemeinschaft (FG 806).

supplementary crystallographic information

Comment

In the last decade, interest in peptidomimetics has lead to a fast growing research field within organic chemistry (Grauer et al., 2009). Artificial peptide-like compounds are used to explore the principles of protein-protein interactions and their modulation (Vagner et al., 2008; Wu et al., 2008). In the synthesis of different peptidomimetics, amino acid based building blocks play a key role in the assembly of these structures (Kemp, Curran et al., 1991; Kemp, Boyd & Muendel, 1991; Beal et al., 2000; Kühne et al. 2008). In the context of our work we used an already known deprotonation/protonation sequence (Bouveault et al., 1901) to synthesize our compound. The protonation of the title compound occurs exclusively at the α-position whereas no protonation of the methylene group was observed (Baldwin et al., 1977).

In the title compound, C₆H₈KNO₄, (I),(Fig. 1), the deconjugation within the molecule combined with the high basicity of the nitro enolate provides a convincing explanation for the high selectivity of this reaction (Fig. 2). The crystal structure supports the assumption made by Baldwin et al. about the geometry of this potassium salt. The potassium cations in the crystal stucture have a coordination number of seven and are surrounded by four azinate anions with K—O distances from 2.704 (1) to 2.908 (1) Å (Fig. 3). These can either bind via the carbonyl group or the nitrogen-bonded oxygen atoms whereas both motifs can be found as bridging units. The resulting polar layers of potassium cations surrounded by oxygen atoms are perfectly shielded by the methyl and methylene residues (Fig. 4). This results in loose interactions between the different layers and explains the facile mechanical fissility of the crystals.

Experimental

The title compound, C₆H₈KNO₄, was prepared in good yield from methyl 3-methyl-2-nitrobut-2-enoate by deprotonation with potassium hydride. In a dry, argon-flushed 50 ml flask, 30.1 mmol of potassium hydride where suspended in 15 ml of dry THF. The suspension was cooled to 0 °C and a solution of 30.1 mmol methyl-3-methyl-2-nitrobut-2-enoate in 5 ml of THF was added via syringe over 30 min. After stirring for 5 h at room temperature a small amount of n-octanol was added at 0 °C to destroy the excess of potassium hydride. The paste was filtrated, washed three times with THF and dried in vacuo to give 4.950 g (25.1 mmol, 83%) of an ochre powder. A portion of the salt was recrystallized from MeOH/THF to give colourless prisms.