Crystal structure of diethyl 3-(3-chlorophenyl)-2,2-dicyanocyclopropane-1,1-dicarboxylate

The crystal structure of diethyl 3-(3-chlorophenyl)-2,2-dicyanocyclopropane-1,1-dicarboxylate shows one-dimensional chain substructures linked into two-dimensional layers of molecules, through both C—H⋯Ocarboxyl and C—H⋯Nnitrile hydrogen bonds.

In the racemic title compound, C 17 H 15 ClN 2 O 4 , which has been synthesized and the crystal structure of the solvent-free molecule determined, the angle between the planes of the benzene and cyclopropane rings is 54.29 (10) . The molecular conformation is stabilized by two weak intramolecular C-HÁ Á ÁO carboxyl interactions. In the crystal, C-HÁ Á ÁO hydrogen bonds form centrosymmetric cyclic R 2 2 (10) dimers which are linked into chain substructures extending along c. Further C-HÁ Á ÁN nitrile hydrogen bonding, including a centrosymmetric cyclic R 2 2 (14) association, link the chain substructures, forming a two-dimensional layered structure extending across the approximate ab plane. No significantor halogen-halogen intermolecular interactions are present in the crystal.

Chemical context
The formation of C-C bonds by the Michael addition of the appropriate carboanionic reagents to ,-unsaturated carbonyl compounds is one of the most useful methods of remote functionalization in organic synthesis (Mather et al., 2006;Little et al., 1995). The Michael Initiated Ring Closure (MIRC) reaction represents an elegant approach which has been applied extensively for the construction of cyclopropane derivatives (Zheng et al., 2005;Aggarwal & Grange, 2006). The cyclopropane ring is an important building moiety for a large number of biologically active compounds and are subunits found in many natural products, so that the development of novel methods to provide new cyclopropane derivatives is a challenge. The MIRC reaction strategy may also be utilized through a one-pot multicomponent reaction which has gained interest among synthetic organic chemists recently (Riches et al., 2010). Many phase-transfer-catalyzed methods have been developed for the Michael reaction that are simple and environmentally friendly (Shioiri, 1997). We have developed a new phase-transfer-catalyzed method for the MIRC reaction that is both simple and environmentally friendly. The novel title compound, C 17 H 15 ClN 2 O 4 , was prepared in good yield in such a reaction using a sugar-based crown ether as the catalyst (Bakó et al., 2015). ISSN 2056-9890

Structural commentary
In the molecular structure of the title compound ( Fig. 1), atom C3 is a chiral centre, but the racemic mixture crystallizes in the centrosymmetric space group P2 1 /c. The dihedral angle between the planes of the benzene and cyclopropane rings is 54.29 (10) , while the conformation is stabilized by two intramolecular C-HÁ Á ÁO carboxyl interactions, a weak C9-HÁ Á ÁO1 hydrogen bond (Table 1) and a short intramolecular C3Á Á ÁO4 interaction [2.8447 (16) Å ] (Fig. 2).

Supramolecular features
In the crystal, C3-HÁ Á ÁO4 i hydrogen bonds (Table 1) form inversion dimers having a graph-set descriptor R 2 2 (10) (Bernstein et al., 1995), and are linked into chain substructures extending along c through weak C15-HÁ Á ÁO3 ii hydrogen bonds (Fig. 3). These chain substructures are further linked through centrosymmetric cyclic R 2 2 (14) C5-HÁ Á ÁN2 iii and C11-HÁ Á ÁN1 iv hydrogen-bonding interactions to nitrile Natom acceptors, forming a two-dimensional layered structure extending across the approximate ab plane (Fig. 4). Although the molecule contains an aromatic ring and a Cl atom, there are no significantor halogen-halogen interactions in the crystal structure. The relatively high calculated density (1.383 Mg m À3 ) and the Kitaigorodskii packing index (KPI = 69.1) (Spek, 2009) show tight packing of the molecules in the unit cell, which results in no residual solvent-accessible voids in the crystal.

Figure 3
The one-dimensional chain polymer substructures in the title compound involving centrosymmetric cyclic C3-HÁ Á ÁO4 i and C15-HÁ Á ÁO3 ii hydrogen bonds (shown as dashed lines). For symmetry codes, see Table 1. although the benzene ring is capable of rotation about the C-C bond, the groups in close proximity on the other two cyclopropane C atoms enforce this 47-53 angle between the planes of the cyclopropane and benzene rings.

Synthesis and crystallization
The title compound was synthesized by the reaction of 2-(3chlorobenzylidene)malononitrile with diethyl 2-bromomalonate under phase-transfer conditions. The reaction was carried out in a solid/liquid two-phase system [Na 2 CO 3 /tetrahydrofuran (THF)] in the presence of a glucopyranosidebased crown ether as the catalyst. The compound was isolated by preparative thin-layer chromatography (TLC) (silica gel) in good yield (m.p. 355-357 K). The chemical structure of the compound was confirmed by 1 H, 13 C NMR and mass spectroscopies. The details of the synthesis were reported previously (Bakó et al., 2015). Single crystals suitable for X-ray diffraction analysis were obtained by crystallization from ethanol.