Crystal structure of (1S,2R)-6,6-dimethyl-4,8-dioxo-2-phenylspiro[2.5]octane-1-carbaldehyde

The title spiro-compound bears trans-bound formyl and phenyl substituents at the cyclopropane ring. In the crystal, molecules are linked by weak C—H⋯O and C—H⋯π contacts, resulting in a three-dimensional supramolecular structure.


Chemical context
Apart from synthetic transformations, cyclopropane derivatives have attracted interest because of their biological and pharmaceutical applications (Wessjohann et al., 2003). They are present in numerous natural products and have been used extensively as reactive intermediates for the formation of complex structures (Reissig & Zimmer, 2003;Thibodeaux et al., 2012). During our studies on the reactivities of iodonium ylides, we have developed a new method for the synthesis of substituted spiro-cyclopropanes by the organocatalytic reaction of ,-unsaturated aldehydes with iodonium ylides. The title compound was obtained by the reaction of the cinnamaldehyde-derived iminium ion derived from MacMillan first generation catalyst and the dimedone-derived phenyliodonium ylide.

Structural commentary
The molecular structure of the title compound is depicted in Fig. 1. The central cyclopropane ring shares the spiro atom C4 with a cyclohexane ring system while atoms C2 and C3 bear a formyl and a phenyl substituent, respectively. The latter two substituents are trans-oriented regarding the plane of the cyclopropane ring. The angles in the three-membered ring range from 58.80 (13) (C2-C4-C3) to 61.67 (13) (C3-C2-C4) being close to the ideal value of 60 for such a ring. The six-membered ring containing the spiro atom C4 and ring ISSN 2056-9890 atoms C5-C9 adopts a chair conformation with a puckering amplitude Q of 0.491 (2) Å and = 16.8 (2) , which indicates a slight deviation from an ideal chair conformation with = 0 . The plane of the central cyclopropane ring forms dihedral angles of 66.89 (16) and 89.33 (16) , respectively, with the plane of the phenyl ring and the mean plane of the cyclohexane ring [maximum deviation from this plane is 0.272 (2) Å for atom C7]. The latter two planes form a dihedral angle of 64.15 (10) . The plane of the formyl group, consisting of atoms C1, H1 and O1, is almost normal to the cyclopropane ring with a dihedral angle of 81.3 (3) .

Supramolecular features
The crystal packing of the title compound shows weak C-HÁ Á ÁO and C-HÁ Á Á interactions (Table 1   A view of the molecular structure of the title compound, showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A view of the double strands along [100] formed by two different weak C-HÁ Á ÁO contacts (red and blue dashed lines; see Table 1 for details).

Figure 3
The packing established by weak C-HÁ Á ÁO contacts (green dotted lines) C-HÁ Á Á contacts (violet and orange dotted lines) viewed along [100]; see Table 1 for details. Slashed dotted lines indicate bonds to a symmetryrelated molecule.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. C-bound H atoms were positioned geometrically (C-H = 0.95-1.00 Å ) and treated as riding on their parent atoms with U iso (H) = 1.5U eq (C-methyl) and 1.2U eq (C) for other H atoms. The methyl groups were allowed to rotate along the C-C bonds to best fit the experimental electron density. As a result of the absence of anomalous scatterers and high angle data, the Flack test results can be considered meaningless. The synthesis resulted in a racemic mixture, hence the structure was refined as an inversion twin.  Data collection: COLLECT (Hooft, 2004); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication: PLATON (Spek, 2009).

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.