Diethyl 2,2-bis(3,5-di-tert-butyl-4-hydroxybenzyl)malonate

The title molecule, C37H56O6, possesses twofold symmetry, with the twofold axis passing through the quaternary C atom. In the crystal, neighbouring molecules are linked via O—H⋯O hydrogen bonds involving the phenol OH group and the carbonyl O atom, forming chains propagating in [101]. Within these chains, rings are formed with an R 2 2(20) motif. There are also C—H⋯O interactions present within the rings.

The title molecule is located about a 2-fold axis (Fig. 1), which passes through the quaternary carbon atom, C16. The bond angles involving C16 vary from 106.2 (2) to 111.9 (2)°. The remainder of the geometric parameters are within normal ranges.
In the crystal, neighbouring molecules are linked by O-H···O hydrogen bonds (Tab. 1 and Fig. 2), involving the phenolic OH group and the carbonyl O atom, forming chains in direction [1 0 1] that contain rings with a R 2 2 (20) motif (Bernstein et al., 1995). These rings are situated about the i nversion centres (the Wyckoff position 4c). C-H···O interactions are also present within the rings (Tab. 1).

Experimental
A mixture of diethyl malonate (4.0 g, 0.025 mol) and 2,6-di-tert-butyl-4-((dimethylamino)methyl)phenol (13.2 g, 0.05 mol) in 80 ml of toluene was heated to 373 K under a nitrogen atmosphere. Lithium amide (0.2 g) was then added and the mixture was stirred for further 6 h. The reaction mixture was then diluted with toluene (60 ml), washed with water (40 ml), and the oil layer was separated and dried with anhydrous MgSO 4 . After filtration and concentration, the solution was allowed to evaporate in the air to give the title product as a white powder [yield 13.1 g; 87.9%]. Block-like colourless crystals with dimensions at about 2-3 mm were obtained by slow evaporation of the solution of the title compound in toluene/ethanol (3:1; v:v).

Refinement
All the H-atoms could be located in difference Fourier maps. The hydroxyl H-atom was refined with a distance restraint of O-H = 0.82 (2) Å, and U iso H = 1.2U eq( O). The C-bound H-atoms were included in calculated positions and refined as riding atoms: C-H = 0.93, 0.97 and 0.96 Å for CH, CH 2 and CH 3 H-atoms, respectively, with U iso (H) = k × U eq (parent C-atom), where k = 1.5 for CH 3 H-atoms and k = 1.2 for all other H-atoms.  Diethyl 2,2-bis(3,5-di-tert-butyl-4-hydroxybenzyl)malonate

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
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 > 2sigma(F 2 ) is used only for calculating R-factors(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.