2-Oxo-2H-chromen-4-yl 4-tert-butylbenzoate

In the title molecule, C20H18O4, the three methyl groups of the tert-butyl substituent show rotational disorder. Each methyl group is split over three positions, with refined site-occupation factors of 0.711 (4), 0.146 (3) and 0.144 (4). The benzene ring of the benzoate group is oriented at a dihedral angle of 60.70 (7)° with respect to the planar chromene ring [maximum deviation = 0.046 (2) Å]. The crystal structure features centrosymmetric R 2 2(8) dimers formed via C—H⋯O interactions, and these dimeric aggregates are connected by C—H⋯π interactions.


Related literature
Cg2 and Cg3 are the centroids of the chromene benzene and benzoate benzene rings. Coumarin constitutes one of the major classes of naturally occurring compounds, and interest in its chemistry continues unabated because of its usefulness as biologically active agents. It also represents the core structure of several molecules of pharmaceutical importance. Coumarin and its derivatives have been reported to serve as anti-bacterial (Ukhov et al., 2001;Abd Elhafez et al., 2003;Basanagouda et al., 2009;Liu et al., 2008), anti-oxidant (Trapkov et al., 1996Vukovic et al., 2010), anti-inflammatory (Emmanuel-Giota et al., 2001;Hamdi & Dixneuf, 2007), anti-coagulant (Hamdi & Dixneuf, 2007 and anti-tumour (Wang et al., 2001;Marchenko, et al., 2006) agents. Therefore, the synthesis of new coumarin derivatives is of considerable interest. In order to study the influence of new substituents on the activity of the coumarin derivatives, the title compound has been synthesized and in this paper, we present its molecular and crystal structure.
In the title compound ( Fig. 1), the three methyl groups of the tert-butyl substituent exhibit rotational disorder, with refined site occupation factors of 0.711 (4), 0.146 (3) and 0.144 (4). The planar chromene ring system resulting from the two fused rings (benzene and 3,6-dihydro-2H-pyran) is oriented with respect to the benzoate-benzene ring at a dihedral angle of 60.70 (7)°.

Experimental
To a solution of 4-tertiobutylbenzoyl chloride (4.10 -2 mole) in dried tetrahydrofuran (150 ml), was added dried triethylamine (0.12 mole) and 4-hydroxycoumarin (4.10 -2 mole) by small portions over 30 min. The mixture was then refluxed for 3 h and poured in 300 ml of chloroform. The solution was acidified with dilute hydrochloric acid until the pH was 2-3. The organic layer was extracted, washed with water, dried over MgSO 4 and the solvent removed. The crude product was recrystallized from chloroform. Colourless crystals of the title compound were obtained in good yield 73.8%; melting point: 381-383 K.

Refinement
In the refinement, positional, site occupation factors and U ij parameters of the disordered C atoms were refined freely.
However, EADP instruction (Sheldrick, 2008) was used to constrain the anisotropic displacement parameters (ADPs) of the disordered C atoms of the two minor components to be the same as their corresponding C atoms in the principal component.
Also, SADI and SAME restrictions were applied to C(methyl)···C(methyl) separations in each component, in order to get a sensible geometry. H atoms were placed in calculated positions [C-H = 0.93 (aromatic) or 0.96 Å (methyl group)] and refined using a riding model approximation with U iso (H) constrained to 1.2 (aromatic) or 1.5 (methyl) times U eq of the supplementary materials sup-2 respective parent atom. Four reflections were omitted from the refinement because of large disagreements: (0 0 1), (0 1 0), (0 -1 1) and (-1 4 6). Fig. 1. The molecular structure of the title compund, showing displacement ellipsoids at the 50% probability level. H atoms are shown as spheres of arbitrary radius.

Special details
Refinement. In the title coumpound, the tert-butyl group may rotate virtually freely at least at room temperature, and in the spatial average one sees this group as a rotational toroid. Since it is hard to describe this situation to the refinement program, we have reduced the problem to a refinement of only three sites per methyl group (see Refinement section). The low U eq as compared to neighbors for atom C17 is caused by this disorder.