Crystal structures of 4-methyl-2-oxo-2H-chromene-7,8-diyl diacetate and 4-methyl-2-oxo-2H-chromene-7,8-diyl bis(pent-4-ynoate)

The structures of two substituted coumarin derivatives are reported, one with acetate and the other with pent-4-ynoate substituents.

In the structures of the two title coumarin derivatives, C 14 H 12 O 6 , (1), and C 20 H 16 O 6 , (2), one with acetate and the other with pent-4-ynoate substituents, both the coumarin rings are almost planar. In (1), both acetate substituents are significantly rotated out of the coumarin plane to minimize steric repulsions. One acetate substituent is disordered over two equivalent conformations, with occupancies of 0.755 (17) and 0.245 (17). In (2), there are two pent-4-ynoate substituents, the C C group of one being disordered over two positions with occupancies of 0.55 (2) and 0.45 (2). One of the pent-4-ynoate substituents is in an extended conformation, while the other is in a bent conformation. In this derivative, the planar part of both pent-4-ynoate substituents deviate from the coumarin plane. The packing of (1) is dominated bystacking involving the coumarin rings and weak C-HÁ Á ÁO contacts link the parallel stacks in the [101] direction. In contrast, in (2) the packing is dominated by R 2 2 (24) hydrogen bonds, involving the acidic sp H atom and the oxo O atom, which link the molecules into centrosymmetric dimers. The bent conformation of one of the pent-4ynoate substituents prevents the coumarin rings from engaging instacking.

Chemical context
Coumarins and their derivatives have wide applications in a number of diverse areas. They are used in the pharmaceutical industry as precursor reagents in the synthesis of a number of synthetic anticoagulant pharmaceuticals (Bairagi et al., 2012), the most notable being warfarin (Holbrook et al., 2005). Modified coumarins are a type of vitamin K antagonist (Marongiu & Barcellona, 2015).

Structural commentary
This paper reports the structures of two derivatives of coumarin (systematic name; 2H-chromen-2-one), C 14 H 12 O 6 (1) and C 20 H 16 O 6 (2), which are to be used as chemical reporters of calreticulin's acyltransferase capabilities. These two compounds will be first discussed individually and then compared.
In the structure of (1) (Fig. 1), the coumarin ring is almost planar (r.m.s. deviation of fitted atoms = 0.0063 Å ) with O2 in the plane [deviation of 0.0048 (9) Å ]. Both acetate substituents are significantly rotated out of this plane to minimize steric repulsions [dihedral angle of 66.19 (7) to the coumarin ring for O3, O4, and C11, and 79.4 (3) for O5, C13 O6A]. One acetate substituent is disordered over two equivalent conformations with occupancies of 0.755 (17) and 0.245 (17). The metrical parameters of both the coumarin ring and acetate substituents are in the normal ranges.
In contrast to (1), for (2) the packing (Fig. 4) is dominated by R 2 2 (24) hydrogen bonds (Table 2) involving the acidic sp H atom and O2 which link the molecules into centrosymmetric dimers. The bent conformation of one of the pent-4-ynoate substituents prevents the coumarin rings from engaging instacking in contrast to (1).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. For (1), the H atoms were positioned geometrically and refined as riding: C-H = 0.95-0.98 Å with U iso (H) = 1.5U eq (C) for methyl H atoms and = 1.2U eq (C) for other H atoms. One acetate substituent is disordered over two equivalent conformations with occupancies of 0.755 (17) and 0.245 (17).

Figure 3
Packing diagram for (1), viewed along the c axis, showing the parallel coumarin rings. C-HÁ Á ÁO secondary interactions are drawn with dashed lines.

2) 4-Methyl-2-oxo-2H-chromene-7,8-diyl bis(pent-4-ynoate)
Crystal data 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.