7-Ethoxy-4′-methoxyisoflavone (monoethylformononetin)

The title compound, C18H16O4, is composed of a benzopyranone core with a 4-methoxyphenyl subsituent in the 3-position and an additional ethoxy group in the 7-position. The benzopyranone ring is not coplanar with the benzene ring, the dihedral angle between them being 41.76 (7)°. The methoxy and ethoxy substituents are nearly coplanar with the ring systems to which they are attached. Individual molecules are linked by two kinds of intermolecular hydrogen bonds into chains containing classical R 2 2(8) rings. The chains are further assembled by aromatic F-tape and T-tape stacking interactions and additional intermolecular hydrogen bonding to give a two-dimensional network.

The title compound, C 18 H 16 O 4 , is composed of a benzopyranone core with a 4-methoxyphenyl subsituent in the 3-position and an additional ethoxy group in the 7-position. The benzopyranone ring is not coplanar with the benzene ring, the dihedral angle between them being 41.76 (7) . The methoxy and ethoxy substituents are nearly coplanar with the ring systems to which they are attached. Individual molecules are linked by two kinds of intermolecular hydrogen bonds into chains containing classical R 2 2 (8) rings. The chains are further assembled by aromatic F-tape and T-tape stacking interactions and additional intermolecular hydrogen bonding to give a two-dimensional network.
The title compound is composed of a benzopyranone core with a p-methoxyphenyl substituent in 3-position and an additional ethoxy group in 7-position ( Fig. 1). The geometry of the isoflavone skeleton of (I) is similar to that of monoethyldaidzein (Zhang et al., 2005) with respect to most of the bond distances and angles. The atoms of the benzopyranone moiety, including ring A (C10,C11,C13-C16) and C (O3/C8-C12), display an almost coplanar configuration with a mean deviation to the least square plane of 0.0152 (17) Å. To minimize steric pressure, the two rigid ring systems, benzene ring B (C2-C7) and the benzopyranone moiety, are rotated by 41.76 (7)° with respect to each other. The methoxy group at atom C2 is nearly coplanar with the benzopyranone moiety, as indicated by the torsional angle C1-O1-C2-C3 = 4.6 (3)°; The ethoxy group at atom C14 is also nearly coplanar with the attached ring, the torsional angle C17-O4-C14-C13 being -7.9 (2)°.
As shown in Fig. 3, two isoflavone skeletons arrange in an anti-parallel fashion with aromatic F-tape and T-tape stacking interactions linking two molecules into a dimeric structure. The two benzopyranone moieties stack with each other with a CgAC-CgAC* distance of 3.686 (2) Å (CgAC and CgAC* are the centres of benzopyranone moieties at (x, y, z) and (-x, 2 -y, -z), respectively). The interplanar spacing measures to 3.425 (2) Å. In addition, another T-tape stacking interaction between H18C and CgB* (the centroid of ring B at (-x, 2 -y, -z)) of 2.818 (3) Å is observed. Both distances obviously lie in the normal range of F-tape and T-tape π-π stacking interactions (Janiak, 2000). At the same time, the carbonyl oxygen atom O2 acts as a hydrogen bond acceptor towards H17B of a neighboring molecule also leading to the formation of a dimeric substructure. The intermolecular hydrogen bond C17-H17B···O2 together with the aromatic F-tape and T-tape stacking interactions assemble the chains mentioned above into a two-dimensional network structure.

Experimental
Formononetin (1.0 g) was dissolved into acetone (30 ml) and KOH (1 ml, 0.3%). Diethylsulfate (1 ml) was added dropwise to the solution under vigorous stirring. The mixture was stirred at room temperature for 3 h and then poured into water (50 ml). A white precipitation appeared, which was filtered after 4 h and terated with NaOH (50 ml, 2 mol/L) to remove traces of remaining formonetin. The precipitate was filtered and washed with water until the pH of the filtrate was 7 yielding the title compound, 4'-methoxy-7-ethoxylisoflavone (yield: 82.4%). Crystals of (I) suitable for X-ray analysis were obtained by slow evaporation of the solvent from an ethanolic solution after 3 d at room temperature.
supplementary materials sup-2 Refinement H atoms bound to O atoms were found in difference maps and refined using a riding model. H atoms bound to C atoms were placed in calculated positions (C-H=0.93-0.97 Å) and refined using a riding model, allowing for free rotation of the rigid methyl groups. U iso (H) values were constrained to be 1.2Ueq (attached atom) [1.5Ueq(C) for methyl H atoms]. Fig. 1. The molecular structure of (I), showing the atom-numbering scheme and 30% probability displacement ellipsoids.