(8-Hydroxy-6-methoxy-1-oxo-1H-isochromen-3-yl)methyl formate: a supramolecular framework

In the crystal of the title compound, molecules are linked by C—H⋯O hydrogen bonds and a C—H⋯π interaction, forming a supramolecular framework.


Structure description
The title compound, I, is an intermediate in the synthesis of cytogenin, a naturally occurring isocoumarin that was first isolated from a cultured broth of Streptoverticillium eurocidicum (Kumagai et al., 1990(Kumagai et al., , 1995. It was shown by these authors to have both antibiotic properties and antitumor activity. The first synthesis of cytogenin was reported in 2004 (Saeed, 2004). More recently, a new synthetic route to cytogenin and similar isocoumarins has been reported (Gadakh & Sudalai, 2014).
As shown in Fig. 1, compound I was prepared via two pathways (see Synthesis and crystallization). The details of the syntheses of the precursors A and B and cytogenin have been described elsewhere (Tiouabi, 2005).
In the crystal, molecules are linked by a series of C-HÁ Á ÁO hydrogen bonds (Table 1), forming interconnected ribbons running normal to each other in planes (012) and (012): see Fig. 3. These interactions lead to the formation of a supramolecular framework, which is reinforced by a C-HÁ Á Á interaction ( Fig. 4 and Table 1).
Method 1: The hydroxybromoisocoumarin A (0.14 g, 0.49 mmol) was dissolved with stirring in 5 ml of anhydrous DMF in a 50 ml flask equipped with a magnetic stirrer and under an atmosphere of argon. HCO 2 Na (0.167 g, 2.46 mmol) was added and the mixture was stirred overnight at room temperature. The evolution of the reaction was monitored by thin-layer chromatography, using dimethylchloride as eluent. On completion of the reaction, the mixture was diluted with ethyl acetate and then washed with an aqueous saturated solution of NaCl. The organic phase was dried using anhydrous Na 2 SO 4 , then filtered and concentrated using a rotary evaporator, yielding compound I in the form of a white solid (yield 0.118 g, 96%).
Method 2: The acetoxybromoisocoumarin B (34.2 mg, 0.104 mmol) was dissolved with stirring in 3 ml of anhydrous DMF in a 50 ml flask equipped with a magnetic stirrer and under an atmosphere of argon. HCO 2 Na (47 mg, 0.69 mmol) was added, the temperature was raised to 80 C and the A view of the molecular structure of compound I, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level. The intramolecular O-HÁ Á ÁO hydrogen bond (see Table 1) is shown as a dashed line. Table 1 Hydrogen-bond geometry (Å , ).

Figure 3
A partial view of the crystal packing of compound I, viewed normal to plane (011). Hydrogen bonds (see Table 1) are shown as dashed lines.

Figure 4
A view along the a axis of the crystal packing of compound I. Hydrogen bonds and C-HÁ Á Á interactions (see Table 1) are shown as dashed lines.

Figure 1
The reaction pathways for the synthesis of compound I and cytogenin (Tiouabi, 2005). mixture stirred for 4 h. The evolution of the reaction was monitored by thin-layer chromatography, using dimethylchloride as eluent. On completion of the reaction, the mixture was diluted with ethyl acetate and then washed with an aqueous saturated solution of NaCl. The organic phase was dried using anhydrous Na 2 SO 4 , then purified by column chromatography (silica, eluent CH 2 Cl 2 /hexane 10/1). Colourless block-like crystals of I were obtained by slow evaporation of a solution in chloroform.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Intensity data were measured using a Stoe IPDS I, a one-circle diffractometer. The alert diffrn_reflns_laue_measured_fraction_full value (0.947) below minimum (0.95) is given. This involves 29 random reflections out of the expected 1034 for the IUCr cut-off limit of (sin )/ = 0.6 Å À1 ; viz. 2.8%. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.32 e Å −3 Δρ min = −0.27 e Å −3 Extinction correction: (SHELXL-2018/3;Sheldrick, 2015), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.061 (11) data-2 IUCrData (2020). 5, x201391 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. Flack x = 0.223 (999) by classical fit to all intensities 1.664 (999) from 481 selected quotients (Parsons′ method) ** Absolute structure cannot be determined reliably ** The hydroxyl H atom and the C-bound H atoms were included in calculated positions and treated as riding on their parent O or C atoms.