[3-Methoxy-5-(methoxycarbonyl)isoxazol-4-yl](4-methoxyphenyl)iodonium 2,2,2-trifluoroacetate

The crystal structure of an unsymmetrical diaryl iodonium salt obtained from the nucleophilic coupling of tributyl(4-methoxyphenyl)stannane with a diacetoxyiodo precursor bearing an isoxazole moiety is described.


Structure description
Hypervalent iodine compounds exhibit attractive features of low cost, mild and selective reagents in organic synthesis (Wirth, 2005;Richardson & Wirth, 2006). These reagents serve as environmentally benign alternatives to toxic heavy-metal-based oxidants and expensive organometallic catalysts (Satam et al., 2010;Wirth, 2001). The application of iodonium reagents in organic transformation encompasses areas such as C-C, Cheteroatom and heteroatom-heteroatom bond formation, oxidations, rearrangements and radical reactions (Frigerio & Santagostino, 1994;Zhdankin & Stang, 2008;Zhdankin, 2009Zhdankin, , 2011. A particularly important application is the reaction of diaryliodonium salts with fluorine anions, allowing the introduction of fluorine into chemical compounds of interest (Tredwell & Gouverneur 2012;Tredwell et al., 2008). Furthermore, by using diaryliodonium salts, both electron-deficient and electron-rich rings can be fluorinated, allowing access to all regioisomers of a particular arene over standard S N Ar chemistry (Shah et al., 1998). Moreover, these types of reaction typically require milder conditions than standard S N Ar reactions, and they can even take place in wet solvents (Chun et al., 2013). Features which are privileged for the incorporation of radioactive [ 18 F]-fluoride into radiotracer molecules established for Positron Emission Tomography.

data reports
The versatility of isoxazoles core components in biologically active compounds, natural products and functional materials (Abdul Manan et al., 2017;Frolund et al., 2002;Lee et al., 2009) led us to examine the synthesis of iodonoum salts bearing an isoxazole motif possessing novel structural features with the possibly of some interest as a precursor to fluoroisoxazole.
The title salt, C 13 H 13 INO 5 , crystallizes in the space group P1 with one ion pair in the asymmetric-unit ( Fig. 1). In the crystal, the ring of the isoxazole group is inclined to the methoxyphenyl ring at an angle of 84.4 (3) and the C-I-C bond angle is 90.8 (3) . Short IÁ Á ÁO contacts of 2.555 (6) and 2.823 (7) Å are observed due to the strong electrostatic interaction between two iodonium cations and two trifluoroacetate counter-ions (Fig. 2). There are also C-HÁ Á ÁF and C-HÁ Á ÁO interactions present (Table 1). The C-HÁ Á ÁO interactions give rise to two-dimensional sheets in the (001) plane, with the C-HÁ Á ÁF interactions holding the trifluoroacetate anion in place within the sheets (Fig. 3). The combination of the weak hydrogen bonds with the IÁ Á ÁO interactions gives rise to double-layered sheets, also in the (001) plane. These interactions are comparable to those observed in phenyl(phenylethynyl)iodonium tosylate and phenyl(phenylethynyl)iodonium trifluoroacetate salts (Dixon et al., 2013).

Synthesis and crystallization
m-CPBA (70% active oxidant, 791 mg, 3.21 mmol, 1.3 eq.) was added to a solution of methyl 4-iodo-3-methoxyisoxazole-5carboxylate (700 mg, 2.47 mmol, 1.0 eq.) in AcOH (20 ml). After stirring at 55 C for 96 h, water (30 ml) was added to the reaction mixture followed by extraction into DCM (3 Â 20 ml). The combined organic layers were washed with a saturated aqueous solution of Na 2 CO 3 (60 ml), dried over Na 2 SO 4 , filtered and concentrated under reduced pressure to afford a colourless solid, which was used without further purification.

Figure 3
View down the [001] axis of the two-dimensional sheet formed by weak hydrogen-bonding interactions, shown as dashed lines. Hydrogen atoms not involved in hydrogen bonding are omitted.

Figure 1
Molecular structures of the constituents of the asymmetric unit of the title compound, showing the atom-labelling scheme and displacement ellipsoids drawn at the 50% probability level.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The maximum residual electron density peak of 1.48 e Å À3 was located 1.01 Å from the I4 atom.   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. Carbon-bound H atoms were included in calculated positions (C-H = 0.95-0.98 Å) and refined as riding atoms with U iso (H) = 1.2U eq (sp 2 ) or U iso (H) = 1.5U eq (sp 3 ).