Synthesis and crystal structure of tert-butyl 1-(2-iodobenzoyl)cyclopent-3-ene-1-carboxylate

The cyclopent-3-ene ring has an envelope conformation with the tertiary C atom as the flap atom.


Chemical context
1-(2-Iodobenzoyl)cyclopent-3-ene-1-carboxylates were recently employed as novel substrates to construct bicyclo[3.2.1]octanes that are widely found in natural products and bioactive molecules with antibacterial and antithrombotic activities (Yuan et al., 2019). Although the authors carried out some control experiments to reveal the reaction mechanism, crystal structures of the substrates have not been reported yet. Moreover, 1-(2-iodobenzoyl)cyclopent-3-ene is crucial to the reductive Heck reaction and thus may provide more direct information on this reaction mechanism if more detailed structural data are available. Herein, the synthesis and crystal structure of tert-butyl 1-(2-iodobenzoyl)cyclopent-3-ene-1carboxylate are reported.

Supramolecular features
In the crystal, molecules are linked by a pair of C-HÁ Á ÁO hydrogen bonds forming inversion dimers (Table 1 and Fig. 2). They stack up the b axis and form layers parallel to the bc plane. There are no other significant intermolecular interactions present in the crystal.

Database survey
A search of the Cambridge Structural Database (CSD, Version 5.39, update of August 2018; Groom et al., 2016) for entities containing (1-methylcyclopent-3-en-1-yl)(phenyl)methanone yielded 27 hits. Only two of these compounds involve no other substituents at the cyclopent-3-ene ring as in the title compound, viz. methyl 4-[(1-methylcyclopent-3-en-1yl)carbonyl]benzoate in the space group Pnma (CSD refcode CIQHAM; Yang et al., 2007), and 4-benzoyl-4-(methoxycarbonyl)cyclopentene in the space group P2 1 /c, with four independent molecules in the asymmetric unit (CSD refcode KOGSIJ; Jiang et al., 2008). In the structures of these two compounds, the folding angles of the cyclopent-3-ene ring are 17.00 (13) and 11.91 (12) , respectively, while in the title compound it is 15.0 (3) . The benzene ring in each structure is inclined to the alkene plane of the cyclopent-3-ene ring by 90.00 (8) and 61.40 (6) , respectively, while the corresponding dihedral angle in the title compound is 26.51 (19) . Apparently, different kinds of intermolecular C-HÁ Á ÁO hydrogen bonds and the presence or not of weakcontacts in the three structures lead to different molecular packing and dihedral angles between the benzene ring and the cyclopent-3ene ring.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms attached to C atoms were included in calculated positions and refined using a riding model: C-H = 0.93-0.97 Å with U iso (H) = 1.5U eq (C-methyl) and 1.2U eq (C) for other H atoms.

Figure 2
A view along [010] of the crystal packing of the title compound. The intermolecular C-HÁ Á ÁO hydrogen bonds are shown as orange dashed lines (Table 1).

tert-Butyl 1-(2-iodobenzoyl)-cyclopent-3-ene-1-carboxylate
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.