Crystal structure and Hirshfeld analysis of di-tert-butyl 2,2′-[(ethylazanediyl)bis(methylene)]bis(1H-pyrrole-1-carboxylate)

In the title compound, intermolecular C—H⋯π interactions and π–π stacking interactions help to stabilize the crystal structure, forming a three-dimensional network.


Chemical context
This work is a continuation of the study of Diels-Alder reactions on bis-diene systems, which was previously carried out on the example of the tandem [4 + 2]/[4 + 2] cycloaddition between bis-furyl dienes similar to 1 and activated alkynes, leading to adducts such as 2, as shown in Fig. 1 (Borisova et al., 2018a,b;Kvyatkovskaya et al., 2020;Lautens & Fillion, 1997;Domingo et al., 2000). Here we aimed to investigate substrates containing two pyrrole moieties under the same reaction conditions. For this reason, N,N-bis(1H-pyrrol-2-ylmethyl) ethanamine (3) was synthesized using a Mannich reaction according to the described procedure (Raines & Kovacs, 1970). It is known that pyrrole fragments are capable of reacting with the most active dienophiles in the [4 + 2] cycloaddition reaction, which requires the presence of electron-deficient groups at the nitrogen atom (Winkler, 1996;Visnick & Battiste, 1985;Butler et al., 2000;Warrener et al., 2003). Thus, the pyrrole rings of amine 3 were activated by Boc-protecting groups to give the title substance 4. Considering that a single example of a successful domino [4 + 2] cycloaddition between hexafluorobut-2-yne and N,N 0dipyrrolylmethane is reported in the literature (Visnick & Battiste, 1985), we tested amine 4 in the reaction with such an active dienophile as dimethyl acetylenedicarboxylate (DMAD). The experiments were performed in a wide temperature range (from room temperature to 413 K) and led to multicomponent mixtures of products at elevated temperatures, from which we were unable to isolate the target adduct 5.

Hirshfeld surface analysis
The Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) was performed and the associated two-dimensional fingerprint plots (McKinnon, et al., 2007) were obtained with Crystal Explorer17 (Turner et al., 2017) to investigate the intermolecular interactions and surface morphology. The Hirshfeld surface mapped over d norm using a standard surface resolution with a fixed colour scale of À0.0919 (red) to 1.6027 (blue) a.u. is shown in Fig. 4.
The percentage contributions of various contacts (Table 2) to the total Hirshfeld surface are listed in Table 3 and shown in the two-dimensional fingerprint plots in Fig. 5, revealing that the crystal packing is dominated by HÁ Á ÁH contacts, representing van der Waals interactions (74.3% contribution to the overall surface), followed by CÁ Á ÁH/HÁ Á ÁC and OÁ Á ÁH/HÁ Á ÁO interactions, which contribute 11.5% and 9.1%, respectively. The molecular structure of the title compound 4 with displacement ellipsoids for the non-hydrogen atoms drawn at the 50% probability level.

D-HÁ
In the crystal of PUKKEO, the distance between two parallel molecules within one column was measured to be 9.333 Å , indicating thatinteractions cannot be formed in the molecule. In the crystal structure of IVIJAA, multiple intermolecular C-HÁ Á ÁN (or C-HÁ Á ÁO) and C-HÁ Á Á interactions were found, which could help to rigidify the molecular conformation. In NANLAP, the dihedral angle between the two pyrrole ring is 82.77 .
In the three structures closely related to the title compound, the different linkers between the two pyrrole units (aromatic vs aliphatic, large vs small) may account for the distinct intermolecular interactions in the crystals.

Synthesis and crystallization
Di-tert-butyl dicarbonate [(Boc) 2 O, 27.8 mL, 0.13 mol] was added to a solution of N,N-bis(1H-pyrrol-2-ylmethyl)ethanamine (12.0 g, 0.06 mol) and DMAP (1.1 g, 0.009 mol) in CH 3 CN (50 mL) at room temperature under an argon atmosphere. The mixture was stirred for 6 h at room temperature. The reaction mixture was poured into a 5% solution of NH 3 in H 2 O (300 mL) and extracted with CH 2 Cl 2 (3 Â 50 mL). The combined organic layers were dried over MgSO 4 , filtered and concentrated. Flash chromatography purification on alumin-  Table 3 Percentage contributions of interatomic contacts to the Hirshfeld surface for the title compound 4.

Figure 4
A view of the three-dimensional Hirshfeld surface for the title compound 4, plotted over d norm in the range À0.0919 to 1.6027 a.u.
ium oxide (hexane) of the residue yielded the title compound as colourless crystals. Single crystals suitable for X-ray diffraction analysis were obtained by slow evaporation of an

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. All H atoms were included as riding contributions in idealized positions (C-H = 0.95-0.99 Å with U iso (H) = 1.2 or 1.5U eq (C).   (Farrugia, 2012); software used to prepare material for publication: PLATON (Spek, 2020).

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.