Crystal structure of 2-tert-butyl 1-methyl 5-{4-[(methoxycarbonyl)amino]phenyl}-2,5-dihydro-1H-pyrrole-1,2-dicarboxylate, C19H24N2O6

Abstract C19H24N2O6, monoclinic, P21 (no. 4), a = 8.3611(7) Å, b = 9.0521(8) Å, c = 13.8988(8) Å, β = 106.710(5)°, V = 1007.52(14) Å3, Z = 2, Rgt(F) = 0.0428, wRref(F2) = 0.1174, T = 293(2) K.

The molecular structure is shown in the figure. Table 1 contains crystallographic data and Table 2 contains the list of the atoms including atomic coordinates and displacement parameters. Absorption correction [1], CAD4 [2,3], SIR2014 [3], SHELX [4], WinGX/ORTEP [5,6] Source of material  NaCl. The solution was then dried with anhydrous Na 2 SO4, filtered and the solvent was removed in a rotary evaporator. The residue was purified by filtration through a layer of silica gel, using a mixture of EtOAc/n-hexane (2:8) as the eluent.
Yield: 148 mg (98%) of Heck products. The products were not separable by flash column chromatography on silica gel, produced a single "spot" by thin layer chromatography and a single signal by capillary gas chromatography. Therefore, the product was dissolved in DMSO and allowed to crystallize slowly. The trans diastereoisomer, (I), precipitated; the cis diastereoisomer remained in solution.
Suitable crystals for the X-ray diffraction analysis were obtained by slow evaporation from a MeOH solution. M. pt: 453-456 K.
The 1 H and 13

Experimental details
The C-bound H atoms were geometrically placed (C-H = 0.93-0.98 Å) and refined as riding with U iso (H) = 1.2-1.5Ueq(C). The N-bound H atom was refined with N-H = 0.86 ± 0.01 Å, and with 1.2Ueq(N). The absolute structure was not determined in the X-ray experiment but, the assignment of stereochemistry at the chiral centres is based on the chirality of the synthetic precursor employed in the synthesis.

Comment
Recent reports have detailed the crystal structure determinations of pyrrole [7] and pyrrolidine [8,9] derivatives having rare or even unprecented substitution patterns. These are crucial intermediates for the synthesis of pharmacologicallyrelevant molecules via Heck-Matsuda arylation reactions, namely the coupling of an olefin with an arenediazonium salt mediated by a catalytic palladium complex [10]. In the present case, the title compound, (I), is an intermediate in the enantioselective synthesis of polyhydroxylated pyrrolidines such as analogues of Schramm's antiprotozoan C-azanucleoside [11], which may display anti-viral, anticancer and anti-microbial activities [12,13]. Herein, the crystal and molecular structures of (I) are described along with an additional analysis of the molecular packing via calculated Hirshfeld surfaces.
The molecular structure of (I) is illustrated in the figure (35% displacement ellipsoids) and features a five-membered ring which is twisted about the N1-C5 bond. The geometry about the N1 atom is close to trigonal with the sum of the angles subtended at N1 = 356.2°. The ring is tri-substituted, with a N1-bound methyloxycarbonyl group flanked on either side by a C2-bound [(methoxycarbonyl)amino]phenyl substituent and a C5-bound tert-butyloxycarbonyl group. The configuration at each of the C2 and C5 atoms is S. The dihedral angle between the N1-substituent and the best plane through the pyrrole ring is 14.91(14)°, being indicative of a twist between the residues. As indicated above, the C2-and C5-bound substituents lie to the opposite side of the pyrrole ring. In fact, they have approximately orthogonal dispositions to the pyrrole ring, forming dihedral angles of 87.83 (9) and 83.42(13)°, respectively, with the former. The [(methoxycarbonyl)amino]phenyl is close to planar with the C 6 /C 2 NO 2 dihedral angle being 2.97(15)°.
There is a single, direct literature precedent for pyrrole (I) which has only been recently described [7]. Here, the N1 atom carries a tert-butyloxycarbonyl group and is flanked by C-bound methylhydroxyl and [(methoxycarbonyl)amino] phenyl groups.
The fingerprint plot delineated into H· · · O/O· · · H contacts showed the distinctive spikes due to the N-H· · · O hydrogen bonds and overall, contributed 24.5% of all contacts, with H· · · H contacts being most dominant, at 57.9%. The next most significant contribution to the calculated surface contacts is from H· · · C/C· · · H contacts [11.6%] with smaller contibutions from N· · · C/C· · · N [2.9%] and H· · · N/N· · · H [2.7%] contacts.