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In the title compound, C16H17NO4, the benzyl­oxy­carbonyl group is anti to the pyrrolic N atom. The mol­ecules are joined into head-to-head dimers by hydrogen bonds involving the carboxyl­ic acid groups. There is orientational disorder of these groups over two positions with approximately equal occupancy. A weaker hydrogen bond between the pyrrolic N atom and the carbonyl O atom of the benzyl­oxy­carbonyl group joins the dimers into chains running parallel to the [110] direction.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S010827010000980X/gd1110sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S010827010000980X/gd1110Isup2.hkl
Contains datablock I

CCDC reference: 152629

Comment top

The class of pyrrole derivatives has many members and includes naturally occurring compounds with important biological functions (Battersby & McDonald, 1976). Synthesized pyrroles have been used widely in the pharmaceutical industry and are precursors for the synthesis of porphyrins and other macrocycles which are of increasing use in the medical (Bonnet, 1995) and material sciences (Hudson et al., 1993; Grieve et al., 1994a,b). The incorporation of one or several fused-pyrrole rings the at β-pyrrolic positions of porphyrins is considered to afford an efficient pathway to a molecular architecture based on fused porphyrins. With this objective in mind, the title compound, (I), was synthesized and an X-ray diffraction study was undertaken to clarify the conformation of the molecule.

The endocyclic angles of the pyrrole ring add up to exactly 540°, indicating that the heterocycle is almost perfectly planar; in fact, no atom deviates by more than 0.0010 (15) Å from the least-squares plane. The two Nsp2—C bonds are consistent with the tabulated average value [1.372 (16) Å; Allen et al., 1987]. The largest bond distance within the heterocyclic ring is that opposite the N atom [1.400 (3) Å]. Whereas the methyl C9 atom is practically within the ring plane, with a deviation from the least-squares plane of just 0.015 (5) Å, the C6, C7 and C10 atoms have small but significant deviations from the plane of the ring [C6 − 0.025 (5), C7 − 0.063 (5) and C10 − 0.058 (5) Å].

The benzyloxycarbonyl group bonds to the pyrrole ring adopting an anti conformation with respect to N atom, as shown by the torsion angle N1—C5—C10—O4 of −178.4 (2)°. The phenyl ring is planar and makes an angle of 60.89 (11)° with the carboxylate group.

The carboxylic acid group exhibits disorder around the C2—C6 single bond, as shown by the similar C6—O1 [1.264 (3) Å] and C6—O2 [1.272 (3) Å] bond lengths. This group is twisted around the C2—C6 bond by an angle of 8.2 (2)°.

The plane formed by the ethyl group and the C3 atom is almost orthogonal to the pyrrole ring, a conformation that minimizes the steric interaction between the ethyl group and the adjacent methyl and carboxylic acid groups. The observed deviation of the C2—C3—C7—C8 torsion angle [−97.9 (3)°] from orthogonality and the small observed asymmetry between the exocyclic angles at C2 have the correct sign as expected from a stronger interaction with the carboxylic acid group.

The molecules are joined into head-to-head dimers by strong hydrogen bonds involving two carboxylic acid groups [O1···O2 2.621 (3) Å]. Weaker hydrogen bonds exist between the N1 atom and the carbonyl O3 atom of the benzyloxycarbonyl group of a neighbouring molecule. This hydrogen-bond pattern joins the molecules into infinite chains running parallel to the [110] direction. C—H···O interactions have been recognized as important secondary interactions and, in many cases, play a dominant role in the molecular conformation (Steiner, 1997). Two such intramolecular interactions can be identified in the present structure, i.e. a weak C7···O2 [3.037 (4) Å] interaction and a strong C11···O3 [2.691 (4) Å] interaction.

Experimental top

The title compound was prepared according to Archibald et al. (1966) from the parent 2,4-dimethyl-3-ethyl-5-carbobinzoxypyrrole by methyl chlorination with sulfuryl chloride followed by hydrolysis, giving the title compound in 60% yield. The compound was crystallized by slow evaporation from dichloromethane/methanol (1:1) giving small translucent plate-shaped crystals. A large number of crystals were examined by photographic methods until a specimen suitable for data collection was found. The crystal was still weakly diffracting (only ~50% of the measured reflections up to θ = 25° have I > 2σ). M.p. 437–438 K [literature 439 K (Archibald et al., 1966)]; elemental analysis: calculated for C16H17NO4: C 66.8, H 5.9, N 4.8%; found: C 65.9, H 6.0, N 4.1%.

Refinement top

The H atoms were placed at calculated positions and refined as riding using SHELX97 defaults (N—H 0.86 Å and C—H 0.93–0.97 Å), except for the carboxylic acid H atom. Inspection of a Fourier difference map showed the carboxylic acid H atom to be disordered. Refinement of the occupancy gave a 53 (8):47 (8)% occupancy ratio of the two alternate positions (attached to O1 or O2). Examination of the crystal structure with PLATON (Spek, 1995) showed that there are no solvent-accessible voids in the crystal lattice.

Computing details top

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: HELENA (Spek, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. ORTEPII (Johnson, 1976) plot of the title compound. Displacement ellipsoids are drawn at the 50% probability level.
[Figure 2] Fig. 2. Packing of the molecules of (I) viewed down the b axis. The carboxylic acid H atom is disordered and only one of the alternate positions is shown for clarity.
benzyl 2-carboxy-3-ethyl-4-methylpyrrole-5-carboxylate top
Crystal data top
C16H17NO4F(000) = 1216
Mr = 287.31Dx = 1.302 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
a = 22.195 (6) ÅCell parameters from 25 reflections
b = 5.2607 (13) Åθ = 6.0–13.1°
c = 25.413 (3) ŵ = 0.09 mm1
β = 98.938 (15)°T = 293 K
V = 2931.3 (11) Å3Plate, colourless translucent
Z = 80.37 × 0.37 × 0.10 mm
Data collection top
Enraf-Nonius CAD-4
diffractometer
Rint = 0.045
Radiation source: fine-focus sealed tubeθmax = 25.0°, θmin = 3.3°
Graphite monochromatorh = 026
ω–2θ scansk = 06
2638 measured reflectionsl = 3029
2568 independent reflections3 standard reflections every 180 min
1253 reflections with I > 2σ(I) intensity decay: 1%
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.041Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.129H atoms treated by a mixture of independent and constrained refinement
S = 0.96 w = 1/[σ2(Fo2) + (0.0669P)2 + 0.6191P]
where P = (Fo2 + 2Fc2)/3
2568 reflections(Δ/σ)max < 0.001
199 parametersΔρmax = 0.16 e Å3
0 restraintsΔρmin = 0.17 e Å3
Crystal data top
C16H17NO4V = 2931.3 (11) Å3
Mr = 287.31Z = 8
Monoclinic, C2/cMo Kα radiation
a = 22.195 (6) ŵ = 0.09 mm1
b = 5.2607 (13) ÅT = 293 K
c = 25.413 (3) Å0.37 × 0.37 × 0.10 mm
β = 98.938 (15)°
Data collection top
Enraf-Nonius CAD-4
diffractometer
Rint = 0.045
2638 measured reflections3 standard reflections every 180 min
2568 independent reflections intensity decay: 1%
1253 reflections with I > 2σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.0410 restraints
wR(F2) = 0.129H atoms treated by a mixture of independent and constrained refinement
S = 0.96Δρmax = 0.16 e Å3
2568 reflectionsΔρmin = 0.17 e Å3
199 parameters
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
N10.15075 (8)0.4042 (4)0.46155 (7)0.0524 (6)
H10.17010.30000.48420.063*
O10.07475 (8)0.0965 (5)0.50807 (8)0.0695 (7)
H1A0.048 (4)0.01 (2)0.517 (3)0.104*0.53 (8)
O20.00716 (8)0.2519 (4)0.45602 (8)0.0662 (6)
H20.030 (4)0.16 (2)0.472 (3)0.099*0.47 (8)
O30.27747 (9)0.4599 (5)0.46634 (9)0.0950 (8)
O40.26078 (8)0.7786 (5)0.40986 (9)0.0898 (8)
C20.08877 (10)0.4190 (5)0.44821 (9)0.0483 (6)
C30.07518 (11)0.6099 (5)0.41066 (9)0.0496 (6)
C50.17672 (10)0.5810 (6)0.43316 (9)0.0511 (7)
C60.04998 (11)0.2466 (6)0.47229 (10)0.0516 (7)
C70.01351 (11)0.6876 (6)0.38249 (11)0.0635 (8)
H7A0.01200.87130.37920.076*
H7B0.01730.63610.40360.076*
C80.00078 (13)0.5699 (8)0.32772 (13)0.0949 (11)
H8A0.03000.61790.30690.142*
H8B0.03980.62900.31050.142*
H8C0.00160.38820.33090.142*
C90.13762 (12)0.9259 (6)0.36351 (11)0.0662 (8)
H9A0.16351.05460.38180.099*
H9B0.09830.99730.35070.099*
H9C0.15540.86270.33400.099*
C100.24292 (11)0.5948 (6)0.43876 (10)0.0578 (7)
C110.32562 (12)0.8112 (8)0.40807 (12)0.0863 (11)
H11A0.34840.66840.42520.104*
H11B0.34040.96550.42660.104*
C120.33374 (11)0.8269 (6)0.35103 (11)0.0594 (8)
C130.36806 (14)0.6519 (6)0.32857 (14)0.0792 (10)
H130.38690.52020.34930.095*
C140.37483 (16)0.6693 (7)0.27582 (16)0.0903 (11)
H140.39870.55100.26140.108*
C150.34672 (14)0.8590 (7)0.24453 (13)0.0764 (9)
H150.35120.86930.20880.092*
C160.31222 (13)1.0324 (7)0.26582 (12)0.0739 (9)
H160.29281.16130.24460.089*
C170.30587 (13)1.0183 (6)0.31852 (13)0.0685 (8)
H170.28241.13940.33270.082*
C40.13078 (10)0.7118 (5)0.40117 (9)0.0504 (7)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N10.0452 (11)0.0716 (16)0.0405 (11)0.0103 (11)0.0069 (8)0.0088 (12)
O10.0484 (10)0.0903 (18)0.0703 (13)0.0121 (11)0.0102 (9)0.0268 (13)
O20.0444 (11)0.0855 (16)0.0678 (12)0.0143 (10)0.0054 (8)0.0152 (11)
O30.0508 (11)0.123 (2)0.1076 (18)0.0135 (12)0.0003 (11)0.0603 (16)
O40.0499 (11)0.123 (2)0.0990 (15)0.0135 (12)0.0185 (10)0.0503 (15)
C20.0435 (13)0.0627 (18)0.0401 (12)0.0079 (13)0.0112 (10)0.0015 (14)
C30.0510 (14)0.0562 (18)0.0436 (13)0.0010 (13)0.0137 (10)0.0007 (13)
C50.0480 (14)0.0652 (18)0.0418 (13)0.0147 (13)0.0121 (11)0.0015 (14)
C60.0462 (15)0.0657 (19)0.0432 (14)0.0084 (14)0.0074 (11)0.0028 (14)
C70.0526 (15)0.071 (2)0.0686 (18)0.0039 (14)0.0137 (13)0.0108 (16)
C80.0676 (19)0.123 (3)0.085 (2)0.005 (2)0.0168 (16)0.006 (2)
C90.0673 (17)0.065 (2)0.0698 (18)0.0048 (16)0.0206 (14)0.0148 (17)
C100.0525 (16)0.077 (2)0.0443 (14)0.0155 (16)0.0087 (12)0.0055 (15)
C110.0501 (16)0.131 (3)0.078 (2)0.0308 (18)0.0109 (14)0.028 (2)
C120.0438 (13)0.065 (2)0.0683 (18)0.0197 (15)0.0061 (13)0.0088 (16)
C130.0704 (19)0.062 (2)0.101 (3)0.0020 (17)0.0014 (18)0.011 (2)
C140.095 (2)0.086 (3)0.090 (3)0.008 (2)0.014 (2)0.023 (2)
C150.082 (2)0.085 (3)0.0624 (18)0.0137 (19)0.0122 (16)0.0132 (19)
C160.080 (2)0.072 (2)0.072 (2)0.0001 (17)0.0202 (16)0.0138 (18)
C170.0641 (17)0.064 (2)0.083 (2)0.0001 (15)0.0282 (15)0.0059 (17)
C40.0546 (14)0.0570 (18)0.0419 (13)0.0030 (13)0.0146 (11)0.0018 (13)
Geometric parameters (Å, º) top
N1—C51.359 (3)C8—H8B0.9600
N1—C21.367 (3)C8—H8C0.9600
N1—H10.8600C9—C41.501 (3)
O1—C61.264 (3)C9—H9A0.9600
O1—H1A0.87 (12)C9—H9B0.9600
O2—C61.272 (3)C9—H9C0.9600
O2—H20.86 (13)C11—C121.491 (4)
O3—C101.190 (3)C11—H11A0.9700
O4—C101.312 (3)C11—H11B0.9700
O4—C111.457 (3)C12—C131.374 (4)
C2—C31.386 (3)C12—C171.386 (4)
C2—C61.450 (3)C13—C141.375 (5)
C3—C41.400 (3)C13—H130.9300
C3—C71.499 (3)C14—C151.365 (5)
C5—C41.385 (3)C14—H140.9300
C5—C101.456 (3)C15—C161.357 (4)
C7—C81.511 (4)C15—H150.9300
C7—H7A0.9700C16—C171.370 (4)
C7—H7B0.9700C16—H160.9300
C8—H8A0.9600C17—H170.9300
C5—N1—C2108.8 (2)C4—C9—H9C109.5
C5—N1—H1125.6H9A—C9—H9C109.5
C2—N1—H1125.6H9B—C9—H9C109.5
C6—O1—H1A111 (5)O3—C10—O4123.1 (2)
C6—O2—H2117 (5)O3—C10—C5125.2 (3)
C10—O4—C11119.3 (2)O4—C10—C5111.7 (3)
N1—C2—C3108.3 (2)O4—C11—C12107.8 (2)
N1—C2—C6120.0 (2)O4—C11—H11A110.1
C3—C2—C6131.6 (2)C12—C11—H11A110.1
C2—C3—C4107.0 (2)O4—C11—H11B110.1
C2—C3—C7127.6 (2)C12—C11—H11B110.1
C4—C3—C7125.2 (2)H11A—C11—H11B108.5
N1—C5—C4108.5 (2)C13—C12—C17117.7 (3)
N1—C5—C10119.2 (2)C13—C12—C11121.7 (3)
C4—C5—C10132.3 (2)C17—C12—C11120.6 (3)
O1—C6—O2123.2 (2)C12—C13—C14120.8 (3)
O1—C6—C2118.3 (2)C12—C13—H13119.6
O2—C6—C2118.5 (2)C14—C13—H13119.6
C3—C7—C8111.9 (2)C15—C14—C13120.5 (3)
C3—C7—H7A109.2C15—C14—H14119.8
C8—C7—H7A109.2C13—C14—H14119.8
C3—C7—H7B109.2C16—C15—C14119.6 (3)
C8—C7—H7B109.2C16—C15—H15120.2
H7A—C7—H7B107.9C14—C15—H15120.2
C7—C8—H8A109.5C15—C16—C17120.2 (3)
C7—C8—H8B109.5C15—C16—H16119.9
H8A—C8—H8B109.5C17—C16—H16119.9
C7—C8—H8C109.5C16—C17—C12121.2 (3)
H8A—C8—H8C109.5C16—C17—H17119.4
H8B—C8—H8C109.5C12—C17—H17119.4
C4—C9—H9A109.5C5—C4—C3107.3 (2)
C4—C9—H9B109.5C5—C4—C9127.5 (2)
H9A—C9—H9B109.5C3—C4—C9125.2 (2)
C5—N1—C2—C30.2 (3)C10—O4—C11—C12129.5 (3)
C5—N1—C2—C6178.9 (2)O4—C11—C12—C13118.6 (3)
N1—C2—C3—C40.2 (3)O4—C11—C12—C1760.5 (4)
C6—C2—C3—C4178.7 (3)C17—C12—C13—C140.7 (4)
N1—C2—C3—C7177.0 (2)C11—C12—C13—C14179.8 (3)
C6—C2—C3—C71.9 (4)C12—C13—C14—C151.0 (5)
C2—N1—C5—C40.1 (3)C13—C14—C15—C160.5 (5)
C2—N1—C5—C10177.3 (2)C14—C15—C16—C170.4 (5)
N1—C2—C6—O14.7 (4)C15—C16—C17—C120.7 (5)
C3—C2—C6—O1176.5 (3)C13—C12—C17—C160.1 (4)
N1—C2—C6—O2174.6 (2)C11—C12—C17—C16179.0 (3)
C3—C2—C6—O24.2 (4)N1—C5—C4—C30.0 (3)
C2—C3—C7—C897.9 (3)C10—C5—C4—C3177.0 (3)
C4—C3—C7—C878.4 (4)N1—C5—C4—C9179.2 (2)
C11—O4—C10—O34.3 (5)C10—C5—C4—C93.8 (5)
C11—O4—C10—C5176.4 (3)C2—C3—C4—C50.1 (3)
N1—C5—C10—O30.8 (4)C7—C3—C4—C5177.0 (2)
C4—C5—C10—O3175.9 (3)C2—C3—C4—C9179.3 (2)
N1—C5—C10—O4178.4 (2)C7—C3—C4—C93.7 (4)
C4—C5—C10—O44.8 (4)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O3i0.862.092.942 (3)175
O1—H1A···O2ii0.87 (12)1.77 (13)2.621 (3)168 (8)
Symmetry codes: (i) x+1/2, y+1/2, z+1; (ii) x, y, z+1.

Experimental details

Crystal data
Chemical formulaC16H17NO4
Mr287.31
Crystal system, space groupMonoclinic, C2/c
Temperature (K)293
a, b, c (Å)22.195 (6), 5.2607 (13), 25.413 (3)
β (°) 98.938 (15)
V3)2931.3 (11)
Z8
Radiation typeMo Kα
µ (mm1)0.09
Crystal size (mm)0.37 × 0.37 × 0.10
Data collection
DiffractometerEnraf-Nonius CAD-4
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
2638, 2568, 1253
Rint0.045
(sin θ/λ)max1)0.594
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.041, 0.129, 0.96
No. of reflections2568
No. of parameters199
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.16, 0.17

Computer programs: CAD-4 Software (Enraf-Nonius, 1989), CAD-4 Software, HELENA (Spek, 1997), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEPII (Johnson, 1976), SHELXL97.

Selected geometric parameters (Å, º) top
N1—C51.359 (3)O4—C111.457 (3)
N1—C21.367 (3)C2—C31.386 (3)
O3—C101.190 (3)C3—C41.400 (3)
O4—C101.312 (3)C5—C41.385 (3)
C10—O4—C11119.3 (2)O4—C10—C5111.7 (3)
O3—C10—O4123.1 (2)O4—C11—C12107.8 (2)
O3—C10—C5125.2 (3)
C11—O4—C10—C5176.4 (3)C10—C5—C4—C93.8 (5)
N1—C5—C10—O30.8 (4)C7—C3—C4—C93.7 (4)
C10—O4—C11—C12129.5 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O3i0.862.092.942 (3)175
O1—H1A···O2ii0.87 (12)1.77 (13)2.621 (3)168 (8)
Symmetry codes: (i) x+1/2, y+1/2, z+1; (ii) x, y, z+1.
 

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