N-(1-Benzene­sulfonyl-4-acetyl­pyrrol-3-yl)­acet­amide

The structure of the title compound, C₁₄H₁₄N₂O₄S, has been determined as part of an investigation into the structure and substitution patterns in benzene­sulfonyl-protected pyrroles.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.059
• wR factor = 0.182
• Data-to-parameter ratio = 22.5

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

Pyrrole readily undergoes electrophilic substitution in solution, leading to α-substitution. Because pyrrole is a π-electron-rich molecule, in many cases, the reaction does not stop with mono-substitution, but continues, to give higher substitutions. One means of controlling the reactivity of pyrrole is to add a blocking group to the pyrrole ring. While it is possible to attach the blocking group to the α-carbon, it is easier to utilize the N atom. Attachment of an electron-withdrawing group to the N atom attenuates the reactivity and provides a degree of regioselective control. When using benzenesulfonyl as the protecting group, the regiospecificity is found to be controlled by hardness of the Lewis acid reaction promoter.

The title compound, (I), was prepared in several steps from 1-benzenesulfonylpyrrole by an initial regioselective acylation to afford 3-acetyl-1-benzenesulfonylpyrrole (Xu et al., 1981; Rokach et al., 1981; Kakushima et al., 1983). Subsequent formation of the corresponding oxime of this ketone followed by Beckmann rearrangement in polyphosphoric acid at 358 K afforded the 3-pyrrolylacetamide (m.p. 443–445 K) as the predominant rearrangement product. Friedel–Crafts acylation using acetic anhydride in the presence of aluminium chloride at 273 K was found to occur regioselectively at the adjacent β site to afford the title 3,4-disubstituted pyrrole (m.p. 424–425 K). Although substitution at the C-4 position of a 3-substituted pyrrole is quite unusual in the absence of a bulky N-substituent, Huckel MO calculations upon 1-benzenesulfonylpyrrole-3-ylacetamide indicate that the C-4 position in this C-3 amino-substituted pyrrole is the most electron-rich site of the pyrrole ring (Dewar et al., 1985; Stewart, 1985), suggesting that electrophilic attack should therefore take place at this site. At present, however, it is not clear if the 3,4-disubstitution pattern obtained in this instance is the result of direct acylation at the C-4 site, or the result of an acyl group migration from a kinetically formed isomer. Numerous examples of rearrangement processes of pyrroles have been reported by Kakushima & Frenette (1984), Carmona et al. (1980), Carson & Davis (1981) and Xiao et al. (1996).

The pyrrole and phenyl ring systems found in the title compound are themselves planar, but none of the rings are observed as being coplanar. Considering the pyrrole and phenyl rings of the benzenesulfonylpyrrole and the tetrahedral geometry of the S atom, this is not unexpected.

S2. Experimental

See above for synthesis details.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: XCAD (McArdle, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEX (McArdle, 1995); software used to prepare material for publication: OSCAIL (McArdle, 1995).

Figures

Fig. 1. The molecular structure of (I). The ellipsoids represent displacement parameters at the 40% probability level.

N-(1-Benzenesulfonyl-4-acetylpyrrol-3-yl)acetamide

Crystal data

C14H14N2O4S	F(000) = 640
Mr = 306.34	Dx = 1.387 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71069 Å
Hall symbol: -P 2ybc	Cell parameters from 25 reflections
a = 8.683 (3) Å	θ = 4.7–13.9°
b = 15.159 (6) Å	µ = 0.24 mm^−1
c = 11.151 (3) Å	T = 298 K
β = 91.06 (3)°	Rectangular, colorless
V = 1467.5 (9) Å^3	0.50 × 0.50 × 0.40 mm
Z = 4

Data collection

Enraf-Nonius CAD-4 diffractometer	Rint = 0.014
Radiation source: fine-focus sealed tube	θmax = 30.0°, θmin = 2.3°
Graphite monochromator	h = −12→12
ω/2θ scans	k = −1→21
4709 measured reflections	l = −4→15
4277 independent reflections	2 standard reflections every 120 min
3261 reflections with I > 2σ(I)	intensity decay: 2.1%

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.059	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.182	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.1082P)^2 + 0.1541P] where P = (Fo^2 + 2Fc^2)/3
4277 reflections	(Δ/σ)max = 0.001
190 parameters	Δρmax = 0.31 e Å^−3
0 restraints	Δρmin = −0.60 e Å^−3

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
S1	0.98517 (5)	0.17629 (3)	0.83792 (5)	0.05889 (18)
O1	0.93276 (19)	0.15396 (12)	0.95467 (17)	0.0774 (5)
O2	0.8872 (2)	0.21917 (12)	0.7521 (2)	0.0944 (7)
N1	1.13260 (17)	0.24692 (10)	0.86122 (15)	0.0516 (4)
O31	1.53711 (17)	0.39693 (9)	1.02189 (13)	0.0617 (4)
N4	1.36706 (17)	0.43674 (9)	0.80433 (12)	0.0471 (3)
H4	1.4267	0.4629	0.8555	0.071*
O41	1.2689 (2)	0.43983 (10)	0.61630 (13)	0.0684 (4)
C2	1.24228 (19)	0.23761 (11)	0.95045 (16)	0.0475 (4)
H2	1.2472	0.1926	1.0070	0.071*
C3	1.34327 (18)	0.30666 (10)	0.94124 (14)	0.0415 (3)
C4	1.29258 (18)	0.35993 (10)	0.84127 (14)	0.0411 (3)
C5	1.1646 (2)	0.32135 (10)	0.79181 (16)	0.0478 (4)
H5	1.1092	0.3408	0.7247	0.072*
C11	1.0713 (2)	0.08373 (12)	0.77344 (16)	0.0509 (4)
C12	1.1168 (2)	0.01502 (13)	0.84714 (17)	0.0536 (4)
H12	1.1033	0.0184	0.9296	0.080*
C13	1.1832 (3)	−0.05925 (15)	0.7964 (3)	0.0698 (6)
H13	1.2128	−0.1063	0.8450	0.105*
C14	1.2051 (3)	−0.06354 (19)	0.6755 (3)	0.0852 (8)
H14	1.2494	−0.1134	0.6421	0.128*
C15	1.1615 (4)	0.0060 (2)	0.6033 (2)	0.0933 (9)
H15	1.1781	0.0029	0.5213	0.140*
C16	1.0932 (4)	0.08033 (18)	0.6506 (2)	0.0791 (7)
H16	1.0628	0.1269	0.6013	0.119*
C31	1.4745 (2)	0.32504 (10)	1.02240 (15)	0.0457 (3)
C32	1.5292 (3)	0.25336 (15)	1.1056 (2)	0.0770 (7)
H32A	1.6148	0.2745	1.1531	0.115*
H32B	1.5608	0.2032	1.0595	0.115*
H32C	1.4471	0.2365	1.1573	0.115*
C41	1.3519 (2)	0.47287 (10)	0.69357 (14)	0.0459 (3)
C42	1.4438 (3)	0.55559 (12)	0.67236 (18)	0.0582 (4)
H42A	1.5010	0.5705	0.7440	0.087*
H42B	1.3751	0.6030	0.6516	0.087*
H42C	1.5137	0.5459	0.6080	0.087*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0404 (2)	0.0484 (3)	0.0876 (4)	−0.00822 (16)	−0.0081 (2)	0.0034 (2)
O1	0.0641 (9)	0.0681 (9)	0.1009 (12)	−0.0138 (7)	0.0290 (9)	−0.0085 (9)
O2	0.0587 (9)	0.0641 (10)	0.1586 (19)	−0.0089 (7)	−0.0487 (10)	0.0181 (11)
N1	0.0455 (7)	0.0425 (7)	0.0663 (9)	−0.0081 (6)	−0.0117 (6)	0.0068 (6)
O31	0.0707 (8)	0.0562 (7)	0.0575 (8)	−0.0222 (6)	−0.0152 (6)	0.0084 (6)
N4	0.0550 (8)	0.0444 (7)	0.0414 (7)	−0.0107 (6)	−0.0079 (5)	0.0041 (5)
O41	0.0996 (11)	0.0545 (8)	0.0500 (7)	−0.0083 (7)	−0.0254 (7)	0.0048 (6)
C2	0.0497 (8)	0.0392 (7)	0.0534 (9)	−0.0039 (6)	−0.0067 (7)	0.0044 (6)
C3	0.0434 (7)	0.0401 (7)	0.0408 (7)	−0.0018 (6)	−0.0038 (6)	0.0000 (5)
C4	0.0437 (7)	0.0377 (7)	0.0416 (7)	−0.0013 (5)	−0.0020 (6)	0.0010 (5)
C5	0.0456 (8)	0.0419 (8)	0.0555 (9)	−0.0019 (6)	−0.0100 (7)	0.0048 (6)
C11	0.0473 (8)	0.0502 (9)	0.0550 (9)	−0.0160 (7)	−0.0036 (7)	0.0017 (7)
C12	0.0517 (9)	0.0533 (9)	0.0557 (10)	−0.0067 (7)	0.0007 (7)	0.0029 (8)
C13	0.0623 (12)	0.0574 (11)	0.0900 (16)	−0.0041 (9)	0.0109 (11)	−0.0011 (10)
C14	0.0835 (16)	0.0715 (15)	0.102 (2)	−0.0215 (12)	0.0363 (15)	−0.0222 (14)
C15	0.121 (2)	0.098 (2)	0.0620 (13)	−0.0392 (18)	0.0301 (14)	−0.0196 (14)
C16	0.1033 (18)	0.0766 (14)	0.0574 (12)	−0.0287 (14)	−0.0003 (11)	0.0126 (10)
C31	0.0485 (8)	0.0464 (8)	0.0419 (7)	−0.0063 (6)	−0.0067 (6)	0.0022 (6)
C32	0.0825 (14)	0.0585 (11)	0.0884 (16)	−0.0132 (10)	−0.0423 (13)	0.0202 (11)
C41	0.0559 (9)	0.0393 (7)	0.0422 (8)	0.0036 (6)	−0.0031 (6)	0.0023 (6)
C42	0.0724 (12)	0.0471 (9)	0.0551 (10)	−0.0046 (8)	−0.0001 (8)	0.0110 (7)

Geometric parameters (Å, º)

S1—O2	1.4255 (18)	C11—C16	1.387 (3)
S1—O1	1.4277 (19)	C12—C13	1.390 (3)
S1—N1	1.6854 (15)	C12—H12	0.93
S1—C11	1.751 (2)	C13—C14	1.366 (4)
N1—C2	1.372 (2)	C13—H13	0.93
N1—C5	1.399 (2)	C14—C15	1.375 (5)
O31—C31	1.218 (2)	C14—H14	0.93
N4—C41	1.355 (2)	C15—C16	1.383 (4)
N4—C4	1.398 (2)	C15—H15	0.93
N4—H4	0.86	C16—H16	0.93
O41—C41	1.221 (2)	C31—C32	1.500 (3)
C2—C3	1.371 (2)	C32—H32A	0.96
C2—H2	0.93	C32—H32B	0.96
C3—C4	1.439 (2)	C32—H32C	0.96
C3—C31	1.468 (2)	C41—C42	1.507 (2)
C4—C5	1.363 (2)	C42—H42A	0.96
C5—H5	0.93	C42—H42B	0.96
C11—C12	1.380 (3)	C42—H42C	0.96
O2—S1—O1	121.58 (13)	C14—C13—C12	120.4 (2)
O2—S1—N1	104.84 (9)	C14—C13—H13	119.8
O1—S1—N1	105.31 (10)	C12—C13—H13	119.8
O2—S1—C11	110.12 (13)	C13—C14—C15	120.0 (3)
O1—S1—C11	109.29 (10)	C13—C14—H14	120.0
N1—S1—C11	104.10 (8)	C15—C14—H14	120.0
C2—N1—C5	109.99 (14)	C14—C15—C16	121.1 (2)
C2—N1—S1	124.17 (12)	C14—C15—H15	119.5
C5—N1—S1	125.82 (13)	C16—C15—H15	119.5
C41—N4—C4	124.58 (14)	C15—C16—C11	118.3 (2)
C41—N4—H4	117.7	C15—C16—H16	120.8
C4—N4—H4	117.7	C11—C16—H16	120.8
C3—C2—N1	107.68 (15)	O31—C31—C3	120.55 (15)
C3—C2—H2	126.2	O31—C31—C32	120.97 (16)
N1—C2—H2	126.2	C3—C31—C32	118.48 (15)
C2—C3—C4	107.44 (14)	C31—C32—H32A	109.5
C2—C3—C31	126.07 (15)	C31—C32—H32B	109.5
C4—C3—C31	126.42 (14)	H32A—C32—H32B	109.5
C5—C4—N4	128.05 (15)	C31—C32—H32C	109.5
C5—C4—C3	107.94 (14)	H32A—C32—H32C	109.5
N4—C4—C3	124.00 (14)	H32B—C32—H32C	109.5
C4—C5—N1	106.92 (14)	O41—C41—N4	121.58 (16)
C4—C5—H5	126.5	O41—C41—C42	122.54 (16)
N1—C5—H5	126.5	N4—C41—C42	115.89 (15)
C12—C11—C16	121.1 (2)	C41—C42—H42A	109.5
C12—C11—S1	118.70 (15)	C41—C42—H42B	109.5
C16—C11—S1	120.19 (18)	H42A—C42—H42B	109.5
C11—C12—C13	119.0 (2)	C41—C42—H42C	109.5
C11—C12—H12	120.5	H42A—C42—H42C	109.5
C13—C12—H12	120.5	H42B—C42—H42C	109.5
O2—S1—N1—C2	170.03 (18)	O2—S1—C11—C12	−153.89 (15)
O1—S1—N1—C2	40.67 (19)	O1—S1—C11—C12	−17.91 (17)
C11—S1—N1—C2	−74.28 (18)	N1—S1—C11—C12	94.19 (15)
O2—S1—N1—C5	−12.0 (2)	O2—S1—C11—C16	26.3 (2)
O1—S1—N1—C5	−141.39 (17)	O1—S1—C11—C16	162.31 (18)
C11—S1—N1—C5	103.66 (17)	N1—S1—C11—C16	−85.59 (18)
C5—N1—C2—C3	1.4 (2)	C16—C11—C12—C13	−1.2 (3)
S1—N1—C2—C3	179.65 (13)	S1—C11—C12—C13	179.04 (14)
N1—C2—C3—C4	−0.3 (2)	C11—C12—C13—C14	1.0 (3)
N1—C2—C3—C31	176.91 (16)	C12—C13—C14—C15	0.0 (4)
C41—N4—C4—C5	−19.9 (3)	C13—C14—C15—C16	−0.9 (4)
C41—N4—C4—C3	159.32 (17)	C14—C15—C16—C11	0.8 (4)
C2—C3—C4—C5	−0.90 (19)	C12—C11—C16—C15	0.3 (3)
C31—C3—C4—C5	−178.12 (16)	S1—C11—C16—C15	−179.91 (19)
C2—C3—C4—N4	179.77 (15)	C2—C3—C31—O31	−164.50 (18)
C31—C3—C4—N4	2.6 (3)	C4—C3—C31—O31	12.2 (3)
N4—C4—C5—N1	−178.99 (16)	C2—C3—C31—C32	15.5 (3)
C3—C4—C5—N1	1.73 (19)	C4—C3—C31—C32	−167.8 (2)
C2—N1—C5—C4	−2.0 (2)	C4—N4—C41—O41	0.3 (3)
S1—N1—C5—C4	179.82 (13)	C4—N4—C41—C42	−179.52 (16)