(5-Bromo­pyrrol-3-yl)­cyclo­hexyl­methano­ne

The title compound, C₁₁H₁₄BrNO, contains a single halo- and keto-substituted pyrrole ring. A very short hydrogen bond between the amine H atom of one mol­ecule and the carbonyl O atom of another has an N...O distance of 2.765 (2) Å.

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.023
• wR factor = 0.056
• Data-to-parameter ratio = 14.6

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level A:



ABSTM_01  Alert A The minimum transmission value cannot exceed the maximum
          value
          Value of T min given =     0.685 Value of Tmax given =     0.611


 Alert Level C:



ABSTM_02  Alert C The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
          Tmin and Tmax reported:      0.685     0.611
          Tmin and Tmax expected:      0.515     0.685
          RR =      1.490
          Please check that your absorption correction is appropriate.

General Notes



ABSTM_02  When printed, the submitted absorption T values will be replaced
          by the scaled T values. Since the ratio of scaled T's is
          identical to the ratio of reported T values, the scaling does
          not imply a change to the absorption corrections used in the
          study.
          Ratio of Tmax expected/reported      1.121
          Tmax scaled      0.685 Tmin scaled      0.768


 1 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

---

S1. Comment

The bromopyrrole moiety of (5-bromopyrrol-3-yl)cyclohexylmethanone, (I), is quite similar to other halopyrroles in the literature (Allen et al., 1983). Notable among them are: oroidin (Walker et al., 1981), pyrrolomycin B (Kaneda et al., 1981), axinohydantoin (Pettit et al., 1990), 2-bromoaldisin (Xu et al., 2001), 2-cyano-4,5-dibromopyrrole (Konig et al., 1998), 5,5'-dibromo-3,3'-diethyl-4,4'-dimethyl-2,2'-pyrromethene (Becker et al., 1978), and ethyl 4,7-ethano-3-iodo-5,6-dihydro-2H-isoindole-1-carboxylate (Uno et al., 2000). The distances and angles of (I) are as expected (Allen et al., 1983), including the relatively longer distance of 1.434 (1) Å for the C—C bond opposite to the N—H group within the pyrrole ring, and the relatively shorter N—C distances of 1.357 (2) and 1.368 (2) Å. The latter N—C distances compare well to those of the substituted pyrroles in 2-bromoaldisin, axinohydantoin, pyrrolomycin B, and ethyl 4,7-ethano-3-iodo-5,6-dihydro-2H-isoindole-1-carboxylate. On the other hand, for the dibromo- and bromo-ethyl-methyl- (e.g. all C atoms) substituted pyrroles of 2-cyano-4,5-dibromopyrrole and 5,5'-dibromo-3,3'-diethyl-4,4'-dimethyl-2,2'-pyrromethene, respectively, the N—C bond of the H—N—C—Br moiety is the shortest in the ring by about 0.03 Å. These inequalities demonstrate that the magnitude and symmetrical disposition of bonds on the pyrrole ring are expected to be quite sensitive to the electronic and chemical properties of substituents on the ring.

Although no intramolecular hydrogen bond (to Br) exists, the Br atom of the H—N—C—Br moiety is closer to the N—H group than the adjacent C—H group. For (I), the Br—C—N angle is 120.8 (1)°, which compares well to the average value of 121.2 (5)° for the above seven referenced compounds. This is significantly shorter than the angle of 125° expected for a symmetrically placed pyrrole-ring substituent.

In (I), there is one H atom that engages in hydrogen bonding, which appears to be the dominant non-dispersive intermolecular interaction. This hydrogen bond may be expected, since it involves the sole H-bond donor atom, namely that of the N—H, and the most likely hydrogen-bond acceptor, the carbonyl O atom. The N—H bond vector is directed nearly along the N···O vector, such that the H···O distance may be regarded as (2.80 - D)Å, where D is the N—H distance. This is useful in considering the hydrogen-bond geometry based upon the X-ray derived value for N—H [here, 0.82 (2) Å] versus the more accurate internuclear value (e.g. D = 1.08 Å) from neutron-diffraction studies. Although it is rather planar and contains sp² pyrrole ring atoms, the title compound does not engage in significant π–π intermolecular interactions. This characteristic of the crystal packing is likely due to the pyrrole ring being only a small part of the entire molecule and the cyclohexyl substituent being quite bulky.

S2. Experimental

Crystals of (5-bromo-pyrrol-3-yl)cyclohexylmethanone (m.p. 418–419 K) were obtained from a solution in 9:1 hexanes–ethyl acetate. Bromination of pyrroles is sometimes difficult to control, both in terms of position selectivity and the extent of bromination (Gilow & Burton, 1981). The initial products may also isomerize under certain reaction conditions (Dvornikova & Kamienska-Trela, 2002). In the course of an alkaloid total synthesis, we had occasion to study the bromination of cyclohexyl(pyrrol-3-yl)methanone. Although bromination with N-bromosuccinimide was non-selective, the use of tetrahydrofuran dibromide/sodium acetate as the bromination reagent (Anderson & Huang, 1967) led smoothly to a single product when the reaction was run to 40% completion. Analysis of ¹H NMR chemical shifts and coupling constants indicated this to be (5-bromo-pyrrol-3-yl)cyclohexylmethanone [(I); 77% yield], by comparison with (5-bromopyrrol-3-yl)ethanone (Anderson & Huang, 1967). Because the earlier assignment had been based on analogy with non-brominated models, and because the coupling constants are of similar magnitude (J_2,4 = 1.8 Hz, J_1,2 = 3.0 Hz and J_1,4 = 2.6 Hz), we undertook the crystallographic study to confirm the site selectivity of bromination.

S3. Refinement

The hydrogen-bond geometry corresponding to the expected 1.08 Å internuclear distance for N—H in this structure is: N1—H1N 1.08 (2), H1N.·O1ⁱ 1.72 (2), N1.·O1ⁱ 2.765 (2) Å, N1—H1N.·O1ⁱ 161 (2)° [symmetry code: (i) x − 1/2, −y + 1/2, z − 1/2]. All H-atom positions were observed on a difference Fourier map and were refined with isotropic displacement parameters. The C—H bond lengths were in the range 0.92–1.02 (2) Å, and the N—H bond length was 0.82 (2) Å.

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SMART; data reduction: SAINT-Plus (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 2000); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The molecular structure of (I). Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. Projection view of the crystal packing of (I), approximately along the b axis. Hydrogen bonds are indicated by dotted lines

(I)

Crystal data

C11H14BrNO	F(000) = 520
Mr = 256.14	Dx = 1.580 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 6056 reflections
a = 12.0951 (6) Å	θ = 2.8–30.5°
b = 7.3006 (3) Å	µ = 3.78 mm^−1
c = 13.0038 (6) Å	T = 100 K
β = 110.280 (1)°	Lathe, colourless
V = 1077.07 (9) Å^3	0.27 × 0.15 × 0.10 mm
Z = 4

Data collection

Bruker SMART APEX CCD area-detector diffractometer	2677 independent reflections
Radiation source: fine-focus sealed tube	2380 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.028
ω scans	θmax = 28.3°, θmin = 2.0°
Absorption correction: multi-scan (SADABS; Bruker, 2000)	h = −16→16
Tmin = 0.685, Tmax = 0.611	k = −9→9
12893 measured reflections	l = −17→17

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)] = 0.023	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.056	All H-atom parameters refined
S = 1.01	w = 1/[σ^2(Fo^2) + (0.023P)^2 + 0.6P] where P = (Fo^2 + 2Fc^2)/3
2677 reflections	(Δ/σ)max < 0.001
183 parameters	Δρmax = 0.38 e Å^−3
0 restraints	Δρmin = −0.30 e Å^−3

Special details

Geometry. All standard uncertainties (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u. values are taken into account individually in the estimation of s.u. values in distances, angles and torsion angles; correlations between s.u. values in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u. values is used for estimating s.u. values involving least-squares 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. No restraints or constraints were used in the refinement. No evidence of extinction was observed and an extinction parameter was not refined. The extended disubstituted pyrrole least-squares plane is given below (x,y,z in crystal coordinates) and deviations from it. The * indicates an atom used to define plane and s.u. values are enclosed in parentheses. 4.220 (6)x − 6.841 (1)y − 1.397 (3)z=1.662 (5) * 0.002 (1) C1 − 1.377 (2) C7 * 0.003 (1) C2 − 1.389 (2) C8 * 0.007 (1) C3 − 1.144 (2) C9 * 0.023 (1) C4 0.154 (2) C10 * 0.022 (1) N1 0.162 (2) C11 * 0.027 (1) O1 * −0.034 (1) Br1 * −0.049 (1) C6 r.m.s. deviation of fitted atoms = 0.026

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Br1	0.877087 (15)	0.29363 (3)	0.046456 (13)	0.02295 (7)
O1	1.06517 (10)	0.30423 (16)	0.51908 (9)	0.0180 (2)
N1	0.77081 (12)	0.18865 (19)	0.19949 (11)	0.0159 (3)
H1N	0.7062 (19)	0.172 (3)	0.1518 (18)	0.020 (5)*
C1	0.87066 (14)	0.2557 (2)	0.18631 (13)	0.0161 (3)
C2	0.95460 (14)	0.2871 (2)	0.28597 (13)	0.0142 (3)
H2	1.0296 (18)	0.332 (3)	0.2985 (16)	0.019 (5)*
C3	0.90230 (13)	0.2380 (2)	0.36566 (12)	0.0131 (3)
C4	0.78927 (14)	0.1776 (2)	0.30835 (13)	0.0152 (3)
H4	0.7272 (16)	0.132 (3)	0.3313 (15)	0.014 (4)*
C5	0.96218 (13)	0.2524 (2)	0.48396 (13)	0.0132 (3)
C6	0.89642 (13)	0.2027 (2)	0.56057 (13)	0.0136 (3)
H6	0.8628 (15)	0.079 (3)	0.5382 (14)	0.015 (5)*
C7	0.79358 (14)	0.3359 (2)	0.54807 (14)	0.0165 (3)
H7A	0.7391 (16)	0.342 (2)	0.4727 (15)	0.012 (4)*
H7B	0.8254 (15)	0.463 (3)	0.5657 (14)	0.014 (4)*
C8	0.72727 (15)	0.2811 (2)	0.62466 (14)	0.0192 (3)
H8B	0.6660 (19)	0.372 (3)	0.6155 (18)	0.033 (6)*
H8A	0.6909 (18)	0.160 (3)	0.6012 (17)	0.027 (5)*
C9	0.80894 (16)	0.2714 (3)	0.74364 (15)	0.0208 (3)
H9B	0.8386 (17)	0.400 (3)	0.7695 (16)	0.023 (5)*
H9A	0.7641 (18)	0.229 (3)	0.7921 (17)	0.018 (5)*
C10	0.91292 (16)	0.1433 (3)	0.75642 (14)	0.0201 (3)
H10A	0.8832 (15)	0.019 (3)	0.7382 (15)	0.015 (4)*
H10B	0.9655 (19)	0.141 (3)	0.8330 (18)	0.030 (6)*
C11	0.97899 (14)	0.1984 (2)	0.68022 (13)	0.0156 (3)
H11B	1.0104 (17)	0.319 (3)	0.6989 (16)	0.015 (5)*
H11A	1.0415 (16)	0.117 (3)	0.6875 (15)	0.015 (4)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.02320 (10)	0.03323 (11)	0.01230 (9)	−0.00038 (7)	0.00597 (7)	0.00246 (7)
O1	0.0120 (5)	0.0262 (6)	0.0137 (5)	−0.0021 (5)	0.0019 (4)	0.0011 (5)
N1	0.0115 (6)	0.0214 (7)	0.0119 (6)	−0.0008 (5)	0.0003 (5)	−0.0018 (5)
C1	0.0171 (8)	0.0177 (7)	0.0138 (7)	0.0010 (6)	0.0059 (6)	0.0006 (6)
C2	0.0130 (7)	0.0153 (7)	0.0142 (7)	−0.0006 (6)	0.0045 (6)	−0.0004 (6)
C3	0.0128 (7)	0.0141 (7)	0.0117 (7)	0.0012 (6)	0.0034 (6)	−0.0006 (6)
C4	0.0129 (7)	0.0188 (8)	0.0130 (7)	−0.0008 (6)	0.0034 (6)	−0.0012 (6)
C5	0.0132 (7)	0.0131 (7)	0.0125 (7)	0.0010 (5)	0.0036 (6)	0.0003 (6)
C6	0.0130 (7)	0.0143 (7)	0.0131 (7)	−0.0011 (6)	0.0039 (6)	−0.0009 (6)
C7	0.0141 (7)	0.0202 (8)	0.0149 (8)	0.0019 (6)	0.0047 (6)	−0.0002 (6)
C8	0.0160 (7)	0.0234 (9)	0.0200 (8)	0.0010 (7)	0.0086 (6)	−0.0025 (7)
C9	0.0229 (8)	0.0243 (9)	0.0185 (8)	0.0018 (7)	0.0113 (7)	−0.0002 (7)
C10	0.0233 (9)	0.0218 (9)	0.0165 (8)	0.0024 (7)	0.0084 (7)	0.0029 (7)
C11	0.0156 (7)	0.0170 (8)	0.0135 (7)	0.0008 (6)	0.0042 (6)	0.0004 (6)

Geometric parameters (Å, º)

Br1—C1	1.8677 (16)	C7—C8	1.533 (2)
O1—C5	1.229 (2)	C7—H7A	0.97 (2)
N1—C4	1.357 (2)	C7—H7B	1.00 (2)
N1—C1	1.368 (2)	C8—C9	1.522 (2)
N1—H1N	0.82 (2)	C8—H8B	0.97 (2)
C1—C2	1.360 (2)	C8—H8A	0.99 (2)
C2—C3	1.434 (2)	C9—C10	1.529 (2)
C2—H2	0.92 (2)	C9—H9B	1.02 (2)
C3—C4	1.383 (2)	C9—H9A	1.01 (2)
C3—C5	1.459 (2)	C10—C11	1.527 (2)
C4—H4	0.96 (2)	C10—H10A	0.98 (2)
C5—C6	1.519 (2)	C10—H10B	0.98 (2)
C6—C11	1.530 (2)	C11—H11B	0.96 (2)
C6—C7	1.543 (2)	C11—H11A	0.94 (2)
C6—H6	0.99 (2)
C4—N1—C1	108.59 (14)	C8—C7—H7B	109.8 (10)
C4—N1—H1N	123.2 (14)	C6—C7—H7B	109.2 (10)
C1—N1—H1N	127.6 (14)	H7A—C7—H7B	105.3 (15)
C2—C1—N1	109.92 (14)	C9—C8—C7	111.80 (14)
C2—C1—Br1	129.31 (12)	C9—C8—H8B	110.8 (13)
N1—C1—Br1	120.77 (12)	C7—C8—H8B	107.0 (13)
C1—C2—C3	106.00 (14)	C9—C8—H8A	109.6 (12)
C1—C2—H2	126.2 (13)	C7—C8—H8A	108.1 (12)
C3—C2—H2	127.8 (12)	H8B—C8—H8A	109.4 (18)
C4—C3—C2	106.96 (14)	C8—C9—C10	111.01 (14)
C4—C3—C5	128.88 (14)	C8—C9—H9B	108.9 (11)
C2—C3—C5	124.17 (14)	C10—C9—H9B	110.1 (11)
N1—C4—C3	108.53 (14)	C8—C9—H9A	110.4 (12)
N1—C4—H4	118.8 (11)	C10—C9—H9A	110.1 (11)
C3—C4—H4	132.6 (11)	H9B—C9—H9A	106.2 (15)
O1—C5—C3	118.87 (14)	C11—C10—C9	111.35 (14)
O1—C5—C6	121.59 (14)	C11—C10—H10A	108.6 (11)
C3—C5—C6	119.54 (13)	C9—C10—H10A	108.9 (11)
C5—C6—C11	111.49 (13)	C11—C10—H10B	111.3 (13)
C5—C6—C7	111.52 (13)	C9—C10—H10B	110.1 (13)
C11—C6—C7	109.77 (13)	H10A—C10—H10B	106.4 (17)
C5—C6—H6	106.3 (10)	C10—C11—C6	111.18 (13)
C11—C6—H6	109.7 (10)	C10—C11—H11B	109.2 (11)
C7—C6—H6	108.0 (10)	C6—C11—H11B	107.6 (12)
C8—C7—C6	110.57 (13)	C10—C11—H11A	110.5 (11)
C8—C7—H7A	109.9 (11)	C6—C11—H11A	109.5 (11)
C6—C7—H7A	111.8 (11)	H11B—C11—H11A	108.8 (16)
C4—N1—C1—C2	0.51 (19)	O1—C5—C6—C11	−8.5 (2)
C4—N1—C1—Br1	−178.96 (11)	C3—C5—C6—C11	171.28 (14)
N1—C1—C2—C3	−0.69 (18)	O1—C5—C6—C7	114.55 (17)
Br1—C1—C2—C3	178.73 (12)	C3—C5—C6—C7	−65.63 (18)
C1—C2—C3—C4	0.61 (18)	C5—C6—C7—C8	179.01 (13)
C1—C2—C3—C5	−179.40 (14)	C11—C6—C7—C8	−56.93 (17)
C1—N1—C4—C3	−0.11 (18)	C6—C7—C8—C9	56.29 (18)
C2—C3—C4—N1	−0.31 (18)	C7—C8—C9—C10	−54.9 (2)
C5—C3—C4—N1	179.70 (15)	C8—C9—C10—C11	54.8 (2)
C4—C3—C5—O1	177.62 (16)	C9—C10—C11—C6	−56.71 (19)
C2—C3—C5—O1	−2.4 (2)	C5—C6—C11—C10	−178.45 (13)
C4—C3—C5—C6	−2.2 (2)	C7—C6—C11—C10	57.46 (17)
C2—C3—C5—C6	177.80 (14)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1N···O1^i	0.82 (2)	1.97 (2)	2.765 (2)	163 (2)

Symmetry code: (i) x−1/2, −y+1/2, z−1/2.