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In the title compound, C21H21NO5, obtained from a Morita–Baylis–Hillman adduct, the hydrogenated five-membered ring adopts a shallow envelope conformation, with the C atom bearing the carb­oxy­lic acid substituent deviating by 0.237 (1) Å from the mean plane of the other four atoms (r.m.s. deviation = 0.007 Å). The dihedral angle between the fused ring system (all atoms; r.m.s. deviation = 0.057 Å) and the pendant trimeth­oxy benzene ring is 66.65 (3)°. The C atoms of the meta-meth­oxy groups lie close to the plane of the benzene ring [deviations = 0.052 (1) and −0.083 (1) Å], whereas the C atom of the para-meth­oxy group is significantly displaced [deviation = −1.289 (1) Å]. In the crystal, carb­oxy­lic acid inversion dimers generate R22(8) loops. The dimers are connected by N—H...O hydrogen bonds, forming [011] chains. A C—H...O inter­action is also observed.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S2056989015008786/hb7417sup1.cif
Contains datablocks I, New_Global_Publ_Block

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S2056989015008786/hb7417Isup2.hkl
Contains datablock I

cdx

Chemdraw file https://doi.org/10.1107/S2056989015008786/hb7417Isup3.cdx
Supplementary material

cml

Chemical Markup Language (CML) file https://doi.org/10.1107/S2056989015008786/hb7417Isup4.cml
Supplementary material

CCDC reference: 1063387

Key indicators

  • Single-crystal X-ray study
  • T = 100 K
  • Mean [sigma](C-C)= 0.001 Å
  • R factor = 0.038
  • wR factor = 0.119
  • Data-to-parameter ratio = 31.6

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Introduction top

Indole skeleton is an aromatic heterocycle possessing a benzene ring fused to a pyrrole ring which exhibits a wide range of biological and pharmacological activities. Compounds presenting this moiety have been successfully synthesized and used in medicinal chemistry (Xu et al., 2012). In spite of the number of developed methods for the preparation of indoles (Xu et al., 2012; Humphrey and Kuethe, 2006), our inter­est to use Morita–Baylis–Hillman adducts as building blocks for organic synthesis resulted in a successful stereoselective strategy to obtain compounds of this class.

Experimental top

Synthesis and crystallization top

\ The synthesis of 3-(3,4,5-tri­meth­oxy­phenyl)-1,2,3,4-tetra­hydro­cyclo­penta­[b]indole-2-\ carb­oxy­lic acid started with a mixture of 1 mmol of (±)-methyl 2-[hy­droxy­(3,4,5-tri­meth­oxy­phenyl)-methyl]­acrylate (the Morita–Baylis–Hillman adduct), 1.2 mmol of indole and 1 mmol of 2-iodoxybenzoic acid, in aceto­nitrile (5 mL). This mixture was kept under reflux to give 1,3-di­carbonyl compound, which was further reduced by sodium tetra­hydro­borate, resulting in the corresponding β-hy­droxy-carbonyl.

This was then treated with tri­fluoro­methane­sulfonic acid and submitted to basic hydrolysis. The cyclo­penta­[b]indole, obtained with excellent diastereoselectivity (>99:1) and overall yield of 70%, was purified by flash chromatography (hexane/ethyl acetate (60:40)). 3-(3,4,5-tri­meth­oxy­phenyl)-1,2,3,4-tetra­hydro­cyclo­penta­[b]indole-2-\ carb­oxy­lic acid was dissolved in 10:1 (v/v) chloro­form/methanol mixture and kept in the freezer to allow slowly formation of irregular colorless single crystals.

Refinement top

The positions of hydrogen atoms bound to carbon atoms were idealized and calculated by riding model, with C—H bond lengths of 0.95, 0.98 and 0.99 Å for phenyl, methyl and methyl­ene, respectively. The isotropic displacement parameters values (Uiso(H)) were fixed at 1.5Ueq(C) for methyl H atoms and 1.2Ueq(C) for all other attached H atoms.

Results and discussion top

The molecules of the title compound present a tri­meth­oxy­phenyl ring bonded to a system of three rings, in which an indole skeleton unit is fused to a five-membered ring possessing a carb­oxy­lic unit (Fig. 1). It crystallized in P1 space group and has a conformational structure determined by intra and inter­molecular nonclassical (C—H—O) and inter­molecular (O—H—O and N—H—O) bonding (Table 1, Fig. 2).

All of the rings in the structure are almost planar, with r.m.s. of 0.010, 0.066, 0.006 and 0.006 Å for tri­meth­oxy­phenyl, five-membered, pyrrole and benzene rings, respectively. The three rings fused system is essentially planar (r.m.s. deviation of 0.057 Å) and make a plane-plane angle of 113.35° with the tri­meth­oxy­phenyl ring.

With respect to the pyrrole ring, the benzene ring and the five-membered ring make dihedral angles C14—C13—N1—C5 = 176.67 (7)° and C3—C4—C16—C17 = -175.72 (8)°, respectively. The dihedral angle between the five-membered ring and its tri­meth­oxy­phenyl substituent (C5—C6—C7—C8) is -164.79 (16)°, while that between the five-membered ring and the carb­oxy­lic unit (C16—C17—C18—O4) is -56.30 (8)°, which is consistent with the expected trans relative configuration of this isomer.

Related literature top

For compounds presenting an indole skeleton unit and examples of them, see: Xu et al. (2012); Humphrey & Kuethe (2006). For methods of synthesis of indoles, see: Jordan et al. (2011); Humphrey & Kuethe (2006). For the use of Morita–Baylis–Hillman adducts as building blocks for organic synthesis, see: Basavaiah & Veeraraghavaiah (2012); Coelho et al. (2002).

Computing details top

Data collection: APEX2 (Bruker, 2010); cell refinement: SAINT (Bruker, 2010); data reduction: SAINT (Bruker, 2010); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXLE (Hübschle et al., 2011); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2003) and publCIF (Westrip, 2010).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title compound with 50% probability displacement ellipsoids.
[Figure 2] Fig. 2. Crystal packing of the title compound, showing hydrogen-bonding interactions.
3-(3,4,5-Trimethoxyphenyl)-1,2,3,4-tetrahydrocyclopenta[b]indole-2-carboxylic acid top
Crystal data top
C21H21NO5Z = 2
Mr = 367.39F(000) = 388
Triclinic, P1Dx = 1.372 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 7.203 (1) ÅCell parameters from 9708 reflections
b = 9.5844 (12) Åθ = 2.6–38°
c = 12.9957 (17) ŵ = 0.10 mm1
α = 91.939 (5)°T = 100 K
β = 97.198 (6)°Irregular, colourless
γ = 91.716 (5)°0.34 × 0.17 × 0.13 mm
V = 889.1 (2) Å3
Data collection top
Bruker APEX CCD
diffractometer
7825 independent reflections
Radiation source: fine-focus sealed tube6558 reflections with I > 2σ(I)
Detector resolution: 8.3333 pixels mm-1Rint = 0.031
phi and ω scansθmax = 35.0°, θmin = 1.6°
Absorption correction: multi-scan
(SADABS; Bruker, 2010)
h = 1111
Tmin = 0.967, Tmax = 0.987k = 1515
100846 measured reflectionsl = 2020
Refinement top
Refinement on F20 restraints
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.038H-atom parameters constrained
wR(F2) = 0.119 w = 1/[σ2(Fo2) + (0.079P)2 + 0.2107P]
where P = (Fo2 + 2Fc2)/3
S = 0.94(Δ/σ)max < 0.001
7825 reflectionsΔρmax = 0.58 e Å3
248 parametersΔρmin = 0.27 e Å3
Crystal data top
C21H21NO5γ = 91.716 (5)°
Mr = 367.39V = 889.1 (2) Å3
Triclinic, P1Z = 2
a = 7.203 (1) ÅMo Kα radiation
b = 9.5844 (12) ŵ = 0.10 mm1
c = 12.9957 (17) ÅT = 100 K
α = 91.939 (5)°0.34 × 0.17 × 0.13 mm
β = 97.198 (6)°
Data collection top
Bruker APEX CCD
diffractometer
7825 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2010)
6558 reflections with I > 2σ(I)
Tmin = 0.967, Tmax = 0.987Rint = 0.031
100846 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0380 restraints
wR(F2) = 0.119H-atom parameters constrained
S = 0.94Δρmax = 0.58 e Å3
7825 reflectionsΔρmin = 0.27 e Å3
248 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O10.67935 (8)0.20458 (6)0.61432 (4)0.01701 (10)
O20.85593 (8)0.13066 (7)0.45301 (4)0.02026 (11)
O30.52886 (8)0.14039 (6)0.07684 (5)0.02004 (11)
O40.27178 (9)0.00009 (6)0.05008 (5)0.02346 (12)
H40.33800.04550.01310.035*
O50.36545 (8)0.34406 (6)0.59020 (4)0.01927 (11)
N10.20865 (9)0.57757 (6)0.22742 (5)0.01503 (10)
H10.29930.62850.26360.018*
C10.33636 (10)0.65445 (9)0.10853 (6)0.01960 (13)
H1A0.46330.66710.08160.024*
C20.25626 (10)0.52708 (8)0.09178 (6)0.01735 (12)
H20.32640.45380.05220.021*
C30.07052 (9)0.50802 (7)0.13406 (5)0.01394 (11)
C40.05337 (9)0.39331 (7)0.13915 (5)0.01372 (11)
C50.21619 (9)0.43919 (7)0.19636 (5)0.01331 (11)
C60.36676 (9)0.33516 (7)0.20740 (5)0.01314 (11)
H60.46700.36240.16450.016*
C70.45411 (9)0.30909 (7)0.31710 (5)0.01289 (11)
C80.62291 (9)0.24015 (7)0.33130 (5)0.01407 (11)
H80.68730.21870.27360.017*
C90.69665 (9)0.20293 (7)0.43061 (5)0.01429 (11)
C100.60455 (9)0.23835 (7)0.51579 (5)0.01402 (11)
C110.58428 (11)0.08561 (8)0.65126 (6)0.02034 (13)
H11A0.44930.10050.64380.031*
H11B0.63020.07370.72460.031*
H11C0.60860.00160.61060.031*
C120.94999 (11)0.08870 (10)0.36769 (7)0.02528 (16)
H12A0.86430.03110.31790.038*
H12B1.05870.03450.39270.038*
H12C0.99180.17160.33370.038*
C130.03194 (10)0.62141 (7)0.19116 (5)0.01434 (11)
C140.04783 (11)0.75053 (8)0.20623 (6)0.01750 (12)
H140.02230.82560.24370.021*
C150.23267 (11)0.76525 (8)0.16470 (6)0.01940 (13)
H150.29050.85170.17430.023*
C160.06472 (10)0.24706 (7)0.09663 (5)0.01538 (12)
H16A0.06820.24480.02070.018*
H16B0.04150.18700.11250.018*
C170.25541 (9)0.20188 (7)0.15655 (5)0.01396 (11)
H170.22390.14320.21460.017*
C180.36696 (10)0.11304 (7)0.09044 (5)0.01515 (12)
C190.36205 (9)0.34551 (7)0.40179 (5)0.01444 (11)
H190.24770.39310.39180.017*
C200.43904 (10)0.31162 (7)0.50143 (5)0.01433 (11)
C210.19448 (12)0.41674 (9)0.58029 (6)0.02137 (14)
H21A0.20900.50110.54110.032*
H21B0.16310.44290.64940.032*
H21C0.09390.35610.54350.032*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0210 (2)0.0173 (2)0.0115 (2)0.00177 (18)0.00212 (16)0.00000 (16)
O20.0164 (2)0.0267 (3)0.0175 (2)0.00815 (19)0.00017 (17)0.00044 (19)
O30.0183 (2)0.0206 (3)0.0210 (2)0.00222 (19)0.00369 (18)0.00790 (19)
O40.0243 (3)0.0181 (3)0.0283 (3)0.0019 (2)0.0082 (2)0.0119 (2)
O50.0259 (3)0.0208 (3)0.0124 (2)0.0063 (2)0.00682 (18)0.00088 (18)
N10.0170 (2)0.0125 (2)0.0146 (2)0.00230 (18)0.00148 (18)0.00317 (18)
C10.0167 (3)0.0230 (3)0.0192 (3)0.0042 (2)0.0019 (2)0.0012 (2)
C20.0155 (3)0.0197 (3)0.0166 (3)0.0007 (2)0.0015 (2)0.0002 (2)
C30.0151 (3)0.0150 (3)0.0116 (2)0.0016 (2)0.00173 (19)0.0009 (2)
C40.0155 (3)0.0137 (3)0.0118 (2)0.0010 (2)0.00152 (19)0.00208 (19)
C50.0160 (3)0.0121 (3)0.0115 (2)0.0017 (2)0.00085 (19)0.00173 (19)
C60.0153 (2)0.0127 (3)0.0113 (2)0.0017 (2)0.00156 (19)0.00173 (19)
C70.0147 (2)0.0127 (3)0.0111 (2)0.0013 (2)0.00167 (19)0.00187 (19)
C80.0146 (2)0.0153 (3)0.0123 (2)0.0017 (2)0.00190 (19)0.0019 (2)
C90.0136 (2)0.0149 (3)0.0139 (2)0.0015 (2)0.00027 (19)0.0019 (2)
C100.0163 (3)0.0142 (3)0.0109 (2)0.0002 (2)0.00008 (19)0.00137 (19)
C110.0230 (3)0.0187 (3)0.0195 (3)0.0007 (2)0.0022 (2)0.0047 (2)
C120.0191 (3)0.0344 (4)0.0229 (3)0.0105 (3)0.0035 (3)0.0029 (3)
C130.0168 (3)0.0141 (3)0.0120 (2)0.0029 (2)0.00133 (19)0.00108 (19)
C140.0212 (3)0.0152 (3)0.0158 (3)0.0046 (2)0.0008 (2)0.0018 (2)
C150.0206 (3)0.0199 (3)0.0181 (3)0.0071 (2)0.0024 (2)0.0002 (2)
C160.0169 (3)0.0139 (3)0.0148 (3)0.0006 (2)0.0008 (2)0.0035 (2)
C170.0176 (3)0.0124 (3)0.0119 (2)0.0016 (2)0.00258 (19)0.00245 (19)
C180.0195 (3)0.0134 (3)0.0124 (2)0.0028 (2)0.0016 (2)0.0023 (2)
C190.0163 (3)0.0156 (3)0.0117 (2)0.0032 (2)0.0025 (2)0.0011 (2)
C200.0179 (3)0.0139 (3)0.0115 (2)0.0014 (2)0.0033 (2)0.00188 (19)
C210.0257 (3)0.0198 (3)0.0208 (3)0.0062 (3)0.0110 (3)0.0001 (2)
Geometric parameters (Å, º) top
O1—C101.3785 (8)C7—C81.3961 (9)
O1—C111.4396 (10)C8—C91.3949 (10)
O2—C91.3632 (9)C8—H80.9500
O2—C121.4229 (10)C9—C101.3974 (9)
O3—C181.2232 (9)C10—C201.3973 (10)
O4—C181.3206 (9)C11—H11A0.9800
O4—H40.8400C11—H11B0.9800
O5—C201.3591 (8)C11—H11C0.9800
O5—C211.4269 (10)C12—H12A0.9800
N1—C51.3779 (9)C12—H12B0.9800
N1—C131.3834 (9)C12—H12C0.9800
N1—H10.8800C13—C141.3980 (10)
C1—C21.3879 (11)C14—C151.3857 (11)
C1—C151.4078 (11)C14—H140.9500
C1—H1A0.9500C15—H150.9500
C2—C31.4009 (10)C16—C171.5719 (10)
C2—H20.9500C16—H16A0.9900
C3—C131.4271 (10)C16—H16B0.9900
C3—C41.4347 (9)C17—C181.5078 (9)
C4—C51.3601 (9)C17—H171.0000
C4—C161.4975 (10)C19—C201.3961 (9)
C5—C61.4921 (9)C19—H190.9500
C6—C71.5164 (9)C21—H21A0.9800
C6—C171.5686 (10)C21—H21B0.9800
C6—H61.0000C21—H21C0.9800
C7—C191.3942 (9)
C10—O1—C11112.48 (6)H11A—C11—H11C109.5
C9—O2—C12116.77 (6)H11B—C11—H11C109.5
C18—O4—H4109.5O2—C12—H12A109.5
C20—O5—C21117.21 (6)O2—C12—H12B109.5
C5—N1—C13107.21 (6)H12A—C12—H12B109.5
C5—N1—H1126.4O2—C12—H12C109.5
C13—N1—H1126.4H12A—C12—H12C109.5
C2—C1—C15121.12 (7)H12B—C12—H12C109.5
C2—C1—H1A119.4N1—C13—C14129.41 (7)
C15—C1—H1A119.4N1—C13—C3108.66 (6)
C1—C2—C3119.10 (7)C14—C13—C3121.91 (6)
C1—C2—H2120.5C15—C14—C13117.73 (7)
C3—C2—H2120.5C15—C14—H14121.1
C2—C3—C13118.90 (6)C13—C14—H14121.1
C2—C3—C4135.29 (7)C14—C15—C1121.22 (7)
C13—C3—C4105.75 (6)C14—C15—H15119.4
C5—C4—C3107.07 (6)C1—C15—H15119.4
C5—C4—C16112.09 (6)C4—C16—C17101.36 (5)
C3—C4—C16140.65 (6)C4—C16—H16A111.5
C4—C5—N1111.28 (6)C17—C16—H16A111.5
C4—C5—C6115.13 (6)C4—C16—H16B111.5
N1—C5—C6133.48 (6)C17—C16—H16B111.5
C5—C6—C7116.44 (5)H16A—C16—H16B109.3
C5—C6—C17100.20 (5)C18—C17—C6113.56 (6)
C7—C6—C17111.15 (5)C18—C17—C16113.05 (5)
C5—C6—H6109.5C6—C17—C16109.05 (5)
C7—C6—H6109.5C18—C17—H17106.9
C17—C6—H6109.5C6—C17—H17106.9
C19—C7—C8120.56 (6)C16—C17—H17106.9
C19—C7—C6120.63 (6)O3—C18—O4123.34 (6)
C8—C7—C6118.70 (6)O3—C18—C17124.14 (6)
C9—C8—C7119.72 (6)O4—C18—C17112.51 (6)
C9—C8—H8120.1C7—C19—C20119.54 (6)
C7—C8—H8120.1C7—C19—H19120.2
O2—C9—C8124.76 (6)C20—C19—H19120.2
O2—C9—C10115.23 (6)O5—C20—C19125.19 (6)
C8—C9—C10120.01 (6)O5—C20—C10114.64 (6)
O1—C10—C20119.89 (6)C19—C20—C10120.17 (6)
O1—C10—C9120.14 (6)O5—C21—H21A109.5
C20—C10—C9119.94 (6)O5—C21—H21B109.5
O1—C11—H11A109.5H21A—C21—H21B109.5
O1—C11—H11B109.5O5—C21—H21C109.5
H11A—C11—H11B109.5H21A—C21—H21C109.5
O1—C11—H11C109.5H21B—C21—H21C109.5
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O4—H4···O3i0.841.842.6748 (8)176
N1—H1···O1ii0.882.202.9041 (8)136
C12—H12B···O2iii0.982.623.3905 (11)137
Symmetry codes: (i) x+1, y, z; (ii) x+1, y+1, z+1; (iii) x+2, y, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O4—H4···O3i0.841.842.6748 (8)176
N1—H1···O1ii0.882.202.9041 (8)136
C12—H12B···O2iii0.982.623.3905 (11)137
Symmetry codes: (i) x+1, y, z; (ii) x+1, y+1, z+1; (iii) x+2, y, z+1.
 

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