supplementary materials


HTML versionpdf versioncif file3d viewstructure factorssupplementary materialsCIF check reportcited insimilar papers Open access

Acta Cryst. (2009). E65, o595-o596    [ doi:10.1107/S1600536809006035 ]

3,3-Ethylenedithio-3,3a,4,5,10,10b-hexahydro-2H-furo[2,3-a]carbazole

N. Uludag, A. Öztürk, T. Hökelek and Ü.I. Erdogan

Abstract top

The title compound, C16H17NOS2, consists of a carbazole skeleton with tetrahydrofuran and dithiolane rings. In the indole ring system, the benzene and pyrrole rings are nearly coplanar, forming a dihedral angle of 1.57 (15)°. The cyclohexenone and tetrahydrofuran rings have envelope conformations, while the dithiolane ring adopts a twist conformation. In the crystal structure, pairs of weak intermolecular N-H...S hydrogen bonds link the molecules into centrosymmetric dimers with R22(16) ring motifs. Weak C-H...[pi] interactions may further stabilize the structure.

Comment top

Tetrahydrocarbazole systems are present in the framework of a number of indole-type alkaloids of biological interest (Phillipson & Zenk, 1980; Saxton, 1983; Abraham, 1975). The structures of tricyclic, tetracyclic and pentacyclic ring systems with dithiolane and other substituents of the tetrahydrocarbazole core, have been the subject of much interest in our laboratory. These include 1,2,3,4-tetrahydrocarbazole-1-spiro-2'-[1,3]dithiolane, (II) (Hökelek et al., 1994), N-(2-methoxyethyl)-N-{2,3,4,9-tetrahydrospiro[1H-carbazole-1, 2-(1,3)dithiolane]-4-yl}benzene-sulfonamide, (III) (Patır et al., 1997), spiro[carbazole-1(2H),2'-[1,3]-dithiolan]-4(3H)-one, (IV) (Hökelek et al., 1998), 9-acetonyl-3-ethylidene-1,2,3,4-tetrahydrospiro[carbazole-1,2'-[1,3] dithiolan]-4-one, (V) (Hökelek et al., 1999), N-(2,2-dimethoxyethyl)-N -{9-methoxymethyl-1,2,3,4-tetrahydrospiro[carbazole-1,2'-[1,3]dithiolan] -4-yl}benzamide, (VI) (Hökelek & Patır, 1999), 3a,4,10,10b-tetrahydro-2H -furo[2,3-a]carbazol-5(3H)-one, (VII) (Çaylak et al., 2007); also the pentacyclic compounds 6-ethyl-4-(2-methoxyethyl)-2,6-methano-5-oxo-hexahydro- pyrrolo(2,3 - d)carbazole-1-spiro-2'-(1,3)dithiolane, (VIII) (Hökelek & Patır, 2002), N-(2-benzyloxyethyl)-4,7-dimethyl-6-(1,3-dithiolan-2-yl)-1,2, 3,4,5,6-hexahydro-1,5-methano-2-azocino[4,3-b]indol-2-one, (IX) (Hökelek et al., 2004) and 4-ethyl-6,6-ethylenedithio-2-(2-methoxyethyl)-7-methoxy- methylene-2,3,4,5,6,7-hexahydro-1,5-methano-1H-azocino[4,3-b]indol-3-one, (X) (Hökelek et al., 2006). The title compound, (I), may be considered as a synthetic precursor of tetracyclic indole alkaloids of biological interests. The present study was undertaken to ascertain its crystal structure.

In the molecule of the title compound (Fig. 1), the bond lengths (Allen et al., 1987) and angles are within normal ranges. It consists of a carbazole skeleton with tetrahydrofuran and dithiolane rings. The bonds N10—C9a [1.378 (5) Å] and N10—C10a [1.371 (5) Å] generally agree with those in compounds (II)-(X). In all structures atom N10 is substituted.

An examination of the deviations from the least-squares planes through individual rings shows that rings A (C5b/C6—C9/C9a) and B (C5a/C5b/C9a/N10/C10a) are planar. They are also nearly coplanar with a dihedral angle of A/B = 1.57 (15)°. Rings C (C3a/C4/C5/C5a/C10a/C10b), D (O1/C2/C3/C3a/C10b) and E (S1/S2/C3/C11/C12) are not planar. Rings C and D have envelope conformations with atoms C4 and C3 displaced by -0.677 (4) Å (for ring C) and 0.568 (4) Å (for ring D) from the planes of the other ring atoms, respectively. Ring E adopts twisted conformation. Rings C and D have pseudo mirror planes running through atoms C10a and C4 (for ring C) and running through atom C3 and midpoint of O1—C10b bond (for ring D), as can be deduced from the torsion angles (Table 1).

In the crystal structure, intermolecular N—H···S hydrogen bonds (Table 2) link the molecules into centrosymmetric dimers (Fig. 2) by forming the R22(16) ring motifs (Bernstein et al., 1995), in which they may be effective in the stabilization of the structure. The weak C—H···π interactions (Table 1) may further stabilize the structure.

Related literature top

For general background, see: Phillipson & Zenk (1980); Saxton (1983); Abraham (1975). For related structures, see: Hökelek et al. (1994, 1998, 1999, 2004, 2006); Patır et al. (1997); Hökelek & Patır (1999,2002); Çaylak et al. (2007). For bond-length data, see: Allen et al. (1987). For hydrogen-bond motifs, see: Bernstein et al. (1995). Cg1 and Cg2 are centroids of the C5b/C6–C9/C9a and C5a/C5b/C9a/N10/C10a rings, respectively.

Experimental top

For the preparation of the title compound, (I), sodium borohydride (5.00 g, 132.00 mmol) was added to a solution of ethyl 2-(1-oxo-2,3,4,9-tetrahydro-1H -carbazol-2yl)-1,3-dithiolane-2-carboxylate (5.00 g, 13.83 mmol) in THF (50 ml), and stirred at room temperature for 3 h. Then, the reaction mixture was poured into HCl (15%, 100 ml). The crude product was filtered and recrystallized from acetone (yield; 3.2 g, 77%, m.p. 468 K).

Refinement top

H10 atom (for NH) was located in difference synthesis and refined isotropically [N—H = 0.81 (3) Å and Uiso(H) = 0.043 (15) Å2]. The remaining H atoms were positioned geometrically, with C—H = 0.93, 0.98 and 0.97 Å for aromatic, methine and methylene H, respectively, and constrained to ride on their parent atoms, with Uiso(H) = 1.2Ueq(C).

Computing details top

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994); cell refinement: CAD-4 EXPRESS (Enraf–Nonius, 1994); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999) and PLATON (Spek, 2009).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title molecule with the atom-numbering scheme. The displacement ellipsoids are drawn at the 50% probability level.
[Figure 2] Fig. 2. A packing diagram for (I). Hydrogen bonds are shown as dashed lines. H atoms not involved in hydrogen bonding have been omitted for clarity.
3,3-Ethylenedithio-3,3a,4,5,10,10b-hexahydro-2H- furo[2,3-a]carbazole top
Crystal data top
C16H17NOS2F(000) = 1280
Mr = 303.43Dx = 1.433 Mg m−3
Orthorhombic, PbcnMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2n 2abCell parameters from 25 reflections
a = 21.7617 (5) Åθ = 9.3–16.7°
b = 8.4992 (2) ŵ = 0.37 mm−1
c = 15.2115 (3) ÅT = 294 K
V = 2813.47 (11) Å3Prism, colorless
Z = 80.35 × 0.20 × 0.15 mm
Data collection top
Enraf–Nonius TurboCAD-4
diffractometer		1105 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.149
graphiteθmax = 24.3°, θmin = 2.6°
Non–profiled ω scansh = −25→25
Absorption correction: ψ scan
(North et al., 1968)		k = −9→9
Tmin = 0.913, Tmax = 0.944l = −17→0
8196 measured reflections3 standard reflections every 120 min
2289 independent reflections 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) = 0.108H atoms treated by a mixture of independent and constrained refinement
S = 0.98 w = 1/[σ2(Fo2) + (0.0328P)2 + 1.8766P]
where P = (Fo2 + 2Fc2)/3
2289 reflections(Δ/σ)max < 0.001
185 parametersΔρmax = 0.24 e Å−3
0 restraintsΔρmin = −0.23 e Å−3
Crystal data top
C16H17NOS2V = 2813.47 (11) Å3
Mr = 303.43Z = 8
Orthorhombic, PbcnMo Kα radiation
a = 21.7617 (5) ŵ = 0.37 mm−1
b = 8.4992 (2) ÅT = 294 K
c = 15.2115 (3) Å0.35 × 0.20 × 0.15 mm
Data collection top
Enraf–Nonius TurboCAD-4
diffractometer		1105 reflections with I > 2σ(I)
Absorption correction: ψ scan
(North et al., 1968)		Rint = 0.149
Tmin = 0.913, Tmax = 0.944θmax = 24.3°
8196 measured reflections3 standard reflections every 120 min
2289 independent reflections intensity decay: 1%
Refinement top
R[F2 > 2σ(F2)] = 0.041H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.108Δρmax = 0.24 e Å−3
S = 0.98Δρmin = −0.23 e Å−3
2289 reflectionsAbsolute structure: ?
185 parametersFlack parameter: ?
0 restraintsRogers parameter: ?
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*/Ueq
S10.32178 (5)0.10773 (14)0.23756 (8)0.0538 (4)
S20.33505 (5)−0.00621 (14)0.05706 (9)0.0538 (3)
O10.48005 (12)0.0372 (3)0.1141 (2)0.0597 (9)
C20.43301 (17)−0.0004 (5)0.1754 (3)0.0499 (12)
H2A0.44500.03100.23430.060*
H2B0.4250−0.11260.17530.060*
C30.37602 (18)0.0902 (5)0.1461 (3)0.0394 (11)
C3A0.40456 (17)0.2447 (4)0.1109 (3)0.0391 (11)
H3A0.37860.28650.06370.047*
C40.41256 (17)0.3698 (4)0.1817 (3)0.0402 (11)
H4A0.37240.40580.20080.048*
H4B0.43320.32380.23200.048*
C50.44962 (17)0.5095 (5)0.1485 (3)0.0423 (11)
H5A0.42720.56320.10230.051*
H5B0.45660.58340.19610.051*
C5A0.50957 (18)0.4512 (4)0.1140 (3)0.0375 (10)
C5B0.56863 (19)0.5223 (5)0.1102 (3)0.0402 (11)
C60.5923 (2)0.6705 (5)0.1333 (3)0.0487 (12)
H60.56640.74830.15520.058*
C70.6542 (2)0.6994 (6)0.1233 (3)0.0582 (14)
H70.67000.79730.13840.070*
C80.6930 (2)0.5844 (7)0.0909 (3)0.0608 (14)
H80.73470.60700.08500.073*
C90.6721 (2)0.4373 (5)0.0671 (3)0.0562 (13)
H90.69850.36070.04540.067*
C9A0.60977 (19)0.4090 (5)0.0771 (3)0.0426 (11)
C10A0.51613 (17)0.3010 (5)0.0837 (3)0.0365 (11)
C10B0.46569 (17)0.1854 (4)0.0715 (3)0.0401 (11)
H10B0.46000.16670.00850.048*
N100.57621 (16)0.2746 (5)0.0610 (3)0.0469 (10)
H100.5901 (17)0.196 (4)0.038 (3)0.043 (15)*
C110.2649 (2)−0.0299 (5)0.1985 (3)0.0658 (14)
H11A0.2507−0.09470.24690.079*
H11B0.22990.02690.17500.079*
C120.2921 (2)−0.1318 (5)0.1286 (3)0.0646 (14)
H12A0.2599−0.18510.09610.078*
H12B0.3188−0.21060.15450.078*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
S10.0516 (7)0.0527 (7)0.0570 (8)−0.0052 (6)0.0097 (7)−0.0042 (7)
S20.0541 (7)0.0516 (7)0.0558 (7)−0.0125 (7)−0.0012 (6)−0.0103 (7)
O10.0462 (19)0.040 (2)0.093 (3)0.0094 (14)0.0183 (18)0.0122 (18)
C20.042 (2)0.042 (2)0.065 (3)0.001 (2)0.001 (2)0.008 (3)
C30.039 (3)0.036 (2)0.042 (3)−0.003 (2)−0.001 (2)−0.001 (2)
C3A0.038 (2)0.035 (2)0.045 (3)0.0018 (19)−0.002 (2)0.000 (2)
C40.034 (2)0.041 (3)0.047 (3)0.000 (2)0.004 (2)−0.007 (2)
C50.048 (3)0.036 (2)0.043 (3)0.001 (2)−0.001 (2)−0.004 (2)
C5A0.040 (3)0.040 (3)0.033 (3)0.000 (2)0.002 (2)−0.001 (2)
C5B0.050 (3)0.042 (3)0.029 (2)−0.003 (2)−0.001 (2)0.001 (2)
C60.059 (3)0.049 (3)0.038 (3)−0.005 (2)0.002 (2)0.002 (2)
C70.067 (3)0.061 (3)0.046 (3)−0.025 (3)−0.002 (3)0.006 (3)
C80.047 (3)0.082 (4)0.054 (3)−0.017 (3)0.000 (2)0.009 (3)
C90.049 (3)0.059 (3)0.061 (3)−0.003 (3)0.007 (3)0.005 (3)
C9A0.044 (3)0.046 (3)0.038 (3)−0.007 (2)−0.001 (2)0.003 (2)
C10A0.034 (3)0.040 (3)0.036 (3)0.002 (2)−0.002 (2)0.002 (2)
C10B0.042 (3)0.034 (2)0.045 (3)−0.004 (2)0.004 (2)0.000 (2)
N100.042 (2)0.040 (2)0.059 (3)0.004 (2)0.011 (2)−0.006 (2)
C110.051 (3)0.066 (4)0.080 (4)−0.017 (3)0.005 (3)0.002 (3)
C120.070 (3)0.048 (3)0.076 (4)−0.020 (3)0.004 (3)−0.007 (3)
Geometric parameters (Å, °) top
S1—C31.830 (4)C5B—C61.405 (5)
S1—C111.803 (4)C6—H60.9300
S2—C31.817 (4)C7—C61.377 (5)
S2—C121.788 (4)C7—C81.383 (6)
O1—C21.421 (5)C7—H70.9300
O1—C10B1.450 (4)C8—H80.9300
C2—H2A0.9700C9—C81.379 (6)
C2—H2B0.9700C9—H90.9300
C3—C21.526 (5)C9A—C91.385 (5)
C3A—C31.548 (5)C9A—C5B1.408 (5)
C3A—C41.523 (5)C10A—C10B1.485 (5)
C3A—C10B1.544 (5)C10B—H10B0.9800
C3A—H3A0.9800N10—C10A1.371 (5)
C4—C51.522 (5)N10—C9A1.378 (5)
C4—H4A0.9700N10—H100.81 (3)
C4—H4B0.9700C11—H11A0.9700
C5—H5A0.9700C11—H11B0.9700
C5—H5B0.9700C12—C111.495 (6)
C5A—C51.491 (5)C12—H12A0.9700
C5A—C10A1.365 (5)C12—H12B0.9700
C5B—C5A1.421 (5)
C11—S1—C398.0 (2)C5B—C6—H6120.3
C12—S2—C394.1 (2)C7—C6—C5B119.3 (4)
C2—O1—C10B109.5 (3)C7—C6—H6120.3
O1—C2—C3106.3 (3)C6—C7—C8120.8 (4)
O1—C2—H2A110.5C6—C7—H7119.6
O1—C2—H2B110.5C8—C7—H7119.6
C3—C2—H2A110.5C9—C8—C7122.1 (4)
C3—C2—H2B110.5C9—C8—H8119.0
H2A—C2—H2B108.7C7—C8—H8119.0
S2—C3—S1106.7 (2)C8—C9—C9A116.9 (4)
C2—C3—S1110.1 (3)C8—C9—H9121.5
C2—C3—S2112.9 (3)C9A—C9—H9121.5
C2—C3—C3A101.7 (3)C9—C9A—C5B122.9 (4)
C3A—C3—S1116.9 (3)N10—C9A—C9130.1 (4)
C3A—C3—S2108.7 (3)N10—C9A—C5B107.1 (4)
C3—C3A—H3A109.3O1—C10B—C3A107.2 (3)
C4—C3A—C3113.2 (3)O1—C10B—C10A111.1 (3)
C4—C3A—H3A109.3O1—C10B—H10B108.9
C4—C3A—C10B113.8 (3)N10—C10A—C10B124.4 (4)
C10B—C3A—C3101.7 (3)C3A—C10B—H10B108.9
C10B—C3A—H3A109.3C5A—C10A—N10109.8 (4)
C3A—C4—H4A109.3C5A—C10A—C10B125.7 (4)
C3A—C4—H4B109.3C10A—C10B—C3A111.9 (3)
C5—C4—C3A111.8 (3)C10A—C10B—H10B108.9
C5—C4—H4A109.3C9A—N10—H10124 (3)
C5—C4—H4B109.3C10A—N10—C9A109.0 (4)
H4A—C4—H4B107.9C10A—N10—H10127 (3)
C4—C5—H5A109.9S1—C11—H11A109.7
C4—C5—H5B109.9S1—C11—H11B109.7
C5A—C5—C4108.7 (3)C12—C11—S1109.8 (3)
C5A—C5—H5A109.9C12—C11—H11A109.7
C5A—C5—H5B109.9C12—C11—H11B109.7
H5A—C5—H5B108.3H11A—C11—H11B108.2
C5B—C5A—C5131.6 (4)S2—C12—H12A110.3
C10A—C5A—C5121.4 (4)S2—C12—H12B110.3
C10A—C5A—C5B106.8 (4)C11—C12—S2107.1 (3)
C6—C5B—C5A134.6 (4)C11—C12—H12A110.3
C6—C5B—C9A118.0 (4)C11—C12—H12B110.3
C9A—C5B—C5A107.4 (4)H12A—C12—H12B108.6
C11—S1—C3—S215.4 (3)C5A—C5B—C6—C7177.8 (4)
C11—S1—C3—C2−107.4 (3)C9A—C5B—C6—C7−0.2 (6)
C11—S1—C3—C3A137.2 (3)C5—C5A—C10A—N10−176.3 (4)
C3—S1—C11—C1217.0 (4)C5—C5A—C10A—C10B7.2 (6)
C12—S2—C3—S1−36.2 (2)C5B—C5A—C10A—N10−0.1 (5)
C12—S2—C3—C284.9 (3)C5B—C5A—C10A—C10B−176.6 (4)
C12—S2—C3—C3A−163.1 (3)C6—C5B—C5A—C5−2.7 (8)
C3—S2—C12—C1149.5 (4)C6—C5B—C5A—C10A−178.4 (5)
C10B—O1—C2—C322.4 (4)C9A—C5B—C5A—C5175.4 (4)
C2—O1—C10B—C3A0.5 (4)C9A—C5B—C5A—C10A−0.2 (4)
C2—O1—C10B—C10A123.0 (4)C8—C7—C6—C5B−0.1 (7)
C4—C3A—C3—S131.6 (4)C6—C7—C8—C90.2 (7)
C4—C3A—C3—S2152.4 (3)C9A—C9—C8—C70.0 (7)
C4—C3A—C3—C2−88.3 (4)N10—C9A—C5B—C5A0.5 (4)
C10B—C3A—C3—S1154.1 (3)N10—C9A—C5B—C6179.0 (4)
C10B—C3A—C3—S2−85.1 (3)C9—C9A—C5B—C5A−178.1 (4)
C10B—C3A—C3—C234.2 (4)C9—C9A—C5B—C60.4 (6)
C3—C3A—C4—C5171.0 (3)N10—C9A—C9—C8−178.5 (4)
C10B—C3A—C4—C555.6 (4)C5B—C9A—C9—C8−0.3 (6)
C4—C3A—C10B—O199.6 (4)N10—C10A—C10B—O155.3 (5)
C3—C3A—C10B—O1−22.4 (4)N10—C10A—C10B—C3A175.1 (4)
C4—C3A—C10B—C10A−22.4 (5)C5A—C10A—C10B—O1−128.7 (4)
C3—C3A—C10B—C10A−144.4 (3)C5A—C10A—C10B—C3A−9.0 (6)
S1—C3—C2—O1−160.3 (3)C9A—N10—C10A—C5A0.4 (5)
S2—C3—C2—O180.6 (4)C9A—N10—C10A—C10B176.9 (4)
C3A—C3—C2—O1−35.7 (4)C10A—N10—C9A—C5B−0.5 (5)
C3A—C4—C5—C5A−55.3 (4)C10A—N10—C9A—C9177.8 (4)
C5B—C5A—C5—C4−149.7 (4)S2—C12—C11—S1−44.2 (4)
C10A—C5A—C5—C425.4 (5)
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
N10—H10···S2i0.81 (4)2.71 (4)3.487 (4)161 (4)
C3A—H3A···Cg2ii0.982.853.725 (4)149
C4—H4B···Cg1iii0.972.793.556 (5)136
C5—H5A···Cg1ii0.972.963.714 (5)135
Symmetry codes: (i) −x+1, −y, −z; (ii) −x, −y+2, −z; (iii) −x, y, −z+1/2.
Table 1
Selected geometric parameters (°) top
C10B—O1—C2—C322.4 (4)C3A—C3—C2—O1−35.7 (4)
C2—O1—C10B—C3A0.5 (4)C3A—C4—C5—C5A−55.3 (4)
C10B—C3A—C3—C234.2 (4)C10A—C5A—C5—C425.4 (5)
C10B—C3A—C4—C555.6 (4)C5—C5A—C10A—C10B7.2 (6)
C3—C3A—C10B—O1−22.4 (4)C5A—C10A—C10B—C3A−9.0 (6)
C4—C3A—C10B—C10A−22.4 (5)
Table 2
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
N10—H10···S2i0.81 (4)2.71 (4)3.487 (4)161 (4)
C3A—H3A···Cg2ii0.982.853.725 (4)149
C4—H4B···Cg1iii0.972.793.556 (5)136
C5—H5A···Cg1ii0.972.963.714 (5)135
Symmetry codes: (i) −x+1, −y, −z; (ii) −x, −y+2, −z; (iii) −x, y, −z+1/2.
Acknowledgements top

The authors acknowledge the purchase of the CAD-4 diffractometer under grant DPT/TBAG1 of the Scientific and Technical Research Council of Turkey.

references
References top

Abraham, D. J. (1975). The Catharanthus Alkaloids, edited by W. I. Taylor & N. R. Fransworth, ch. 7 and 8. New York: Marcel Decker.

Allen, F. H., Kennard, O., Watson, D. G., Brammer, L., Orpen, A. G. & Taylor, R. (1987). J. Chem. Soc. Perkin Trans. 2, pp. S1–19.

Bernstein, J., Davies, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. Engl. 34, 1555–1573.

Çaylak, N., Hökelek, T., Uludağ, N. & Patır, S. (2007). Acta Cryst. E63, o3913–o3914.

Enraf–Nonius (1994). CAD-4 EXPRESS. Enraf–Nonius, Delft, The Netherlands.

Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565.

Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838.

Harms, K. & Wocadlo, S. (1995). XCAD4. University of Marburg, Germany.

Hökelek, T., Gündüz, H., Patir, S. & Uludaug, N. (1998). Acta Cryst. C54, 1297–1299.

Hökelek, T. & Patir, S. (1999). Acta Cryst. C55, 675–677.

Hökelek, T. & Patır, S. (2002). Acta Cryst. E58, o374–o376.

Hökelek, T., Patır, S., Gülce, A. & Okay, G. (1994). Acta Cryst. C50, 450–453.

Hökelek, T., Patir, S. & Uludağ, N. (1999). Acta Cryst. C55, 114–116.

Hökelek, T., Uludağ, N. & Patır, S. (2004). Acta Cryst. E60, o25–o27.

Hökelek, T., Uludağ, N. & Patır, S. (2006). Acta Cryst. E62, o791–o793.

North, A. C. T., Phillips, D. C. & Mathews, F. S. (1968). Acta Cryst. A24, 351–359.

Patır, S., Okay, G., Gülce, A., Salih, B. & Hökelek, T. (1997). J. Heterocycl. Chem. 34, 1239–1242.

Phillipson, J. D. & Zenk, M. H. (1980). Indole and Biogenetically Related Alkaloids, ch 3. New York: Academic Press.

Saxton, J. E. (1983). Editor. Heterocyclic Compounds, Vol. 25, The Monoterpenoid Indole Alkaloids, ch 8 and 11. New York: Wiley.

Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.

Spek, A. L. (2009). Acta Cryst. D65, 148–155.