A New Index for the Estimation of the Aromatic Character
Letters in Organic Chemistry, 2015, Vol. 12, No. 5 335
ꢃ=ꢁ=ꢁ= 90°, V = 1398.2 Å3, Z = 4, Dx = 1.237 Mgmꢄ3, ꢂ =
0.073 mmꢄ1, F(000) = 552. Collected reflections: 10165
within a theta range of 1.91-27.07°. Unique reflections:
1794. Observed reflections: 1794 with F>4ꢅ(F) the absorp-
tion correction was not applied. Refinement: (refinement on
F2), final R = 0.0494, wR2 = 0.1302, goodness-of-fit = 0.976,
1794 reflections, 190 parameters, maximum and minimum
difference electron densities were 0.183 eÅꢄ3 and -0.118
eÅꢄ3, respectively.
Typical Procedure for the Preparation of bis(indolyl)
methanes
A solution of indole (0.2 g, 3.4 mmol) and aldehyde
(0.07 g, 1.7 mmol) in ClCH2CH2Cl (0.5 mL) was treated
with Et3B (0.05 mL) and the resulting reaction mixture was
stirred at room temperature for 20 min. The solvent was re-
moved in vacuo and the resulting mixture was purified by
flash column chromatography eluting with hexane-ethyl ace-
tate 7:3 or 9:1. The spectral data of some of the
bis(indolyl)methanes are summarized below.
3,3'-Bis(indolyl)-2-(hydroxyphenyl)methane (Entry 3,
14): IR (ꢂ, cm-1 KBr): 3382, 3226, 2918, 2849, 1735, 1664,
1
Fig. (3). The crystal packing of the title compound, viewed along
the c axis. The dashed lines indicate the X-H…ꢃ interactions.
1619, 1459, 1376, 1268, 1195, 1108, 749. NMR H 400
MHz (CDCl3), ꢀ: 7.80 (1H, s, NH), 7.40 (1H, d, H-5, J =
7.7Hz), 7.31 (1H, d, H-8, J = 8.1Hz), 7.20 (3H, m, H-12, H-
13 y H-14), 7.04 (1H, td, H-6, J = 0.7, 7.3 Hz), 6.87 (2H, d,
H-2, H-7, H-15, J =2.2 Hz), 6.63 (1H, s, H-2), 5.9 (1H, s, H-
3´), 5.48 (1H, s broad, OH). NMR 13C 100 MHz (CDCl3), ꢀ:
154.5, (C-10), 136.9 (C-3), 130.1 (C-12), 129.2 (C-10),
128.1 (C-13), 126.8 (C-9), 123.8 (C-2), 122.4 (C-14), 120.9
(C-15), 120.0 (C-5), 119.9 (C-4), 119.6 (C-6), 117.1 (C-11),
116.6 (C-7), 111.4 (C-8), 35.9 (C-3´).
the natural bisindoles arsindoline B (2) and streptindole (6).
The structure of vibrindole A (5) was unequivocally estab-
lished by single-crystal X-ray diffraction. The reaction is
simple, non-toxic, easy to handle, and with shorter reaction
times. The triethylborane catalyzed C3-selective Friedel-
Crafts alkylation of indoles with aldehydes. Work along
these lines is underway.
3,3'-Bis(indolyl)-4-(bromophenyl)methane (Entry 6,
20): IR (ꢂ, cm-1 KBr): 3417, 2918, 2849, 1618, 1482, 1455,
EXPERIMENTAL
1
1414, 1199, 1033, 742, 541. NMR H 400 MHz (CDCl3), ꢀ:
IR spectra were acquired on a Perkin Elmer TF-IR Sys-
7.78 (1H, s, NH), 7.39 (2H, m, H-5 y H-11), 7.33 (1H, d, J =
8.8 Hz, H-8), 7.20 (1H, t, H-6, H-12, J = 8.2 Hz), 7.04 (1H,
d, H-7, J = 8.2 Hz), 6.56 (1H, s, H-2), 5.85 (1H, s, H-3´).
NMR 13C 100 MHz (CDCl3), ꢀ: 143.22 (C-10), 136.79 (C-
14), 131.41 (C-3), 130.59 (C-4), 126.98 (C-13), 123.70 (C-
6), 123.01 (C-9), 122.19 (C-2), 120.02 (C-7), 119.90 (C-5),
119.48 (C-12), 119.16 (C-11), 111.25 (C-8), 39.81 (C-10).
tem 2000 using KBr pellets (
ꢀ
, cm-1). NMR spectra (1H,
13C, HETCOR and COSY) were determined on JEOL
Eclipse +400 spectrometer, and chemical shifts are stated in
1
ppm (ꢀ) and are referred to the residual H signal (ꢀ = 7.27)
or to the central 13C triplet signal (ꢀ = 77.0) for CDCl3. The
products were separated by chromatography over silica gel
(70-230 mesh). Crystals of 5, suitable for X-ray analysis,
were obtained from hexane-ethyl acetate 7:3 by slow evapo-
ration of the solvent at room temperature. The X-ray meas-
urement was performed at 293 K on a Bruker SMART CCD
diffractometer with Mo Kꢀ-radiation, ꢁ = 0.71073 Å. The
structure was solved by direct methods (SHELXS-86) and
refined using SHELXL-97. All non-hydrogen atoms were
refined anisotropically, and the hydrogen atoms were in-
cluded at calculated positions with the use of a riding model.
CCDC 1050231 contained crystallographic data for this pub-
lication. These data can be obtained free of charge from The
CONFLICT OF INTEREST
The authors confirm that this article content has no con-
flict of interest.
ACKNOWLEDGEMENTS
Financial support from CONACYT (project No. 183980)
and CIC-UMSNH is gratefully acknowledged. The authors
thank Ms. Carolina López Ortíz for revision of the manu-
script. One of the authors, J.P.G.M. is thankful to CONA-
CYT for a scholarship (grant: 186053).
Cambridge
Crystallographic
Data
Centre
via
Crystal Data for Compound 5
REFERENCES
Crystal data for compound 5: C18H16N2, colorless prisms,
0.2 mm ꢂ 0.18 mm ꢂ 0.19 mm, formula weight M = 260.33,
triclinic, P1, a = 6.562 Å, b = 9.977 Å, c = 21.357 Å,
[1]
Bartoli, G.; Dalpozzo, R.; Nardi, M. Applications of Bartoli indole
synthesis. Chem. Soc. Rev. 2014, 43, 4728-4750.