A practical synthesis of bis(indolyl)methanes catalyzed by BF 3·Et2O

Article abstract of DOI:10.1016/j.cclet.2013.11.038

Practical BF₃·Et₂O catalyzed reactions between indoles and a series of carbonyl compounds at room temperature are described, which afford bis(indolyl)methanes with isolated yields up to 96%.

Full text of DOI:10.1016/j.cclet.2013.11.038

Chinese Chemical Letters 25 (2014) 406–410
Contents lists available at ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Original article
A practical synthesis of bis(indolyl)methanes catalyzed by BF3ꢀEt2O
a
a
a
a
Xia-Fei Xu a, Yan Xiong a,b, , Xue-Ge Ling , Xi-Mi Xie , Jie Yuan , Shu-Ting Zhang ,
Zhong-Rong Song
*
c,**
a School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400030, China
b State Key Laboratory of Elemento-organic Chemistry, Nankai University, Tianjin 300071, China
c School of Materials and Chemical Engineering, Chongqing University of Arts and Science, Chongqing 402160, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Practical BF3ꢀEt2O catalyzed reactions between indoles and a series of carbonyl compounds at room
temperature are described, which afford bis(indolyl)methanes with isolated yields up to 96%.
ß 2013 Yan Xiong and Zhong-Rong Song. Published by Elsevier B.V. on behalf of Chinese Chemical
Society. All rights reserved.
Received 19 August 2013
Received in revised form 8 November 2013
Accepted 11 November 2013
Available online 28 November 2013
Keywords:
Bis(indolyl)methanes
BF3ꢀEt2O
Indoles
Aldehydes
Ketones
1. Introduction
[15], Al2O3 [16], zirconyldodecylsulfate [17], I2 [18], silica gel [19],
pyridinium tribromide [20] and SiO2/AlCl3 [21]. Protic acids, such
Boron trifluoride, as a typical electron deficient Lewis acid,
exhibits markedly strong interactions with numerous electron
donors [1]. In most cases, it can form complexes with nitrogen and
oxygen moieties with strong Lewis basicities such as R2COꢀ ꢀ ꢀBF3
and R3Nꢀ ꢀ ꢀBF3, in Fig. 1. Among these strong electron donor/
acceptor complexes, their interaction energies have been investi-
gated quantitatively [2] along with the BF3 affinity scale [3] and
they play an essential role in many catalytic applications in organic
chemistry, such as alkylation [4], acylation [5] and cyclization [6].
Compounds with an indole ring possess plentiful bioactivities
and pharmacological activities [7], such as cytotoxic [8], and
antifungal properties [9], in inhibiting the growth of tumor cells
[10]. B is(indolyl)methanes containing important indole ring units
are useful intermediates and can be utilized in interesting
transformations of indole chemistry [11]. Great efforts have been
made to seek efficient and convenient synthetic routes of
bis(indolyl)methanes and therefore over the past few years,
bis(indolyl)methanes have been synthesized by electrophilic
substitution of indoles with carbonyl compounds catalyzed by
Lewis acids, such as Ln(OTf)3 [12], GaCl3 [13], ZnO [14], FeCl3ꢀ6H2O
as montmorillonite clay [22,23], oxone [24], NH4Cl [25], cellulose
sulfuric acid [26], ion liquid [27] and oxalic acid [28] were also
utilized to promote these transformations. Moreover, Schiff base–
Cu(II) complex [29] and surfactant SLES [30] were proved to be
effective for the synthesis of bis(indolyl)methanes. Based on the
understanding of strong electron donor/acceptor interaction
patterns between carbonyl/amine and BF3 [31], it is highly
anticipated that this transformation would be accelerated in the
presence of a catalytic amount of BF3ꢀEt2O. In previous work, we
have reported on Cs2CO3-catalyzed transesterification, primary
amine-catalyzed aldol condensation, theoretical halo-exchange
reactions, iodination of sp3 C–H with hypervalent iodide, and Lewis
acid-promoted oxidative coupling of anilines [32]. Herein we
describe an efficient and practical method for the synthesis of
bis(indolyl)methanes between indoles and a series of carbonyl
compounds at room temperature catalyzed by BF3ꢀEt2O, which is
attractive due to low cost, high catalytic efficiency and metal-free
profile.
2. Experimental
BF3ꢀEt2O (21.3 mg, 0.15 mmol) was added to a mixture of indole
1 (234.4 mg, 2 mmol) and benzaldehyde 2a (106.1 mg, 1 mmol) in
diethyl ether (2 mL). The reaction mixture was stirred at room
temperature for 2 h in the atmosphere and monitored by TLC. After
completion of the reaction, the volatile components were removed
*
Corresponding author at: School of Chemistry and Chemical Engineering,
Chongqing University, Chongqing 400030, China.
**
Corresponding author.
E-mail addresses: xiong@cqu.edu.cn (Y. Xiong), hxxsong@163.com (Z.-R. Song).
1001-8417/$ – see front matter ß 2013 Yan Xiong and Zhong-Rong Song. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2013.11.038

X.-F. Xu et al. / Chinese Chemical Letters 25 (2014) 406–410
407
determinedby1H NMRspectroscopy usingmesityleneasaninternal
standard. When the amount of BF3ꢀEt2O was increased to 0.15 equiv,
increasing yields of 3a were obtained with 0.15 equiv of BF3ꢀEt2O
resulting in a 99% yield (entries 1–5). Nevertheless, further increases
in the amount of BF3ꢀEt2O resulted in dramatically decreasing yields
(entries 6–9). Performances in different solvents were scanned
(entries 10–17), eventually confirming that diethyl ether afforded a
comparative yield (entry 17). Higher temperatures were tolerated
for this reaction (entries 17–19). In an effort to get a milder reaction
condition, studies with prolonged reaction times at room tempera-
ture were tried and, to our delight, an excellent yield was provided
after 2 h in diethyl ether (entry 21), while dichloromethane only led
to lower yield of 82% (entry 22). Therefore, the following optimal
reaction conditions were established: aldehyde 2a (1 mmol), indole
1 (2 equiv), and BF3ꢀEt2O (0.15 equiv) in Et2O (2 mL) at room
temperature for 2 h.
Fig. 1. Structures of R2COꢀ ꢀ ꢀBF3 and R3Nꢀ ꢀ ꢀBF3 complexes.
using a vacuum rotary evaporator. The resulting residue was
purified by column chromatography on silica gel column using
EtOAc/petroleum ether solution (1:15–1:8, v/v) as eluent to afford
the desired product bis(indolyl)phenylmethane 3a. Yield: 290 mg
(90%); pink solid. 1H NMR (500 MHz, CDCl3):
d 7.91 (s, 2H), 7.39 (d,
2H, J = 8.0 Hz), 7.36 (d, 2H, J = 8.0 Hz), 7.35 (d, 2H, J = 7.0 Hz), 7.28
(t, 2H, J = 7.0 Hz), 7.22–7.19 (m, 1H), 7.17 (t, 2H, J = 7.0 Hz), 7.00 (t,
2H, J = 7.5 Hz), 6.66 (d, 2H, J = 1.5 Hz), 5.89 (s, 1H). 13C NMR
(125 MHz, CDCl3):
122.1, 120.1, 119.9, 119.4, 111.2, 40.4.
For detailed experimental procedure, crystallographic data,
characterization data of the products, and copies of 1H NMR and
13C NMR, see Supporting information.
d
144.2, 136.9, 128.9, 128.4, 127.2, 126.3, 123.8,
With the optimal conditions in hand, we set about expanding the
scope of aldehydes (Table 2). Aromatic, heteroaromatic, fused,
aliphatic and enal aldehydes are suitable substrates to synthesize
bis(indolyl)methanes with moderate to excellent yields. Aromatic
aldehydes with neutral, electron-donating and electron-withdraw-
ing groups on the phenyl ring were tolerated. Methyl (2b), nitro (2e),
p-chloro (2g), o-chloro (2h) and 2,4-dichloro (2i) substituents
produced the corresponding products in excellent yields of above
89%. Benzaldehydes with oxygen-bearing functional groups, such as
methoxyl (2c) and hydroxy (2d), gave somewhat lower yields,
presumably due to the complexation of oxygen with BF3ꢀEt2O.
Cyanobenzaldehyde 2f with a versatile cyano group in known
organic transformation produced 3f in 63% yield. Reaction of
naphthaldehyde 2j gave 3j which also occurred in good yield of 87%
(entry10) withthe structureof 3j further confirmed by single crystal
X-ray crystallography (Fig. 2) [33]. Heteroaromatic aldehydes, such
as thiophenecarboxaldehyde 2k and furfural 2l provided moderate
yields (entries 11 and 12). Cinnamyl aldehyde 2m was also tested,
and only a low yield was obtained (entries 13). Aliphatic aldehydes,
such as phenylacetaldehyde 2n, formaldehyde 2o and isovaler-
aldehyde 2p afforded the corresponding products 3n, 3o and 3p in
36%, 40% and 72% yields, respectively (entries 14–16). The reactions
of 7-methyl-1H-indole and 5-bromo-1H-indole were also examined
and the corresponding products 3q and 3r were obtained in good
yields of 88% and 92%, respectively.
3. Results and discussion
Initially, we aimed at determining the optimal reaction condi-
tions for the synthesis of bis(indolyl)methanes (Table 1). The
treatment of indole 1 with benzaldehyde 2a was used as a model
reaction to screen various amount of catalysts, diverse solvents, and
different reaction times and temperatures. The yields of 3a were
Table 1
Optimization of reaction conditions.
CHO
H
H
N
.
BF3 Et2O
2
+
solvent, T, t
HN
NH
1
2a
3a
Entrya
BF3.Et2O (equiv.)
Solvent
t (min)
T (8C)b
1H NMR
Furthermore, the less reactive ketonic substrates 4a–f were
chosen to evaluate this methodology with indoles (Table 3).
Aliphatic ketones such as acetone 4a and 2-pentanone 4b were
yield (%)c
1
0
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
DMF
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
60
120
120
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
60
100
r.t.
r.t.
r.t.
3
24c
71
2
0.03
0.05
0.10
0.15
0.20
0.30
0.80
1.20
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
3
4
89
5
99 (90)d
59d
59
6
7
8
26
9
3
10
11
12
13
14
15
16
17
18
19
20
21
22
74
CH3OH
CH3CN
Toluene
EtOAc
THF
75
79
85
96
97
t-BuOMe
Et2O
98
99
Et2O
93
Et2O
97
Et2O
90
Et2O
98 (90)d
82
CH2Cl2
a
Reaction conditions: benzaldehyde 2a (1 mmol), indole 1 (2 equiv), BF3ꢀEt2O
(specified amount) in solvent (2 mL).
b
The heating temperature of oil bath.
1H NMR yields, using mesitylene as an internal standard.
c
d
Isolated yield.
Fig. 2. X-ray single crystal structure of 3j.

408
X.-F. Xu et al. / Chinese Chemical Letters 25 (2014) 406–410
Table 2
Reactions of indole with aldehydes catalyzed by BF3ꢀEt2O.
Entrya
1
Aldehyde
Product
Yield (%)b
90
Entrya
10
Aldehyde
Product
Yield (%)b
87
2a
2j
3a
3j
2
89
11
69
2k
2b
3k
3b
3
66
12
50
2l
3l
2c
3c
4
58
13
12
2d
2m
3d
3m
5
6
7
93
63
91
14
15
16
36c
2n
2o
2e
2f
3n
3o
3e
3f
40
72d
2p
3p
2g
2h
3g
3h
8
9
94
96
17
18
88
92
2a
2a
3q
3r
2i
3i
a
Reaction conditions: aldehydes 2 (1.0 mmol), indole 1 (2.0 equiv.), and BF3ꢀEt2O (0.15 equiv.) in Et2O (2 mL) at room temperature for 2 h.
b
c
Isolated yields.
3 h.
d
100 min.

X.-F. Xu et al. / Chinese Chemical Letters 25 (2014) 406–410
409
Table 3
Reactions of indole with ketones catalyzed by BF3ꢀEt2O.a
R4
R3
H
O
.
N
BF3·Et2O
+
2
Et2O, r.t., 2 h
R3
R4
HN
NH
1
5
4
Entry
1
Ketone
Product
Time (h)
29
Yield (%)b
56
Entry
4
Ketone
Product
Time (h)
24
Yield (%)b
4a
4d
9
C
HN
NH
5a
C
HN
NH
5d
2
4b
4c
10
16
81
5
6
4e
Cl
40
40
35
C
C
HN
HN
NH
NH
5b
5c
HN
NH
5e
3
2
4f
11
C
C
HN
NH
5f
a
Reaction conditions: ketones 4 (1 mmol), indole 1 (2 equiv.), and BF3ꢀEt2O (0.15 equiv.) in Et2O (2 mL) at room temperature.
b
Isolated yields.
examined and gave moderate yields over 24 h. It is noteworthy
that cyclohexanone provided the target product 5c in 81% yield. In
the case of aromatic ketones 5d–f, yields of 9%, 35% and 11% were
obtained, respectively.
afford complex E. With
a
molecule BF3ꢀEt2O released, the
bis(indolyl)methane F is produced, and the catalyst BF3ꢀEt2O then
enters another catalytic cycle.
Based on the features of BF3ꢀEt2O, catalyzed reactions with
BF3ꢀEt2O were carried out under mild reaction conditions, and the
mechanismin Fig. 3 was proposed. The initial step of the mechanism
is the interaction between BF3ꢀEt2O and analog A to form the
complex B, as in the R2COꢀ ꢀ ꢀBF3 complex, and then a molecule of
indole attacks B to generate intermediate C, as in the R3Nꢀ ꢀ ꢀBF3
complex. Through the strong interaction between nitrogen and
BF3ꢀEt2O in C, an elimination of a molecule H2O is accelerated, and
intermediate C is transformed into D. Subsequently, another
molecule indole is reacted with D via an aza-Michael addition to
4. Conclusion
To sum up, a strategy for using BF3ꢀEt2O as an efficient catalyst
for electrophilic substitution reactions of indoles with carbonyl
compounds has been developed as anticipated, which gives
structurally diverse bis(indolyl)methanes with yields up to 96%.
The mild and metal-free reaction conditions render this method-
ology a practical protocol. A possible mechanism is proposed to
interpret the observed reactivities.
Acknowledgments
We are grateful for scientific research fundings from the
Scientific Research Foundation for the Returned Overseas Chinese
Scholars, State Education Ministry, Partenariats Hubert Curien Xu
Guangqi 2012 (No. 27967RE), Fundamental Research Funds for the
Central Universities (Nos. CDJRC10220004 and CDJZR11220005),
and Natural Science Foundation Project of CQ CSTC (Nos.
2010BB5064 and cstc2013jcyjA0217) for financial support.
Appendix A. Supplementary data
Supplementary material related to this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.cclet.2013.
11.038.
References
[1] K. Ishihara, Lewis Acids in Organic Synthesis, Wiley-VCH, Weinheim, 2008p. 96.
[2] H. Umeyama, K. Morokuma, Molecular orbital studies of electron donor–acceptor
complexes. 3. Energy and charge decomposition analyses for several strong
complexes: OC–BH3, H3N–BH3, CH3H2N–BH3, (CH3)3N–BH3, and H3N–BF3, J.
Am. Chem. Soc. 98 (1976) 7208–7220.
Fig. 3. A proposed mechanism for the synthesis of indoles with different carbonyl
compounds.

410
X.-F. Xu et al. / Chinese Chemical Letters 25 (2014) 406–410
[3] C. Laurence, J.F. Gal, Lewis Basicity and Affinity Scales: Data and Measurement,
[19] S.R. Mendes, S. Thurow, M.P. Fortes, et al., Synthesis of bis(indolyl)methanes using
silica gel as an efficient and recyclable surface, Tetrahedron Lett. 53 (2012) 5402–
5406.
[20] Q. Yang, Z.L. Yin, B.L. Ouyang, Y.Y. Peng, Pyridinium tribromide catalyzed con-
densation of indoles and aldehydes to form bisindolylalkanes, Chin. Chem. Lett.
22 (2011) 515–518.
[21] K.P. Boroujeni, K. Parvanak, Efficient and solvent-free synthesis of bis-indolyl-
methanes using silica gel supported aluminium chloride as a reusable catalyst,
Chin. Chem. Lett. 22 (2011) 939–942.
[22] M. Chakrabarty, N. Ghosh, R. Basaka, Y. Harigaya, Dry reaction of indoles with
carbonyl compounds on montmorillonite K10 clay: a mild, expedient synthesis of
diindolylalkanes and vibrindole A, Tetrahedron Lett. 43 (2002) 4075–4078.
[23] J.S. Yadav, B.V.S. Reddy, G. Satheesh, Montmorillonite clay catalyzed alkylation of
pyrroles and indoles with cyclic hemi-acetals, Tetrahedron Lett. 45 (2004) 3673–
3676.
John Wiley & Sons, Wiltshire, 2010p. 85.
[4] G.K.S. Prakash, F. Paknia, T. Mathew, et al., Fluoroanalogs of DDT: superacidic BF3–
H2O catalyzed facile synthesis of 1,1,1-trifluoro-2,2-diarylethanes and 1,1-
difluoro-2,2-diarylethanes, Org. Lett. 13 (2011) 4128–4131.
[5] J. Zakrzewski, M. Karpin´ ska, Z. Malin´ ski, A large scale synthesis of a natural
antibiotic 2,4-diacetylophloroglucinol (DAPG), Arch. Pharm. Chem. Life Sci. 340
(2007) 103–106.
[6] (a) N.C. Ma, K.M. Wu, L. Huang, An interesting cyclization of N-methyl-3-phenyl-
N-(2-(Z)-phenylethenyl)-cis-oxiranecarboxamide, J. Heterocycl. Chem. 45 (2008)
785–787;
(b) D.J. Xiao, L.J. Wang, X.M. Feng, A practical synthetic pathway to polysubsti-
tuted tetrahydropyridines via multicomponent reactions catalyzed by BF3ꢀOEt2,
Synlett 10 (2005) 1531–1540.
[7] B. Xu, Z.L. Guo, W.Y. Jin, et al., Multistep one-pot synthesis of enantioenriched
polysubstituted cyclopenta[b]indoles, Angew. Chem. Int. Ed. 51 (2012) 1059–
1062.
[24] C.L. Zhang, Z.Q. Du, Synthesis of bis-indolylmethanes catalyzed by oxone, Chin.
Chem. Lett. 20 (2009) 1411–1414.
[8] B.Q. Bao, Q.S. Sun, X.S. Yao, et al., Cytotoxic bisindole alkaloids from a marine
sponge Spongosorites sp., J. Nat. Prod. 68 (2005) 711–715.
[9] S. Sakemit, H.H. Sun, Nortopsentins A, B, and C. Cytotoxic and antifungal imida-
zolediylbis[indoles] from the sponge spongosorites ruetzleri, J. Org. Chem. 56
(1991) 4304–4307.
[10] (a) S. Tsujii, K.L. Rinehart, S.P. Gunasekera, et al., Topsentin, bromotopsentin, and
dihydrodeoxybromotopsentin: antiviral and antitumor bis(indoly1)imidazoles
from caribbean deep-sea sponges of the family halichondriidae. Structural and
synthetic studies, J. Org. Chem. 53 (1988) 5446–5453;
[25] J. Azizian, F. Teimouri, M.R. Mohamadizadeh, Ammonium chloride catalyzed one-
pot synthesis of diindolylmethanes under solvent-free conditions, Catal. Com-
mun. 8 (2007) 1117–1121.
[26] H. Alinezhad, A.H. Haghighi, F. Salehian, A green method for the synthesis of bis-
indolylmethanes and 3,30-indolyloxindole derivatives using cellulose sulfuric
acid under solvent-free conditions, Chin. Chem. Lett. 21 (2010) 183–186.
[27] P.J. Das, J. Das, Synthesis of aryl/alkyl(2,20-bis-3-methylindolyl)methanes and
aryl(3,30-bis indolyl)methanes promoted by secondary amine based ionic liquids
and microwave irradiation, Tetrahedron Lett. 53 (2012) 4718–4720.
[28] N.D. Kokare, J.N. Sangshetti, D.B. Shinde, Oxalic acid as a catalyst for efficient
synthesis of bis-(indolyl)methanes, and 14-aryl-14H-dibenzo[a,j]xanthenes in
water, Chin. Chem. Lett. 19 (2008) 1186–1189.
[29] Y.L. Yang, N.N. Wan, W.P. Wang, Z.F. Xie, J.D. Wang, Synthesis of bis(indolyl)
methanes catalyzed by Schiff base–Cu(II) complex, Chin. Chem. Lett. 22 (2011)
1071–1074.
[30] E. Kolvari, M.A. Zolfigol, H. Banary, Surfactant-assisted synthesis of bis(indolyl)-
methanes in water, Chin. Chem. Lett. 22 (2011) 1305–1308.
[31] A. Chatterjee, S. Manna, J. Bawrji, et al., Lewis-acid-induced electrophilic substi-
tution in indoles with acetone. Part 2, J. Chem. Soc., Perkin Trans. 1 (1980) 553–
555.
[32] (a) S.Y. Zheng, Y. Xiong, J.Y. Wang, Theoretical studies on identity SN2 reactions of
lithium halide and methyl halide: a microhydration model, J. Mol. Model. 16
(2010) 1931–1937;
(b) C.M. Cover, S.J. Hsieh, S.H. Tran, et al., Indole-3-carbinol inhibits the expres-
sion of cyclin-dependent kinase-6 and induces a G1 cell cycle arrest of human
breast cancer cells independent of estrogen receptor signaling, J. Biol. Chem. 273
(1998) 3838–3847;
(c) S. Safe, S. Papineni, S. Chintharlapalli, Cancer chemotherapy with indole-3-
carbinol, bis(30-indolyl)methane and synthetic analogs, Cancer Lett. 269 (2008)
326–338;
(d) T.P. Pathak, J.G. Osiak, R.M. Vaden, B.E. Welm, M.S. Sigman, Synthesis and
preliminary biological study of bisindolylmethanes accessed by an acid-catalyzed
hydroarylation of vinyl indoles, Tetrahedron 68 (2012) 5203–5215.
[11] M. Shiri, M.A. Zolfigol, H.G. Kruger, Z. Tanbakouchian, Bis- and trisindolyl-
methanes (BIMs and TIMs), Chem. Rev. 110 (2010) 2250–2293.
[12] D. Chen, L. Yu, P.G. Wang, Lewis acid-catalyzed reactions in protic media.
Lanthanide-catalyzed reactions of indoles with aldehydes or ketones, Tetrahe-
dron Lett. 37 (1996) 4467–4470.
[13] J.S. Yadav, B.V.S. Reddy, B. Padmavani, M.K. Gupta, Gallium(III) halide-catalyzed
coupling of indoles with phenylacetylene: synthesis of bis(indolyl)pheny-
lethanes, Tetrahedron Lett. 45 (2004) 7577–7579.
[14] M. Hosseini-Sarvari, Synthesis of bis(indolyl)methanes using a catalytic amount
of ZnO under solvent-free conditions, Synth. Commun. 38 (2008) 832–840.
[15] S.J. Ji, M.F. Zhou, D.G. Gu, Z.Q. Jiang, T.P. Loh, Efficient FeIII-catalyzed synthesis of
bis(indolyl)methanes in ionic liquids, Eur. J. Org. Chem. 2004 (2004) 1584–1587.
[16] S.A. Sadaphal, A.H. Kategaonkar, V.B. Labade, M.S. Shingare, Synthesis of bis(in-
dolyl) methanes using aluminium oxide (acidic) in dry media, Chin. Chem. Lett. 21
(2010) 39–42.
(b) Y. Xiong, X.Q. Zhang, Significant heterogeneous carbonate salt catalyzed
acetylation of alcohols via a transesterification process with carbonate salt-
activated alcohol 1H NMR evidence, Chin. J. Chem. 29 (2011) 1143–1148;
(c) Y. Xiong, S.T. Zhang, X.G. Ling, X. Zhang, J.Y. Wang, Theoretical investigation
on identical anionic halide-exchange SN2 reaction processes on N-haloammo-
nium cation NH3X+ (X = F, Cl, Br, and I), Int. J. Quantum Chem. 112 (2012) 2475–
2481;
(d) X. Zhang, Y. Xiong, S.T. Zhang, et al., Aldol condensations of aldehydes and
ketones catalyzed by primary amine on water, Asian J. Chem. 24 (2012) 751–755;
(e) X.G. Ling, Y. Xiong, S.T. Zhang, R.F. Huang, X.H. Zhang, Effective synthesis of
benzyl halides triggered by in situ prepared hypervalent halides, Chin. Chem. Lett.
24 (2013) 45–48;
[17] M. Jafarpour, A. Rezaeifard, T. Golshani, A new catalytic method for ecofriendly
synthesis of bis- and trisindolylmethanes by zirconyldodecylsulfate under mild
conditions, J. Heterocycl. Chem. 46 (2009) 535–539.
[18] (a) B.P. Bandgar, K.A. Shaikh, Molecular iodine-catalyzed efficient and highly
rapid synthesis of bis(indolyl)methanes under mild conditions, Tetrahedron Lett.
44 (2003) 1959–1961;
(f) X.G. Ling, Y. Xiong, R.F. Huang, et al., Synthesis of benzidine derivatives via
FeCl3ꢀ6H2O-promoted oxidative coupling of anilines, J. Org. Chem. 78 (2013)
5218–5226.
[33] The crystal data of compound 3j (CCDC reference number 946729): C27H20N2,
M = 372.46, crystal system: monoclinic, space group: P21/c, lattice parameters:
˚
˚
˚
(b) S.J. Ji, S.Y. Wang, Y. Zhang, T.P. Loh, Facile synthesis of bis(indolyl)methanes
using catalytic amount of iodine at room temperature under solvent-free con-
ditions, Tetrahedron 60 (2004) 2051–2055.
a = 10.722(6) A, b = 15.124(6) A, c = 15.355(9) A, a = 908, b = 105.159(11)8,
g = 908, V = 2406(2) A , Z = 4, Dc = 1.244 g/cmꢁ3
[I > 2sigma(I)]: R1 = 0.0670, wR2 = 0.2023.
, F000 = 952, final R indices
3
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