One-pot tandem synthesis of 2,3-unsubstituted indoles, an improved Leimgruber-Batchoindole synthesis

Article abstract of DOI:10.1039/c3ra45548c

A concise, fast and efficient one-pot methodology has been developed for preparing 2,3-unsubstituted indoles from 2-nitrotoluenes and dimethylformamide dimethyl acetal. Compared with the classical Leimgruber-Batcho reaction, such a one-pot process simplified the operation procedures, generated less by-products and chemical residues, and resulted in higher overall yields in a shorter reaction time.

Full text of DOI:10.1039/c3ra45548c

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One-pot tandem synthesis of 2, 3-unsubstituted
indoles, an improved Leimgruber-Batchoindole
synthesis
Cite this: DOI: 10.1039/x0xx00000x
Jinchun Chen,a Zhikai Zhang,a,b Sujing Liu,b,c Cuiyun Yangb and Chuanhai Xiab,*
Received 00th January 2012,
Accepted 00th January 2012
A concise, fast and efficient one-pot methodology has been developed for preparing 2, 3-
unsubstituted indoles from 2-nitrotoluenes and dimethylformamide dimethyl acetal. Compared
with the classical Leimgruber-Batcho reaction, such one-pot process simplified the operation
procedures, generated less by-products and chemical residues, and resulted in higher overall
yields in a shorter reaction time.
DOI: 10.1039/x0xx00000x
www.rsc.org/
enamine intermediates. The method was more concise and obtained
higher yields with a much shorter reaction time compared with the
Introduction
conventional Leimgruber-Batcho indolization routes.
The indole ring system is a significant structural component of a
great number of biologically active natural and synthetic
compounds, and it exists in plenty of pharmaceutical agents,
dyestuffs, and pharmaceutical or agrochemical intermediates.1
Despite numerous methods for the construction of indole ring have
been developed in the past decades,2 organic chemists are still to
search for more straightforward, economical and green ways to make
various substituted indoles, such as the transition-metal-catalyzed
synthesis 3 and multistep one-pot synthesis 4.
Results and discussion
We began our study by examining the one-pot reaction of 4-
chloro-2-nitrotoluene (1b) and DMF-DMA (Scheme 1; R = Cl) as
the standard reaction (Table 1). Gratifyingly, the expected product
3b was obtained when the reaction was carried out in DMF, which
was usually used in the first step in the classic Leimgruber-Batcho
indole synthesis (Table 1, entry 1). It means that the one-pot
synthesis of indoles via Leimgruber-Batcho reaction method is
feasible. However, the total yield of 3b was relatively low, just 36%
within 10 h. According to the reaction process, the influence factors
on this one-pot reaction are including solvent, additive, reducing
agent, catalyst, and temperature. Thus, we thoroughly studied these
influence factors on the one-pot reaction.
The Leimgruber-Batcho indole synthesis is an important and
efficient method of synthesizing substituted indoles, especially for
the preparation of 2, 3-unsubstituted indoles. The classical
Leimgruber-Batchoindole synthesis involves two steps reaction
process, including the condensation of an appropriately substituted
o-nitrotoluene with dimethylformamide dimethyl acetal (DMF-
DMA) to give intermediate o-nitrophenylacetaldehyde enamine, and
the subsequent reductive cyclization to furnish the substituted
indoles.5 Due to the fact that the starting material o-nitrotoluene
derivatives are easily prepared and both two steps proceed under
mild reaction conditions, this method has enjoyed widespread
applications from laboratory to industry owing to the high functional
group compatibility.2d, 6 Nevertheless, there are also some drawbacks
including relatively prolonged reaction time and cumbersome
isolation procedures of enamine intermediates.7 Some modification
of this reaction has been developed, including the variation of the
applied base, the reducing reagents, and the available acetals of
From Table 1, it was noted that the solvent had a great influence
on both the yield and the rate of the reaction. The solvent screening
showed that dioxane was the best option (Table 1, entries 1-5), and
then following toluene, THF, DMF and methanol, respectively.
DMF was unsuitable to this one-pot synthesis, due to the inhibition
effect of DMF on Raney Ni and Pd/C in catalytic hydrogenation
reaction.9 In THF, because of its lower reflux temperature (about 66
℃) in the reaction, the one-pot synthesis rate and yield were both
lower than those in dioxane. The yield was only 13% when methanol
was used (Table 1, entry 5). We supposed that, with methanol as a
solvent, the formation of the intermediate carbanion B was probably
suppressed and so the reaction was inhibited (Scheme 2).
8
7b
dimethylformamide as well as microwave-assisted synthesis
,
etc..
The presence of pyrrolidine, as an additive, especially excess
amount of pyrrolidine could greatly promote the reaction (Table 1,
entries 4, 6, and 10), which could be predicted from the reaction
mechanism presented in Scheme 2. We thought that excess amount
of pyrrolidine could not only promote step a to generate compound
A with a much higher reactivity than DMF-DMA, but also would be
advantageous to o-nitrotoluene deprotonation (step b) to generate
carbanion B as a proton acceptor. Additionally, the influence of
other nitrogenous nucleophilic reagents, such as diethylamine,
4
6
6
NMe2
CH3
NO2
9
5
4
Me2NCH(OMe)2
Reflux
3
2
5
4
5
6
Reduction
R'
R
R
1
N
8
NO2
7
H
3
3
Scheme 1. One-pot tandem synthesis of 2, 3-unsubstituted indoles.
Here, a concise, fast and efficient method was reported to
synthesize indoles via the Leimgruber-Batcho reaction, which is a
one-pot reaction directly from o-nitrotoluene derivatives to
corresponding indole products (Scheme 1) without separation of
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piperazine, morpholine, were also investigated. Nevertheless, all
results were inferior compared with pyrrolidine (Table 1, entries 7-
9).
DMA (4.8 mmol), additive (5 equiv), hydrazine (10 equiv),
catalyst: 200 mg Raney nickel, in solvent (50 ml), under nitrogen
atmosphere. b Reduction temperatures. c Isolated yields. d Catalyst:
Table 1. Optimization of the one-pot synthesis.a
e
40 mg 5%Pt/C. Catalyst: 40 mg 5%Pd/C. f Examined by GC/MS.
g Catalyst: 40 mg Raney nickel.
The yield of product 3b reached 85% within 5.5 h when hydrogen
gas was used as the reducing agent. If considering the safety and the
large scale of the reactions, we thought that H2 was also a good
reducing agent compared with hydrazine hydrate (Table 1, entries 4
and 20). Additionally, the yields of 3b reduced from 90% to 77%
(entries 4 and 14) as the concentration of hydrazine hydrate
decreased from 85% to 30%, which maybe because such decreased
concentration of hydrazine hydrate produced a small amount of 1-
hydroxindoles as by-product at the expense of indoles 3.10 Also, the
decreased amount of hydrazine hydrate resulted in both lower yields
and reaction rate (Table 1, entries 4, 11 and 12). We also examined
the reactions with different catalysts (Ni, Pt, Pd). The results showed
that the reaction catalyzed by Raney nickel worked much better
than others (Table 1, entries 4, 15, and 16). When the amount of
Raney nickel was reduced to 40 mg, the yield of 3b decreased to
46%, meanwhile, the reaction time was prolonged to 10 h (Table 1,
entry 19).
Reducing
agents
T/℃b
Y/%c
Entry Solvents Additives
t/h
1
2
3
4
5
DMF
THF
Pyrrolidine
Pyrrolidine
85% N2H4 45
85% N2H4 45
85% N2H4 45
85% N2H4 45
85% N2H4 45
10
36
65
72
10
10
Toluene Pyrrolidine
Dioxane Pyrrolidine
5.5 90
MeOH
Pyrrolidine
10
18
13
57
Besides, the reaction temperatures in the reduction procedure were
also evaluated. The yields were both reduced whether the reaction
was performed at 20 ℃or 60 ℃(Table 1, entries 4, 17-18), in which
some enamine intermediates were still present in one-pot reaction at
20 ℃, however, some hydrodechlorinated products were formed at
60 ℃according to the analysis of GC-MS.
Pyrrolidine
(1.2 equiv)
6
Dioxane
85% N2H4 45
7
Dioxane Diethylamine 85% N2H4 45
Dioxane Piperazine 85% N2H4 45
Dioxane Morpholine 85% N2H4 45
24
15
15
32
22
8
trace e
trace e
trace e
After optimizing the reaction conditions, that the reaction
proceeded in dioxane at the presence of pyrrolidine (5 equiv), using
85% hydrazine hydrate (10 equiv) as reducing agent, catalyzed by
Raney nickel (200 mg) at 45 ℃ was selected to be an optimal
condition for such one-pot synthesis of indole derivatives 3.
9
10
Dioxane
—
85% N2H4 45
85% N2H4
To explore the generality of one-pot methodology, the optimized
reaction condition was applied to synthesize a series of differently
substituted indoles summarized in Table 2. The results suggested
that all the o-nitrotoluene derivatives with various substituents could
be performed smoothly, producing desired products, of which the
11
12
Dioxane Pyrrolidine
Dioxane Pyrrolidine
45
9
63
28
（6 equiv）
85% N2H4
45
（2 equiv）
reaction rates were greatly increased compared with those reported
15
7a
in literature
(Table 2, entries 2-4). It was also noted that the
developed one-pot protocol provided higher yields than the
conventional Leimgruber-Batcho routes (Table 2, entries 2-4).
Especially, the yield of 3b was up to 90%, while the overall yield via
the conventional routes was only 30% (Table 2, entry 2). However,
the synthesis for 7-methylindole (3l) obtained a relatively low yield
even with prolonged heating for 22 h or longer (Table 2, entry 12)
and the similar results could be seen in the literature 7a. The low
yields of 3l as well as 3j probably resulted from steric effect.
13
Dioxane Pyrrolidine
Dioxane Pyrrolidine
Dioxane Pyrrolidine
Dioxane Pyrrolidine
Dioxane Pyrrolidine
Dioxane Pyrrolidine
Dioxane Pyrrolidine
Dioxane Pyrrolidine
60% N2H4 45
30% N2H4 45
85% N2H4 45
85% N2H4 45
85% N2H4 20
85% N2H4 60
85% N2H4 45
6.5 82
7.5 77
14
15d
16e
17
14
14
35
8 f
As shown in Table 2, both the variety and position of substituents
have a significant influence on the reaction. As for the same
substituent group, the o-nitrotoluene derivatives substituted in 4 and
5 positions resulted in both better yields and higher reaction rate
compared with those substituted in 3 and 6 positions (Table 2,
entries 2-12). Additionally, the substituted o-nitrotoluenes with an
electron-withdrawing group on the aromatic ring moiety showed
higher reaction rate than the unsubstituted o-nitrotoluene, which
were also faster than those having an electron-donating group (Table
2, entries 1-9, 11-12). The synthesis of 3j was an exception with
higher reaction rate than unsubstituted 3a with the lowest yield
5.5 70
5.5 76
18
19 g
20
10
46
H2
45
5.5 85
a Reaction conditions (unless otherwise stated): 1b (4 mmol), DMF-
2 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C3RA45548C
instead (Table 2, entries 1 and 10). Also, as to o-nitrotoluenes Scheme 2. The reaction mechanism from o-nitrotoluenes to indoles.
substituted at the same position, o-nitrotoluenes with an electron-
On the basis of these preliminary results, the reaction
withdrawing group afforded higher yields than those with an
mechanism was hypothesized as shown in Scheme 2, DMF-
DMA is initially attacked by pyrrolidine via nucleophilic
electron-donating group (Table 2, entries 5-7, 9-12). It was
concluded that electron-withdrawing group substituted o-
substitution to produce compound
subsequently attacked by carbanion
A
,
which could be
generated by
-nitrotoluene derivatives to produce
. The intermediate then undergoes
nitrotoluenes exhibited higher reactivities than those electron-
donating group substituted o-nitrotoluenes, which was consistent
with the reaction mechanism presented in Scheme 2 suggesting that
electron-withdrawing groups involving halogenatoms with stronger
electronegativity could accelerate step b to generate carbanion B due
to the inductive effect.
B
deprotonation from
enamine intermediate
o
2
2
reduction by hydrogen coming from hydrazine hydrate under
the catalysis of Raney nickel, followed by cyclization to obtain
the expected product 3. According to the mechanism, we can
infer that both excess amounts of pyrrolidine and electron-
withdrawing groups on the aromatic ring moiety could promote
Table 2. One-pot synthesis of indole derivatives 3
.
step b to generate carbanion
rates.
B and thus lead to quicker reaction
Experimental
General Procedure for One-Pot Reaction from O-nitrotoluenes
Y/%a
Entry
R
1
t/h
R’
3
A 100 mL three-necked flask equipped with magnetic stir bar and a
condenser was charged with o-nitrotoluenes (4 mmol), DMF-DMA
(4.8 mmol), pyrrolidine (20 mmol), and dioxane (50 mL) at 102 ℃
under nitrogen atmosphere for 2.5-22 h. The progress of the reaction
was monitored by TLC. After the reaction was cooled to 45 ℃, 0.2 g
of Raney nickel was added followed by 0.8 g of 85% hydrazine
hydrate. Vigorous gas evolution was observed. An additional 0.8 g
of 85% hydrazine hydrate was added after 30 min and again 30 min
later. The temperature was maintained at 45 ℃. After completion of
the reaction, the mixture was cooled to room temperature and the
catalyst was filtered off and washed carefully with 5×10 ml
dichloromethane or acetone. The filtrate was evaporated under
reduced pressure, and the residue thus obtained was then purified by
1
2
H
10
H
71
90, 30 b
82, 37 b
52, 35 b
65
1a
1b
1c
1d
1e
1f
3a
3b
3c
3d
3e
3f
4-Cl
5.5, 24b
6-Cl
3
4-Br
3.5, 31 b
6-Br
4
4-NO2
5-CH3
5-CN
5-Cl
5
14
2.5
6
6-NH2
5-CH3
5-CN
5-Cl
5
6
71
column chromatography on silica gel using
a mixture of
7
74
1g
1h
1i
3g
3h
3i
dichloromethane and petroleum ether as eluent to afford the desired
product 3.
8
4,5-Cl
6-Cl
5
5,6-Cl
4-Cl
92
Conclusions
9
9
55
In conclusion, we developed a simple and efficient one-pot
tandem methodology to synthesize 2, 3-unsubstituted indoles
from o-nitrotoluenes which was derived from the Leimgruber-
10
11
12
6-NH2
3-Cl
6.5
9
4-NH2
7-Cl
34
1j
3j
Batcho reaction. Compared with the conventional Leimgruber-
Batcho indole synthesis, not only would such one-pot process
eliminate the need for isolation of the potentially unstable
enamine intermediates, but also it would decrease the amounts
of by-products and chemical wastes generated. Furthermore, it
has been shown that the overall yields for one-pot procedures
were higher (about twice) in a shorter reaction time than those
of step-by-step processes. Additionally, it was found that the
70
1k
1l
3k
3l
3-CH3
22
7-CH3
53
a Isolated yields. b Data reported for the classic Leimgruber-Batcho
routes.7a
electron-withdrawing groups substituted
o-nitrotoluenes
exhibited higher reactivities and yields than those electron-
donating groups substituted o-nitrotoluenes.
Acknowledgements
Support by the Cooperation Program of Chinese Academy of
Sciences and District (No. Y12B051011), the National Key
Technology Research and Development Program (No.
2011BAC02B04) and Yantai Science and Technology
Development Project (No. 2011063) is gratefully
acknowledged.
Notes and references
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a College of Chemistry and Chemical Engineering, Yantai University, Yantai
264005, P. R. China
R. Nagata, Tetrahedron, 2002, 58, 3605; f) A. Shahrisa, Z. Ghasemi and
M. Saraei, J. Heterocyclic Chem., 2009, 46, 273.
b Key Laboratory of Coastal Biology and Biological Resources Utilization, 7. a) A. D. Batcho and W. Leimgruber, Org. Synth., 1990, 7, 34; b) J. Siu, I.
Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences,
R. Baxendale and S. V. Ley, Org. Biomol. Chem., 2004, 2, 160.
8. a) E. C. Taylor and W. B. Young, J. Org. Chem., 1995, 60, 7947; b) J. W.
Coe, M. G. Vetelino and M. J. Bradle, Tetrahedron Lett., 1996, 37, 6045;
c) J. M. Bentley, J. E. Davidson, M. A. J. Duncton, P. R. Giles and R. M.
Pratt, Synth. Commun., 2004, 34, 2295; d) J. Tois, M. Vahermo and A.
Koskinen, Tetrahedron Lett., 2005, 46, 735.
Yantai, 264003, P. R. China E-mail: chxia@yic.ac.cn
c University of Chinese Academy of Sciences, Beijing, 100049, P. R. China
1. a) T. Eicher and S. Hauptmann, The Chemistry of Heterocycles: Structure,
Reactions, Syntheses, and Applications, 2nd ed., Wiley-VCH, Weinheim,
2003; b) M. Somei and F. Yamada, Nat. Prod. Rep., 2005, 22, 73; c) K. 9. a) C. Xia, Y. Liu, S. Zhou, C. Yang, S. Liu, J. Xu, J. Yu, J. Chen and X.
Krueger, A. Tillack and M. Beller, Adv. Synth. Catal., 2008, 350, 2153; d)
A. J. Kochanowska-Karamyan and M. T. Hamann, Chem. Rev., 2010,
Liang, J. Hazard. Mater., 2009, 169, 1029; b) F. Turek and B. Rennert,
Trends Chem. Eng., 1993, 1, 165.
110, 4489; e) M. Inman and C. J. Moody, Chem. Sci., 2013, 4, 29, and 10.R. D. Clark and D. B. Repke, J. Heterocyclic Chem., 1985, 22, 121.
references therein.
11.a) G. Bratulescu, Tetrahedron Lett., 2008, 49, 984; b) A. Kasahara, T.
Izumi, T. Kikuchi and X. Lin, J. Heterocycl. Chem., 1987, 24, 1555; c) S.
Raucher and G. A. Koolpe, J. Org. Chem., 1983, 48, 2066; d) Y. Konda-
Yamada, C. Okada, K. Yoshida, Y. Umeda, S. Arima, M. Sato, T. Kai, H.
Takayanagi and Y. Harigaya, Tetrahedron, 2002, 58, 7851; e) B. M. Trost
and A. McClory, Angew. Chem . Int. Ed., 2007, 46, 2074; f) H. E. Johnson
and D. G. Crosby, J. Org. Chem.., 1963, 28, 2794; g) M. Somei, S. Inoue,
S. Tokutake, F. Yamada and C. Kaneko, Chem. Pharm. Bull., 1981, 29,
726; h) H. Rie, O. Hideo, M. Atsuya, O. Hideo, E. Mamoru, M. Wataru
and K. Kazumi, Chem. Abstr., 1996, 124, 343108.
2. For some reviews, see: a) G. W. Gribble, J. Chem. Soc., Perkin Trans. 1,
2000, 1045; b) I. Nakamura and Y. Yamamoto, Chem. Rev., 2004, 104,
2127; c) S. Cacchi and G. Fabrizi, Chem. Rev., 2005, 105, 2873; d) G. R.
Humphrey and J. T. Kuethe, Chem. Rev., 2006, 106, 2875; e) L.
Ackermann, Synlett., 2007, 507; f) S. Cacchi and G. Fabrizi, Chem. Rev.,
2011, 111, 215; g) D. F. Taber and P. K. Tirunahari, Tetrahedron, 2011,
67, 7195; h) R. Vicente, Org. Biomol. Chem., 2011, 9, 6469; i) M. Shiri,
Chem. Rev., 2012, 112, 3508; j) M. Platon, R. Amardeil, L. Djakovitch
and J. C. Hierso, Chem. Soc. Rev., 2012, 41, 3929.
3. a) R. C. Larock, E. K. Yum and M. D. Refvik, J. Org. Chem., 1998, 63,
7652; b) L. Ackermann, L. T. Kaspar and C. J. Gschrei, Chem. Commun.,
2004, 2824; c) R. Yanada, S. Obika, M. Oyama and Y. Takemoto, Org.
Lett., 2004, 6, 2825; d) G. Zeni and R. C. Larock, Chem. Rev., 2006, 106,
4644; e) L. Djakovitch, V. Dufaud and R. Zaidi, Adv. Synth. Catal., 2006,
348, 715; f) M. Inman, A. Carbone and C. J. Moody, J. Org. Chem., 2012,
77, 1217; g) C. Wang, H. Sun, Y. Fang and Y. Huang, Angew. Chem. Int.
Ed., 2013, 52, 5795; h) W. Song and L. Ackermann, Chem. Commun.,
2013, 49, 6638.
4. a) V．Khedkar, A. Tillack, M. Michalik and M. Beller, Tetrahedron Lett.,
2004, 45, 3123; b) L. Djakovitch, V. Dufaud and R. Zaidi, Adv. Synth.
Catal., 2006, 348, 715; c) B. Z. Lu, W. Zhao, H. X. Wei, M. Dufour, V.
Farina and C. H. Senanayake, Org. Lett., 2006, 8, 3271; d) O. Leogane
and H. Lebel, Angew. Chem. Int. Ed., 2008, 47, 350; e) G. Bratulescu,
Tetrahedron Lett., 2008, 49, 984; f) N. Okamoto, Y. Miwa, H. Minami, K.
Takeda and R. Yanada, Angew. Chem. Int. Ed., 2009, 48, 9693; g) Y
Chen, N. A. Markina and R. C. Larock, Tetrahedron, 2009, 65, 8908; h) J.
Liu, Y. Zhang, G. Li, F. Roschangar, V. Farina, C. H. Senanayake and B.
Z. Lu, Adv. Synth. Catal., 2010, 352, 2667; i) G. Cera, S. Piscitelli, M.
Chiarucci, G. Fabrizi, A. Goggiamani, R. S. Ram, S. P. Nolan and M.
Bandini, Angew. Chem. Int. Ed., 2012, 51, 9891; j) V. Kavala, D.
Janreddy, M. J. Raihan, C. Kuo, C. Ramesh and C. Yao, Adv. Synth.
Catal., 2012, 354, 2229; k) F. S. Melkonyan, D. E. Kuznetsov, M. A.
Yurovskaya and A. V. Karchava,RSC Adv., 2013, 3, 8388.
5. J. Li and J. M. Cook, Batcho–LeimgruberIndole Synthesis in Name
Reactions in Heterocyclic Chemistry, J. J. Li and E. J. Corey, Eds.; Wiley
& Sons: Hoboken, NJ, 2005.
6. a) A. D. Batcho and W. Leimgruber, US Patent, 1973, 3732245; b) A. D.
Batcho and W. Leimgruber, US Patent, 1976, 3976639; c) D. B. Repke
and R. D. Clark, Heterocycles, 1984, 22, 195; d) A. D. Batcho and W.
Leimgruber, Org. Synth., 1985, 63, 214; e) W. E. Hume, T. Tokunaga and
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