A novel and efficient method for the synthesis of 1 H -indol-3-yl acetates

Article abstract of DOI:10.1055/s-0030-1258240

A catalyst-free method for the synthesis of 1H-indol-3-yl acetates from 1H-indoles is described. The reaction takes place in the presence of (diacetoxyiodo)benzene (DIB) and potassium hydroxide as the base under mild conditions (MeCN, 35°C, 1.5 h). This represents a simple and efficient new method for 1H-indol-3-yl acetate synthesis.

Full text of DOI:10.1055/s-0030-1258240

PAPER
3623
A Novel and Efficient Method for the Synthesis of 1H-Indol-3-yl Acetates
N
ovel Synthesis of
e
1
H
-Indol-
x
3-yl
A
cetatesin Liu, Ping Wen, Jin Liu, Guosheng Huang*
State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, P. R. of China
Fax +86(931)8912582; E-mail: hgs2368@163.com
Received 30 June 2010; revised 29 July 2010
20 °C under air atmosphere for one hour. During the reac-
tion, iodobenzene was detected by TLC. The desired
product 1b was isolated in 35% yield (Table 1, entry 1).
After that, we found that the yield was increased when the
Abstract: A catalyst-free method for the synthesis of 1H-indol-3-yl
acetates from 1H-indoles is described. The reaction takes place in
the presence of (diacetoxyiodo)benzene (DIB) and potassium hy-
droxide as the base under mild conditions (MeCN, 35 °C, 1.5 h).
This represents a simple and efficient new method for 1H-indol-3- reaction was undertaken in the presence of base. The rea-
yl acetate synthesis.
son for this increase is that base can neutralize acetic acid,
keeping the reaction under an alkaline environment. Thus,
base is suitable for the reaction and the effect of different
bases on the reaction was tested. It can be seen from
Table 1 that potassium hydroxide gave the best result, su-
perior to Cs2CO3, NaH, K2CO3, Et3N, pyridine and t-
BuOK (entries 2–8). This revealed that potassium hydrox-
ide is by far the best base for the reaction.
Key words: indoles, (diacetoxyiodo)benzene (DIB), 1H-indol-3-yl
acetates, oxidation
The direct formation of C–O bonds from C–H bonds is
one of the most challenging projects in organic synthesis.1
Recently, the direct formation of C–O bonds based on the
b-C–H activation of amines has received great attention.2
In this context, the functionalization of C–H bonds adja-
cent to a nitrogen atom is of great importance. It has been
widely proved that the C3-position of indole has the prior-
ity in substitution reactions.3 During the past few years,
much attention has been devoted to 1H-indol-3-yl acetates
because of their potential applications in medicinal and
bioorganic chemistry. For example, 1H-indol-3-yl ace-
tates are important materials for the preparation of bio-
chemical reagents for the identification of campylobacter.
Meanwhile, as starting materials, 1H-indol-3-yl acetates
can be used to synthesize N-hydroxysuccinimidylindol-3-
yl acetates, which are used for amino acid analysis.4
Table 1 Optimization of the Reaction of 1H-Indole with DIBa
H
H
N
N
PhI(OAc)2 (1.5 equiv)
base (2.0 equiv)
O
1a
1b
O
Entry
Solvent
Base
Temp
(°C)
Time
(h)
Yieldb
(%)
1
2
MeCN
–
20
20
20
20
20
20
20
20
35
45
55
75
35
35
35
35
35
1
35
53
63
57
28
30
27
31
68
65
51
28
76
74
68
72
75
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
Cs2CO3
KOH
NaH
1
3
1
During a literature search we found only little information
on the synthesis of 1H-indol-3-yl acetate. Arnold and co-
workers revealed that indole reacts with iodine–potassium
iodide. Subsequent stirring of the resulting crude 3-iodo-
indole with acetic acid for 20 hours results in the 1H-in-
dol-3-yl acetate product;5 however, the reported
procedures are complex to perform and also need harsh
reaction conditions.
4
1
5
K2CO3
Et3N
1
6
1
7
pyridine
t-BuOK
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
1
8
1
Our efforts have been aimed at achieving this transforma-
tion by oxidation using hypervalent iodine(III) reagents.
Hypervalent iodine reagents have recently received much
attention due to their low toxicity, ease of handling and
high reactivity.6 The most well known representative of
this class is (diacetoxyiodo)benzene (DIB), which is use-
ful for the oxidative functionalization of various function-
al groups.7
9
1
10
11
12
13
14
15
16c
17d
1
1
1
1.5
2
Our initial study began with the reaction of 1H-indole (1a;
0.2 mmol) and DIB (1.5 equiv) in acetonitrile (2 mL) at
6
1.5
1.5
SYNTHESIS 2010, No. 21, pp 3623–3626
x
x.
x
x
.
2
0
1
0
Advanced online publication: 01.09.2010
DOI: 10.1055/s-0030-1258240; Art ID: F11410SS
© Georg Thieme Verlag Stuttgart · New York

3624
K. Liu et al.
PAPER
Table 1 Optimization of the Reaction of 1H-Indole with DIBa
(continued)
mainly influenced by the electronic effect.8 Electron-
withdrawing or electron-donating groups may affect the
activity of the 3-position of indoles and the activity of the
N–H bond. Strongly electron-withdrawing substituents on
the aryl moiety of the indole nucleus affect the efficiency
of the reaction as lower yields are observed (Table 2, en-
tries 10, 11). This is probably due to the strong modifica-
tion of the electronic density at the C3-position of the
nucleus due to the presence of such substituents.9 On the
other hand, different substituent positions of a substituent
group may have a greater or lesser effect on the yield
(Table 2, entries 2–5 and 7, 8).10 In all cases, the indoles
are inevitably consumed by oxidation. Finally, 1-phenyl-
1H-indole (12a) gave no reaction (Table 2, entry 12),
probably because it does not have a N–H bond like the N-
unsubstituted indoles.11
H
H
N
N
PhI(OAc)2 (1.5 equiv)
base (2.0 equiv)
O
1a
1b
O
Entry
Solvent
Base
Temp
(°C)
Time
(h)
Yieldb
(%)
18e
19f
20g
21
22
23
24
25
26
27
28
29
MeCN
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
–
35
35
35
35
35
35
35
35
35
35
35
35
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
67
74
0
MeCN
MeCN
CH2Cl2
DCE
40
51
38
43
32
35
0
Table 2 Synthesis of 1H-Indol-3-yl Acetatesa
THF
H
H
i-PrOH
Et2O
N
N
PhI(OAc)2 (1.5 equiv)
KOH (2.0 equiv), MeCN, 35 °C, 1.5 h
O
R
R
O
DMF
Entry Indole
Product
Yieldb
(%)
DMSO
1,4-dioxane
AcOH
65
trace
H
N
H
N
1
2
3
4
1a
2a
3a
4a
1b
76
66
62
67
a Reaction conditions: 1H-indole (0.2 mmol), PhI(OAc)2 (DIB, 1.5
equiv), base (2.0 equiv), solvent (2 mL), air atmosphere.
b Isolated yield of 1b.
O
O
O
O
c KOH (1.5 equiv) was added.
H
N
H
N
d KOH (2.5 equiv) was added.
2b
3b
4b
e PhI(OAc)2 (1.0 equiv) was added.
f PhI(OAc)2 (2.0 equiv) was added.
g MCPBA (1.0 equiv) was added.
O
O
H
N
H
N
Next, we evaluated the influence of the reaction tempera-
ture and time. As is obvious from the results in Table 1
(entries 3, 9–15), the best yield was obtained at 35 °C after
reaction for 1.5 hours (entry 13). Furthermore, the quanti-
ty of potassium hydroxide did not obviously affect the re-
action yield (Table 1, entries 16, 17).
H
N
H
N
O
O
According to our investigation, the optimal ratio of 1H-
indole to DIB is 1:1.5, which gives the highest yield.
Changes in the amount of DIB had little effect on the yield
(Table 1, entries 18, 19). Further optimization of the reac-
tion conditions revealed that acetonitrile as solvent is
more effective than CH2Cl2, DCE, THF, i-PrOH, Et2O,
DMF, DMSO, 1,4-dioxane and AcOH (Table 1, entries
21–29). In addition, excessively strong oxidant may
hinder the reaction (Table 1, entry 20).
H
N
H
N
5
5a
5b
61
O
O
H
N
H
N
6
7
6a
7a
6b
7b
68
82
O
MeO
MeO
O
Having optimized the reaction conditions, we examined
the scope and limitations of the procedure. As shown in
Table 2, compounds 1a, 7a, 8a and 9a produced the cor-
responding acetates in moderate to good yields when re-
acted with DIB (entries 1, 7–9), while compounds 2a, 3a,
4a, 5a and 6a produced the corresponding acetates in
moderate yields (entries 2–6). In general, the reaction is
H
N
H
N
O
O
Br
Br
Synthesis 2010, No. 21, 3623–3626 © Thieme Stuttgart · New York

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Novel Synthesis of 1H-Indol-3-yl Acetate
3625
Table 2 Synthesis of 1H-Indol-3-yl Acetatesa (continued)
a silica gel column to obtain 1H-indol-3-yl acetate (the silica gel
should be washed once with Et3N before being used). The product
was decolorized with activated carbon to give pure white needles;
yield: 39.6 mg (76%); mp 128 °C.
H
H
N
N
PhI(OAc)2 (1.5 equiv)
KOH (2.0 equiv), MeCN, 35 °C, 1.5 h
O
IR (KBr): 3345, 1751, 1350, 1222, 741 cm–1.
R
R
O
1H NMR (400 MHz, CDCl3): d = 7.88 (s, 1 H), 7.54 (d, J = 7.6 Hz,
1 H), 7.29 (s, 1 H), 7.22 (d, J = 4.8 Hz, 1 H), 7.20 (t, J = 7.4 Hz, 1
H), 7.12 (t, J = 7.2 Hz, 1 H), 2.36 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 168.9, 133.1, 130.4, 122.7, 120.0,
119.8, 117.4, 113.4, 111.4, 20.94.
MS (EI): m/z = 175 [M+], 133 (fission of C–O bond), 104, 77, 51,
43.
Entry Indole
Product
Yieldb
(%)
H
N
H
N
8
9
8a
9a
8b
78
72
43
O
O
Br
O
Br
Anal. Calcd for C10H9NO2: C, 68.56; H, 5.18; N, 8.00. Found: C,
68.55; H, 5.20; N, 8.04.
H
N
H
N
9b
2-Methyl-1H-indol-3-yl Acetate (2b)
Yield: 37.1 mg (66%); yellow oil.
IR (neat): 3393, 1743, 1217, 742 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.69 (s, 1 H), 7.34 (d, J = 7.2 Hz,
1 H), 7.21 (d, J = 7.2 Hz, 1 H), 7.14–7.06 (m, 2 H), 2.39 (s, 3 H),
2.27 (s, 3 H).
BnO
BnO
N
O
H
N
N
H
N
10 10a
10b
O
O
13C NMR (100 MHz, CDCl3): d = 169.5, 132.8, 126.7, 123.8, 121.7,
121.5, 119.9, 116.6, 110.8, 20.57, 10.40.
H
N
H
MS (EI): m/z = 189 [M+], 147, 91, 77, 43.
N
11 11a
12 12a
11b
–
36
O
Anal. Calcd for C11H11NO2: C, 69.83; H, 5.86, N, 7.40. Found: C,
69.76; H, 5.84, N, 7.46.
O2N
O2N
O
4-Methyl-1H-indol-3-yl Acetate (3b)
Yield: 34.9 mg (62%); yellow needles; mp 120–121 °C.
Ph
–
n.r.c
N
IR (KBr): 3310, 1727, 1341, 1258, 1069, 736 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.87 (s, 1 H), 7.18 (d, J = 2.4 Hz,
1 H), 7.10–7.04 (m, 2 H), 6.85 (t, J = 0.6 Hz, 1 H), 2.61 (s, 3 H),
2.33 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 169.5, 133.3, 131.1, 129.3, 122.8,
121.1, 118.9, 113.4, 109.1, 21.10, 18.71.
a Reaction conditions: indole (0.3 mmol), PhI(OAc)2 (DIB, 1.5
equiv), KOH (2.0 equiv), MeCN (3 mL), air atmosphere, 35 °C, 1.5 h.
b Isolated yield.
c No reaction.
MS (EI): m/z = 189 [M+], 147, 91, 43.
In conclusion, we have developed a novel and mild meth-
odology for the synthesis of 1H-indol-3-yl acetates. The
reaction of 1H-indoles with DIB, without the presence of
any catalyst, affords moderate to good yields of 1H-indol-
Anal. Calcd for C11H11NO2: C, 69.83; H, 5.86; N, 7.40. Found: C,
69.82; H, 5.92; N, 7.45.
5-Methyl-1H-indol-3-yl Acetate (4b)
3-yl acetates. This is a better option than the known meth- Yield: 37.5 mg (67%); white needles; mp 117–118 °C.
IR (KBr): 3357, 1747, 1222, 798, 604 cm–1.
od for 1H-indol-3-yl acetate synthesis.
1H NMR (400 MHz, CDCl3): d = 7.80 (s, 1 H), 7.30 (s, 1 H), 7.19–
7.13 (m, 2 H), 7.01 (d, J = 8.0 Hz, 1 H), 2.43 (s, 3 H), 2.35 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 168.9, 131.5, 130.0, 129.1, 124.4,
120.1, 116.8, 113.5, 111.1, 21.36, 20.90.
NMR spectra were recorded on a Bruker Avance III 400 spectrom-
eter (1H: 400 MHz, 13C: 100 MHz), using CDCl3 as the solvent and
TMS as the internal standard. IR spectra were recorded as KBr pel-
lets or neat on a Nicolet Nexus 670 FT-IR spectrophotometer. Mass
spectra were recorded using the EI method on a HP 5988A mass
spectrometer. Elemental analyses were performed on an Elementar
vario EL analyzer. Melting points are uncorrected.
MS (EI): m/z = 189 [M+], 147, 118, 91, 65, 43.
Anal. Calcd for C11H11NO2: C, 69.83; H, 5.86; N, 7.40. Found: C,
69.77; H, 5.98; N, 7.36.
1H-Indol-3-yl Acetate (1b); Typical Procedure
7-Methyl-1H-indol-3-yl Acetate (5b)
A mixture of 1H-indole (1a; 35.1 mg, 0.3 mmol), DIB (144.9 mg,
0.45 mmol) and KOH (33.6 mg, 0.6 mmol) was stirred in MeCN (3
mL) at 35 °C for 1.5 h (the progress of the reaction was monitored
by TLC). During this time, the color of the mixture changed from
colorless to orange. When the reaction was completed, the liquid
was extracted with EtOAc (3 × 40 mL). The combined organic ex-
tracts were washed with H2O (50 mL) and saturated brine (100 mL).
The organic layer was dried (MgSO4), filtered and concentrated on
a rotary evaporator. The residue was purified by chromatography on
Yield: 34.1 mg (61%); yellow solid; mp 118–119 °C.
IR (KBr): 3291, 1729, 1250, 1222, 776 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.78 (s, 1 H), 7.41 (d, J = 7.6 Hz,
1 H), 7.36 (d, J = 2.8 Hz, 1 H), 7.09–7.02 (m, 2 H), 2.47 (s, 3 H),
2.37 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 169.0, 132.6, 130.8, 123.1, 120.5,
120.0, 119.4, 115.0, 113.1, 20.91, 15.95.
MS (EI): m/z = 189 [M+], 147, 118, 91, 65, 43.
Synthesis 2010, No. 21, 3623–3626 © Thieme Stuttgart · New York

3626
K. Liu et al.
PAPER
Anal. Calcd for C11H11NO2: C, 69.83; H, 5.86; N, 7.40. Found: C,
69.74; H, 5.79; N, 7.51.
MS (EI): m/z = 176 [M+], 134, 118, 91, 63, 43.
Anal. Calcd for C9H8N2O2: C, 61.36; H, 4.58; N, 15.90. Found: C,
61.58; H, 4.78; N, 15.66.
5-Methoxy-1H-indol-3-yl Acetate (6b)
Yield: 41.2 mg (68%); white needles; mp 82–84 °C.
IR (KBr): 3378, 2934, 1753, 1457, 1225, 1028, 797 cm–1.
5-Nitro-1H-indol-3-yl Acetate (11b)
Yield: 23.4 mg (36%); yellow solid; mp 172–173 °C.
1H NMR (400 MHz, CDCl3): d = 7.76 (s, 1 H), 7.32 (d, J = 2.8 Hz,
IR (KBr): 3368, 2914, 1744, 1519, 1332, 1213, 743 cm–1.
1H NMR (400 MHz, CDCl3): d = 8.95 (s, 1 H), 7.71 (s, 1 H), 7.44–
7.31 (m, 3 H), 2.05 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 176.8, 137.5, 132.7, 131.8, 130.2,
127.4, 118.0, 117.6, 111.0, 29.67.
1 H), 7.20 (s, 1 H), 6.96–6.86 (m, 2 H), 3.86 (s, 3 H), 2.37 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 168.7, 154.2, 130.4, 128.3, 120.1,
114.1, 113.6, 112.3, 98.5, 55.77, 21.01.
MS (EI): m/z = 205 [M+], 163, 148, 63, 43.
Anal. Calcd for C11H11NO3: C, 64.38; H, 5.40; N, 6.83. Found: C,
64.32; H, 5.55; N, 6.86.
MS (EI): m/z = 220 [M+], 178, 162, 132, 116, 104, 89.
Anal. Calcd for C10H8N2O4: C, 54.55; H, 3.66; N, 12.72. Found: C,
54.75; H, 3.42; N, 12.98.
4-Bromo-1H-indol-3-yl Acetate (7b)
Yield: 61.9 mg (82%); yellow solid; mp 112–113 °C.
IR (KBr): 3311, 1749, 1370, 1333, 1221, 1190, 906, 732, 672 cm–1.
Acknowledgment
1H NMR (400 MHz, CDCl3): d = 8.23 (s, 1 H), 7.20 (d, J = 0.4 Hz,
1 H), 7.02 (d, J = 8.0 Hz, 1 H), 6.91 (t, J = 8.0 Hz, 1 H), 6.83 (d,
J = 2.8 Hz, 1 H), 2.37 (s, 3 H).
The authors thank the State Key Laboratory of Applied Organic
Chemistry for financial support.
13C NMR (100 MHz, CDCl3): d = 170.9, 134.7, 129.0, 123.9, 123.4,
118.7, 115.8, 111.1, 111.0, 21.11.
References
MS (EI): m/z = 253 [M+], 211, 131, 103, 75, 43.
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47.36; H, 3.14; N, 5.60.
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5-Bromo-1H-indol-3-yl Acetate (8b)
Yield: 58.9 mg (78%); yellow solid; mp 118–119 °C.
IR (KBr): 3331, 1746, 1216, 1080, 795 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.88 (s, 1 H), 7.56 (s, 1 H), 7.16–
7.13 (m, 2 H), 7.01 (d, J = 8.8 Hz, 1 H), 2.24 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 168.8, 131.7, 129.7, 125.7, 121.5,
120.0, 114.7, 113.1, 112.9, 20.87.
MS (EI): m/z = 253 [M+], 211, 132, 75, 43.
Anal. Calcd for C10H8BrNO2: C, 47.27; H, 3.17; N, 5.51. Found: C,
47.33; H, 3.21; N, 5.57.
5-(Benzyloxy)-1H-indol-3-yl Acetate (9b)
Yield: 60.1 mg (72%); yellow needles; mp 84–85 °C.
IR (KBr): 3411, 1745, 1490, 1455, 1220, 1062, 739 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.78 (s, 1 H), 7.48 (d, J = 7.2 Hz,
2 H), 7.42–7.31 (m, 4 H), 7.21 (d, J = 8.8 Hz, 1 H), 7.07 (d, J = 2.0
Hz, 1 H), 6.95 (dd, J = 2.4, 2.4 Hz, 1 H), 5.11 (s, 2 H, CH2), 2.37 (s,
3 H).
13C NMR (100 MHz, CDCl3): d = 168.7, 153.4, 137.4, 130.4,
128.52, 128.47, 127.79, 127.60, 120.1, 114.20, 114.05, 112.3,
100.3, 70.8, 20.9.
MS (EI): m/z = 281 [M+], 239, 149, 91, 43.
Anal. Calcd for C17H15NO3: C, 72.58; H, 5.38; N, 4.98. Found: C,
72.61; H, 5.41; N, 5.01.
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(10) (a) Xiang, W.; Gribkov, D. V.; Sames, D. J. Org. Chem.
2007, 72, 1476. (b) Yanlong, G.; Ogawa, C.; Kobayashi, S.
Org. Lett. 2007, 9, 175.
1H-Pyrrolo[2,3-b]pyridin-3-yl Acetate (10b)
Yield: 22.4 mg (43%); yellow solid; mp 132–134 °C.
IR (KBr): 2919, 1713, 1265, 662 cm–1.
(11) (a) Bartoli, G.; Bosco, M.; Carlone, A.; Pesciaioli, F.;
Sambri, L.; Melchiorre, P. Org. Lett. 2007, 9, 1403.
(b) Hyeyeon, Y.; Youngtaek, H.; Sunggak, K. Org. Lett.
2007, 9, 2281. (c) Blay, G.; Fernández, I.; Pedro, J. R.; Vila,
C. Org. Lett. 2007, 9, 2601.
1H NMR (400 MHz, CDCl3): d = 11.24 (s, 1 H), 7.98–7.90 (m, 2 H),
7.40 (d, J = 3.6 Hz, 1 H), 6.47 (t, J = 7.8 Hz, 1 H), 3.70 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 176.2, 148.0, 141.4, 129.4, 125.4,
120.8, 115.5, 100.5, 21.75.
Synthesis 2010, No. 21, 3623–3626 © Thieme Stuttgart · New York