Synthesis of 3-acylindoles: via copper-mediated oxidative decarbethoxylation of ethyl arylacetates

Article abstract of DOI:10.1039/c9ob02550b

An efficient regioselective C-3 acylation of free indoles (N-H) has been accomplished via oxidative decarbethoxylation of easily available ethyl arylacetates using Cu(OAc)₂ and KOtBu in DMSO.

Full text of DOI:10.1039/c9ob02550b

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DOI: 10.1039/C9OB02550B
ARTICLE
Synthesis of 3-acylindoles via copper-mediated oxidative
decarbethoxylation of ethyl arylacetates
Anjali Jaiswal, Anup Kumar Sharma and Krishna Nand Singh*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
An efficient regioselective C-3 acylation of free indoles (N-H) has been accomplished via oxidative decarbethoxylation of
easily available ethyl arylacetates using Cu(OAc)2 and KOtBu in DMSO.
acylation of indoles using α-oxocarboxylic acids.10 Li and Wang
have reported a similar decarboxylative C-3 acylation of
indoles by α-oxocarboxylic acids under photoredox catalysis.11
Introduction
Indole containing molecules are prevalent in natural products
and pharmaceuticals. 3-Acylated indoles are especially
important as they constitute the core nucleus of many
alkaloids, inhibitors of HIV-1 integrase, anticancer compounds
and antidiabetics.1 From synthetic perspectives, the carbonyl
function of 3-acylindole is amenable to many significant
transformations including CC and CN coupling reactions.
Traditional methods for the preparation of 3-acylindoles
include FriedelCrafts reaction,2 VilsmeierHaack acylation,3
and Grignard reaction.4 The Friedel–Crafts acylation requires
N-protection/deprotection, metal based Lewis acid promoters,
and strict exclusion of moisture;2 whereas VilsmeierHaack
acylation necessitates an excess use of environmentally
precarious POCl3 and suffers from the want of the amides used
as carbonyl source.3 The conventional methods often involve
uncommon acylating reagents or malevolent reaction
conditions. After the advent of transition-metal catalyzed C-H
activation reactions using Fe, Ru or Pd catalysts,5 many notable
contributions for the synthesis of 3-acylindoles have appeared
(Scheme 1). Su et al have established the formylation and
acylation of unprotected indoles via Ru/Fe-catalysed oxidative
coupling using anilines as carbonyl source.6 Acylation of free
indoles (NH) has also been achieved with nitriles using Pd
based catalysts by Wang and Song.7 Carbonylation of indoles
to produce 3-acylindole is also accomplished using arylsulfonyl
chloride,8a and arylboronic acids,8b under metal- and metal-
free conditions. Intramolecular oxidative cyclization is also
described using o-alkynylated N,N-dialkylamines under
photochemical, as well as metal- and metal-free conditions.9
Further, α-oxocarboxylic acids are exploited as decarboxylative
coupling partner for the direct acylation of the arene CH
bonds to afford ketones. Wang and Zhang group has
developed an efficient Cu-catalyzed decarboxylative C-3
Su group has lately extended the decarboxylative acylation of
indoles employing potassium 2-oxo-2-phenylacetate by copper
catalysis and liquid-assisted grinding (LAG).12 Due to the high
cost and poor accessibility of phenylglyoxalic acids, it is
imperative to look for a new and easily available acylating
reactant under eco-safe conditions. Alkyl arylacetates have
been recently exploited as synthon by our group for acylation
of nitrobenzene, as well as for cross dehydrogenative and
Some Important Existing Strategies:
1. J. Am. Chem. Soc. 2011, 133, 11924.
O
RuCl3 or FeCl2
H
R2
N
N
R2
TBHP, PivOH, DDQ
R1
H
N
DMSO, 25-50 o
C
R1
H
2. Org. Lett. 2013, 15, 788.
O
R'
Pd(OAc)2 (5 mol%)
2,2'-Bipyridine (6 mol%)
N
R'
D-CSA (1.5 equiv.), H2O
NMA, 120 oC
N
N
R
H
H
R
3. ACS Catal. 2015, 5, 1210.
O
R2
B(OH)2
Pd(OAc)2, I2, KOH
Py, CsF, toluene, CO, 80 o
N
R
C
R1
N
R
R2
R1
4.
O
R2
O
Conditions
OH/K
R2
N
H/R
N
R1
R1
O
H/R
Conditions: a) Cu(OAc)2.H2O, CH3CN, 110 o
C
Chem. Commun. 2013, 49,2368
Green Chem., 2016, 18, 1201
b) Ir, Ni, I2, dtbbpy, base, blue LED
c) Rose bengal, MS, EtOH, air, green LED Green Chem., 2016, 18, 4916
d) Cu(OAc)2.H2O, O2, LAG, CH3CN
Org. Biomol. Chem., 2019, 17, 4446
Our Approach:
O
Ar
Cu(OAc)2 (40 mol%)
KOtBu, DMSO, 110 o
OEt
Ar
N
C
N
X
R
O
X
H
H
R
a. Department of Chemistry, Institute of Science, Banaras Hindu University, Varanasi
221005, India. E-mail: knsingh@bhu.ac.in; knsinghbhu@yahoo.co.in.
(X = CH, N)
Scheme 1. Previous reports and present strategy
Electronic
Supplementary
Information
(ESI)
available:
See
DOI: 10.1039/x0xx00000x
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ARTICLE
Journal Name
decarbethoxylative oxidative coupling,13 wherein activation of The initial reaction was carried out using Cu(OAc)2 (40 mol%)
View Article Online
DOI: 10.1039/C9OB02550B
benzylic methylene is readily brought about by cheap metal and K2CO3 in DMSO under open atmosphere at 110 C which
catalysts or metal-free conditions. In view of the above and as led to the formation of the product 2-methyl-1H-indol-3-
a part of our ongoing research,14 we report herein a yl)(phenyl)methanone (3a) in 35% yield (entry 1). Changing the
regioselective acylation of free indoles (NH) via oxidative base from K2CO3 to DABCO, DBU, K3PO4, NaOH, and KOtBu
decarbethoxylation using inexpensive and readily available (entries 2-6) bettered the yield in all cases; the best being
ethyl arylacetate involving sp3 CH activation by KOtBu. Markedly the reaction without Cu(OAc)2 or KOtBu
Cu(OAc)2/KOtBu in DMSO at 110 C (Scheme 1).
either remained futile or reduced the product yield
considerably (entries 7 & 8). Afterwards, the effect of molar
ratio of the reactants, catalyst loading, base concentration,
and temperature, was examined (entry 9); however, it did not
add any value to the reaction profile. As regards the effect of
medium; different solvents such as DMSO-H2O (3:1), DMF,
DMA, p-xylene, toluene, PEG-600, water, 1,4-dioxane, ethanol
and CH3CN (entries 10-19) were tried in the reaction, but they
all either remained unproductive or could not bypass the
performance of DMSO. Other copper salts such as CuI, Cu2O,
CuCl2.2H2O, and Cu(OAc)2.H2O were also examined (entries 20-
23), but none of them could match the efficacy of Cu(OAc)2.
The reaction using Cu(OAc)2.H2O in the presence of molecular
sieves (4Å) also offered somewhat lower product yield as
compared to Cu(OAc)2 anhydrous. The combination of
Cu(OAc)2 with some other oxidants also remained ineffective
(entries 24 & 25). The replacement of Cu(OAc)2 by DIB
((Diacetoxyiodo)benzene) also stayed of no use (entry 26).
Conclusively, the best result was obtained by using 1:2 molar
ratio of 1a and 2a in the presence of 40 mol% Cu(OAc)2 and 1.0
equiv. KOtBu in DMSO at 110 C under open atmosphere
(entry 6).
Under established conditions, the scope and versatility of the
reaction was then systematically studied using different sets
of indoles/7-azaindole (1) and ethyl arylacetates (2) with
varying substitution patterns, which delivered the products 3a-
3zb in reasonably high yields (Table 2). The reaction of 2-
methylindole with ethyl arylacetates gave somewhat better
yield (3a-3e), but was diminished a little by the presence of
ortho-substituent at the ethyl arylacetate partner (cf. 3b).
Arylacetate containing the thiophene core also participated
nicely in the reaction to give the product 3d in 75% yield. The
reaction of 2-methylindole with ethyl 2-([1,1'-biphenyl]-4-
yl)acetate also gave rise to the product 3e in 71% yield. The
reaction of unsubstituted indole with ethyl phenylacetate as
well as ethyl arylacetates having electron-withdrawing or
electron-donating substituent like halo, nitro, methoxy, and
methyl worked well to afford the products 3f-3n in fairly good
yields. Ethyl arylacetates bearing naphthyl and biphenyl core
nucleus also participated well in the reaction to give the
products 3o and 3p in 67% and 52% yields respectively. As
such no consistent and significant effect of the presence of
electron donating or electron withdrawing substituent at
indole core on the yield of the products was observed (cf. 3q-
3t & 3u-3w). 7-Azaindole was also made to react with different
ethyl arylacetates under the same set of reaction conditions to
afford the products 3z-3zb in good yields. The lower product
yield in some cases may be attributed to the side product
formation such as dimerization of indole, and oxidation of
ethyl arylacetates to form α-oxo-ester.
Results and discussion
In order to optimize the reaction conditions, a model reaction
involving 2-methylindole (1a) and ethyl phenylacetate (2a) was
thoroughly investigated by varying different parameters such
as catalyst, oxidant, base and solvent (Table 1).
Table 1: Optimization of reaction conditionsa
O
OEt
catalyst, base
O
N
solvent
N
H
3a
H
1a
2a
Entry
Catalyst
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
-
Base
Solvent
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
Yield (%)b
35
1
2
3
4
5
6
7
8
9
K2CO3
DABCO
DBU
K3PO4
NaOH
KOtBu
KOtBu
-
60
58
71
72
78
Trace
55
74c, 78d,
78e, 45f,
71g, 68h
53
Cu(OAc)2
Cu(OAc)2
KOtBu
10
Cu(OAc)2
KOtBu
DMSO-
H2O (3:1)
DMF
11
12
13
14
15
16
17
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
KOtBu
K2CO3
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
75
42
Trace
Trace
62
DMA
p-Xylene
Toluene
PEG-600
H2O
-
-
1,4-
dioxane
EtOH
18
19
20
21
22
23
24
25
26
Cu(OAc)2
Cu(OAc)2
CuI
Cu2O
CuCl2.2H2O
Cu(OAc)2.H2O
Cu(OAc)2/ TBHPj
Cu(OAc)2/ K2S2O8
DIB
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
-
-
28f
70
65
51
63, 61i
Trace
-
CH3CN
DMSO
DMSO
DMSO
DMSO
-
j
DMSO
DMSO
KOtBu
-
aReaction conditions: 1a (1 mmol), 2a (2 mmol), catalyst (40 mol%), base (1.0
equiv.), solvent (1mL), temperature 110 °C, 24 h. bIsolated yield after column
c
chromatography. Cu(OAc)2 (20 mol%). dCu(OAc)2 (1.0 equiv.). eBase (2.0 equiv.).
fat 80 C. gat 130 C. h2a (1 mmol). iUsing MS (4Å). jOxidant (2.0 equiv.)
2 | J. Name., 2012, 00, 1-3
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ARTICLE
To get an insight into the reaction mechanism, some control as an oxygen donor besides its role as reactionVmieweAdrtiiuclme O.nlTinoe
DOI: 10.1039/C9OB02550B
experiments in the presence of radical scavengers like TEMPO ascertain the involvement of 3-indolylarylmethane as
and BHT were performed, which completely inhibited the intermediate, the reaction of a separately prepared 3-(4-
reaction thereby implicating a radical pathway (Scheme 2, Eq methoxybenzyl)-1H-indole (VI) was also carried out under the
I). To establish the role of air as oxidant, the reaction was also
standard conditions which led to the formation of the
expected product 3l in 58% yield (Scheme 2, eq. II).
Based on product formation, control experiments, and
existing literature,10,12,13,15 a plausible mechanism is outlined in
Scheme 3. Cu (II) is assumed to get inserted into the C3-H of 1
as well as into the benzylic C-H of 2 to form the species I and II,
which on subsequent reaction with each other form the
intermediate III followed by its aromatization to IV. The
intermediate IV then undergoes reductive elimination to form
the intermediate V, which on decarbethoxylation gives the
molecule VI. The compound VI finally affords the product 3 via
intermediates VII and VIII involving sequential SET and DMSO
participation.
Table 2. Scope and versatility of the reactiona,b
O
Ar
Cu(OAc)2, KOtBu
DMSO, 110 oC
OEt
Ar
N
N
O
X
X
H
H
R
R
3
2
1 (X = CH, N)
Cl
O
O
Cl
O
O
S
N
H
(75%)
N
N
H
(78%)
N
H
Ar
H
3b
3c
3a
(67%)
(73%)
3d
3h
Cu(OAc)
Cu
H
OEt
Ph
Cl
O
O
O
F
O
Cu(OAc)2
O
N
N
N
N
H
(71%)
N
N
H
(72%)
H
N
H
(56%)
H
H
H
Ar
O
1
I
III
3e
3g
3f
(68%)
Cu(OAc)
OEt
Cu
Cl
OEt
OEt
O
Cu(OAc)2
KOtBu
Br
O
O
OMe
NO2
O
O
Ar
Ar
O
2
N
II
N
N
H
H
N
H
3l
N
H
(62%)
Ar
IV
H
O
3i
(55%)
DMSO
Cu(II)
3k
3j
(68%)
(65%)
O
S
Reductive
Elimination
-Me2S
H
3
Ph
O
O
O
Cu(0)
DMSO
N
H
OEt
VIII
Ar
N
H
N
H
3m
N
H
N
Ar
Ar
H
KOtBu,
Cu(OAc)2
Cu(I) Cu(II)
(66%)
3n
3o
(67%)
(63%)
3p
(52%)
O
O
Br
O
O
Cl
O
e
Decarbe-
thoxylation
MeO
MeO
MeO
MeO
N
N
N
H
DMSO
H
H
N
N
H
N
H
N
H
(68%)
H
VII
VI
V
3q
(46%)
O
3s
3r
3t
(72%)
(66%)
O
Cl
O
O
Scheme 3. Plausible mechanism
Br
NC
NC
NC
N
H
N
H
N
H
N
H
3u
3x
(81%)
(71%)
3v
(66%)
3w
(75%)
Conclusions
NO2
OMe
O
O
O
Cl
O
In summary, a new and simple method for the synthesis of 3-
acylindoles has been developed via oxidative
Br
N
H
(62%)
N
N
H
(58%)
N
N
N
H
N
3zb
H
3z
)
(71%
3za
decarbethoxylation of bench stable and readily available ethyl
arylacetates using Cu(OAc)2 and KOtBu. The strategy involves
in situ removal of ester group as well as oxidative C-3 acylation
of free indoles (N-H), and offers a valuable method to access 3-
acylindoles.
3y
(73%)
aReaction conditions: 1 (1mmol), 2 (2 mmol), Cu(OAc)2 (40 mol%), KOtBu (1.0
equiv.), DMSO (1mL), 110 C, 24 h. bIsolated yield after column chromatography.
investigated under N2 atmosphere which did not suppress the
product yield at all (eq. I). The DMSO was thus assumed to act
OEt
Standard conditions
3a
(I)
Experimental Section
O
N
H
(0%) using TEMPO/BHT
(78%) under N2
General Information
OMe
OMe
O
All the reagents were purchased from Alfa Aesar or Merck, and
were used as received. The reactions were monitored by thin
layer chromatography (TLC) using Merck Kieselgel 60GF 254
plates (thickness 0.25 mm). Visualization of TLC was performed
using UV light, and the product purification was done using
Merck silica gel (100-200 mess) column chromatography. NMR
Standard conditions
(II)
N
H
N
H
VI
3I
(58%)
Scheme
2.
Control
Experiments
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J. Name., 2013, 00, 1-3 | 3
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Journal Name
(d, J = 7.5 Hz, 2H), 7.70-7.74 (m, 3H), 7.85 (t, J = 8.0 Hz, 1H),
DOI: 10.1039/C9OB02550B
8.10 (s, 1H), 8.62 (d, J = 8.5 Hz, 1H), 11.97 (s, 1H); C NMR
spectra were recorded with a 500 MHz spectrometer (JNM-
ECZ500R/S1) for 1H NMR, and 126 MHz for 13C NMR
spectroscopy using DMSO-d6 solution. Chemical shifts are
given in δ ppm and are measured relative to tetramethylsilane
(TMS) as internal standard. Mass spectra were recorded on
SCIEX X500R QTOF (TOF-MS).
View Article Online
13
(126 MHz, DMSO-d6) δC = 24.4, 90.0, 117.4, 119.9, 124.7,
124.8, 125.7, 126.7, 127.3, 127.7, 128.9, 136.1, 138.3, 139.3,
140.6, 152.5, 169.8, 196.0; HRMS: (M+H)+ calcd. for C22H18NO:
312.1388; found: 312.1378.
(1H-Indol-3-yl)(phenyl)methanone (3f).10b Yellow solid (68%,
General procedure for the synthesis of 3-acylindoles (3)
1
150 mg); H NMR (500 MHz,DMSO-d6) δH = 7.22-7.28 (m, 2H),
A mixture of indole/7-azaindole 1 (1.0 mmol), ethyl arylacetate
2 (2.0 mmol), KOtBu (1.0 equiv.), Cu(OAc)2 (40 mol %) and
DMSO (1mL) was stirred in a glass vessel at 110 C for 24 h
under open atmosphere [Open atmosphere simply means the
reaction without any special precautions to make it free from
air]. After completion of reaction (as indicated by TLC), the
mixture was quenched with aqueous NaHCO3 saturated
solution (5 mL), and then extracted with diethyl ether (3 × 5
mL). The combined organic phase was dried over anhydrous
sodium sulfate, concentrated under reduced pressure, and
then purified by silica gel column chromatography using a
mixture of EtOAc and n-hexane (1:4) to give the pure product
3.
7.51-7.55 (m, 3H), 7.59-7.62 (m, 1H), 7.77 (d, J = 7.5 Hz, 2H),
7.92 (d, J = 3.0 Hz, 1H), 8.24 (d, J = 7.5 Hz, 1H), 12.06 (s, 1H);
13C NMR (126 MHz, DMSO-d6) δC = 112.2, 115.0, 121.4, 121.9,
123.1, 126.2, 128.3, 128.4, 131.0, 135.8, 136.7, 140.5, 190.0.
(4-Chlorophenyl)(1H-indol-3-yl)methanone (3g).10b Yellow
1
solid (72%, 183 mg); H NMR (500 MHz, DMSO-d6) δH = 7.17-
7.22 (m, 2H), 7.46 (d, J = 7.5 Hz, 1H), 7.52 (d, J = 8.5 Hz, 2H),
7.73 (d, J = 8.5, 2H), 7.90 (d, J = 3.0 Hz, 1H), 8.17 (d, J = 7.5,
1H), 12.06 (s, 1H); 13C NMR (126 MHz, DMSO-d6) δC = 112.3,
114.8, 121.4, 122.1, 123.3, 126.2, 128.5, 130.3, 135.9, 136.0,
136.8, 139.1, 188.7.
(4-Fluorophenyl)(1H-indol-3-yl)methanone (3h).7a Reddish
1
yellow solid (56%, 133 mg); H NMR (500 MHz, DMSO-d6) δH =
(2-Methyl-1H-indol-3-yl)(phenyl)methanone (3a).10b Yellow
solid (78%, 183 mg); 1H NMR (500 MHz, DMSO-d6) δH = 2.37 (s,
3H), 6.99 (t, J = 7.5 Hz, 1H), 7.10 (t, J = 7.5 Hz, 1H), 7.31 (d, J =
8.0 Hz, 1H), 7.37 (d, J = 8.0 Hz, 1H), 7.49 (t, J = 7.5 Hz, 2H), 7.57
(t, J = 10.0 Hz, 3H), 11.95 (br s, 1H, NH); 13C NMR (126 MHz,
DMSO-d6) δC = 14.1, 111.2, 112.4, 120.0, 120.9, 121.8, 127.2,
128.0, 128.3, 131.0, 134.9, 141.6, 144.4, 191.7.
7.22-7.26 (m, 2H), 7.34-7.37 (m,2H), 7.51 (d, J = 8.0 Hz, 1H),
7.85-7.88 (m, 2H), 7.95 (d, J = 3.0 Hz, 1H), 8.22 (d, J = 7.5 Hz,
1H), 12.09 (s, 1H); 13C NMR (126 MHz, DMSO-d6) δC = 112.7,
115.3, 115.7, 115.9, 121.9 122.4, 123.7, 126.7, 131.5, 131.6,
136.3, 137.2, 137.5, 189.0; 19F (470 MHz, DMSO-d6) δF = -
109.31.
(2-Chlorophenyl)(1H-indol-3-yl)methanone (3i).11b Reddish
1
(2-Chlorophenyl)(2-methyl-1H-indol-3-yl)methanone
(3b).
brown solid (55%, 140 mg); H NMR (500 MHz, DMSO-d6) δH =
Yellow solid (67%, 180 mg); 1H NMR (500 MHz, DMSO-d6) δH =
2.26 (s, 3H), 7.03 (t, J = 7.5 Hz, 1H), 7.12 (t, J = 7.5 Hz, 1H),
7.35-7.39 (m, 3H), 7.46-7.53 (m, 2H), 7.57 (d, J = 8.0 Hz, 1H),
12.09 (s, 1H); 13C NMR (126 MHz, DMSO-d6) δC = 13.8, 111.3,
112.4, 119.8, 121.6, 122.2, 126.9, 127.6, 127.7, 128.9, 129.6,
130.5, 135.0, 141.9, 146.2, 188.5; HRMS : (M+H)+ calcd. for
C16H1335ClNO: 270.0686; found: 270.0674.
7.23-7.28 (m, 2H), 7.45-7.58 (m, 5H), 7.64 (s, 1H), 8.14 (d, J =
7.0 Hz, 1H), 12.12 (s, 1H); 13C NMR (126 MHz, DMSO-d6) δC =
112.5, 116.0, 121.1, 122.2, 123.3, 125.3, 127.0, 128.6, 129.6,
129.7, 130.6, 136.9, 137.0, 140.2, 188.2.
(4-Bromophenyl)(1H-indol-3-yl)methanone (3j).10b Reddish
1
yellow solid (68%, 202 mg); H NMR (500 MHz, DMSO-d6) δH =
7.22-7.28 (m, 2H), 7.51 (d, J = 7.5 Hz, 1H), 7.73 (s, 4H), 7.96 (d,
J = 2.5 Hz, 1H), 8.23 (d, J = 7.5 Hz, 1H), 12.12 (s, 1H), 13C NMR
(126 MHz, DMSO-d6), δC = 112.2, 114.7, 121.4, 122.0, 123.2,
124.7, 126.1, 130.4, 131.4, 136.0, 136.7, 139.4, 188.7.
(4-Chlorophenyl)(2-methyl-1H-indol-3-yl)methanone
(3c).7a
Brownish yellow solid (73%, 196 mg); 1H NMR (500 MHz,
DMSO-d6) δH = 2.38 (s, 3H), 7.01 (t, J = 7.5 Hz, 1H), 7.10 (t, J =
7.5 Hz, 1H), 7.32 (d, J = 8.0 Hz, 1H), 7.38 (d, J = 8.0 Hz, 1H), 7.55
(dd, J = 8.0 Hz, J = 32.5 Hz, 4H), 11.97 (s, 1H); 13C NMR (126
MHz, DMSO-d6) δC = 14.2, 111.3, 112.2, 119.9, 121.1, 121.9,
127.1, 128.5, 130.0, 135.0, 135.8, 140.2, 144.7, 190.3.
(1H-Indol-3-yl)(4-nitrophenyl)methanone (3k).10b Reddish
1
yellow solid (62%, 165 mg); H NMR (500 MHz, DMSO-d6) δH =
7.28 (d, J = 4.5 Hz, 2H), 7.53 (d, J = 6.0 Hz, 1H), 7.99 (d, J = 7.5,
3H), 8.26 (d, J = 6.5, 1H), 8.35 (d, J = 7.5 Hz, 2H), 12.25 (s, 1H),
13C NMR (126 MHz DMSO-d6) δC = 112.4, 114.8, 121.4, 122.2,
123.5, 123.6, 125.9, 129.6, 136.8, 136.9, 145.9, 148.6, 188.1.
(1H-Indol-3-yl)(4-methoxyphenyl)methanone (3l).12 Reddish
(2-Methyl-1H-indol-3-yl)(thiophen-3-yl)methanone
(3d).
Reddish yellow solid (75%, 180 mg); 1H NMR (500 MHz, DMSO-
d6) δH = 2.43 (s, 3H), 7.02 (t, J = 7.5 Hz, 1H), 7.10 (t, J = 7.5 Hz,
1H), 7.37 (d, J = 6.0 Hz, 2H), 7.47 (d, J = 8.0 Hz, 1H), 7.63 (t, J =
3.5, 1H), 7.99 (s, 1H), 11.87 (s, 1H); 13C NMR (126 MHz, DMSO-
d6) δC = 14.0, 111.1, 113.4, 119.9, 120.8, 121.7, 126.6, 127.1,
127.5, 130.8, 134.9, 143.4, 144.1, 185.5; HRMS : (M+H)+ calcd.
for C14H12NOS: 242.0640; found: 242.0631.
1
yellow solid (65%, 163 mg); H NMR (500 MHz, DMSO-d6) δH =
3.85 (s, 3H), 7.06 (d, J = 8.5 Hz, 2H), 7.20-7.26 (m, 2H), 7.51 (d,
J = 7.5 Hz, 1H), 7.80 (d, J = 8.5 Hz, 2H), 7.94 (d, J = 2.5 Hz, 1H),
8.22 (d, J = 7.5 Hz, 1H), 12.01 (s, 1H); 13C NMR (126 MHz,
DMSO-d6) δC = 55.3, 112.1, 113.6, 115.0, 121.4, 121.6, 122.9,
126.4, 130.5, 132.9, 134.8, 136.6, 161.7, 188.7.
(1H-Indol-3-yl)(p-tolyl)methanone (3m).7a Reddish yellow
solid (66%, 146 mg); 1H NMR (500 MHz, DMSO-d6) δH = 2.40 (s,
[1,1'-Biphenyl]-4-yl(2-methyl-1H-indol-3-yl)methanone (3e).
Reddish yellow solid (71%, 220 mg); 1H NMR (500 MHz, DMSO-
d6) δH = 1.98 (s, 3H), 7.32-7.37 (m, 2H), 7.43-7.46 (m, 3H), 4.64
4 | J. Name., 2012, 00, 1-3
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3H), 7.20 (quin, J = 7.0 Hz, 2H ), 7.33 (d, J = 7.5 Hz, 2H), 7.50 (d, 117.1, 124.9, 125.3, 125.5, 126.2, 126.6, 126.7, 128.2, 129.5,
View Article Online
+
DOI: 10.1039/C9OB02550B
J = 7.5 Hz, 1H), 7.69 (d, J = 7.5 Hz, 2H), 7.92 (d, J = 2.5, 1H), 8.22 130.0, 132.0, 133.6, 136.7, 138.4, 155.9, 191.4; HRMS: (M+H)
(d, J = 7.5 Hz, 1H), 12.03 (s, 1H); 13C NMR (126 MHz, DMSO-d6) calcd. for C20H16NO2: 302.1181; found: 302.1172.
δC = 21.0, 112.2, 115.0, 121.4, 121.8, 123.0, 126.3, 128.5,
3-Benzoyl-1H-indole-5-carbonitrile (3u).11b Greenish yellow
(81%, 199 mg); H NMR (500 MHz, DMSO-d6) δH = 7.56 (d, J =
1
128.9, 135.4, 136.6, 137.8, 141.0,190.4.
(1H-Indol-3-yl)(o-tolyl)methanone (3n).7a Reddish yellow solid 6.0 Hz, 2H), 7.63 (d, J = 6.5 Hz, 2H), 7.69 (d, J = 7.5 Hz, 1H), 7.82
(63%, 148 mg); 1H NMR (500 MHz, DMSO-d6) δH = 2.27 (s, 3H), (d, J = 6.0 Hz, 2H), 8.18 (s, 1H), 8.61 (s, 1H), 12.54 (s, 1H); 13C
7.21-7.27 (m, 4H), 7.37-7.41 (m, 2H), 7.50 (d, J = 8.0 Hz, 1H), NMR (126 MHz, DMSO-d6) δC = 104.1, 113.7, 115.0, 120.1,
7.59 (d, J = 3.0, 1H), 8.18 (d, J = 7.5 Hz, 1H), 12.01 (s,1H); 13C 126.0, 126.5, 128.4, 128.5, 131.5, 137.8, 138.5, 139.6,141.5,
NMR (126 MHz, DMSO-d6) δC = 19.1, 112.3, 116.5, 121.2, 189.8.
122.0, 123.1, 125.2, 125.6, 127.1, 129.1, 130.5, 134.7, 136.2,
136.9, 141.0, 192.1.
3-(4-Chlorobenzoyl)-1H-indole-5-carbonitrile (3v). Yellow solid
(66%, 185 mg); H NMR (500 MHz, DMSO-d6) δH = 7.60 (d, J =
(1H-Indol-3-yl)(naphthalen-1-yl)methanone (3o).16a Reddish 8.0 Hz, 2H), 7.63 (d, J = 8.5 Hz, 1H), 7.70 (d, J = 8.5 Hz, 1H), 7.83
1
1
yellow solid (67%, 181 mg); H NMR (500 MHz, DMSO-d6) δH (d, J = 8.0 Hz, 2H), 8.20 (s, 1H), 8.60 (s, 1H), 12.58 (s, 1H); 13C
=7.27 (t, J = 3.5 Hz, 2H), 7.49-7.57 (m, 3H), 7.60 (t, J = 7.0 Hz, NMR (126 MHz, DMSO-d6) δC = 104.3, 113.8, 114.9, 120.1,
1H), 7.67-7.70 (m, 2H), 8.0 (t, J = 8.0 Hz, 2H), 8.07 (d, J = 8.5 Hz, 126.0, 126.2, 126.5, 128.6, 130.4, 136.4, 138.0, 138.3, 138.6,
1H), 8.29 (d, J = 6.0 Hz, 1H), 12.06 (s, 1H); 13C NMR (126 MHz, 188.6; HRMS: (M+H)+ calcd. for C16H1035ClN2O: 281.0482;
DMSO-d6) δC = 112.4, 117.1, 121.4, 122.2, 123.3, 124.9, 125.3, found: 281.0472.
125.7, 125.8, 126.2, 126.7, 128.3, 129.6, 130.1, 133.3, 136.7,
137.0, 138.6, 191.3.
3-(4-Methylbenzoyl)-1H-indole-5-carbonitrile
(3w). Light
yellow solid (75%, 195 mg); 1H NMR (500 MHZ, DMSO-d6) δH =
[1,1'-Biphenyl]-4-yl(1H-indol-3-yl)methanone (3p).12 Reddish 2.37 (s, 3H), 7.31 (d, J =8.0 Hz, 2H), 7.58 (d, J = 8.5 Hz, 1H), 7.65
1
yellow solid (52%, 154 mg); H NMR (500 MHz, DMSO-d6) δH = (d, J = 8.5 Hz, 1H), 7.69 (d, J = 7.5, 2H), 8.14 (s, 1H), 8.56 (s, 1H),
7.23-7.29 (m, 2H), 7.41 (t, J = 7.5 Hz,1H), 7.50-7.54 (m, 3H), 12.47 (s, 1H); 13C NMR (126 MHz,DMSO-d6) δC = 21.0, 104.0,
7.54 (d, J = 7.5 Hz, 2H), 7.82 (d, J = 8.5 Hz, 2H), 7.88 (d, J = 8.0 113.7, 115.1, 120.1, 125.9, 126.1, 126.5, 128.6, 129.0, 136.9,
Hz, 2H), 8.01 (d, J = 3.5 Hz, 1H), 8.27 (d, J = 7.5 Hz, 1H), 12.01 137.4, 138.5, 141.7, 189.4; HRMS: (M+H)+ calcd. for C17H13N2O:
(s, 1H); 13C NMR (126 MHz, DMSO-d6) δC = 112.7, 115.5, 122.0, 261.1028; found: 261.1015.
122.4, 123.6, 126.8, 127.1, 127.4, 128.5, 129.4, 129.6, 129.7,
136.2, 137.2, 139.8, 143.1, 189.9.
(5-Bromo-1H-indol-3-yl)(phenyl)methanone (3x).12 Yellow
solid (71%, 211 mg); H NMR (500 MHz, DMSO-d6) δH = 7.39
(5-Methoxy-1H-indol-3-yl)(phenyl)methanone (3q).10b Light (d, J = 8.5 Hz, 1H), 7.49 (d, J = 9.0 Hz, 1H), 7.53 (t, J = 7.5 Hz,
1
yellow solid (46%, 115 mg); 1H NMR (500 MHZ, DMSO-d6) δH
=
2H), 7.60 (t, J = 7.5 Hz, 1H), 7.78 (d, J = 7.0 Hz, 2H), 8.01 (d, J =
3.80 (s, 3H), 6.88-6.90 (m, 1H), 7.40, (d, J = 9.0 MHz, 1H), 7.52 2.0 Hz, 1H), 8.39 (s, 1H), 12.25 (s, 1H); 13C NMR (126 MHz,
(t, J = 8.0 Hz, 2H), 7.58 (t, J = 7.5 Hz, 1H), 7.76 (q, J = 7.0 Hz, DMSO-d6) δc = 114.3, 114.4, 114.7, 123.6, 125.7, 128.0, 128.4,
3H), 7.86 (d, J = 2.0 Hz, 1H), 11.98 (s, 1H); 13C NMR (126 MHz, 128.5, 131.3, 135.4, 136.8, 140.0, 189.8.
DMSO-d6) δC = 55.2, 103.1, 112.9, 113.0, 114.8, 127.0, 128.2,
128.3, 130.9, 131.5, 135.9, 140.6, 155.5, 189.9.
(5-Bromo-1H-indol-3-yl)(3-nitrophenyl)methanone
(3y).
Yellow solid (58%, 200 mg); 1H NMR (500 MHz, DMSO-d6) δH =
(4-Bromophenyl)(5-methoxy-1H-indol-3-yl)methanone (3r).10b 7.42 (d, J = 8.5 Hz, 1H), 7.52 (d, J = 8.5 Hz, 1H), 7.82 (t, J = 7.5
Yellow solid (72%, 237 mg); 1H NMR (500 MHz, DMSO-d6) δH
=
Hz, 1H), 8.16 (d, J = 2.5 Hz, 1H), 8.22 (d, J = 7.5 Hz, 1H), 8.41-
3.80 (s, 3H), 6.89-6.91 (m, 1H), 7.41 (d, J = 8.5 Hz, 1H), 7.70- 8.48 (m, 3H), 12.41 (s, 1H); 13C NMR (126 MHz, DMSO-d6) δC =
7.77 (m, 5H), 7.90 (d, J = 3.5 Hz, 1H), 12.01 (s, 1H); 13C NMR 114.0, 114.5, 115.0, 123.0, 123.5, 125.7, 126.1, 127.8, 130.3,
(126 MHz, DMSO-d6) δC = 55.3, 103.1, 113.0, 113.1, 114.6, 134.6, 135.6, 137.7, 141.1, 147.7, 187.3; HRMS: (M-H)- calcd.
124.6, 126.9, 130.3, 131.4, 131.5, 136.1, 139.6, 155.6, 188.6.
for C15H879BrN2O3: 342.9718; found: 342.9721.
(4-Chlorophenyl)(5-methoxy-1H-indol-3-yl)methanone (3s).10b
Phenyl(1H-pyrrolo[2,3-b]pyridin-3-yl)methanone
(3z).16b
Yellow solid (68%, 194 mg); 1H NMR (500 MHz, DMSO-d6) δH = Yellow solid (71%, 157 mg); H NMR (500 MHz, DMSO-d6) δH =
3.80 (s, 3H), 6.89 (d, J = 7.5 Hz, 1H), 7.40 (d, J = 9.0 Hz, 1H), 7.26 (s, 2H), 7.49 (t, J = 7.5 Hz, 2H), 7.56 (t, J = 6.5 Hz, 1H), 7.77
7.58 (d, J = 8.0 Hz, 2H), 7.77-7.79 (m, 3H), 7.90 (d, J = 2.5 Hz, (d, J = 7.5 Hz, 2H), 8.04 (s, 1H), 8.49 (d, J = 7.5 Hz, 1H), 12.60 (s,
1H), 12.02 (s, 1H); 13C NMR (126 MHz, DMSO-d6) δC = 55.3, 1H); 13C NMR (126 MHz, DMSO-d6) δC = 113.6, 118.2, 118.7,
103.2, 113.0, 113.1, 114.6, 127.0, 128.5, 130.2, 131.5, 135.7, 128.2, 128.5, 129.8, 131.4, 135.8, 139.6, 144.5, 149.0, 189.2.
1
136.1, 139.2, 155.6, 188.6.
(4-Methoxyphenyl)(1H-pyrrolo[2,3-b]pyridin-3-yl)methanone
(5-Methoxy-1H-indol-3-yl)(naphthalen-1-yl)methanone (3t). (3za). Yellow solid (62%, 156 mg); 1H NMR (500 MHz, DMSO-d6)
Reddish brown solid (66%, 198 mg); 1H NMR (500 MHz, DMSO- δH = 3.83 (s, 3H), 7.05 (d, J = 9.0 Hz, 2H), 7.25 (q, J = 4.5 Hz, 1H),
d6) δH = 3.85 (s, 3H), 6.91 (d, J = 9.0 Hz, 1H), 7.41 (d, J = 8.5 Hz, 7.80 (d, J = 9.0Hz, 2H), 8.06 (s, 1H), 8.34 (d, J = 3.0 Hz, 1H), 8.47
1H), 7.50-7.62 (m, 4H), 7.66 (d, J = 7.0 Hz, 1H), 7.82 (s, 1H), (m, 1H), 12.56 (s, 1H); 13C NMR (126 MHz, DMSO-d6) δC = 55.4,
7.99 (t, J = 9.5 Hz, 2H), 8.06 (d, J = 8.0 Hz, 1H), 11.94 (s, 1H); 13
C
113.7, 113.8, 118.0, 129.9, 130.8, 132.0, 134.9, 141.3, 144.3,
NMR (126 MHz, DMSO-d6) δC = 55.2, 103.2, 113.0, 113.1,
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Journal Name
148.8, 162.0, 188.5; HRMS: (M+H)+ calcd. for C15H13N2O2:
253.0977; found: 253.0946.
8
9
(a) X. Li, D. Liang, W. Huang, H. Zhou, Z. Li, B.ViWewaAnrtgic,leYOnMlinae
and H Wang, Tetrahedron., 2016, 72, 8442, (b) M. N. Zhao, L.
DOI: 10.1039/C9OB02550B
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2015, 5, 1210.
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2014, 16, 3264; (b) A. Gogoi, S. Guin, S.K Rout and B. K. Patel,
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10445.
(4-Chlorophenyl)(1H-pyrrolo[2,3-b]pyridin-3-yl)methanone
(3zb). Yellow solid (73%, 187 mg); 1H NMR (500 MHz, DMSO-d6)
δH = 7.29 (q, J = 4.5 Hz, 1H), 7.59 (d, J = 8.0 Hz, 2H), 7.82 (d, J =
8.0 Hz, 2H), 8.13 (s, 1H), 8.39 (s, 1H), 8.52 (d, J = 7.5 Hz, 1H),
12.71 (s, 1H); 13C NMR (126 MHz, DMSO-d6) δC = 113.4, 118.3,
118.7, 128.6, 129.8, 130.4, 136.1, 136.2, 138.2, 144.5, 149.0,
188.6; HRMS: (M+H)+ calcd. for C14H1035ClN2O: 257.0482;
Found: 257.0447.
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Conflicts of interest
“There are no conflicts to declare”.
Acknowledgements
We are thankful to CSIR, New Delhi for financial support (Ref.
No. 02(0285)/16/EMR-II) and for Junior Research Fellowship to
one of us (AJ).
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6 | J. Name., 2012, 00, 1-3
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