Pd-catalyzed direct C2-acylation and C2,C7-diacylation of indoles: Pyrimidine as an easily removable C-H directing group

Article abstract of DOI:10.1039/c4ra15162c

Pyrimidine is successfully used as an easily removable C(sp²)-H directing group for the synthesis of 2-acyl indoles and 2,7-diacyl indoles through direct C-H functionalization using a Pd-catalyst from 1-(pyrimidin-2-yl)-1H-indoles and aldehydes. Easy removal of the pyrimidine directing group using EtONa in DMSO provides C2-acyl indoles.

Full text of DOI:10.1039/c4ra15162c

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Pd-catalyzed direct C2-acylation and C2,C7-
diacylation of indoles: pyrimidine as an easily
Cite this: RSC Adv., 2015, 5, 28292
removable C–H directing group†
*
Govindharaj Kumar and Govindasamy Sekar
Received 24th November 2014
Accepted 12th March 2015
Pyrimidine is successfully used as an easily removable C(sp2)–H directing group for the synthesis of 2-acyl
indoles and 2,7-diacyl indoles through direct C–H functionalization using a Pd-catalyst from 1-(pyrimidin-
2-yl)-1H-indoles and aldehydes. Easy removal of the pyrimidine directing group using EtONa in DMSO
provides C2-acyl indoles.
DOI: 10.1039/c4ra15162c
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directed the acyl group to the less reactive C2 position of indole
ring yielding 43% of expected selective C2-acylated product 3a
Introduction
Transformation of unactivated C(sp2)–H bonds to C(sp2)–C
and C(sp2)-hetero atom bonds is one the most important
chemical transformations in synthetic chemistry.1 Transition
metal catalysts such as Rh, Ru, Pd, Cu, Fe, etc. play vital roles in
C–H bond functionalization reactions. Particularly, Pd
compounds occupy a central role as a catalyst for C–H bond
functionalization reactions.2 The nature of the directing
groups play a crucial role in the activation of unactivated C–H
bonds.3 Easily removable directing groups add more advan-
tages to C–H bond functionalization reactions.4 Herein, we
report, direct C2-acylation and C2,C7-diacylation of N-pyrimi-
dine substituted indoles to synthesize C2-acyl and C2,C7-diacyl
indoles using a Pd-catalyst and aldehyde as an acyl source
(Scheme 1).
Table 1 Optimization for Pd-catalyzed C2-acylation of indole using
pyrimidine directing groupa
Entry Pd salt
Oxidant Solvent
Time (h) Yieldb (%)
1
2
3
4
5
6
7
8
Pd(OAc)2
PdCl2
Pd(CH3CN)2Cl2 TBHP
Pd(PPh3)2Cl2
Pd(TFA)2
Pd2(dba)3
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
TBHP
TBHP
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
THF
DMF
Benzene 15
Toluene 12
Dioxane 24
DCE 24
Hexanes 24
Toluene
Toluene
Toluene
24
12
24
24
24
24
36
36
36
36
36
26
36
43
70
47
20
55
51
40
22
20
14
17
21
<5
62
80
44
60
26
67c
00
00
The direct C–H bond functionalization of indole was started
with 1-(pyrimidin-2-yl)-1H-indole 1a. The initial reaction was
carried out with 10 mol% of Pd(OAc)2 in chlorobenzene at 90 ꢀC
using benzaldehyde 2a as acyl source in the presence of tert-
butyl hydrogen peroxide (TBHP) oxidant.5 The pyrimidine group
TBHP
TBHP
TBHP
DTBP
TBPB
H2O2
O2
K2S2O8
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
—
9
10
11
12
13
14
15
16
17
18
19
20
21
Scheme 1 Pd-catalyzed direct C2-acylation and C2,C7-diacylation of
indoles using removable pyrimidine directing group.
12
25
26
—
PdCl2
Department of Chemistry, Indian Institute of Technology Madras, Chennai, Tamil
Nadu-600 036, India. E-mail: gsekar@iitm.ac.in; Web: http://chem.iitm.ac.in/faculty/
sekar/
a
Reaction condition: 1a (0.5 mmol), 2a (0.75 mmol), and 70% of aq.
TBHP. b Isolated yield. c TBHP (5.0 equiv.).
† Electronic supplementary information (ESI) available: Copy of all the
compounds 1H and 13C spectra. See DOI: 10.1039/c4ra15162c
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(Table 1, entry 1). In this reaction, neither C3-acylation nor C7-
Aer successful optimizing the reaction conditions for the
acylation product was observed. To increase the efficiency of synthesis of C2-acylated indole, the substrate scope of this
this pyrimidine directed C2-acylation reaction, several Pd-salts synthetic methodology was examined and the results are
were screened and among them PdCl2 provided a maximum summarized in Table 2. Both electron-releasing (3c) and
of 70% isolated yield of 3a (entry 2).
electron-withdrawing group (3d and 3e) containing aromatic
Then the reaction was screened with several oxidants such as aldehydes yielded the corresponding 2-acylated products in
di-tert-butyl peroxide, tert-butyl peroxybenzoate (TBPB), H2O2 moderate to good yields. Sterically hindered 1-naphthyl alde-
etc. and all of them gave inferior result compared with TBHP hyde also gave C2-acylated product in 79% yield (3b). Hetero-
(entries 6–11). Solvent screening (entries 12–18) was fruitful and aromatic aldehydes such as furan-2-carbaldehyde and
toluene provided a maximum of 80% isolated yield of 3a (entry thiophene-2-carbaldehyde also provided the corresponding
15). Increasing the quantity of TBHP reduced the efficiency of C–H activation product in good yields (3f and 3i). Electron-
the C–H activation reaction. And the reaction without Pd- releasing and electron-withdrawing groups at 5th position of
catalyst or oxidant TBHP failed to yield any 2-acylation indole also yielded the C2-acylated product in moderate yield
product (entries 20 and 21).
range (3g and 3h). Sterically hindered ortho-substituted alde-
hyde, aliphatic aldehyde, cyclic and a–b unsaturated aldehydes
were yielded the expected acylated product in good yield (3k, 3l,
3m and 3n). When a mixture of benzaldehyde and acetaldehyde
were used for acylation, only C2-benzoylated indole was selec-
tively obtained. In this reaction condition, acylation took place
neither at C2 position nor at C7 position of indole ring.
Table 2 Pd-catalyzed direct C2-acylation of indoles using removable
pyrimidine directing groupa
Usage of excess (3 equiv.) aldehyde under same reaction
conditions yielded symmetric C2,C7-diacylated product
4
through functionalization of C2 and C7 C–H bonds with good
yields. Acylation of two different aldehydes (1.5 equiv. each) one
aer another aldehyde yielded unsymmetric diacylated prod-
ucts 5. These results clearly shows that in indole molecule,
pyrimidine group functionalize both C2 and C7 C–H bonds
whereas C2 C–H bond functionalization is more facile than C7
C–H bond of indole moiety (Scheme 2).
When pyrrole and carbazole were used instead of indole
molecule, both of them gave mixture of mono and diacylated
products as both the C2 and C5 C–H bonds of pyrrole and C2
and C8 C–H bonds of carbazole are identical for C–H func-
tionalization. Using excess of benzaldehyde with N-pyrimidine
protected carbazole, the reaction gave C2 and C8-dibenzoylated
carbazole (7) with 65% isolated yield (Scheme 3).
The pyrimidine group in acylated indole molecule could be
easily removed as shown in Scheme 4.6 Reaction of 3a–c with
EtONa in DMSO yielded 2-acylated indole 8a–c. In this C–H
acylation, the palladium catalyst will coordinate with pyrimi-
dine nitrogen before activating nearby C–H bond. In the pres-
ence of Pd catalyst and TBHP, acyl radical will be generated
from aldehyde7 which will be attached to Pd catalyst. Reductive
elimination of palladium complex should yield C2-acylated
indole. In the presence of excess aldehyde, the mono acylated
a
Reaction condition: 1a (0.5 mmol), 2a (0.75 mmol), and 70% of aq.
Scheme 2 Double C–H functionalization using pyrimidine directing
TBHP in toluene (2 mL). All of them are isolated yield.
group.
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heated at 90 ꢀC. The progress of the reaction was monitored by
TLC. Upon disappearance of indole, the reaction mixture was
brought to room temperature. The reaction mixture was dis-
solved in ethyl acetate (30 mL), and washed with saturated
solution of sodium bicarbonate (2 ꢂ 10 mL). The combined
organic layers were dried with Na2SO4. The organic solvent was
evaporated under reduced pressure and the resulting crude
product was puried by silica gel column chromatography
(hexanes–ethyl acetate) to give the desired acylation product.
The product was conrmed by 1H and 13C NMR, FT-IR and
HRMS spectroscopic analysis.
Scheme
directing group.
3 C–H functionalization of carbazole using pyrimidine
Typical experimental procedure for C2,C7-acylation. Indole
(0.5 mmol, 97.6 mg), PdCl2 (0.05 mmol, 8.9 mg), benzaldehyde
(3 equiv.), TBHP (2.5 mmol, 321 mL, 70% equiv.) and toluene (2
mL) were taken in a reaction tube. The reaction mixture was
heated at 90 ꢀC. The progress of the reaction was monitored by
TLC. Upon disappearance of indole, the reaction mixture was
brought to room temperature. The reaction mixture was dis-
solved in ethyl acetate (30 mL), and washed with saturated
solution of sodium bicarbonate (2 ꢂ 10 mL). The combined
organic layers were dried with Na2SO4. The organic solvent was
evaporated under reduced pressure and the resulting crude
product was puried by silica gel column chromatography
(hexanes–ethyl acetate) to give the desired acylation product.
The product was conrmed by 1H and 13C NMR, FT-IR and
HRMS spectroscopic analysis.
Typical experimental procedure for unsymmetrical acyla-
tion. Monosubstituted indole 3a (0.33 mmol, 100 mg), PdCl2
(0.033 mmol, 5.9 mg), aldehyde (Ar00-CHO) (1.5 equiv.), TBHP
(0.99 mmol, 127 mL, 70% aq.) and toluene (2 mL) were taken in a
reaction tube. The reaction mixture was heated at 90 ꢀC. The
progress of the reaction was monitored by TLC. Upon disap-
pearance of indole 3a, the reaction mixture was brought to room
Scheme
directing group.
4 Synthesis of 2-acyl indole by removal of pyrimidine
indole will be acylated at C7 position. This result shows that
functionalization at C2 position is easier than functionalization
of indole at C7 which is slightly far from indole nitrogen atom.
Conclusions
In conclusion, we have demonstrated an efficient methodology
using Pd-catalyst for the synthesis of C2-acylated indole using
pyrimidine as directing group. Usage of excess aldehyde
provides C2,C7-diacylated indole through double C–H func-
tionalization reaction. Easily removal of pyrimidine directing
group using EtONa in DMSO yields C2-acyl indoles.
Typical experimental procedure
General considerations. All the reactions were carried out in temperature. The reaction mixture was dissolved in ethyl
reaction tubes. All the solvents were obtained from Merck or acetate (30 mL), and washed with saturated solution of sodium
RANKEM chemicals. Reactions were monitored by Thin-layer bicarbonate (2 ꢂ 10 mL). The combined organic layers were
Chromatography (TLC) using Merck silica gel 60 F254 pre- dried with Na2SO4. The organic solvent was evaporated under
coated plates (0.25 mm) and visualized by UV uorescence reduced pressure and the resulting crude product was puried
quenching using appropriate mixture of ethyl acetate and by silica gel column chromatography (hexanes–ethyl acetate) to
hexanes. PdCl2, TBHP were purchased from Sigma Aldrich give the desired acylation product. The product was conrmed
1
chemicals. Benzaldehyde was distilled before use. Other alde- by H and 13C NMR, FT-IR and HRMS spectroscopic analysis.
hydes were used as received. All the 2-pyrimidine indoles were
Typical experimental procedure for removal of pyrimidine
prepared according to the literature procedure.8 Silica gel directing group. Under N2 atmosphere, monoacylated indole
(particle size 100–200 mesh) was purchased from SRL India and (0.41 mmol 124 mg) and sodium ethoxide (3.0 equiv.) were
used for column chromatography using hexanes and ethyl dissolved in DMSO (5 mL) at room temperature. Then the
acetate mixtures as eluent. 1H and 13C NMR spectra were reaction mixture was heated upto 100 ꢀC for 12 h. The reaction
recorded on a Bruker 400 MHz instrument. 1H NMR spectra mixture was quenched with water and extracted with ethyl
were reported relative to residual CHCl3 (d 7.26 ppm) or DMSO- acetate. The combined organic layers were dried with Na2SO4.
d6 (d 2.50 ppm). 13C NMR were reported relative to CDCl3 (d The organic solvent was evaporated under reduced pressure and
77.16 ppm) or DMSO-d6 (d 39.52 ppm). FT-IR spectra were the resulting crude product was puried by silica gel column
recorded on a JASCO spectrometer and are reported in chromatography (hexanes–ethyl acetate) to give the desired
1
frequency of absorption (cmꢁ1). High resolution mass spectra acylation product. The product was conrmed by H and 13C
(HRMS) were recorded on Q-Tof Micro mass spectrometer.
NMR, FT-IR and HRMS spectroscopic analysis.
Typical experimental procedure for C2-acylation. Indole (0.5
Phenyl(1-(pyrimidin-2-yl)-1H-indol-2-yl)methanone 3a. Yield
mmol, 97.6 mg), PdCl2 (0.05 mmol, 8.9 mg), benzaldehyde (0.75 80%; colorless solid; mp ¼ 121–123 ꢀC [122–124 ꢀC];9a Rf ¼ 0.23
mmol, 76 mL), TBHP (1.5 mmol, 193 mL, 70% aq.) and toluene (2 (hexanes : ethyl acetate 8 : 2); IR (KBr) 3408, 2327, 1655, 1570,
mL) were taken in a reaction tube. The reaction mixture was 1523, 1426, 1277, 748, 717 cmꢁ1; H NMR (400 MHz, CDCl3) d
1
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7.08 (m, 1H), 7.15 (s, 1H), 7.28–7.36 (m, 1H) 7.46 (m, 3H), 7.53– (d, J ¼ 7.6 Hz, 1H), d 8.27 (d, J ¼ 8.4 Hz, 1H), d 8.61 (d, J ¼ 4.8 Hz,
7.63 (m, 1H), 7.73 (d, J ¼ 8.0 Hz, 1H), 8.00 (d, J ¼ 7.6 Hz, 2H), 2H); 13C NMR (100 MHz, CDCl3) d 112.4, 114.2, 115.4, 117.6,
8.43 (d, J ¼ 8.4, 1H), 8.65 (d, J ¼ 4.4 Hz, 2H); 13C NMR (100 MHz, 119.5, 122.7, 122.9, 126.8, 128.0, 136.2, 138.7, 147.0, 152.7,
CDCl3) d 114.4, 115.5, 117.4, 122.6, 122.9, 126.6, 128.1, 128.4, 157.5, 158.2, 174.4; HRMS (ESI) calcd for C17H12N3O2 [M + H]+
129.6, 132.8, 137.3, 138.1, 138.4, 157.4, 158.0, 187.7; HRMS (ESI) 290.0930; found 290.0933.
calcd for C19H13N3O [M + H]+ 300.1137; found 300.1136.
(5-Methoxy-1-(pyrimidin-2-yl)-1H-indol-2-yl)(phenyl)methanone
Naphthalen-1-yl(1-(pyrimidin-2-yl)-1H-indol-2-yl)methanone 3b. 3g. Yield 70%; colorless solid; mp ¼ 129–131 ꢀC [134–135 ꢀC];9a
Yield 79%; colorless solid; mp ¼ 136–138 ꢀC [136–138 ꢀC];9a Rf ¼ Rf ¼ 0.20 (hexanes–ethyl acetate 8 : 2); IR (KBr) 2987, 2361, 1657,
0.25 (hexanes : ethyl acetate 8 : 2); IR (KBr) 3048, 1653, 1573, 1607, 1440, 1234, 804, 706 cmꢁ1; H NMR (400 MHz, CDCl3) d
1
1449, 813, 777, 751 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 6.95 (t, J 3.88 (s, 3H), 7.02 (t, J ¼ 4.8 Hz, 1H), 7.05 (d, J ¼ 0.4 Hz, 1H), 7.08
¼ 4.8 Hz, 1H), 7.16 (s, 1H), 7.30 (t, J ¼ 8.0 Hz, 1H), 7.38 (t, J ¼ 7.6 (dd, J ¼ 9.2, 2.4 Hz, 1H), 7.12 (d, J ¼ 2.4 Hz, 1H), 7.39–7.46 (m,
Hz, 1H), 7.46 (t, J ¼ 8.4 Hz, 1H), 7.51–7.56 (m, 1H), 7.57–7.64 (m, 1H), 7.50–7.56 (m, 1H), 7.92–7.98 (m, 2H), 8.34 (d, J ¼ 9.2 Hz,
1H), 7.70 (d, J ¼ 8.0 Hz, 1H), 7.76 (d, J ¼ 7.2 Hz, 1H), 7.87 (d, J ¼ 1H), 8.59 (d, J ¼ 4.8 Hz, 2H); 13C NMR (100 MHz, CDCl3) d 55.8,
7.6 Hz, 1H), 7.93 (d, J ¼ 8.4 Hz, 1H), 8.38 (d, J ¼ 8.4 Hz), 8.53 (d, J 103.6, 115.1, 115.5, 116.6, 117.3, 128.4, 128.8, 129.6, 132.8,
¼ 4.8 Hz, 2H), 8.72 (d, J ¼ 8.4 Hz, 1H); 13C NMR (100 MHz, 133.3, 137.7, 138.2, 156.1, 157.3, 158.0, 187.8; HRMS (ESI) calcd
CDCl3) d 114.4, 116.3, 117.4, 122.8, 123.0, 124.3, 126.2, 126.5, for C20H16N3O2 [M + H]+ 330.1243; found 330.1230.
126.8, 127.7, 128.1, 128.3, 129.1, 131.2, 132.4, 133.8, 136.2,
(5-Bromo-1-(pyrimidin-2-yl)-1H-indol-2-yl)(phenyl)methanone 3h.
138.6, 139.1, 157.5, 158.0, 189.0; HRMS (ESI) calcd for Yield 61%; light yellow solid; mp ¼ 116–118 ꢀC [120–122 ꢀC];9a Rf
C
23H15N3O [M + H]+ 350.1288; found 350.1281.
¼ 0.25 (hexanes : ethyl acetate); IR (KBr) 2922, 1667, 1572, 1443,
(1-(Pyrimidin-2-yl)-1H-indol-2-yl)(p-tolyl)methanone 3c. Yield 800, 713 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 7.02 (s, 1H), 7.04 (t, J
64%; colorless solid; mp ¼ 128–130 C [121–123 C];9a Rf ¼ 0.3 ¼ 8.4 Hz, 1H), 7.43 (t, J ¼ 7.6 Hz, 2H), 7.50 (dd, J ¼ 9.2, 2.0 Hz,
ꢀ
ꢀ
(hexanes : ethyl acetate 8 : 2); IR (KBr) 2924, 2856, 1643, 1570, 1H), 7.52–757 (m, 1H), 7.81 (d, J ¼ 1.6 Hz, 1H), 7.91–7.98 (m, 2H),
1434, 1282, 958, 826, 751 cmꢁ1; H NMR (400 MHz, CDCl3) d 8.32 (d, J ¼ 9.2 Hz, 1H), 8.59 (d, J ¼ 4.8 Hz, 2H); 13C NMR (100
1
2.41 (s, 3H), 7.04 (t, J ¼ 5.2 Hz, 1H),7.09 (s, 1H), 7.23 (d, J ¼ 8.4 MHz, CDCl3) d 113.7, 116.0, 116.1, 117.7, 124.8, 128.5, 129.2,
Hz, 1H), 7.38 (t, J ¼ 7.6 Hz, 2H), 7.40–7.46 (m, 1H), 7.69 (d, J ¼ 129.5, 129.8, 133.0, 136.7, 137.7, 138.1, 156.9, 158.1, 187.5; HRMS
8.0 Hz, 1H), 7.88 (d, J ¼ 8.0 Hz, 2H), 8.40 (d, J ¼ 8.4 Hz, 1H), 8.62 (ESI) calcd for C19H13N3OBr [M + H]+ 378.0242; found 378.0229.
(d, J ¼ 4.8 Hz, 2H); 13C NMR (100 MHz, CDCl3) d 21.8, 114.4,
(1-(Pyrimidin-2-yl)-1H-indol-2-yl)(thiophen-2-yl)methanone 3i.
115.0, 117.4, 122.5, 122.9, 126.4, 128.2, 129.2, 129.9, 135.6, Yield 54%; colorless solid; mp ¼ 144–146 ꢀC [136–138 ꢀC];9a Rf ¼
137.6, 138.4, 143.6, 157.5, 158.1, 187.5; HRMS (ESI) calcd for 0.20 (hexanes : ethyl acetate 8 : 2); IR (KBr) 3071, 1624, 1570,
1
C
20H15N3O [M + H]+ 314.1281; found 314.1288.
1521, 1425, 742 cmꢁ1; H NMR (400 MHz, CDCl3) d 7.00–7.04
4-(1-(Pyrimidin-2-yl)-1H-indole-2-carbonyl)benzonitrile
3d. (m, 1H), 7.05–7.09 (m, 1H), 7.17–7.25 (m, 2H), 7.33–7.39 (m,
Yield 68%; white solid; mp ¼ 150–153 ꢀC; Rf ¼ 0.26 (hex- 1H), 7.60–7.66 (m, 2H), 7.75 (dd, J ¼ 4, 1.2 Hz, 1H), 8.29 (dd, J ¼
anes : ethyl acetate 7 : 3); IR (KBr) 3122, 2226, 1646, 1564, 1434, 8.4, 0.4 Hz, 1H), 8.61 (d, J ¼ 4.8 Hz, 2H); 13C NMR (100 MHz,
1208, 7601 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 7.07 (t, J ¼ 4.4 Hz, CDCl3) d 113.7, 116.2, 116.3, 117.8, 124.9, 128.9, 129.4, 129.8,
1H), 7.20 (s, 1H), 7.32 (t, J ¼ 7.6 Hz, 1H), 7.44–7.52 (m, 1H), 7.68– 130.9, 136.2, 136.7, 137.7, 139.5, 157.0, 158.2, 186.4; HRMS (ESI)
7.76 (m, 3H), 8.01 (d, J ¼ 8.4 Hz, 2H), 8.45 (d, J ¼ 8.4 Hz, 1H), calcd for C17H12N3O [M + H]+ 306.0701; found 306.0711.
8.61 (d, J ¼ 4.8 Hz, 2H); 13C NMR (100 MHz, CDCl3) d 114.7,
(4-Chlorophenyl)(1-(pyrimidin-2-yl)-1H-indol-2-yl)methanone 3j.
115.8, 116.1, 117.6, 118.2, 122.8, 123.3, 127.2, 128.1, 129.7, Yield 54%; colorless solid; mp ¼ 144–146 ꢀC [136–138 ꢀC];9a Rf ¼
132.3, 136.4, 138.5, 141.7, 157.2, 158.1, 186.0; HRMS (ESI) calcd 0.20 (hexanes : ethyl acetate 8 : 2); IR (KBr) 3072, 1623, 1569,
for C20H12N4O [M + H]+ 325.1089; found 325.1100.
1520, 1426, 741 cmꢁ1; H NMR (400 MHz, CDCl3) d 7.00–7.04
1
Methyl-4-(1-(pyrimidin-2-yl)-1H-indole-2-carbonyl)benzoate 3e. (m, 1H), 7.05–7.08 (m, 1H), 7.17–7.24 (m, 2H), 7.34–7.39 (m,
Yield 55%; colorless solid; mp ¼ 134–136 ꢀC; Rf ¼ 0.22 (hex- 1H), 7.60–7.65 (m, 2H), 7.75 (dd, J ¼ 4, 1.2 Hz, 1H), 8.29 (dd, J ¼
anes : ethyl acetate 8 : 2); IR (KBr) 2938, 1723, 1653, 1569, 1438, 8.4, 0.4 Hz, 1H), 8.61 (d, J ¼ 4.8 Hz, 2H); 13C NMR (100 MHz,
1287, 729 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 3.94 (s, 3H), 7.04 (t, CDCl3) d 113.7, 116.2, 116.3, 117.8, 124.9, 128.9, 129.4, 129.8,
J ¼ 4.8 Hz, 1H), 7.16 (s, 1H), 7.31 (t, J ¼ 7.2 Hz, 1H), 7.47 (t, J ¼ 130.9, 136.2, 136.7, 137.7, 139.5, 157.0, 158.2, 186.4; HRMS (ESI)
7.6 Hz, 1H), 7.72 (d, J ¼ 7.6 Hz, 1H), 7.98 (d, J ¼ 8.0 Hz, 2H), 8.08 calcd for C17H12N3O [M + H]+ 306.0701; found 306.0711.
(d, J ¼ 8.4 Hz, 2H), 8.43 (d, J ¼ 8.4 Hz, 1H), 8.60 (d, J ¼ 4.4 Hz,
(1-(Pyrimidin-2-yl)-1H-indol-2-yl)(o-tolyl)methanone 3k. Yield
2H); 13C NMR (100 MHz, CDCl3) d 52.6, 114.6, 115.8, 117.5, 60%; colorless solid; mp ¼ 124–126 ꢀC; Rf ¼ 0.20 (hex-
122.7, 123.1, 126.9, 128.1, 129.3, 129.7, 133.5, 136.9, 138.4, anes : ethyl acetate 8 : 2); IR (KBr) 3050, 1653, 1540, 1520, 1450,
141.7, 157.2, 158.1, 166.5, 187.0; HRMS (ESI) calcd for 756 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 2.59 (s, 3H), 7.11 (s, 2H),
C
21H16N3O3 [M + H]+ 358.1192; found 358.1184.
7.18 (t, J ¼ 7.6 Hz, 1H), 7.24–7.33 (m, 2H), 7.37 (td, J ¼ 6, 1.2 Hz,
Furan-2-yl(1-(pyrimidin-2-yl)-1H-indol-2-yl)methanone 3f. Yield 1H), 7.43–7.49 (m, 1H), 7.56–7.61 (m, 1H), 7.70 (d, J ¼ 8.0 Hz,
58%; light yellow solid; mp ¼ 120–122 C [122–124 C];9a Rf ¼ 1H), 8.32 (d, J ¼ 8.4 Hz, 1H), 8.69 (d, J ¼ 4.8 Hz, 2H); 13C NMR
0.26 (hexanes : ethyl acetate 7 : 3); IR (KBr) 2926, 1640, 1568, (100 MHz, CDCl3) d 20.5, 114.1, 116.3, 117.7, 122.8, 122.9, 125.2,
ꢀ
ꢀ
1
1468, 1292, 827, 793, 750 cmꢁ1; H NMR (400 MHz, CDCl3) d 126.9, 128.0, 130.1, 131.2, 131.3, 138.3, 138.8, 138.9, 157.6,
6.47 (d, J ¼ 1.6 Hz, 1H), d 7.03 (t, J ¼ 4.8 Hz, 1H), d 7.16–7.25 (m, 158.1, 189.4; HRMS (ESI) calcd for C20H15N3O [M + H]+
2H), d 7.29 (s, 1H), d 7.36 (t, J ¼ 7.6 Hz, 1H), d 7.55 (s, 1H), 7.65 314.1284; found 314.1288.
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1-(1-(Pyrimidin-2-yl)-1H-indol-2-yl)hexan-1-one 3l. Yield 61%;
(1-(Pyrimidin-2-yl)-1H-indole-2,7-diyl)bis(cyclohexylmethanone)
liquid; Rf ¼ 0.34 (hexanes : ethyl acetate 8 : 2); IR (KBr) 3069, 4c. Yield 50%; white solid; mp ¼ 163–165 ꢀC Rf ¼ 0.26 (hexanes–
1640, 1558, 1510, 1458, 860, 790, 756 cmꢁ1; 1H NMR (400 MHz, ethyl acetate 7 : 3); IR (KBr) 3058, 1656, 1573, 1428, 1350, 1214,
CDCl3) d 0.82 (t, J ¼ 7.2 Hz, 3H), 1.23–1.36 (m, 4H), 1.63–1.74 (m, 1150, 835, 720 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 1.3–1.24 (m,
2H), 2.84 (t, J ¼ 7.2 Hz, 2H), 7.12 (t, J ¼ 4.8 Hz, 1H), 7.14–7.19 (m, 3H), 1.25–1.45 (m, 4H), 1.47–1.60 (m, 4H), 1.69–1.90 (m, 5H),
1H), 7.21 (s, 1H), 7.27–7.33 (m, 1H), 7.59–7.62 (m, 1H), 7.89–7.92 1.96–2.12 (m, 5H), 2.68 (tt, J ¼ 11.6, 3.6 Hz, 1H), 3.08 (tt, J ¼ 11.2,
(m, 1H), 8.68 (d, J ¼ 4.8 Hz, 2H); 13C NMR (100 MHz, CDCl3) d 3.6 Hz, 1H), 7.19 (t, J ¼ 4.8 Hz, 1H), 7.36–7.47 (m, 2H), 7.85–7.92
14.1, 22.6, 24.5, 31.6, 40.6, 113.3, 113.5, 118.3, 122.7, 122.8, (m, 1H), 8.69 (d, J ¼ 8.4, Hz) 8.74 (d, J ¼ 4.8, Hz, 2H); 13C NMR
126.8, 127.6, 138.1, 139.3, 158.0, 158.1, 158.4, 194.1; HRMS (ESI) (100 MHz, CDCl3) d 26.0, 26.1, 26.2, 29.0, 29.1, 50.3, 51.6, 116.0,
calcd for C18H19N3O [M + H]+ 294.1597; found 294.1601.
118.0, 121.0, 121.3, 124.2, 125.5, 126.7, 135.9, 140.6, 156.9,
Cyclohex-3-en-1-yl(1-(pyrimidin-2-yl)-1H-indol-ꢀ2-yl)methanone 3m. 158.1, 201.9, 202.2; HRMS (ESI) calcd for C18H19N3O [M + H]+
Yield 51%; colourless solid; mp ¼ 122–124 C Rf ¼ 0.23 (hex- 294.1597; found 294.160.
anes : ethyl acetate 8 : 2); IR (KBr) 3040, 1655, 1556, 1515, 1470,
4-(2-Benzoyl-1-(pyrimidin-2-yl)-1H-indole-7-carbonyl)benzonitrile
1100, 840, 800, 745 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 1.73–1.87 5a. Yield 64%; white solid; mp ¼ 190–191 ꢀC Rf ¼ 0.26 (hexanes–
(m, 1H), 2.08–2.23 (m, 3H), 2.27–2.37 (m, 1H), 2.40–2.52 (m, ethyl acetate 7 : 3); IR (KBr) 2924, 2231, 1656, 1573, 1428, 1255,
1H), 3.26–3.35 (m, 1H), 5.80 (s, 2H), 7.21 (t, J ¼ 4.8 Hz, 1H), 7.28 1214, 718 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 7.00 (t, J ¼ 4.8 Hz,
(t, J ¼ 7.6 Hz, 2H), 7.42 (td, J ¼ 7.2, 1.2 Hz, 1H), 7.73 (d, J ¼ 8.0 1H), 7.21 (s, 1H), 7.29–7.37 (m, 2H), 7.45–7.51 (m, 2H), 7.60 (tt,
Hz, 1H), 8.14 (d, J ¼ 8.4 Hz, 1H), 8.80 (d, J ¼ 4.8 Hz, 2H); 13C J ¼ 7.6, 1.2 Hz, 1H), 7.70–7.76 (m, 2H), 7.89–7.95 (m, 3H), 7.96–
NMR (100 MHz, CDCl3) d 25.0, 25.9, 28.0, 44.8, 113.0, 113.8, 8.01 (m, 2H), 8.35 (t, J ¼ 4.8 Hz, 1H); 13C NMR (100 MHz, CDCl3)
118.1, 122.7, 122.8, 125.9, 126.7, 126.7, 127.9, 137.7, 139.1, d 114.8, 116.1, 118.2, 119.0, 121.7, 125.0, 126.3, 127.5, 128.6,
158.0, 158.3, 197.3; HRMS (ESI) calcd for C19H17N3O [M + H]+ 129.2, 129.9, 130.3, 132.3, 134.8, 137.6, 137.8, 141.1, 157.3, 157.8,
304.1450; found 304.1446.
187.2, 193.6; HRMS (ESI) calcd for C27H17N4O2 [M + H]+
(E)-1-(1-(Pyrimidin-2-yl)-1H-indol-2-yl)but-2-en-1-one 3n. Yield 429.1352; found 429.1355.
45%; light yellow solid; mp ¼ 123–125 ꢀC; Rf ¼ 0.30 (hex-
(2-Benzoyl-1-(pyrimidin-2-yl)-1H-indol-7-yl)(p-tolyl)methanone 5b.
ꢀ
anes : ethyl acetate 6 : 4); IR (KBr) 3100, 3020, 1665, 1585, 1520, Yield 68%; light yellow solid; mp ¼ 179–180 C Rf ¼ 0.26 (hex-
1426, 1010, 860, 756 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 2.00 (d, J anes : ethyl acetate 7 : 3); IR (KBr) 2925, 1649, 1570, 1422, 1262,
¼ 6.8 Hz, 3H), 6.71 (d, J ¼ 15.6 Hz, 1H), 6.97–7.09 (m, 1H), 7.21 747, 716 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 2.34 (s, 3H), 6.92 (t, J
(t, J ¼ 4.8 Hz, 1H), 7.28 (t, J ¼ 8.0 Hz, 2H), 7.42 (t, J ¼ 7.6 Hz, 1H), ¼ 4.8 Hz, 1H), 7.12 (s, 1H), 7.14 (d, J ¼ 8.0 Hz, 2H), 7.17–7.23 (m,
7.73 (d, J ¼ 7.6 Hz, 1H), 8.15 (d, J ¼ 8.4 Hz, 1H), 8.79 (d, J ¼ 4.8 1H), 7.32 (dd, J ¼ 7.2, 1.2 Hz, 1H), 7.39 (t, J ¼ 7.6 Hz, 2H), 7.51 (t, J
Hz, 2H); 13C NMR 18.6, 113.6, 114.3, 118.1, 122.7, 126.7, 127.8, ¼ 7.6 Hz, 1H), 7.63 (d, J ¼ 8.0 Hz, 2H), 7.78 (d, J ¼ 8.0 Hz, 1H),
130.3, 138.0, 139.2, 144.4, 157.9, 158.3, 184.1; HRMS (ESI) calcd 7.91 (d, J ¼ 6.8 Hz, 2H), 8.30 (d, J ¼ 4.8 Hz, 2H); 13C NMR (100
for C16H13N3O [M + H]+ 264.1137; found 264.1129.
MHz, CDCl3) d 21.8, 114.9, 119.0, 121.4, 125.5, 126.1, 127.8, 128.4,
(1-(Pyrimidin-2-yl)-1H-indole-2,7-diyl)bis(phenylmethanone) 4a. 128.5, 128.8, 129.1, 130.0, 130.2, 130.4, 133.1, 135.1, 135.3, 137.2,
Yield 72%; light yellow solid; mp ¼ 160–161 ꢀC; Rf ¼ 0.25 137.8, 143.7, 157.7, 158.0, 187.1, 195.2; HRMS (ESI) calcd for
(hexanes : ethyl acetate 7 : 3); IR (KBr) 3042, 1645, 1562, 1443, C27H20N3O2 [M + H]+ 418.1556; found 418.1572.
863, 717 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 6.96 (t, J ¼ 4.8 Hz,
(9-(Pyrimidin-2-yl)-9H-carbazole-1,8-diyl)bis(phenylmethanone)
1H), 7.19 (s, 1H), 7.28 (t, J ¼ 7.6 Hz, 1H), 7.37–7.40 (m, 2H), 7.41– 7. Yield 62%; light yellow solid; mp ¼ 160–162 ꢀC; Rf ¼ 0.28
7.44 (m, 2H), 7.45–7.48 (m, 2H), 7.49–7.53 (m, 1H), 7.54–7.59 (hexanes : ethyl acetate 7 : 3); IR (KBr) 3090, 1670, 1530, 1510,
(m, 1H), 7.78–7.82 (m, 2H), 7.86 (dd, J ¼ 8.0, 1.2 Hz, 2H), 7.98 1434, 1208, 854, 800, 760 cmꢁ1; H NMR (400 MHz, CDCl3) d
1
(dd, J ¼ 8.0, 1.2 Hz, 2H), 8.34 (d, J ¼ 4.8 Hz, 2H); 13C NMR (100 6.72 (t, J ¼ 5.2 Hz, 1H), 7.38 (t, J ¼ 7.6 Hz, 4H), 7.42–7.49 (m, 4H),
MHz, CDCl3) d 114.8, 118.9, 121.4, 125.6, 125.9, 127.8, 128.3, 7.50–7.52 (m, 2H), 7.83 (d, J ¼ 7.2 Hz, 4H), 7.96 (d, J ¼ 4.8 Hz,
128.5, 128.8, 129.9, 130.1, 132.8, 133.0, 135.2, 137.3, 137.7, 2H), 8.27 (d, J ¼ 7.6 Hz, 2H); 13C NMR (100 MHz, CDCl3) d 118.0,
137.7, 157.6, 157.9, 187.1, 195.4; HRMS (ESI) calcd for 122.1, 122.2, 126.7, 127.6, 128.0, 128.3, 129.9, 134.5, 136.9,
C
26H18N3O2 [M + H]+ 404.1399; found 404.1392.
137.9, 156.6, 156.8, 194.7; HRMS (ESI) calcd for C30H19N3O2 [M
(1-(Pyrimidin-2-yl)-1H-indole-2,7-diyl)bis(p-tolylmethanone) 4b. + H]+ 454.1556; found 454.1551.
Yield 52%; white solid mp ¼ 179–180 ꢀC Rf ¼ 0.26 (hex-
(1H-Indol-2-yl)(phenyl)methanone 8a. Yield 75%; white solid;
anes : ethyl acetate 7 : 3); IR (KBr) 3036, 1650, 1602, 1427, 1276, mp ¼ 145–146 ꢀC [149–150 ꢀC];9b Rf ¼ 0.26 (hexanes : ethyl
1214, 749, 700 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 2.34 (s, 3H), acetate 9 : 1); IR (KBr) 3354, 1620, 1517, 1260, 1125, 736, 680
2.36 (s, 3H), 2.36 (s, 3H), 6.91 (t, J ¼ 4.8 Hz, 1H), 7.09 (s, 1H), 7.13 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 7.14–7.21 (m, 2H), 7.35–7.42
(d, J ¼ 8.0 Hz, 2H), 7.17–7.22 (m, 3H), 7.31 (dd, J ¼ 7.2, 1.2 Hz, (m, 1H), 7.47–7.59 (m, 3H), 7.60–7.67 (m, 1H), 7.73 (d, J ¼ 8.0
1H), 7.63 (d, J ¼ 8.4 Hz, 2H), 7.77 (dd, J ¼ 8.0, 1.2 Hz, 1H), 7.83 Hz, 1H), 7.98–8.1 (m, 2H), 9.56 (bs, 1H); 13C NMR (100 MHz,
(d, J ¼ 8.4 Hz, 2H), 8.29 (d, J ¼ 4.8 Hz, 2H); 13C NMR (100 MHz, CDCl3) d 112.4, 113.0, 121.2, 123.4, 126.7, 127.9, 128.6, 129.4,
CDCl3) d 21.8, 114.5, 118.9, 121.3, 125.4, 126.1, 127.6, 128.8, 132.5, 134.5, 137.7, 138.2, 187.4; HRMS (ESI) calcd for C15H12NO
129.1, 129.2, 130.2, 130.4, 135.1, 135.2, 137.4, 143.7, 143.9, [M + H]+ 222.0919; found 222.0917.
157.7, 157.9, 186.9, 195.3; HRMS (ESI) calcd for C28H22N3O2 [M
+ H]+ 432.1712; found 432.1709.
(1H-Indol-2-yl)(naphthalen-1-yl)methanone 8b. Yield 73%;
light yellow solid; mp ¼ 144–145 ꢀC [150–151 ꢀC];9c Rf ¼ 0.26
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(hexanes : ethyl acetate 9 : 1); IR (KBr) 3327, 1614, 1520, 783,
746 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 6.98 (dd, J ¼ 2.0, 0.8 Hz,
1H), 7.13–7.19 (m, 1H), 7.35–7.42 (m, 1H), 7.52 (dd, J ¼ 8.4, 0.8
Hz, 1H), 7.54–7.60 (m, 3H), 7.66 (dd, J ¼ 8.0, 0.8 Hz, 1H), 7.90
(dd, J ¼ 7.2, 1.2 Hz, 1H) 7.92–7.98 (m, 1H), 8.05 (d, J ¼ 8.4 Hz,
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CDCl3) d 112.5, 113.9, 121.2, 123.5, 124.5, 125.7, 126.7, 126.9,
127.5, 127.7, 127.9, 128.5, 131.0, 131.7, 134.0, 135.8, 136.2,
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found 272.1077.
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(1H-Indol-2-yl)(p-tolyl)methanone 8c. Yield 71%; light yellow
solid; mp ¼ 174–176 ꢀC [187–188 ꢀC];9d Rf ¼ 0.26 (hexanes–ethyl
acetate 9 : 1); IR (KBr) 3350, 1616, 1515, 1261, 825, 750 cmꢁ1; 1H
NMR (400 MHz, CDCl3) d 2.48 (s, 3H), 7.14–7.20 (m, 2H), 7.32–
7.41 (m, 3H), 7.50 (dd, J ¼ 8.4, 0.8 Hz, 1H), 7.73 (d, J ¼ 8.4 Hz,
1H), 7.94 (dd, J ¼ 8.4, 1.6 Hz, 2H), 9.54 (bs, 1H); 13C NMR (100
MHz, CDCl3) d 21.8, 112.3, 112.5, 121.1, 123.3, 126.5, 127.9,
129.3, 134.7, 135.5, 137.6, 143.3, 187.1; HRMS (ESI) calcd for
C
16H14NO [M + H]+ 236.1075; found 236.1071.
Acknowledgements
We thank DST (Project no. SB/S1/OC-72/2013) and DST nano
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