Palladium-catalyzed regioselective oxidative coupling of indoles and one-pot synthesis of acetoxylated biindolyls

Article abstract of DOI:10.1021/jo902265s

(Chemical Equation Presented) Mild conditions have been developed to achieve Pd-catalyzed homocoupling of indoles with excellent regioselectivity in the presence of Cu(OAc)₂·H₂O in DMSO at room temperature in high efficiency. This method provides a simple route to 2,3′-biindolyls from the electron-rich to moderately electron-poor indoles. The reaction tolerates the bromide substituent on indoles. In addition, a one-pot approach to C3-position acetoxylated biindolyls is realized via palladium catalysis by the use of AgOAc under oxygen atmosphere as oxidants. 2009 American Chemical Society.

Full text of DOI:10.1021/jo902265s

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Palladium-Catalyzed Regioselective Oxidative Coupling of Indoles and
One-Pot Synthesis of Acetoxylated Biindolyls
Zunjun Liang, Jinlong Zhao, and Yuhong Zhang*
Department of Chemistry, Zhejiang University, Hangzhou 310027, P. R. China
yhzhang@zju.edu.cn
Received October 21, 2009
Mild conditions have been developed to achieve Pd-catalyzed homocoupling of indoles with excellent
regioselectivity in the presence of Cu(OAc)2 H2O in DMSO at room temperature in high efficiency.
3
This method provides a simple route to 2,30-biindolyls from the electron-rich to moderately electron-
poor indoles. The reaction tolerates the bromide substituent on indoles. In addition, a one-pot
approach to C3-position acetoxylated biindolyls is realized via palladium catalysis by the use of
AgOAc under oxygen atmosphere as oxidants.
Introduction
most traditional method for the preparation of biindolyls.3
For instance, exposing the indole to anhydrous hydrogen
chloride and subsequent dehydrogenation using 10 mol %
Pd/C results in 2,30-biindolyls in 65% overall yield.4 It has
been reported that 0.5 equiv of thallium(III) trifluoroacetate
Biindolyls are useful structural units that are frequently
found in pharmaceuticals and functional materials.1 Both
chemical and enzymatic synthetic methods have been re-
ported for the construction of biindolyls,2 and the acidic
dimerization of indoles followed by dehydrogenation is the
and 10 equiv of BF3 Et2O can transform indoles into
3
biindolyls.5 On the other hand, the methods based on the
transition-metal-catalyzed coupling of aryl halides with aryl-
metals have emerged as versatile tools for the synthesis of
biaryls over the past decades,6 and biindolyls have been
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Published on Web 12/03/2009
DOI: 10.1021/jo902265s
r
2009 American Chemical Society

Liang et al.
JOCArticle
TABLE 1. Effects of Metals and Oxidants on the Dimarizationa
constructed facilely by Stille reaction and Suzuki reaction.7
Recently, an efficient strategy by the palladiun-catalyzed
annulation of o-ethynylanilines with iodoindoles was re-
ported for the synthesis of biindolyls.8 However, these
methods require the prefunctionalization of indoles to their
halide or metallic derivatives. From both scientific and
environmental points of view, the development of methodol-
ogy for direct activation of C-H bonds is of great signifi-
cance, and metal-catalyzed C-H bond functionalization has
attracted much attention currently.9 For example, palla-
dium-catalyzed C-H activation has been successfully ap-
plied in the homocoupling of thiophenes to approach the
bithiophene units in the presence of silver salt,10 and biindo-
lizines have been prepared by combination of palladium
catalyst and copper reagent via C-H bond cleavage.11 As
part of our ongoing investigations on selective and control-
lable C-H bond functionalization,12 we studied the palla-
dium-catalyzed oxidative coupling of indoles. Herein, we
report a mild and selective method for dimerization of
indoles by palladium catalysis to give 2,30-biindolyls in high
yields at room temperature. Moreover, a one-pot procedure
for C3-position acetoxylated biindolyls is established by
using AgOAc as oxidant at 60 °C for 12 h.
entry
catalyst
Pd(OAc)2
PdCl2
oxidative
temp (°C) yield (%)b
1
2
3
4
5
6
7
8
Cu(OAc)2 H2O
3
90
90
90
90
90
90
60
rt
40
69
75
75
78
80
86
91
Cu(OAc)2 H2O
3
Pd(CH3CN)2Cl2 Cu(OAc)2 H2O
3
Pd(PPh3)4
Pd(dba)2
Cu(OAc)2 H2O
3
Cu(OAc)2 H2O
3
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Cu(OAc)2 H2O
Cu(OAc)2 H2O
Cu(OAc)2 H2O
3
3
3
9
Cu(OAc)2
Cu(OAc)2 H2O
rt
rt
92
nr
10
11
12
13
14
15
16
17
18
3
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
rt
rt
rt
trace
trace
36
CuO
AgOAc
Ag2O
Ag2CO3
K2S2O8
O2
rt
rt
rt
rt
trace
trace
trace
trace
15 c
Cu(OAc)2 H2O
rt
3
aReaction condition: N-methyl indole (1 mmol), oxidant (1.5 mmol),
catalyst (0.05 mmol), DMSO (6 mL), 8 h, N2. bIsolated yields based on
N-methyl indole. TFA = trifluoroacetate, rt = room temperature, nr =
no reaction. c1,4-Dioxane as the solvent instead of DMSO.
Results and Discussion
On the outset of our study, we examined the homocou-
pling of N-methylindole in the presence of palladium cata-
lysts. It was found that the dimerization reaction occurred by
use of 5 mol % Pd(OAc)2 catalyst to give the 2,30-dimer of
N-methylindole 1,10-dimethyl-1H,10H-2,30-biindole in 40%
of 2,20- and 3,30-biindolyls were not observed under the
reaction conditions, showing excellent regioselectivity. A
higher efficiency was observed by the use of other palladium
catalysts such as PdCl2, Pd(CH3CN)2Cl2, Pd(PPh3)4, and
Pd(dba)2 (Table 1, entries 2-5), and the best result was
obtained with Pd(TFA)2 to give 80% yield (Table 1, entry 6).
To our delight, when we performed the reaction at 60 °C, the
yield of the product was increased under these reaction condi-
tions (Table 1, entry 7). The reaction was further improved to
afford 91% yield at room temperature (Table 1, entry 8). The
reaction in the absence of palladium catalysts or copper
reagents resulted in no homocoupling (Table 1, entries
10-11). Although Cu(OAc)2 showed slightly higher efficiency
than Cu(OAc)2 H2O (Table 1, entry 9), Cu(OAc)2 H2O was
used as oxidant in the subsequent experiments because of its
low cost and ease of handling. Silver(I) reagents such as
AgOAc, Ag2CO3, and Ag2O were found to be ineffective
(Table 1, entries 13-15), and only trace amounts of the product
were observed when K2S2O8, CuO, or O2 were used as oxidants
(Table 1, entries 12, 16, 17). The reaction in other solvents
tested, including 1,4-dioxane, DMF, THF, acetone, and to-
luene, was sluggish (Table 1, entry 18).
yield in the presence of 1.5 equiv of Cu(OAc)2 H2O in
3
DMSO at 90 °C for 8 h (Table 1, entry 1). The derivatives
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3
3
The scope of the reaction was examined and Pd(TFA)2/
Cu(OAc)2 H2O is an efficient and selective catalytic system
3
for the dimerization of various indoles as summarized in
Table 2. The indoles containing electron-donating substi-
tutes such as methyl and methoxy reacted smoothly to give
2,30-dimers of indoles in high yields (Table 2, entries 3-6 and
13, 14). 4-Methyl-N-methylindole and 4-methyl-N-benzylin-
dole gave relatively lower yield, possibly due to the steric
hindrance (Table 2, entries 2 and 12). However, the reaction
of 6-methoxy-N-methylindoles and 6-methoxy-N-benzylin-
dole showed similar tendency of reactivity as in the direct
arylation of indoles12c and displayed moderate reactivity
(Table 2, entries 7 and 15). The presence of bromine in
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J. Org. Chem. Vol. 75, No. 1, 2010 171

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TABLE 2. Oxidative Homocoupling of Various Substituted Indolesa
indoles did not alter the reaction pathway, and moderate
yields were obtained for these moderately electron-
poor indoles (Table 2, entries 8 and 16). In the case of strongly
electron-poor indoles, the reactivity in the homocoupling
reaction dropped markedly (Table 2, entries 9 and 17),
albeit the reaction temperature was enhanced and the reac-
tion time was prolonged. A possible reason is that the
presence of an electron-withdrawing group might render
the indoles highly electron-deficient and retard the electro-
philic palladation. Similarly, N-acetyl indole was incompa-
tible with the reaction, and no desired dimerization
compound was isolated (Table 2, entry 10). N-Benzyl and
N-phenyl indole tolerated the reaction conditions well
and generated the homocoupling products in good yields
(Table 2, entries 11 and 18).
Encouraged by the successful homocoupling of indoles,
the homocoupling reaction of thiazoles, which are important
π-stacking five-membered rings,13 was next examined. Un-
fortunately, thiazoles failed to homocouple under the above
optimal reaction conditions. To our delight, the homocou-
pling products of thiazoles were isolated when AgOAc was
used as oxidant at 90 °C for 12 h (Table 2, entries 19 and 20).
During the screening of reaction conditions for this homo-
coupling reaction, we isolated a small amount of C3-position
acetoxylated biindolyls. Since substituted 3-oxyindoles are
common scaffolds in medicinal chemistry14 and their synth-
esis through direct catalytic methods is very limited,15 we
investigated the reaction conditions for selective formation
of acetoxylated biindolyl products as shown in Table 3. It
was found that oxygen played the key role for the acetoxyla-
tion. For example, only a trace of acetoxylated product was
detected using the Pd(OAc)2/Cu(OAc)2 H2O catalytic sys-
3
tem when the reaction was performed under nitrogen, but the
yield of acetoxylated product increased to 38% under oxy-
gen (Table 3, entries 1-2). Similar results were obtained by
using the Pd(TFA)2/Cu(OAc)2 H2O system (Table 3, entries
3
3 and 4). In addition, the reaction efficiency was decreased
when the reaction was performed at lower temperature
(Table 3, entry, 5). The replacement of Cu(OAc)2 H2O with
3
AgOAc markedly improved the selective acetoxylation
(Table 3, entries 6-12), and the best conditions for the
formation of acetoxylation product was indole derivatives
(1 mmol), Pd(TFA)2 (0.05 mmol), and AgOAc (2 mmol) in
DMSO (6.0 mL) at 60 °C for 12 h under oxygen atmosphere
(Table 3, entry 13). PhI(OAc)2 was ineffective under the
reaction conditions (Table 3, entry 14).
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(13) (a) Gonzalez Ronda, L.; Martin, D. C. Macromolecules 1997, 30,
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T.; Matsuda, H. J. Am. Chem. Soc. 1998, 120, 2047–2058. (c) Chang, Y. T.;
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Adv. Funct. Mater. 2008, 18, 1–10. (d) Li, K.-C.; Huang, J.-H.; Hsu, Y.-C.;
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Macromolecules 2009, 42, 3681–3693.
(14) (a) Campbell, J. A.; Bordunov, V.; Broka, C. A.; Browner, M. F.;
Kress, J. M.; Mirzadegan, T.; Ramesha, C.; Sanpablo, B. F.; Stabler, R.;
Takahara, P.; Villasenor, A.; Walker, K. A. M.; Wang, J.-H.; Welch, M.;
Weller, P. Bioorg. Med. Chem. Lett. 2004, 14, 4741–4745. (b) Bruncko, M.;
Song, X.; Ding, H.; Tao, Z.; Kunzer, A. R. WO 130970 A1, 2008; Chem. Abstr.
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Bioorg. Med. Chem. Lett. 2005, 15, 5035–5038.
aReaction conditions: indole derivatives (1 mmol), Pd(TFA)2 (0.05
mmol), Cu(OAc)2 H2O (1.5 mmol), DMSO (6 mL), room temperature,
3
8 h, N2. bIsolated yields based on indole. c60 °C, 12 h. dPd(TFA)2 (0.05
mmol), AgOAc (1.5 mmol), 90 °C, 12 h.
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172 J. Org. Chem. Vol. 75, No. 1, 2010

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TABLE 3. Optimization of Acetoxylated Biindolylsa
entry
catalyst
oxidant
temp (°C)
atmosphere
yield (%) of 3a
yield (%) of 2a
1
2
3
4
5
6
7
8
Pd(OAc)2
Pd(OAc)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Cu(OAc)2 H2O
3
90
90
90
90
40
90
90
rt
90
rt
90
40
60
60
N2
O2
N2
O2
O2
N2
O2
O2
N2
N2
O2
O2
O2
O2
trace
38
trace
40
trace
44
51
38
41
41
41
55
80
40
30
80
trace
81
25
<5
42
18
37
<5
26
<5
0
Cu(OAc)2 H2O
3
Cu(OAc)2 H2O
Cu(OAc)2 H2O
Cu(OAc)2 H2O
3
3
3
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
PhI(OAc)2
9
10
11
12
13
14
trace
aReaction conditions: indole derivative (1 mmol), catalyst (0.05 mmol), oxidant (2 mmol), DMSO (6 mL), 12 h.
The generality and scope of the acetoxylation reaction
were briefly examined, and the results are summarized in
Table 4. Again, the electron-rich indoles reacted smoothly to
give moderate to good yields (Table 4, entries 1, 3-6, 10, 11).
The steric hindrance by the methyl group in 1,4-dimethyl-
1H-indole might explain the low yield (Table 4, entry 2).
6-Methoxy-1-methyl-1H-indole furnished a relatively low
yield (Table 4, entry 7). Again, the presence of bromine in
indoles did not alter the reaction pathway but contributed to
a very low yield (Table 4, entry 8). Only traces of the
dimerized and acetoxylated products were observed for
electron-deficient indoles such as 1-methyl-1H-indole-5-car-
bonitrile under the reaction conditions. N-Benzyl indole and
N-phenyl indole were also not so active in the acetoxylated
reaction (Table 4, entries 9 and 12).
reductive elimination to afford acetoxylated product. The
treatment of 2,30-dimer in the presence of 5 mol % Pd(TFA)2
and 1 equiv of AgOAc in DMSO at 60 °C for 12 h under
oxygen atmosphere led to the formation of acetoxylated
product in 71% yield (Scheme 2), indicating that the one-
pot sequence might lead to the formation of acetoxylated
biindolyls. The Pd(II)/Pd(IV) mechanism is another possible
pathway for this regioselective oxidative homocoupling re-
action.18 Further research is required to elucidate the de-
tailed reaction mechanism.
In summary, we have developed an efficient method for
the homocoupling of indoles with excellent regioselectivity.
The method involves the use of catalytic Pd(TFA)2 and
1.5 equiv of Cu(OAc)2 H2O and is tolerant of bromine
3
on indoles. This new protocol provides a facile route to
2,30-biindolyls under very mild reaction conditions. Further-
more, the C3-position acetoxylated biindolyls were prepared
by a one-pot sequence. The reaction requires the presence of
catalytic Pd(TFA)2, 2 equiv of AgOAc, and oxygen. Only
electron-rich indoles are reactive. The possible pathway
for the homocoupling of indoles and one-pot formation of
C3-position acetoxylated biindolyls are discussed.
On the basis of the previous chemistry16 and the results of
our study, a plausible Pd(0)/Pd(II) mechanism for the homo-
coupling reaction as shown in Scheme 1 was proposed. The
electrophilic palladation first occurs at the preferential
C3-position of indoles and the subsequent migration of the
C3-PdX bond to the 2-position leads to the formation of
intermediate 1,17 which undergoes the electrophilic pallada-
tion with the second indole to form intermediate 2. The
following reductive elimination generates the 2,30-dimer of
indole, and the formed Pd(0) is oxidized to Pd(II) by Cu(II)
or Ag(I) salts in the system to furnish the cycle. In addition,
the electrophilic palladation of produced 2,30-dimer may
take place to give intermediate 3, which undergoes the
Experimental Section
General Procedure for Homocoupling Reaction. A mixture of
indole derivative (1 mmol), Cu(OAc)2 H2O (300 mg, 1.5 mmol),
3
Pd(TFA)2 (17 mg, 0.05 mmol), and DMSO (6 mL) was stirred at
room temperature under N2 for 8 h. The reaction mixture was
filtered through a plug of Celite, and the residue was washed
(16) (a) Lane, B. S.; Sames, D. Org. Lett. 2004, 6, 2897–2900.
(b) Lebrasseur, N.; Larrosa, I. J. Am. Chem. Soc. 2008, 130, 2926–2927.
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(d) Bellina, F.; Benelli, F.; Rossi, R. J. Org. Chem. 2008, 73, 5529–5535.
(e) Deprez, N. R.; Kalyani, D.; Krause, A.; Sanford, M. S. J. Am. Chem. Soc.
2006, 128, 4972–4973. (f) Yang, S.-D.; Sun, C.-L.; Fang, Z.; Li, B.-J.; Li,
Y.-Z.; Shi, Z.-J. Angew. Chem., Int. Ed. 2008, 47, 1473–1476. (g) Stuart,
D. R.; Villemure, E.; Fagnou, K. J. Am. Chem. Soc. 2007, 129, 12072–12073.
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Stowers, K. J.; Sanford, M. S. J. Am. Chem. Soc. 2008, 130, 13285–13293.
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TABLE 4. Synthesis of Acetoxylated Biindolylsa
SCHEME 1. Plausible Mechanism
SCHEME 2. Direct Acetoxylation of 2,30-Biindolyls
petroleum ether (Pet) as eluent to afford the corresponding
products.
1,10-Dimethyl-1H,10H-2,30-biindole (2a). 91% yield; white
solid; mp 111-112 °C; 1H NMR (400 MHz, CDCl3, TMS)
δ 7.71 (d, 1H, J = 8.4 Hz), 7.64 (d, 1H, J = 7.2 Hz), 7.40 (d, 1H,
J = 8.0 Hz), 7.37 (d, 1H, J = 8.4 Hz), 7.31 (m, 1H), 7.18-7.25
(m, 3H), 7.14 (m, 1H), 6.61 (br s, 1H), 3.88 (s, 3H), 3.76 (s, 3H);
13C NMR (100 MHz, CDCl3, TMS) δ 138.0, 137.0, 135.3, 128.5,
128.4, 127.7, 122.4, 121.0, 120.4, 120.3, 120.1, 119.6, 109.6,
109.4, 107.3, 101.2, 33.0, 31.0; MS (EI) m/z (%) 260 (100)
[M þ], 245 (10), 130 (11).
1,10,4,40-Tetramethyl-1H,10H-2,30-biindole (2b). 70% yield;
white solid; mp 154-155 °C ; 1H NMR (400 MHz, CDCl3,
TMS) δ 7.13-7.25 (m, 4H), 7.08 (s, 1H), 6.94 (d, 1H, J = 7.2
Hz), 6.90 (d, 1H, J = 6.8 Hz), 6.52 (br s, 1H), 3.84 (s, 3H), 3.52
(s, 3H), 2.57 (s, 3H), 2.13 (s, 3H); 13C NMR (100 MHz, CDCl3,
TMS) δ 137.1, 137.0, 135.3, 131.2, 129.7, 129.6, 127.9, 127.1,
122.3, 121.3, 121.2, 119.7, 107.3, 107.0, 106.9, 101.8, 33.0, 30.6,
18.8, 18.5; HRMS (EI) calcd for C20H20N2 (Mþ) 288.1626,
found 288.1620.
1,10,5,50-Tetramethyl-1H,10H-2,30-biindole (2c). 88% yield,
white solid; mp 160-161 °C; 1H NMR (400 MHz, CDCl3,
TMS) δ 7.48 (s, 1H), 7.43 (s, 1H), 7.24-7.29 (m, 2H),
7.12-7.16 (m, 2H), 7.05 (d, 1H, J = 8.4 Hz), 6.5 (br s, 1H),
3.84 (s, 3H), 3.72 (s, 3H), 2.48 (s, 3H), 2.46 (s, 3H); 13C NMR
(100 MHz, CDCl3, TMS) δ 136.4, 135.4, 129.5, 128.7, 128.6,
128.4, 127.9, 123.9, 122.5, 119.9, 119.7, 109.2, 109.0, 106.8, 33.0,
31.0, 21.5, 21.5; HRMS (EI) calcd for C20H20N2 (Mþ) 288.1626,
found 288.1622.
aReaction conditions: indole derivatives (1 mmol), Pd(TFA)2 (5mol%),
AgOAc (2 mmol), DMSO (6 mL), 60 °C, 12 h, O2. bIsolated yields.
with diethyl ether (2 ꢀ 20 mL). The filtrate was washed with
80 mL of H2O, and the organic layer was collected. The aqueous
phase was extracted with diethyl ether (3ꢀ20 mL). The com-
bined organic phases were washed with saturated sodium
chloride solution (40 mL), dried over anhydrous sodium
sulfate, filtered, and concentrated. The residue was purified
by flash column chromatography with ethyl acetate (EA) and
174 J. Org. Chem. Vol. 75, No. 1, 2010

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1,10,6,60-Tetramethyl-1H,10H-2,30-biindole (2d). 88% yield;
white solid; mp 133-134 °C; 1H NMR (400 MHz, CDCl3,
TMS) δ 7.56 (d, 1H, J=8.4 Hz), 7.51 (d, 1H, J=8.0 Hz), 7.18
(s, 1H), 7.15 (s, 1H), 7.12 (s, 1H), 7.02 (d, 1H, J = 8.0 Hz), 6.97
(d, 1H, J = 8.0 Hz), 6.52 (br s, 1H), 3.82 (s, 3H), 3.71 (s, 3H),
2.52 (s, 6H); 13C NMR (100 MHz, CDCl3, TMS) δ 138.4, 137.3,
132.2, 130.7, 127.8, 126.2, 125.6, 121.9, 121.2, 120.0, 119.6,
109.5, 109.4, 107.3, 32.8, 30.9, 22.0, 21.9; HRMS (EI) calcd
for C20H20N2 (Mþ) 288.1626, found 288.1619.
1,10,7,70-Tetramethyl-1H,10H-2,30-biindole (2e). 95% yield,
white solid; mp 184-185 °C; 1H NMR (400 MHz, CDCl3,
TMS) δ 7.46 (t, 2H, J = 6.4 Hz), 6.97-7.05 (m, 4H), 6.91 (d, 1H,
J = 7.8 Hz), 6.51 (br s, 1H), 4.13 (s, 3H), 3.93 (s, 3H), 2.82
(s, 3H), 2.81 (s, 3H); 13C NMR (100 MHz, CDCl3, TMS) δ
137.0, 136.0, 135.6, 130.4, 129.2, 128.9, 124.8, 123.9, 121.5,
121.1, 120.3, 119.6, 118.4, 118.1, 107.3, 102.1, 36.9, 34.2, 20.1,
19.6; HRMS (EI) calcd for C20H20N2 (Mþ) 288.1626, found
288.1623.
(s, 3H), 2.19 (s, 3H); 13C NMR (100 MHz, CDCl3, TMS)
δ 138.5, 137.0, 136.6, 136.4, 134.9, 131.4, 129.8, 129.6, 128.8,
128.3, 128.2, 127.7, 127.2, 126.9, 126.8, 126.3, 122.4, 121.6,
121.5, 119.9, 107.8, 107.8, 107.2, 102.8, 50.2, 47.4, 18.8, 18.8;
HRMS (ESI) calcd for C32H29N2 (M þ H)þ 441.2331, found
441.2331.
1,10-Dibenzyl-5,50-dimethyl-1H,10H-2,30-biindole (2m). 91%
yield; white solid; mp 134-135 °C; 1H NMR (400 MHz, CDCl3,
TMS) δ 7.54 (s, 1H), 7.47 (s, 1H), 7.24-7.27 (m, 3H), 7.19 (t, 4H,
J = 6.8 Hz), 7.11 (d, 1H, J = 8.4 Hz), 7.03-7.05 (m, 3H), 6.96
(d, 3H, J = 7.6 Hz), 6.92 (s, 1H), 6.67 (br s, 1H), 5.35 (s, 2H),
5.22 (s, 2H), 2.46 (s, 3H), 2.41 (s, 3H); 13C NMR (100 MHz,
CDCl3, TMS) δ 138.9, 137.1, 136.1, 135.1, 134.9, 129.8, 129.1,
129.0, 128.8, 128.7, 128.4, 127.7, 127.5, 127.0, 126.9, 126.0,
124.2, 122.8, 120.0, 119.9, 109.8, 109.7, 107.2, 101.7, 50.2,
47.6, 21.5, 21.5; HRMS (EI) calcd for C32H28N2 (Mþ)
440.2252, found 440.2255.
1,10-Dibenzyl-5,50-dimethoxy-1H,10H-2,30-biindole (2n). 93%
yield; white solid; mp 159-160 °C; 1H NMR (400 MHz, CDCl3,
TMS) δ 7.17-7.28(m, 9H), 7.06-7.11 (m, 3H), 6.98 (d, 3H, J =
9.2 Hz), 6.85-6.88 (m, 1H), 6.78-6.82 (m, 1H), 6.65 (br s, 1H),
5.35 (s, 2H), 5.22 (s, 2H), 3.87 (s, 3H), 3.71 (s, 3H); 13C NMR
(100 MHz, CDCl3, TMS) δ 154.9, 154.4, 138.7, 137.0, 135.7,
132.9, 131.6, 129.1, 128.8, 128.7, 128.4, 128.1, 127.8, 127.0,
126.9, 126.0, 113.1, 111.3, 110.9, 110.9, 107.3, 102.0, 101.6,
101.4, 55.9, 55.7, 50.4, 47.7; HRMS (EI) calcd for
C32H28N2O2 (Mþ) 472.2151, found 472.2147.
5,50-Dimethoxy-1,10-dimethyl-1H,10H-2,30-biindole (2f). 94%
yield; white solid; mp 165-166 °C; 1H NMR (400 MHz, CDCl3,
TMS) δ 7.24-7.29 (m, 2H), 7.17 (s, 1H), 7.13 (t, 2H, J = 6.4 Hz),
6.96 (dd, 1H, J=2.0, 2.4 Hz), 6.90 (dd, 1H, J = 2.8, 2.4 Hz), 6.50
(br s, 1H), 3.88 (s, 3H), 3.85 (s, 3H), 3.82 (s, 3H), 3.72 (s, 3H); 13
C
NMR (100 MHz, CDCl3, TMS) δ 154.8, 154.2, 133.3, 132.1,
128.8, 128.6, 128.0, 112.9, 111.0, 110.3, 110.0, 106.9, 102.0,
101.6, 56.0, 55.9 33.1, 31.0; HRMS (EI) calcd for C20H20N2O2
(Mþ) 320.1525, found 320.1524.
6,60-Dimethoxy-1,10-dimethyl-1H,10H-2,30-biindole (2g). 50%
yield; white solid; mp 149-150 °C; 1H NMR (400 MHz, CDCl3,
TMS) δ 7.56 (d, 1H, J=8.4 Hz), 7.50 (d, 1H, J=8.4 Hz), 7.06
(s, 1H), 6.80-6.86 (m, 4H), 6.51 (br s, 1H), 3.90 (s, 6H), 3.80
(s, 3H), 3.70 (s, 3H); 13C NMR (100 MHz, CDCl3, TMS)
δ 156.8, 155.9, 138.7, 137.6, 127.1, 122.7, 122.0, 121.0, 120.5,
110.0, 109.1, 107.4, 93.4, 93.0, 55.8, 55.7, 32.9, 31.0; HRMS (EI)
calcd for C20H20N2O2 (Mþ) 320.1525, found 320.1523.
5,50-Dibromo-1,10-dimethyl-1H,10H-2,30-biindole (2h). 68%
yield; light yellow solid; mp 182-183 °C; 1H NMR (400 MHz,
CDCl3, TMS) δ 7.78 (d, 1H, J=2.0 Hz), 7,74 (d, 1H, J=1.6 Hz),
7.38 (dd, 1H, J=2.0, 2.0 Hz), 7.30 (dd, 1 H, J =1.6, 2.0 Hz), 7.26
(d, 1H, J=9.2 Hz), 7.21 (d, 1H, J = 8.4 Hz), 7.18 (s, 1H), 6.52
(br s, 1H), 3.86 (s, 3H), 3.70 (s, 3H); 13C NMR (100 MHz,
CDCl3, TMS) δ 136.6, 135.6, 135.4, 129.9, 129.4, 129.1, 125.3,
123.9, 122.6, 122.4, 113.9, 112.9, 111.1, 110.7, 106.4, 101.1, 33.2,
31.0; HRMS (EI) calcd for C18H14Br2N2 (Mþ) 417.9503, found
417.9500.
1,10-Dimethyl-1H,10H-2,30-biindole-5,50-dicarbonitrile (2i). 28%
yield; brown solid; mp 237-238 °C; 1H NMR (400 MHz, CDCl3,
TMS) δ 8.00 (s, 1H), 7.97 (s,1H), 7.55 (dd, 1H, J=1.2, 1.2 Hz),
7.47-7.49 (m, 2H), 7.41 (d, 1H, J=8.4 Hz), 7.36 (s, 1H), 6.68
(s, 1H), 3.96 (s, 3H), 3.77 (s, 3H); 13C NMR (125 MHz, CDCl3,
TMS) δ 139.7, 138.6, 135.9, 130.9, 128.1, 127.5, 125.8, 125.8,
124.7, 121.1, 120.5, 111.0, 110.5, 107.6, 104.1, 103.1, 33.7, 31.5;
HRMS (EI) calcd for C20H14N4 (Mþ) 310.1218, found 310.1214.
1,10-Dibenzyl-1H,10H-2,30-biindole (2k). 92% yield; white
solid; mp 133-134 °C; 1H NMR (400 MHz, CDCl3, TMS)
δ 7.85 (d, 1H, J = 8.0 Hz), 7.68 (q, 1H, J = 2.8 Hz),7.13-7.33
(m, 12H), 7.05-7.08 (m, 2H), 6.95-6.97 (m, 3H), 6.77 (br s, 1H),
5.39 (s, 2H), 5.24 (s, 2H); 13C NMR (100 MHz, CDCl3, TMS)
δ 138.7, 137.7, 136.9, 136.5, 134.8, 128.8, 128.8, 128.7, 128.7,
128.1, 127.8, 127.4, 127.0, 127.0, 126.9, 126.0, 122.6, 121.3,
120.5, 120.3, 120.2, 120.0, 110.1, 110.0, 107.6, 102.3, 50.2,
47.5; HRMS (EI) calcd for C30 H24N2 (Mþ) 412.1939, found
412.1935.
1,10-Dibenzyl-6,60-dimethoxy-1H,10H-2,30-biindole (2o). 52%
yield; white solid; mp 129-130 °C; 1H NMR (500 MHz, CDCl3,
TMS) δ 7.65 (d, 1H, J = 9.0 Hz), 7.54 (d, 1H, J = 8.5 Hz), 7.18-
7.27 (m, 6H), 7.05-7.07 (m, 2H), 6.96-6.98 (m, 2H), 6.81-6.82
(m, 3H), 6.74 (d, 1H, J = 1.5 Hz), 6.70 (d, 1H, J = 2.0 Hz), 6.67
(br s, 1H), 5.33 (s, 2H), 5.17 (s, 2H), 3.80 (s, 3H), 3.77 (s, 3H); 13
C
NMR (125 MHz, CDCl3, TMS) δ 157.1, 156.3, 138.8, 138.6,
137.5, 137.1, 134.1, 129.0, 128.9, 128.0, 127.2, 127.2, 126.3,
126.2, 123.3, 122.6, 121.2, 120.9, 110.2, 109.5, 108.1, 102.1,
94.5, 93.8, 56.0, 55.9, 50.4, 47.8; HRMS (ESI) calcd for C32
H29 N2 O2 (M þ H)þ 473.2229, found 473.2231.
1,10-Dibenzyl-5,50-dibromo-1H,10H-2,30-biindole (2p). 55%
yield; light yellow solid; mp 165-166 °C; 1H NMR (500 MHz,
CDCl3, TMS) δ 7.85 (d, 1H, J=2.0 Hz), 7.79 (d, 1H, J=2.0 Hz),
7.27-7.31 (m, 4H), 7.20-7.23 (m, 4H), 7.17 (d, 1H, J = 8.5 Hz),
7.08 (d, 1H, J = 8.0 Hz), 7.03 (t, 2H, J = 3.5 Hz), 6.94 (s, 1H),
6.88-6.90 (m, 2H), 6.68 (s, 1H), 5.33 (s, 2H), 5.21 (s, 2H); 13
C
NMR (125 MHz, CDCl3, TMS) δ 138.2, 136.6, 136.5, 135.4,
130.5, 129.8, 129.2, 129.1, 128.7, 128.3, 127.6, 127.1, 126.0,
125.9, 124.6, 123.0, 114.4, 113.5, 111.8, 111.7, 107.0, 102.3,
50.7, 47.8; HRMS (EI) calcd for C30H22Br2N2 (Mþ) 570.0129,
found 570.0139.
1,10-Dibenzyl-1H,10H-2,30-biindole-5,50-dicarbonitrile (2q). 27%
yield; brown solid; mp 198-199 °C; 1H NMR (500 MHz, CDCl3,
TMS) δ 8.02-8.03 (m, 2H), 7.46-7.48 (m, 1H), 7.39-7.41
(m, 2H), 7.29-7.32 (m, 4H), 7.23-7.25 (m, 3H), 7.08 (s, 1H),
7.05-7.07 (m, 2H), 6.86-6.87 (m, 2H), 6.82 (s, 1H), 5.37
(s, 2H), 5.29 (s, 2H); 13C NMR (125 MHz, CDCl3, TMS) δ
139.5, 138.2, 137.4, 135.7, 135.7, 129.9, 129.4, 129.3, 128.6, 128.4,
127.9, 127.9, 127.2, 126.0, 126.0, 125.9, 125.1, 120.9, 120.3, 111.3,
111.1, 107.8, 104.4, 103.9, 103.6, 50.9, 47.9; HRMS (ESI) calcd for
C32H21N4(M - H)- 461.1772, found 461.1777.
1,10-Diphenyl-1H,10H-2,30-biindole (2r). 76% yield; white
solid; mp 66-67 °C; 1H NMR (400 MHz, CDCl3, TMS)
δ 7.98-8.00 (m, 1H), 7.71-7.73 (m, 1H), 7.52-7.54(m, 1H),
7.23-7.47 (m, 13H), 7.16-7.19 (m, 2H), 7.03 (s, 1H), 6.62 (s,
1H); 13C NMR (100 MHz, CDCl3, TMS) δ 139.2, 138.9, 138.5,
135.9, 134.2, 129.6, 129.3, 128.9, 128.6, 127.9, 127.6, 127.1,
126.7, 124.3, 123.0, 121.8, 121.1, 120.7, 120.5, 120.1, 110.6,
110.3, 109.4, 102.8; HRMS (EI) calcd for C28H20N2 (Mþ)
384.1626, found 384.1629.
1,10-Dibenzyl-4,40-dimethyl-1H,10H-2,30-biindole (2l). 80%
yield; white solid; mp 169-170 °C; 1H NMR (400 MHz, CDCl3,
TMS) δ 7.23-7.24 (m, 3H), 7.17 (d, 1H, J = 8.8 Hz), 7.02-7.13
(m, 8H), 6.99 (s, 1H), 6.94 (d, 1H, J = 7.2 Hz), 6.89 (d, 1H, J =
6.8 Hz), 6.82 (m, 2H), 6.64 (s, 1H), 5.24 (s, 2H), 5.21 (s, 2H), 2.59
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4,40-Dimethyl-2,20-bithiazole (2s). 40% yield; light yellow
solid; mp 134-135 °C; 1H NMR (400 MHz, CDCl3, TMS)
δ 6.96 (s, 2H), 2.51 (s, 6H); 13C NMR (100 MHz, CDCl3, TMS)
δ 160.5, 153.8, 115.1, 16.8; MS (EI) m/z (%) 196 (100) [Mþ], 125
(19), 72 (84).
5,50-Dimethoxy-1,10-dimethyl-1H,10H-2,30-biindol-3-yl Acetate
(3f). 71% yield; white solid; mp 141-142 °C; H NMR (400
1
MHz, CDCl3, TMS) δ 7.27 (d, 1H, J = 5.6 Hz), 7.24-7.26
(m, 1H), 7.12 (s, 1H), 6.93-6.97 (m, 2H), 6.90 (dd, 1H, J=2.4,
2.4 Hz), 6.86 (d, 1H, J = 3.6 Hz), 3.87 (s, 3H), 3.83 (s, 3H), 3.79
(s, 3H), 3.63 (s, 3H), 2.21 (s, 3H); 13C NMR (100 MHz, CDCl3,
TMS) δ 170.3, 154.8, 154.4, 132.1, 130.4, 129.6, 128.0, 126.4,
125.3, 120.9, 113.0, 112.3, 110.7, 110.5, 103.0, 101.3, 98.5, 55.9,
55.8, 33.2, 30.9, 20.7; HRMS (EI) calcd for C22H22N2 O4 (Mþ)
378.1580, found 378.1576.
4,40,5,50-Tetramethyl-2,20-bithiazole (2t). 80% yield; light yel-
low solid; mp 184-185 °C; 1H NMR (400 MHz, CDCl3, TMS)
δ 2.39 (s, 6H), 2.36 (s, 6H); 13C NMR (100 MHz, CDCl3, TMS)
δ 156.9, 149.4, 128.0, 14.6, 11.4; MS (EI) m/z (%) 224 (100)
[Mþ], 209 (5), 191 (7), 139 (10), 112 (4), 86 (44), 71 (46), 59 (26).
General Procedure for Acetoxylation Reaction. A mixture
of indole derivative (1 mmol), AgOAc (334 mg, 2 mmol),
Pd(TFA)2 (17 mg, 0.05 mmol), and DMSO (6 mL) was stirred
at at 60 °C under O2 for 12 h. The reaction mixture was filtered
through a plug of Celite, and the residue was washed with
CH2Cl2 (2 ꢀ 20 mL). The filtrate was washed with 80 mL of
H2O, and the organic layer was collected. The aqueous phase
was extracted with CH2Cl2 (3 ꢀ 20 mL). The combined organic
phases were washed with saturated sodium chloride solution
(40 mL), dried over anhydrous sodium sulfate, filtered, and
concentrated. The residue was purified by flash column chro-
matography with ethyl acetate (EA) and petroleum ether (Pet)
as eluent to afford the corresponding products.
6,60-Dimethoxy-1,10-dimethyl-1H,10H-2,30-biindol-3-yl Acetate
(3g). 40% yield; white solid; mp 185-186 °C; H NMR (400
1
MHz, CDCl3, TMS) δ 7.40 (d, 1H, J = 10.0 Hz), 7.31
(d, 1H, J = 9.2 Hz), 7.03 (s, 1H), 6.81-6.85 (m, 4H), 3.89
(s, 3H), 3.88 (s, 3H), 3.80 (s, 3H), 3.60 (s, 3H), 2.19 (s, 3H);
13C NMR (100 MHz, CDCl3, TMS) δ 170.3, 156.7, 156.5, 137.6,
135.7, 128.1, 126.6, 123.2, 121.9, 121.0, 117.8, 115.5, 110.1,
109.7, 103.6, 93.4, 93.0, 55.8, 55.7, 33.0, 30.8, 20.6; HRMS
(EI) calcd for C22H22N2O4 (Mþ) 378.1580, found 378.1574.
5,50-Dibromo-1,10-dimethyl-1H,10H-2,30-biindol-3-yl Acetate
1
(3h). 25% yield; white solid; mp 225-226 °C; H NMR (500
MHz, CDCl3, TMS) δ 7.65 (d, 1H, J = 1.5 Hz), 7.57 (d, 1H, J =
1.5 Hz), 7.37 (dd, 1H, J = 1.5, 2.0 Hz), 7.31 (dd, 1H, J = 2.0,
1.5 Hz), 7.25-7.26 (m, 1H), 7.21 (d, 1H, J=8.5 Hz), 7.16(s, 1H),
3.84 (s, 3H), 3.62 (s, 3H), 2.20 (s, 3H); 13C NMR (125 MHz,
CDCl3, TMS) δ 170.2, 135.9, 133.9, 130.7, 129.2, 126.3, 125.6,
125.4, 125.1, 123.0, 122.6, 119.9, 114.2, 113.4, 111.5, 111.4,
102.9, 33.6, 31.3, 20.8; HRMS (ESI) calcd for C20H17Br2N2O2
(M þ H) þ 474.9657, found 474.9669.
1,10-Dimethyl-1H,10H-2,30-biindol-3-yl Acetate (3a). 80% yield;
white solid; mp 156-157 °C; 1H NMR (400 MHz, CDCl3, TMS)
δ 7.54 (d, 1H, J = 7.6 Hz), 7.44 (d, 1H, J = 8.0 Hz), 7.40 (d, 1H,
J = 8.4 Hz), 7.36 (d, 1H, J = 8.4 Hz), 7.28-7.32 (m, 1H), 7.23-
7.26 (m, 1H), 7.13-7.20 (m, 3H), 3.88 (s, 3H), 3.67 (s, 3H), 2.20
(s, 3H); 13C NMR (100 MHz, CDCl3, TMS) δ 170.3, 136.9, 135.0,
129.4, 127.5, 126.6, 124.6, 122.2, 121.8, 120.9, 120.3, 120.2, 119.7,
117.0, 109.7, 109.6, 103.3, 33.0, 30.8, 20.7; HRMS (EI) calcd for
C20H18N2O2 (Mþ) 318.1368, found 318.1373.
1,10-Dibenzyl-1H,10H-2,30-biindol-3-yl Acetate(3k). 34% yield;
white solid; mp 184-185 °C; 1H NMR (400 MHz, CDCl3, TMS)
δ 7.56 (d, 1H, J = 8.0 Hz), 7.46-7.49 (m, 1H), 7.33 (d, 1H, J =
7.6 Hz), 7.12-7.28 (m, 11H), 7.05-7.07 (m, 2H), 7.02 (s, 1H),
6.92 (d, 2H, J = 7.2 Hz), 5.30 (s, 2H), 5.27 (s, 2H), 2.15 (s, 3H);
13C NMR (100 MHz, CDCl3, TMS) δ 169.8, 138.3, 136.9, 136.4,
134.7, 128.8, 128.8, 128.6, 127.8, 127.5, 127.0, 126.9, 126.0, 124.4,
122.4, 122.1, 121.4, 120.5, 120.3, 120.0, 117.3, 110.4, 110.0, 103.9,
50.2, 47.6, 20.6; HRMS (EI) calcd for C32H26N2O2 (Mþ)
470.1994, found 470.1987.
1,10,4,40-Tetramethyl-1H,10H-2,30-biindol-3-yl Acetate (3b).
26% yield; white solid; mp 206-207 °C; H NMR (400 MHz,
1
CDCl3, TMS) δ 7.16-7.25 (m, 3H), 7.10-7.14 (m, 2H), 6.90
(d, 1H, J = 6.4 Hz), 6.87 (d, 1H, J = 7.2 Hz), 3.83 (s, 3H), 3.46
(s, 3H), 2.56 (s, 3H), 2.16 (s, 3H); 13C NMR (100 MHz, CDCl3,
TMS) δ 171.2, 137.1, 134.5, 131.2, 130.4, 128.5, 128.2, 127.3,
125.5, 122.2, 121.9, 121.3, 120.8, 119.7, 107.3, 107.2, 102.5, 33.1,
30.4, 20.8, 18.5, 18.2; HRMS (EI) calcd for C22H22N2O2 (Mþ)
346.1681, found 346.1675.
1,10-Dibenzyl-5,50-dimethyl-1H,10H-2,30-biindol-3-yl Acetate
(3m). 50% yield; white solid; mp 199-200 °C; H NMR (500
1
1,10,5,50-Tetramethyl-1H,10H-2,30-biindol-3-yl Acetate (3c).
64% yield; white solid; mp 159-160 °C; H NMR (400 MHz,
MHz, CDCl3, TMS) δ 7.29 (s, 1H), 7.23-7.27 (m, 4H),
7.15-7.20 (m, 4H), 7.11 (d, 1H, J = 8.0 Hz), 7.01-7.04 (m,
3H), 6.96-6.99 (m, 2H), 6.92-6.93 (m, 2H), 5.26 (s, 2H), 5.23 (s,
2H), 2.44 (s, 3H), 2.36 (s, 3H), 2.15 (s, 3H); 13C NMR (125 MHz,
CDCl3, TMS) δ 170.2, 138.8, 137.3, 135.1, 133.4, 130.0, 129.5,
129.2, 129.0, 128.8, 128.4, 128.0, 127.3, 127.2, 127.0, 126.3,
124.8, 124.2, 124.0, 121.7, 120.2, 117.1, 110.4, 109.9, 103.7,
50.4, 47.8, 21.7, 21.6, 20.8; HRMS (ESI) calcd for
C34H31N2O2 (M þ H) þ 499.2386, found 499.2387.
1
CDCl3, TMS) δ 7.30 (s, 1H), 7.26 (d, 1H, J = 4.0 Hz), 7.24 (d,
1H, J = 4.0 Hz), 7.22 (s, 1H), 7.10-7.12 (m, 2H), 7.04-7.07 (m,
1H), 3.83 (s, 3H), 3.62 (s, 3H), 2.46 (s, 3H), 2.43 (s, 3H), 2.20 (s,
3H); 13C NMR (100 MHz, CDCl3, TMS) δ 170.4, 135.4, 133.6,
129.6, 129.5, 129.0, 127.9, 126.3, 124.9, 123.9, 123.5, 121.1,
120.0, 116.6, 109.5, 109.4, 103.0, 33.0, 30.9, 21.5, 20.7; HRMS
(EI) calcd for C22H22N2O2 (Mþ) 346.1681, found 346.1684.
1,10,6,60-Tetramethyl-1H,10H-2,30-biindol-3-yl Acetate (3d).
1,10-Dibenzyl-5,50-dimethoxy-1H,10H-2,30-biindol-3-yl Acetate
(3n). 60% yield; white solid; mp 175-176 °C; 1H NMR
(400 MHz, CDCl3, TMS) δ 7.25-7.26 (m, 3H), 7.16-7.22
(m, 4H), 7.09 (d, 1H, J = 8.8 Hz), 7.03-7.05 (m, 2H), 6.99 (s,
1H), 6.95 (d, 3H, J = 8.0 Hz), 6.89 (s, 1H), 6.80-6.85 (m, 2H),
5.25 (s, 2H), 5.21 (s, 2H), 3.85 (s, 3H), 3.64 (s, 3H), 2.17 (s, 3H);
13C NMR (100 MHz, CDCl3, TMS) δ 170.0, 154.9, 154.5,
138.4, 137.0, 131.5, 130.0, 129.2, 128.8, 128.6, 128.3, 127.8,
127.2, 127.0, 126.8, 126.0, 125.2, 121.5, 113.3, 112.5, 111.5,
110.9, 103.6, 101.1, 98.8, 55.9, 55.6, 50.4,þ47.6, 20.7; HRMS
1
74% yield; white solid; mp 165-166 °C; H NMR (400 MHz,
CDCl3, TMS) δ 7.40 (d, 1H, J=8.0 Hz), 7.31 (d, 1H, J=8.0 Hz),
7.18 (s, 1H), 7.14 (s, 1H), 7.07 (s, 1H), 6.70 (t, 2H, J = 5.2 Hz),
3.82 (s, 3H), 3.61 (s, 3H), 2.52 (s, 3H), 2.50 (s, 3H), 2.18 (s, 3H);
13C NMR (100 MHz, CDCl3, TMS) δ 170.3, 137.3, 135.4, 132.1,
131.6, 128.8, 126.7, 125.5, 124.0, 122.0, 121.5, 120.0, 118.9,
116.8, 109.7, 109.5, 103.4, 32.9, 30.8, 22.0, 21.9, 20.7; HRMS
(EI) calcd for C22H22N2O2 (Mþ) 346.1681, found 346.1683.
1,10,7,70-Tetramethyl-1H,10H-2,30-biindol-3-yl Acetate (3e).
1
78% yield; white solid; mp 182-183 °C; H NMR (400 MHz,
(ESI) calcd for C34H31N2O4 (M þ H)
531.2284, found
CDCl3, TMS) δ 7.34 (d, 1H, J = 8.0 Hz), 7.23-7.25 (m, 1H),
6.92-7.04 (m, 5H), 4.12 (s, 3H), 3.84 (s, 3H), 2.81 (s, 3H), 2.80
(s, 3H), 2.19 (s, 3H); 13C NMR (100 MHz, CDCl3, TMS)
δ 170.4, 135.7, 134.3, 131.3, 128.9, 127.0, 125.5, 124.9, 124.8,
121.9, 121.7, 121.6, 120.5, 120.0, 118.4, 114.9, 103.3, 37.1, 34.1,
20.6, 20.4, 19.7; HRMS (EI) calcd for C22H22N2O2 (Mþ)
346.1681, found 346.1677.
531.2283.
1,10-Diphenyl-1H,10H-2,30-biindol-3-yl Acetate (3r). 44%
yield; white solid; mp 166-167 °C; 1H NMR (500 MHz, CDCl3,
TMS) δ 7.68 (d, 1H, J = 9.0 Hz), 7.50-7.53 (m, 2H), 7.43-7.46
(m, 2H), 7.31-7.38 (m, 7H), 7.25-7.27 (m, 2H), 7.14-7.22
(m, 4H), 6.88 (s, 1H). 2.26 (s, 3H); 13C NMR (125 MHz, CDCl3,
TMS) δ 169.9, 139.3, 138.3, 136.1, 135.9, 129.8, 129.4, 128.7,
176 J. Org. Chem. Vol. 75, No. 1, 2010

Liang et al.
JOCArticle
128.5, 128.4, 128.0, 127.5, 127.0, 124.6, 124.1, 123.0, 122.9,
121.7, 121.1, 121.1, 120.9, 117.6, 110.9, 110.8, 106.6, 21.0;
HRMS (ESI) calcd for C30H23N2O2 (M þ H) þ 443.1760, found
443.1769.
Natural Science Foundation of China (no. 20872126) is
acknowledged.
Supporting Information Available: General experimental
procedures and spectroscopic data (1H NMR, 13C NMR,
HRMS and MS) for the corresponding products. This material
is available free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. Funding from Zhejiang Provincial
Natural Science Foundation of China (R407106) and
J. Org. Chem. Vol. 75, No. 1, 2010 177