Rhodium-Catalyzed/Copper-Mediated Selective C2 Alkynylation of Indoles and C1 Alkynylation of Carbazoles with γ-Substituted tert-Propargyl Alcohols

Article abstract of DOI:10.1002/cctc.201600218

A novel rhodium-catalyzed/copper-mediated C2-selective C?H alkynylation of indoles using γ-substituted tert-propargyl alcohols as the alkynylating reagent and a removable 6-methylpyridin-2-yl as the directing group has been developed, which provides a viable pathway for direct C2-selective alkynylation of indoles. Moreover, this strategy could be extended to the C?H alkynylation of carbazoles at the C1 position.

Full text of DOI:10.1002/cctc.201600218

DOI: 10.1002/cctc.201600218
Full Papers
Rhodium-Catalyzed/Copper-Mediated Selective C2
Alkynylation of Indoles and C1 Alkynylation of Carbazoles
with g-Substituted tert-Propargyl Alcohols
+
+
[a]
Ting Li , Zhen Wang , Wen-Bing Qin, and Ting-Bin Wen*
A novel rhodium-catalyzed/copper-mediated C2-selective CÀH
alkynylation of indoles using g-substituted tert-propargyl alco-
hols as the alkynylating reagent and a removable 6-methylpyri-
din-2-yl as the directing group has been developed, which
provides a viable pathway for direct C2-selective alkynylation
of indoles. Moreover, this strategy could be extended to the
CÀH alkynylation of carbazoles at the C1 position.
Introduction
[
11]
Indoles are among the most widely distributed heterocyclic
compounds in nature and are common structural motifs in
by Garcia Ruano and co-workers. The use of a strong base
such as butyllithium in this method limited the scope of the
transformation.
[
1]
a wide range of pharmaceuticals and bioactive molecules.
Consequently, the synthesis and functionalization of indoles
On the other hand, considering the importance of acety-
[2]
[13]
are of utmost importance in organic chemistry. However, C2
functionalization of indoles is especially challenging because of
the inherent property of indoles, which show strong prefer-
lenes in organic synthesis and the great success of CÀH acti-
[
14]
vation for the construction of CÀX bonds (X=C, N, O, etc.),
tremendous efforts have been put into the development of CÀ
H alkynylation in recent years. Although it is appealing to
employ terminal alkynes as alkynylating reagents in CÀH alky-
nylation, owing to the polymerization of terminal alkynes
under high temperatures, only a narrow scope of electron-rich
heteroarenes such as thiophenes or highly electron-poor
arenes with reactive acidic CÀH bonds have been successfully
[3]
ence for the C3 transformations. Nevertheless, substantial
progress has been achieved in the field of indole C2 function-
[4]
[5]
alization in recent years, including arylation, alkenylation, al-
[
6]
[7]
kylation, and acylation. By contrast, C2-selective alkynylation
of indoles remains difficult to accomplish. Notably, the tedious
procedure and harsh reaction conditions for the C2 prefunc-
tionalization of indoles prevents the use of Sonogashira type
coupling reactions for the introducing of the alkynyl function-
[
15]
[16]
achieved. Instead, haloalkynes and terminal alkynes bear-
[
17]
ing a bulky silyl group have been used, while the substrate
scope still remains limited despite of the progress. Very recent-
ly, Loh and Feng, Loh et al., Li et al., and Glorius et al. disclosed
elegant examples of Rhodium-catalyzed CÀH alkynylation
of diversified arenes using hypervalent iodine-alkyne
[
8]
ality. A survey of the literature reveals that only rare examples
[
9–12]
of C2 alkynylation of indoles have been reported to date.
In 2010, Li and co-workers described a palladium-catalyzed
direct oxidative Heck–Cassar–Sonogashira type method for the
C2 alkynylation of indoles, which could be applied to a broad
[
10c,18,19]
reagents.
This method are suitable for triisopropylsilyl-
[
9]
scope of acetylenes, but only 3-methylindoles were reported.
based alkynyliodonium reagents, whereas aryl- or alkyl-substi-
tuted substrates could not afford the alkynylation products. As
such, it is desirable to exploit new and efficient alkynylating re-
agents to achieve CÀH alkynylation of generically and intrinsi-
cally less reactive arenes. Notably, tert-propargyl alcohols have
been introduced into coupling reactions as masked terminal al-
kynes, which can generate alkynyl–metal intermediates by lib-
[10a,b]
[10c]
Recently, Waser et al.
and Li et al.,
respectively, reported
the C2-selective alkynylation of indoles utilizing 1-[(triisopropyl-
silyl)-ethynyl]-1,2-benziodoxol-3(1H)-one (TIPS–EBX) or other si-
[
10d]
lylated EBX
as the alkynylating reagent. However, the strat-
egy was limited to silyl-based EBX reagents, and aryl- or alkyl-
based alkynylation reagents were not involved in these trans-
formations. Besides, C2 alkynylation of lithiated indoles using
ethynylsulfonates as alkynylating reagents was also achieved
[
20]
eration of ketones through b-carbon elimination. We were
thus inspired to design direct CÀH alkynylation of arenes utiliz-
ing g-substituted tert-propargyl alcohols as the alkynylating re-
agent. Taking into consideration of the advantage of rhodium
+
+
[
a] Dr. T. Li, Z. Wang, W.-B. Qin, Prof. Dr. T.-B. Wen
Department of Chemistry, College of Chemistry and Chemical Engineering
Xiamen University
[
21]
catalysis for CÀH bond activations, we have recently investi-
gated the rhodium/copper-catalyzed reactions of 1-(pyridin-2-
yl)-1H-indoles with g-substituted tert-propargyl alcohols, which
led to the novel synthesis of pyrido[2,1-a]indoles through mul-
tiple CÀH, CÀC, and CÀN bonds cleavages and construction
Xiamen, Fujian 361005 (P.R. China)
E-mail: chwtb@xmu.edu.cn
+
[
] These authors contributed equally to this work.
Supporting Information and the ORCID identification number(s) for the
author(s) of this article can be found under http://dx.doi.org/10.1002/
cctc.201600218.
[
22]
(
Scheme 1). Our ongoing studies revealed that the reaction
would afford the C2-selective alkynylated indoles if the more
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[a]
Table 1. Optimization of reaction conditions.
Scheme 1. Rh/Cu-catalyzed C2-selective CÀH alkynylation.
[b]
Entry
Substrate
Conditions
Yield [%]
[
c]
1
2
3
4
5
6
7
8
9
1a
1b
1’a
1’b
1’c
1’d
1’e
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
[RhCl(cod)]
[RhCl(cod)]
[RhCl(cod)]
[RhCl(cod)]
[RhCl(cod)]
[RhCl(cod)]
[RhCl(cod)]
2
2
2
2
2
2
2
, 1258C
, 1258C
, 1258C
, 1258C
, 1258C
, 1258C
, 1258C
61
68
0
hindered 6-methylpyridin-2-yl was employed as the directing
group (Scheme 1), which provides a flexible and straightfor-
ward pathway for C2-selective CÀH alkynylation of indoles. In
addition, direct CÀH alkynylation of carbazoles at the C1 posi-
tion is also disclosed herein.
[d]
[c]
0
0
0
0
52
26
0
[Cp*RhCl]
2
, 1258C
[RhCl(cod)]
[RhCl(cod)]
[RhCl(cod)]
[RhCl(cod)]
2
2
2
2
, 1408C
, 1108C
, 1258C
, 1258C
Results and Discussion
1
0
[
e]
1
1
35
In our previous studies on the synthesis of pyrido[2,1-a]indoles
[f]
1
13
14
1
16
2
trace
0
0
catalyzed by [RhCl(cod)] /Cu(OAc) , the reaction on the C3-sub-
[g]
2
2
Cu(OAc) ·H O, 1258C
2
2
[
[
[
h]
stituted indole substrate 1a afforded the C2-alkynylation prod-
uct 3a instead of the corresponding pyrido[2,1-a]indole
[RhCl(cod)]
2
2
2
2
, 1258C
i]
5
[RhCl(cod)]
[RhCl(cod)]
[RhCl(cod)]
, 1258C
, 1258C
, 1258C
54
70
14
j]
[
22]
(
Table 1, entry 1). Probably, the steric hindrance of the Me
[k]
1
7
group at C6 position of the pyridinyl directing group prevents
the further transformation of the alkynylation product, which
suggested that the alkynylation step was presumably involved
in the cascade transformation for the formation of the
pyrido[2,1-a]indoles. More importantly, this result provided us
further incentives to develop a general method for the C2-se-
lective alkynylation of indoles. As the C3-methyl substituted
indole was used in the above stated reaction, the C2-alkynyla-
tion is probably not surprising. Therefore, the reaction of 3-un-
substituted N-protecting indole 1b with tert-propargyl alcohol
[
%
a] Standard reaction conditions: 1 (0.2 mmol), 2 (0.6 mmol), cat. (1.5 mol
), Cu(OAc) ·H O (2.2 equiv.), toluene (2 mL), air, 10 h. [b] Yield of isolated
2
2
products based on 1. [c] Reference [22]. [d] 41% Glaser coupling product
was isolated. [e] DCE was used as solvent. [f] DMSO was used as solvent.
[
g] Performed in absence of [RhCl(cod)]
Cu(OAc) ·H O. [i] 2 equiv. of 2a were used. [j] 4 equiv. of 2a were used.
k] Phenylacetylene was used instead of 2a, 66% Glaser coupling product
2
. [h] Performed in the absence of
2
2
[
was also isolated.
ed 3ba in a relatively low yield (52%) (entry 8). Temperature
and solvent screening indicated that 1258C and toluene were
the most suitable reaction conditions for this transformation
(entries 9–12). Control experiments revealed that the reaction
2
a using [RhCl(cod)] (1.5 mol %) as precatalyst was examined.
2
Encouragingly, more promising result was obtained to produce
the desired C2-selective alkynylation product 3ba in 68% iso-
lated yield (entry 2). Subsequently, different directing groups
were screened to investigate the influence on the C2 alkynyla-
tion. Our previous study on the C3-methyl indole substrate 1’a
has shown that installation of a Me group on the C3 position
of the pyridinyl directing group (which was subject to the CÀC
bond formation for the construction of the pyrido[2,1-a]indole
product) could totally suppress the reaction to yield the Glaser
coupling product of 2a only (entry 3). Again, similar result was
observed in the case of the 3-unsubstituted indole substrate
did not work at all in the absence of either [RhCl(cod)] or
2
Cu(OAc) ·H O (entries 13–14). Besides, it was found that lower-
2
2
ing the use of 2a to two equivalents led to a lower yield of
3ba in 54%, whereas using four equivalents of 2a only result-
ed in slightly increasing of the yield to 70% (entries 15, 16).
Notably, the C3 or C7 position on the indole ring is untouched
at all in all cases.
In an attempt to employ simple terminal alkynes for this CÀ
H alkynylation reaction, we have also investigated the reaction
of substrate 1b with phenylacetylene under our standard con-
ditions. However, the alkynylated product was afforded in only
14% yield along with a large amount of diyne product
(entry 17), which clearly indicated that the Glaser coupling can
be inhibited effectively by using g-substituted tert-propargyl al-
cohols as the alkynylating reagent instead of terminal alkynes.
1
’b (entry 4). The N-pyrimidyl indole 1’c as well as the N-acyl
substrates 1’d and 1’e were also tested. However, no desired
alkynylation product could be detected at all except the Glaser
coupling product (entries 5–7). Thus 6-methylpyridin-2-yl di-
recting group was found to be the best choice. As a different
rhodium precatalyst [Cp*RhCl ] was also tested, which provid-
2
2
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Under the optimized conditions, we investigated the sub-
strate scope of this CÀH alkynylation reaction (Scheme 2). To
our delight, 1-(6-methylpyridin-2-yl)-1H-indoles containing elec-
tron-donating or electron-withdrawing substituents, including
OMe, Me, Cl, or F, at C5 position of the indole ring all coupled
smoothly with 2a to provide the corresponding alkynylation
products 3ca–3 fa in moderate to good yields (53–73%). In
contrast, the indole substrate with an ester functionality
reactions of both 3-methylated and 3-unsubstituted indole
substrates 1a and 1b with tert-propargyl alcohols 2 bearing
various substitution patterns have been extensively investigat-
ed. Firstly, the reactions of 1a with tert-propargyl alcohols con-
taining different electron-withdrawing or electron-donating
substituents such as Cl, Ph, and Et at the para position on the
phenyl ring were studied, which proceeded smoothly to give
the desired alkynylation products 3ab–3ad in moderate to
good yields. If the C3-unsubstituted indole 1b was employed,
the alkynylation reaction worked even better to provide the
corresponding alkynylation products (3bb, 3bc, and 3be) in
good to excellent yields. However, the reaction of 1a and 1b
with ethyl 4-(3-hydroxy-3-methylbut-1-yn-1-yl)benzoate 2 f
[
23a]
showed poor reactivity to yield the desired product 3ga.
As
for the scope of the g-substituted tert-propargyl alcohols, the
[
23a]
showed poor conversion (3af, 3bf).
Next, tert-propargyl al-
cohols 2 bearing a methoxy group at the ortho, meta, and
para position on the phenyl ring of the alkynyl group were
studied to examine the influences of the different positions of
the substituent for the reaction. It was found that, for 1a, sub-
strate bearing a methoxy group at the para position on the
phenyl ring proceeded smoothly to give the alkynylation prod-
uct 3ag, whereas that with a methoxy group at the meta and
ortho position failed to yield the desired product 3ah and 3ai.
In contrast, reactions between the para-substituted substrate
2
g or the meta-substituted substrate 2h and 1b were all suc-
cessful to afford 3bg and 3bh, with the latter in a considerably
lower yield. Again, if it came to the ortho-substituted substrate
2
i, alkynylation of 1b also failed (3bi). These observations may
reflect the influences of steric hindrance for the reaction to
some extent. On the other hand, if the ortho-CO Me tert-prop-
2
argyl alcohol 2j was employed, the alkynylated product 3bj
could be obtained in 24% yield, which, together with the re-
sults of 3ga, 3af, 3bf, and 3bi, suggested that the electronic
effect played key roles for the outcome of the reactions. More-
over, thiophene-containing 2-methyl-4-(thiophen-2-yl)but-3-yn-
2
-ol 2k was also tested. Although the reaction with 1b provid-
ed the corresponding alkynylated 3bk in a low yield of
[
23b]
1
5%,
the alkynylation of 1a proceeded smoothly to give
3
ak in 72% yield. Notably, aliphatic 2-methyloct-3-yn-2-ol 2l
was also compatible with this transformation to produce the
C2-alkynylated products 3al and 3bl in moderate yields. How-
ever, the reactivity decreased significantly for the 4-cycloprop-
yl-2-methylbut-3-yn-2-ol substrate 2m, which gave the alkyny-
lated product 3bm in only 15% yield, perhaps because of the
more steric hindrance of the cyclopropyl substituent.
The definite structure of the alkynylation products came
[
24]
from an X-ray crystallography study of 3ag, which clearly
shows that the pyridine N atom is oriented away from the al-
kynyl functionality because of the steric interaction between
the methyl group at the pyridine C6 position and the alkynyl
group, and thus prevents further transformation of the alkyny-
lation product into the corresponding pyrido[2,1-a]indole
(
Figure 1).
In addition, given the importance of carbazole derivatives in
[
25]
various biologically active compounds and materials science,
Scheme 2. Substrate scope for the C2-selective CÀH alkynylation of indoles.
we were also intrigued to extend this CÀH alkynylation reac-
tion to carbazole substrates. To the best of our knowledge, the
CÀH functionalization of carbazoles is much less developed
2
General reaction conditions: 1 (0.2 mmol), 2 (0.6 mmol), [RhCl(cod)] (1.5 mol
%
), Cu(OAc)
2 2
·H O (2.2 equiv.), PhMe (2 mL), 1258C, air, 10 h. Yield of isolated
products based on 1. [a] Previously reported in Ref. [22].
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worked well to afford the C1 alkynylated carbazoles in good to
excellent yields (5a–5d, 5 f, and 5g). As was the case in the al-
kynylation of indoles, a methoxy group at the para or meta po-
sition on the phenyl ring of the alkynyl group can be tolerated
to provide the alkynylcarbazoles in good yields (5g, 5h),
whereas tert-propargyl alcohol with a methoxy group at the
ortho position of the phenyl ring failed to afford the alkynylat-
ed product (5i). The ortho-CO Me tert-propargyl alcohol 2j was
2
also tested to give product 5j in 55% yield. Moreover, the sub-
strate scope could also be extended to heterocycle-containing
tert-propargyl alcohols and aliphatic tert-propargyl alcohols, af-
fording the thiophenylethynyl (5k) and hex-1-yn-1-yl (5l)
carbazoles in moderate and good yields, respectively.
[
24]
Figure 1. X-ray crystal structure of product 3ag.
In an effort to highlight the synthetic utility of this alkynyla-
tion protocol, 1 mmol and 3 mmol scale reactions were con-
ducted by using 1b as a substrate, and the reaction with 1a
proceeded smoothly to give the target alkynylated product
3ba in 59% and 47% yields, respectively (Scheme 4).
[
26,27]
than other heteroarenes owing to their intrinsic inertness,
in which direct and specific C1 alkynylation is especially chal-
lenging. The only one example prior to our study was reported
by Zhou and Li very recently, in that the Ir-catalyzed C1 alkyny-
lation of N-pyrimidyl-carbazole was achieved by using the hy-
[28]
pervalent iodine alkynylating reagent TIPS–EBX. Pleasingly, it
was found that C1-selective alkynylation of N-pyridyl-carbazole
[26]
4
with g-substituted tert-propargyl alcohols could be realiz-
ed under our conditions for the alkynylation of indoles. As
shown in Scheme 3, tert-propargyl alcohols with various elec-
tron-withdrawing or -donating substituents including H, Cl, Ph,
Scheme 4. Gram-scale synthesis of 2-alkynyl indole 3ba.
Et, CO Et, and OMe at the para position of the phenyl ring all
Finally, the pyridyl directing group of the indole alkynylation
2
product could be removed by treatment of 3ba with MeOTf/
[
29]
NaOH (Tf=trifluoromethanesulfonyl) affording the free (NÀ
H) 2-alkynyl indole 6 in 67% yield, which provides promising
applicability of this alkynylation reaction in further synthetic
transformation (Scheme 5). For instance, the very recent stud-
Scheme 5. Removal of the pyridine directing group and transformation of
free 2-alkynyl indole.
ies have demonstrated that 2-alkynyl indoles could serve as
a potential candidate for CO2 fixation, which readily reacts
with CO in the presence of TBD (TBD=1,3,4,6,7,8-hexahydro-
2
2
H-pyrimido[1,2-a]pyrimidine) as organocatalyst to provide
[
30]
a series of tricyclic indole-containing complexes 7. Unfortu-
nately, our efforts to remove the pyridyl directing group of the
alkynylated carbazole 5a under similar conditions were unsuc-
cessful, although there has been a report on the cleavage of
Scheme 3. CÀH alkynylation of carbazoles at C1 position. General reaction
2
conditions: 4 (0.2 mmol), 2 (0.6 mmol), [RhCl(cod)] (1.5 mol %), Cu(OA-
2 2
c) ·H O (2.2 equiv.), PhMe (2 mL), 1258C, air, 16 h. Yield of isolated products
based on 4.
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the pyridyl group of 1-aryl-9-(pyridin-2-yl)-9H-carbazoles under
hols as the alkynylating reagent. The broader substrate scope
as well as the removable directing group of this strategy
allows for the construction of C2 alkynylated indoles accessible
in organic synthesis. Moreover, this protocol has also been ap-
plied to the CÀH alkynylation of carbazoles to afford the corre-
sponding C1 alkynylated carbazoles.
[26]
similar N-methylation/hydrolysis conditions.
Our previous studies on the rhodium/copper-catalyzed syn-
thesis of pyrido[2,1-a]indoles have showed that no appreciable
reaction could be observed if the stoichiometric reaction of
[
RhCl(cod)] with pyridyl indole was performed in the absence
2
III
of Cu(OAc) ·H O, however, the biscyclometalated Rh complex
2
2
was obtained in the presence of Cu(OAc) ·H O, which clearly
2
2
Experimental Section
indicated that the cyclometalation of the pyridyl indole was
III
enforced with the Rh species. In addition, we have demon-
General remarks
strated that Cu(OAc) ·H O is not only an oxidant but also re-
2
2
All reagents and solvents were obtained from commercial suppliers
and used without further purification. All glassware was dried over-
night at 110 8C prior to use. Chromatography was performed on
sponsible for the CÀC bond cleavage of tert-propargyl alcohols
[22]
to generate the alkynylcopper species. Consequently, a simi-
lar plausible mechanism for this CÀH alkynylation reaction is il-
3
00–400 mesh silica gel. Melting points were determined on a Mel-
lustrated in Scheme 6. Reaction of [RhCl(cod)] with 1b in the
2
Temp apparatus and are reported uncorrected. Mass spectra
(HRMS) were obtained on Bruker En Apex ultra 7.0T FTMS by the
Public Instrument Platform of College of Chemistry and Chemical
presence of Cu(OAc) ·H O generates the biscyclometalated in-
2
2
termediate I. Transmetalation of the alkynyl group from the
in situ generated alkynylcopper to I provides the alkynylrhodi-
um II, which undergoes a reductive elimination to release the
1
Engineering at Xiamen University. H NMR spectra were recorded
on a Bruker AV-400 spectrometer and a Bruker AV-500 spectrome-
ter in chloroform-d3. Chemical shifts are reported in ppm with the
internal TMS signal at 0.0 ppm as a standard. The data is being re-
ported as (s=singlet, d=doublet, t=triplet, m=multiplet or unre-
solved, brs=broad singlet, coupling constant (s) in Hz, integration).
I
alkynylation product and extrudes Rh species IV via intermedi-
ate III. Reaction of IV with 1b in the presence of Cu(OAc) ·H O
2
2
as an oxidant regenerates the CÀH activation intermediate I.
13
C NMR spectra were recorded on a Bruker AV-400 spectrometer
and a Bruker AV-500 spectrometer in chloroform-d3. Chemical
shifts are reported in ppm with the internal chloroform signal at
7
7.0 ppm as a standard.
General procedure for the synthesis of indoles C-2 alkynyla-
tion products 3
A mixture of indole derivatives 1 (0.20 mmol), tert-propargyl alco-
hols 2 (0.60 mmol), [RhCl(cod)] (1.5 mol%), Cu(OAc) ·H O (88 mg,
2
2
2
2
.2 mmol), and toluene (2 mL) was added to a Schlenk tube under
an air atmosphere. Then the mixture was stirred at 1258C (bath
temperature, preheated) under air for desired time (usually 10 h)
until complete consumption of starting materials judged by TLC.
Then the reaction mixture was filtered through a short plug of
silica gel, washed with ethyl acetate and concentrated, the residue
was purified by chromatography (petroleum ether/ethyl acetate=
1
00:1 to 30:1) to afford the desired products 3.
3
-Methyl-1-(6-methylpyridin-2-yl)-2-(phenylethynyl)-1H-indole
1
(3aa): Colorless solid; 39 mg, 61% yield; m.p.: 150–1528C; H NMR
(
500 MHz, CDCl ): d=7.82 (d, J=8.3 Hz, 1H), 7.76 (t, J=7.7 Hz, 1H),
3
7
7
7
.59 (d, J=7.8 Hz, 1H), 7.51 (d, J=8.0 Hz, 1H), 7.44–7.42 (m, 2H),
.34–7.30 (m, 3H), 7.29 (t, J=7.3 Hz, 1H), 7.20 (t, J=7.5 Hz, 1H),
.14 (d, J=7.5 Hz, 1H), 2.66 (s, 3H), 2.53 ppm (s, 3H). C NMR
1
3
(
125 MHz, CDCl ): d=158.0, 150.9, 137.9, 136.6, 131.0, 128.6, 128.3,
3
1
9
28.2, 124.4, 123.2, 121.2, 121.0, 120.8, 119.1, 118.5, 116.6, 112.1,
+
8.2, 81.5, 24.3, 9.9 ppm; HRMS (ESI) Calcd for C H N Na [M+Na
23
18
2
]
, 345.1362, found 345.1367.
1
-(6-Methylpyridin-2-yl)-2-(phenylethynyl)-1H-indole (3ba): Red
Scheme 6. Proposed mechanism for the CÀH alkynylation.
1
solid; 42 mg, 68% yield; m.p.: 143–1458C; H NMR (500 MHz,
CDCl ): d=7.82 (m, 2H), 7.76 (t, J=7.7 Hz, 1H), 7.59 (d, J=7.8 Hz,
3
1
H), 7.44–7.42 (m, 2H), 7.34–7.30 (m, 3H), 7.29 (t, J=7.3 Hz, 1H),
1
3
Conclusions
7.20 (m, 2H), 7.14 (d, J=7.5 Hz, 1H), 2.68 ppm (s, 3H); C NMR
125 MHz, CDCl ): d=158.2, 150.5, 138.0, 136.9, 131.1, 128.4, 128.3,
(
3
We have presented an efficient approach for rhodium-cata-
lyzed/copper-mediated C2-selective CÀH alkynylation of in-
doles by taking advantage of g-substituted tert-propargyl alco-
1
28.0, 124.2, 122.8, 121.5, 121.3, 120.8, 120.5, 117.2, 112.1, 111.5,
+
95.3, 81.9, 24.3 ppm. HRMS (ESI) Calcd for C H N Na [M+Na ]:
331.1206, found: 331.1203.
22
16
2
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Full Papers
5
-Methoxy-1-(6-methylpyridin-2-yl)-2-(phenylethynyl)-1H-indole
2-((4-Ethylphenyl)ethynyl)-3-methyl-1-(6-methylpyridin-2-yl)-1H-
1
(3ca): Colorless solid; 43 mg, 64% yield; m.p.: 163–1658C; H NMR
indole (3ad): Colorless solid; 52 mg, 74% yield; m.p.: 186–1888C;
1
(
500 MHz, CDCl ): d=7.69 (dd, J=5.7, 8.2 Hz, 2H), 7.53 (d, J=
H NMR (500 MHz, CDCl ): d=7.73 (d, J=8.1 Hz, 1H), 7.62 (t, J=
3
3
7
1
3
1
1
.8 Hz, 1H), 7.42 (d, J=7.8 Hz, 1H), 7.27 (d, J=8.1 Hz, 2H), 7.18 (m,
H), 7.10 (t, J=7.8 Hz, 2H), 6.91 (s, 1H), 6.77 (d, J=8.7 Hz, 2H),
7.9 Hz, 1H), 7.47 (d, J=8.0 Hz, 1H), 7.40 (d, J=8.0 Hz, 1H), 7.25 (d,
J=8.1 Hz, 2H), 7.17 (dt, J=0.9, 7.1 Hz, 1H), 7.09 (dt, J=0.9, 7.2 Hz,
1H), 7.05 (d, J=8.1 Hz, 2H), 7.00 (d, J=7.6 Hz, 1H), 2.54 (m, 5H),
1
3
.74 (s, 3H), 2.59 ppm (s, 3H); C NMR (125 MHz, CDCl ): d=159.8,
3
13
58.1, 150.6, 137.9, 136.8, 132.7, 128.1, 124.0, 121.4, 121.2, 120.9,
2.42 (s, 3H), 1.13 ppm (t, J=7.6 Hz, 3H); C NMR (125 MHz, CDCl3):
d=157.9, 150.8, 144.7, 137.8, 136.5, 131.0, 128.6, 127.9, 124.3,
120.9, 120.8, 120.7, 120.3, 119.0, 118.6, 116.6, 112.1, 98.3, 80.7, 28.8,
20.7, 117.2, 145.0, 114.1, 112.1, 111.0, 95.3, 80.6, 55.3, 24.4 ppm.
+
HRMS (ESI) Calcd for C H N ONa [M+Na ]: 361.1311, found:
3
2
3
18
2
+
61.1313.
24.3, 15.3, 9.9 ppm; HRMS (ESI) Calcd for C H N Na [M+Na ]:
25
22
2
3
73.1675, found: 373.1671.
5
-Methyl-1-(6-methylpyridin-2-yl)-2-(phenylethynyl)-1H-indole
1
(3da): Colorless solid; 47 mg, 73% yield; m.p.: 169–1718C; H NMR
2-((4-Chlorophenyl)ethynyl)-1-(6-methylpyridin-2-yl)-1H-indole
(
7
6
500 MHz, CDCl ): d=7.67 (dd, J=7.8, 9.1 Hz, 2H), 7.53 (d, J=
(3bb): Light yellow solid: 51 mg, 75% yield; m.p.: 126–1288C;
3
1
.8 Hz, 1H), 7.41 (d, J=7.8 Hz, 1H), 7.20 (m, 2H), 7.16 (dd, J=5.7,
.8 Hz, 1H), 7.08 (m, 2H), 7.03 (d, J=7.8 Hz, 2H), 6.92 (s, 1H), 2.57
H NMR (500 MHz, CDCl ): d=7.71–7.67 (m, 2H), 7.55 (d, J=7.8 Hz,
3
1H), 7.39 (d, J=7.8 Hz, 1H), 7.25–7.20 (m, 5H), 7.14–7.10 (m, 2H),
1
3
13
(
s, 3H), 2.26 ppm (s, 3H); C NMR (125 MHz, CDCl ): d=158.1,
6.90 (s, 1H), 2.59 ppm (s, 3H); C NMR (125 MHz, CDCl ) d=158.3,
3
3
1
50.5, 138.7, 136.8, 131.0, 129.1, 128.1, 124.1, 121.4, 121.2, 120.7,
150.4, 138.7, 136.9, 134.4, 132.3, 128.7, 127.9, 124.4, 121.6, 121.4,
121.3, 120.9, 120.2, 117.1, 112.0, 111.8, 94.1, 82.9, 24.3 ppm; HRMS
119.7, 117.2, 112.1, 111.2, 95.5, 81.2, 24.3, 21.5 ppm. HRMS (ESI)
+
+
Calcd for C H N Na [M+Na ], 345.1362, found 345.1367.
(ESI) Calcd for C H ClN [M+H ]: 343.0997, found: 343.0997.
2
3
18
2
22 16
2
5
-Chloro-1-(6-methylpyridin-2-yl)-2-(phenylethynyl)-1H-indole (3ea):
2-([1,1’-Biphenyl]-4-ylethynyl)-1-(6-methylpyridin-2-yl)-1H-indole
(3bc): Yellow solid; 62 mg, 81% yield; m.p.: 146–1488C; H NMR
1
1
Colorless solid; 36 mg, 53% yield; m.p.: 152–1548C; H NMR
500 MHz, CDCl ): d=7.69 (dd, J=7.8, 9.3 Hz, 2H), 7.55 (d, J=
(
(500 MHz, CDCl ): d=7.72–7.69 (m, 2H), 7.54 (d, J=7.8 Hz, 1H),
3
3
7
6
.9 Hz, 1H), 7.38 (d, J=7.9 Hz, 1H), 7.22 (m, 5H), 7.11 (dd, J=4.8,
.8 Hz, 2H), 6.95 (s, 1H), 2.58 ppm (s, 3H); C NMR (125 MHz,
7.51–7.46 (m, 4H), 7.43 (d, J=7.8 Hz, 1H), 7.39–7.34 (m, 4H), 7.27
1
3
(m, 1H), 7.20 (m, 1H), 7.12–7.10 (m, 2H), 6.96 (s, 1H), 2.60 ppm (s,
13
CDCl ): d=158.3, 150.4, 138.0, 136.9, 134.5, 132.3, 128.7, 128.0,
3H); C NMR (125 MHz, CDCl ) d=158.2, 150.5, 141.2, 140.2, 138.0,
3
3
1
8
3
24.4, 121.6, 121.4, 121.3, 120.9, 120.2, 117.1, 112.0, 111.8, 94.1,
136.9, 131.5, 128.9, 128.0, 127.7, 127.1, 127.0, 124.2, 121.7, 121.5,
121.4, 120.8, 120.6, 117.2, 112.1, 111.6, 95.2, 82.6, 24.4 ppm; HRMS
+
2.9, 24.3 ppm; HRMS (ESI) Calcd for C H ClN Na [M+Na ]:
2
2
15
2
+
65.0816, found: 365.0814.
(ESI) Calcd for C H N Na [M+Na ]: 407.1519, found: 407.1524.
28
20
2
5
-Fluoro-1-(6-methylpyridin-2-yl)-2-(phenylethynyl)-1H-indole (3 fa):
1-(6-Methylpyridin-2-yl)-2-(p-tolylethynyl)-1H-indole (3be): Yellow
solid; 46 mg, 71% yield; m.p.: 134–1368C; H NMR (500 MHz,
1
1
Colorless solid; 42 mg, 64% yield; m.p.: 162–1648C; H NMR
500 MHz, CDCl ): d=7.68 (t, J=8.1 Hz, 2H), 7.53 (d, J=7.9 Hz, 1H),
(
CDCl ): d=7.69–7.66 (m, 2H), 7.53 (d, J=7.8 Hz, 1H), 7.41 (d, J=
3
3
7
.38 (d, J=7.9 Hz, 1H), 7.28 (m, 2H), 7.19 (t, J=7.2 Hz, 1H), 7.10
7.8 Hz, 1H), 7.22–7.19 (m, 2H), 7.18–7.16 (m, 1H), 7.11–7.08(m, 2H),
13
(
dd, J=8.8, 9.9 Hz, 2H), 6.93 (m, 3H), 2.58 ppm (s, 3H); C NMR
125 MHz, CDCl ): d=162.5 (d, J =250.7 Hz), 158.2, 150.5, 138.0,
7.04 (d, J=7.8 Hz, 2H), 6.92 (s, 1H), 2.58 (s, 3H), 2.27 ppm (s, 3H);
13
(
C NMR (125 MHz, CDCl ): d=158.1, 150.5, 138.7, 138.0, 136.8,
3
3
CF
1
36.9, 130.0 (d, J =8.3 Hz), 128.0, 124.2, 121.5, 121.3, 120.8, 120.4,
131.1, 129.1, 128.1, 124.1, 121.5, 121.3, 120.7, 119.7, 117.2, 112.1,
111.3, 95.5, 81.2, 24.3, 21.5 ppm; HRMS (ESI) Calcd for C H N Na
[M+Na ]: 345.1362, found: 345.1367.
CF
1
9
3
18.9 (d, J =3.5 Hz), 117.1, 115.7 (d, J =21.9 Hz),112.0, 111.5,
C
F
C
F
23 18
2
+
+
4.1, 81.6, 24.3 ppm; HRMS (ESI) Calcd for C H FN Na [M+Na ]:
2
2
15
2
49.1111, found: 349.1114.
2
-((4-Methoxyphenyl)ethynyl)-3-methyl-1-(6-methylpyridin-2-yl)-1H-
2
-((4-Chlorophenyl)ethynyl)-3-methyl-1-(6-methylpyridin-2-yl)-1H-
indole (3ag): Colorless solid; 52 mg, 74% yield; m.p.: 152–1548C;
1
indole (3ab): Colorless solid; 36 mg, 49% yield; m.p.: 181–1838C;
H NMR (500 MHz, CDCl ): d=7.85 (d, J=8.2 Hz, 1H), 7.76 (t, J=
3
1
H NMR (500 MHz, CDCl ): d=7.80 (d, J=8.4 Hz, 1H), 7.75 (t, J=
7.7 Hz, 1H), 7.61 (d, J=7.9 Hz, 1H), 7.53 (d, J=8.0 Hz, 1H), 7.42–
7.39 (m, 2H), 7.30 (t, J=7.4 Hz, 1H), 7.22 (t, J=7.4 Hz, 1H), 7.15 (d,
3
7
7
3
.8 Hz, 1H), 7.59 (d, J=7.7 Hz, 1H), 7.46 (d, J=7.6 Hz, 1H), 7.33–
.30 (m, 5H), 7.20 (t, J=6.8 Hz, 1H), 7.14 (d, J=7.6 Hz, 1H), 2.65 (s,
J=7.6 Hz, 1H), 6.90–6.88 (m, 2H), 3.85 (s, 3H), 2.68 (s, 3H),
1
3
13
H), 2.52 ppm (s, 3H); C NMR (125 MHz, CDCl ): d=158.1, 150.7,
2.55 ppm (s, 3H); C NMR (125 MHz, CDCl ): d=159.7, 158.0, 150.9,
3
3
1
1
9
37.9, 136.7, 134.2, 133.7, 132.2, 128.9, 128.7, 128.5, 124.6, 121.7,
21.5, 121.1, 120.9, 119.2, 118.1, 116.5, 112.1, 97.0, 82.5, 24.4,
137.8, 136.5, 132.6, 128.7, 124.2, 120.9, 120.6, 120.5, 119.0, 118.8,
116.6, 115.3, 114.1, 112.1, 98.1, 80.1, 55.3, 24.3, 9.9 ppm; HRMS (ESI)
+
+
.9 ppm; HRMS (ESI) Calcd for C H N ClNa [M+Na ]: 379.0972,
Calcd for C H N ONa [M+Na ]: 375.1468, found: 375.1469.
2
3
17
2
24 20
2
found: 379.0973.
2
-((4-Methoxyphenyl)ethynyl)-1-(6-methylpyridin-2-yl)-1H-indole
1
2
-([1,1’-Biphenyl]-4-ylethynyl)-3-methyl-1-(6-methylpyridin-2-yl)-1H-
(3bg): Yellow solid; 57 mg, 85% yield; m.p.: 131–1338C; H NMR
indole (3ac): Colorless solid; 45 mg, 56% yield; m.p.: 177–1798C;
(500 MHz, CDCl ): d=7.70 (m, 2H), 7.53 (d, J=7.7 Hz, 1H), 7.43 (d,
3
1
H NMR (500 MHz, CDCl ): d=7.86 (d, J=8.2 Hz, 1H), 7.80 (t, J=
J=7.8 Hz, 1H), 7.28–7.26 (m, 2H), 7.18 (m, 1H), 7.12–7.09 (m, 2H),
3
1
3
7
7
.7 Hz, 1H), 766-7.60 (m, 6H), 7.54 (t, J=5.7 Hz, 2H), 7.48 (t, J=
.5 Hz, 2H), 7.41 (t, J=4.9 Hz, 1H), 7.33 (t, J=7.9 Hz, 1H), 7.24 (t,
6.90 (s, 1H), 6.77 (m, 2H), 3.74 (s, 3H), 2.59 ppm (s, 3H); C NMR
(125 MHz, CDCl ): d=159.8, 158.1, 150.6, 138.0, 136.8, 132.7, 128.1,
3
J=7.7 Hz, 1H), 7.18 (d, J=7.5 Hz, 1H), 2.70 (s, 3H), 2.59 ppm (s,
124.0, 121.5, 121.3, 120.9, 120.7, 117.2, 114.9, 114.1, 112.1, 111.0,
1
3
+
3
H); C NMR (125 MHz, CDCl ): d=158.1, 150.8, 141.0, 140.3,
95.3, 80.6, 55.3, 24.3 ppm; HRMS (ESI) Calcd for C H N O [M+H ]:
3
23 19
2
1
1
9
37.9, 136.6, 132.9, 131.4, 128.9, 128.6, 127.7, 127.1, 127.0, 124.4,
22.1, 121.2, 121.0, 120.8, 119.1, 118.5, 116.6, 112.1, 98.1, 82.2, 24.4,
339.1492, found: 339.1496.
+
2-((3-Methoxyphenyl)ethynyl)-1-(6-methylpyridin-2-yl)-1H-indole
.9 ppm. HRMS (ESI) Calcd for C H N Na [M+Na ]: 421.1675,
2
9
22
2
1
(3bh): Yellow solid; 39 mg, 57% yield; m.p. 106–1088C; H NMR
found: 421.1677.
(
500 MHz, CDCl ): d=7.70–7.67 (m, 2H), 7.53 (d, J=7.8 Hz, 1H),
3
7
.41 (d, J=7.8 Hz, 1H), 7.20–7.17 (m, 1H), 7.15–7.08 (m, 3H), 6.95
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Full Papers
(
s, 1H), 6.91 (m, 1H), 6.85 (m, 1H), 6.79 (m, 1H), 3.70 (s, 3H),
d=158.0, 150.6, 137.8, 136.5, 128.0 123.7, 121.3, 121.2, 121.1,
1
3
2
1
1
.58 ppm (s, 3H); C NMR (125 MHz, CDCl ): d=159.3, 158.2, 150.4,
120.5, 117.2, 112.0, 110.7, 99.7, 67.9, 29.7, 24.3, 8.6 ppm; HRMS (ESI)
3
+
38.0, 136.9, 129.4, 128.0, 124.2, 123.8, 123.7, 121.5, 121.3, 120.8,
Calcd for C H N [M+H ]: 273.1386, found: 273.1386.
19
17
2
20.5, 117.2, 116.2, 114.9, 112.1, 111.6, 95.2, 81.7, 55.3, 24.3 ppm;
+
HRMS (ESI) Calcd for C H N O [M+H ]: 339.1492, found:
2
3
19
2
3
39.1493.
General procedure for the synthesis of carbazoles C-1 alky-
nylation products 5
Methyl 2-((1-(6-methylpyridin-2-yl)-1H-indol-2-yl)ethynyl)benzoate
1
(3bj): Yellow oil; 17 mg, 24% yield; H NMR (500 MHz, CDCl ): d=
3
A mixture of carbazole derivative 4 (0.20 mmol), tert-propargyl al-
7
1
2
3
1
1
1
.98 (d, J=7.8 Hz, 1H), 7.87 (d, J=7.8 Hz, 1H), 7.80 (t, J=7.8 Hz,
H), 7.66 (d, J=7.8 Hz, 1H), 7.62 (d, J=7.8 Hz, 1H), 7.50–7.46 (m,
H), 7.38 (m, 1H), 7.32 (m, 1H), 7.24–7.19 (m, 2H), 7.13 (s, 1H),
cohols
88 mg, 2.2 mmol), and toluene (2 mL) was added to a Schlenk
tube under an air atmosphere. Then the mixture was stirred at
258C (bath temperature, pre-heated) under air for desired time
usually 16 h) until complete consumption of starting materials
2 (0.60 mmol), [RhCl(cod)]2 (1.5 mol%), Cu(OAc) ·H O
2 2
(
1
3
.86 (s, 3H), 2.69 ppm (s, 3H); C NMR (125 MHz, CDCl ): d=
3
1
(
66.45,158.08, 150.60, 138.23, 136.99, 133.65, 131.68, 131.41,
30.54, 128.12, 128.03, 124.44, 123.30, 121.61, 121.21, 120.90,
judged by TLC. Then the reaction mixture was filtered through
a short plug of silica gel, washed with ethyl acetate and concen-
trated, the residue was purified by chromatography (petroleum
ether/ethyl acetate=50:1 to 30:1) to afford the desired products 5.
20.51, 117.29, 112.62, 112.39, 94.30, 86.77, 52.07, 24.36 ppm;
+
HRMS (ESI) Calcd for C H N O [M+H ]: 367.1441, found:
3
2
4
19
2
2
67.1447.
3
-Methyl-1-(6-methylpyridin-2-yl)-2-(thiophen-3-ylethynyl)-1H-
1
4
-(phenylethynyl)-9-(pyridin-2-yl)-9H-carbazole (5a): Colorless solid;
indole (3ak): Orange solid; 47 mg, 72% yield; m.p.: 176–1788C;
1
1
2 mg, 61%; m.p.: 173–1758C; H NMR (500 MHz, CDCl ): d=8.73
H NMR (500 MHz, CDCl ): d=7.72 (d, J=8.3 Hz, 1H), 7.65 (t, J=
3
3
(
dd, J=1.3, 4.9 Hz, 1H), 8.16 (dd, J=1.1, 8.4 Hz, 2H), 7.83 (dt, J=
7
.8 Hz, 1H), 7.50 (d, J=7.8 Hz, 1H), 7.39 (d, J=8.0 Hz, 1H), 7.35
1
7
7
1
1
1
.9, 7.8 Hz, 1H), 7.68 (dd, J=1.1, 7.6 Hz, 1H), 7.52 (t, J=8.9 Hz, 2H),
.45 (dt, J=1.1, 7.2 Hz, 1H), 7.37–7.32 (m, 3H), 7.28–7.25 (m, 3H),
(
(
dd, J=1.1, 3.0 Hz, 1H), 7.20 (m, 2H), 7.11 (t, J=7.8 Hz, 1H), 7.03
m, 2H), 2.57 (s, 3H), 2.43 ppm (s, 3H). C NMR (125 MHz, CDCl3):
1
3
13
.06 ppm (dt, J=1.5, 5.5 Hz, 2H); C NMR (125 MHz, CDCl ): d=
d=158.0, 150.8, 137.9, 136.5, 129.5, 128.6, 128.2, 125.4, 124.4,
1
9
3
51.3, 149.1, 141.8, 139.2, 137.6, 131.5, 131.4, 129.7, 128.4, 127.9,
27.8, 126.6, 125.2, 123.4, 123.2, 123.1, 122.7, 121.0, 120.8, 120.4,
22.2, 121.0, 120.9, 120.7, 119.1, 118.4, 116.5, 112.0, 93.2, 80.8, 24.3,
+
.9 ppm; HRMS (ESI) Calcd for C H N SNa [M+Na ]: 351.0926,
2
1
16
2
20.1, 110.7, 106.8, 96.2, 86.9 ppm; HRMS (ESI): Calcd for C H N
2
found: 351.0925.
25 16
+
[M+Na ]: 367.1206, found: 367.1210.
1
-(6-Methylpyridin-2-yl)-2-(thiophen-3-ylethynyl)-1H-indole (3bk):
1
1
-((4-chlorophenyl)ethynyl)-9-(pyridin-2-yl)-9H-carbazole (5b): Light
Light yellow liquid; 9 mg, 15% yield; H NMR (500 MHz, CDCl ): d=
3
1
yellow solid; 62 mg, 82% yield; m.p.: 104–1068C; H NMR
500 MHz, CDCl ): d=8.59(m, 1H), 8.02 (m, 2H), 7.69 (td, J=7.8 Hz,
7
7
2
3
1
.80–7.77 (m, 2H),7.64 (d, J=7.8 Hz, 1H), 7.50 (d, J=7.8 Hz, 1H),
.45 (dd, J=2.8 Hz, J=1.0 Hz, 1H), 7.31–7.29 (m, 2H), 7.22–7.19 (m,
H), 7.11 (dd, J=4.8 Hz, J=1.0 Hz, 1H), 7.03 (s, 1H), 2.69 ppm (s,
(
3
J=2.0 Hz, 1H), 7.52 (dd, J=7.8 Hz, J=1.0 Hz, 1H), 7.39–7.30 (m,
1
3
3
H), 7.23–7.17 (m, 3H), 7.11 (m, 2H), 6.84–6.81 ppm (m, 2H);
H); C NMR (125 MHz, CDCl ): d=158.2,150.5, 138.0, 136.9, 129.5,
3
13
C NMR (125 MHz, CDCl ): d=151.2, 149.1, 141.7, 139.2, 137.6,
28.7, 128.0, 125.5, 124.2, 121.9, 121.5, 121.3, 120.8, 120.5, 117.1,
3
1
1
33.9, 132.5, 131.4, 128.3, 126.7, 125.2, 123.4, 123.0, 122.7, 121.6,
1
12.1, 111.5, 90.5, 81.3, 24.4 ppm; HRMS (ESI) Calcd for C H N S
20 15 2
+
21.1, 121.0, 120.5, 120.1, 110.7, 106.3, 95.0, 87.9 ppm; HRMS (ESI)
[M+H ]: 315.0950, found: 315.0947.
+
Calcd for C H ClN [M+H ]: 379.0997, found: 379.0995.
25
16
2
2
-(Hex-1-yn-1-yl)-3-methyl-1-(6-methylpyridin-2-yl)-1H-indole (3al):
1
1
-([1,1’-biphenyl]-4-ylethynyl)-9-(pyridin-2-yl)-9H-carbazole
Yellow solid; 61 mg, 73% yield; m.p.; 160–1628C; H NMR
500 MHz, CDCl ): d=8.64 (s, 2H), 8.04 (m, 2H), 7.73 (t, J=7.8 Hz,
(5c):
Red solid; 28 mg, 46% yield; m.p.: 89–918C; H NMR (500 MHz,
CDCl ): d=7.67 (d, J=8.2 Hz, 1H), 7.61 (t, J=7.7 Hz, 1H), 7.45 (d,
J=7.6 Hz, 1H), 7.33 (d, J=7.6 Hz, 1H), 7.15 (t, J=8.0 Hz, 1H), 7.08
1
3
(
3
1
7
H), 7.58–7.54 (m, 1H), 7.50–7.48 (m, 3H), 7.41–7.31 (m, 6H), 7.28–
.20 (m, 4H), 6.98 ppm (d, J=8.3 Hz, 1H). C NMR (125 MHz,
(
d, J=7.6 Hz, 1H), 7.03 (m, 2H), 2.55 (s, 3H), 2.36 (t, J=6.8 Hz, 2H),
13
2
.34 (s, 3H), 1.46 (m, 2H), 1.32 (m, 2H), 0.83 ppm (t, J=7.4 Hz, 3H);
1
3
CDCl ): d=151.3, 149.1, 141.7, 140.6, 140.3, 139.2, 137.6, 132.9,
C NMR (125 MHz, CDCl ): d=157.9, 151.0, 137.8, 136.2, 128.6,
3
3
1
1
8
4
31.8, 131.5, 128.9, 128.8, 127.6, 127.1, 126.9, 126.6, 125.2, 123.5,
1
2
23.8, 120.7, 120.6, 119.6, 119.2, 118.8, 116.8, 111.9, 99.4, 72.3, 30.6,
4.3, 21.9, 19.5, 13.6, 9.7 ppm; HRMS (ESI) Calcd for C H N Na
23.1, 122.7, 122.0, 121.0, 120.8, 120.5, 120.1, 110.7, 106.8, 96.2,
21
22
2
+
+
7.6 ppm; HRMS (ESI) Calcd for C H N [M+H ]: 421.1699, found:
[M+Na ]: 325.1675, found: 325.1671.
31 21
2
21.1703.
2
-(Hex-1-yn-1-yl)-1-(6-methylpyridin-2-yl)-1H-indole (3bl): Light
1
1
-((4-Ethylphenyl)ethynyl)-9-(pyridin-2-yl)-9H-carbazole (5d): Color-
yellow liquid; 33 mg, 55% yield; H NMR (500 MHz, CDCl ): d=
7
7
3
1
less solid; 58 mg, 78% yield; m.p.: 168–1708C; H NMR (500 MHz,
CDCl ): d=8.74 (dd, J=1.3, 4.8 Hz, 1H), 8.17 (dt, J=1.1, 8.0 Hz,
.62–7.59 (m, 2H), 7.48 (d, J=7.8 Hz, 1H), 7.31 (d, J=7.8 Hz, 1H),
.15–7.12 (m, 1H), 7.07–7.03 (m, 2H), 6.76 (s, 1H), 2.55 (s, 3H), 2.29
3
2
(
H), 7.83 (dt, J=2.2, 7.7 Hz, 1H), 7.69 (dd, J=1.0, 6.6 Hz, 1H), 7.53
t, J=7.7 Hz, 2H), 7.46 (t, J=7.4 Hz, 1H), 7.37–7.32 (m, 3H), 7.12 (d,
J=7.9 Hz, 2H), 6.98 (d, J=7.9 Hz, 2H), 2.67 (q, J=7.6 Hz, 2H),
(
t, J=6.8 Hz, 2H), 1.41 (m, 2H), 1.27 (m, 2H), 0.80 ppm (t, J=
1
3
7
1
9
.2 Hz, 3H); C NMR (125 MHz, CDCl ): d=158.0, 150.6, 137.8,
3
36.5, 127.9 123.6, 121.3, 121.2, 121.1, 120.5, 117.3, 111.9, 110.3,
13
1
1
1
.27 ppm (t, J=7.6 Hz, 3H); C NMR (125 MHz, CDCl ): d=151.2,
6.7, 72.8, 30.3, 24.3, 21.82, 19.3, 13.5 ppm; HRMS (ESI) Calcd for
3
+
49.0, 141.7, 139.1, 137.5, 131.5, 131.3, 128.3, 127.4, 127.3, 126.5,
25.8, 125.1, 123.4, 123.0, 122.6, 121.0, 120.5, 120.4, 120.3, 120.1,
C H N Na [M+Na ]: 311.1519, found: 311.1520.
20
20
2
2
-(Cyclopropylethynyl)-1-(6-methylpyridin-2-yl)-1H-indole
(3bm):
110.7, 107.0, 96.5, 86.2, 28.7, 15.2 ppm; HRMS (ESI): Calcd for
1
Light yellow liquid; 8 mg, 15% yield; H NMR (500 MHz, CDCl ): d=
+
3
C H N [M+Na ]: 395.1519, found: 395.1520.
27
20
2
7
7
1
.71–7.73 (m, 2H), 7.59 (d, J=7.8 Hz, 1H), 7.41 (d, J=7.8 Hz, 1H),
Ethyl 4-((9-(pyridin-2-yl)-9H-carbazol-1-yl)ethynyl)benzoate (5 f):
Light yellow solid; 32 mg, 39% yield; m.p.: 181–1838C; H NMR
.25 (m, 1H), 7.19–7.16 (m, 2H), 6.86 (s, 1H), 2.67 (s, 3H), 1.45 (m,
1
1
3
H), 0.87 (m, 2H), 0.75 ppm (m, 2H); C NMR (125 MHz, CDCl3):
(
500 MHz, CDCl ) d=8.59 (m, 1H), 8.05 (dd, J=7.8 Hz, J=1.0 Hz,
3
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1
2
7
H), 8.01 (d, J=7.8 Hz, 1H), 7.80 (m, 2H), 7.71 (td, J=7.8 Hz, J=
.0 Hz, 1H), 7.54 (dd, J=7.5 Hz, J=1.0 Hz, 1H), 7.40–7.30 (m, 3H),
.23–7.19 (m, 3H), 6.94 (m, 2H), 4.27 (q, J=6.9 Hz, 2H), 1.29 ppm
General procedure for the synthesis of indoles C-2 alkynyla-
tion products 3
1
3
Methyltrifluoromethanesulfonate (0.36 mmol, 1.2 equiv) was added
(
t, J=6.9 Hz, 3H); C NMR (125 MHz, CDCl ): d=166.1, 151.2,
3
dropwise to a solution of 3ba (0.20 mmol) in CH Cl (5 mL) at 08C,
1
1
9
49.1, 141.7, 139.3, 137.8, 131.7, 131.2, 129.6, 129.1, 127.7, 126.8,
25.3, 123.4, 123.1, 122.8, 121.3, 121.2, 120.5, 120.2, 110.7, 106.2,
5.5, 89.9, 61.1, 14.3 ppm; HRMS (ESI) Calcd for C H N NaO [M+
2
2
and the resulting solution was stirred for 24 h at RT. Then the sol-
vent was removed under vacuum, and the residue was dissolved
in MeOH (5 mL). A 2m aqueous NaOH solution (2 mL) was added,
and stirring was continued at 608C for 12 h. The solvents were re-
moved, and the resulting residue was extracted with EtOAc (3”
2
8
20
2
2
+
Na ]: 439.1417, found: 439.1420.
1
-((4-Methoxyphenyl)ethynyl)-9-(pyridin-2-yl)-9H-carbazole
(5g):
Colorless solid; 49 mg, 66% yield; m.p.: 179–1818C; H NMR
500 MHz, CDCl ): d=8.73 (d, J=3.7 Hz, 1H), 8.15 (dd, J=3.1,
1
3
0 mL). The combined organic layers were washed with brine,
(
3
dried over MgSO , and concentrated in vacuo. The residue was pu-
4
7
7
3
3
1
1
.5 Hz, 2H), 7.82 (dt, J=1.5, 7.8 Hz, 1H), 7.65 (d, J=7.5 Hz, 1H),
.523 (dd, J=3.1, 7.8 Hz, 2H), 7.45 (t, J=7.8 Hz, 1H), 7.37–7.31 (m,
H), 6.98 (d, J=8.6 Hz, 2H), 6.80 (d, J=8.6 Hz, 2H), 3.83 ppm (s,
rified by flash column chromatography to afford product 6.
2
-(Phenylethynyl)-1H-indole (6): Colorless solid; 29 mg, 67%; m.p.:
1
1
3
101–1038C; H NMR (500 MHz, CDCl ): d=8.26 (br, 1H), 7.65 (d, J=
H); C NMR (125 MHz, CDCl ): d=159.3, 151.3, 149.0, 141.7,
3
3
8
.0 Hz, 1H), 7.59 (m, 2H), 7.41 (m, 3H), 7.36 (d, J=8.5 Hz, 1H), 7.28
39.0, 137.5, 132.8, 131.3, 126.5, 125.1, 123.5, 123.1, 122.6, 121.0,
1
3
(t, J=6.9 Hz, 1H), 7.18 (t, J=7.2 Hz, 1H), 6.88 ppm (s, 1H); C NMR
(125 MHz, CDCl ): d=136.2, 131.5, 128.6, 128.5, 127.9, 123.6, 122.6,
20.5, 120.4, 120.1, 115.3, 113.6, 110.7, 107.1, 96.3, 85.6, 55.2 ppm;
+
HRMS (ESI): Calcd for C H N O [M+Na ]: 397.1311, found:
3
3
2
6
18
2
1
20.9, 120.5, 118.8, 110.7, 108.9, 92.6, 81 ppm; HRMS (ESI): Calcd for
97.1314.
+
C H NNa [M+Na ]: 240.0784, found: 240.0781.
16
11
1
-((3-Methoxyphenyl)ethynyl)-9-(pyridin-2-yl)-9H-carbazole
(5h):
1
Yellow solid; 44 mg, 59% yield; m.p.: 129–1318C; H NMR
500 MHz, CDCl ): d=8.63 (dd, J=4.8 Hz, J=1.3 Hz, 1H), 8.0 (m,
(
3
General procedure for the synthesis of indoles C-2 alkynyla-
tion products 3
2
7
6
H), 7.75 (td, J=7.8 Hz, J=2.0 Hz, 1H), 7.57 (m, 1H), 7.42 (t, J=
.8 Hz, 2H), 7.34 (m, 1H), 7.26–7.22 (m, 3H), 7.06 (t, J=7.8 Hz, 1H),
13
.74 (m, 1H), 6.55 (m, 1H), 6.45 (m, 1H), 3.71 ppm (s, 3H). C NMR
A mixture of indole derivatives 1 (0.20 mmol), tert-propargyl alco-
(
125 MHz, CDCl ): d=159.1, 151.2, 149.0, 141.7, 139.2, 137.7, 131.6,
hols 2 (0.60 mmol), [RhCl(cod)] (1.5 mol%), Cu(OAc) ·H O (88 mg,
2 2 2
3
1
1
29.0, 126.6, 125.2, 124.1, 124.0, 123.5, 123.1, 122.7, 121.1, 120.8,
2.2 mmol), and toluene (2 mL) was added to a Schlenk tube under
an air atmosphere. Then the mixture was stirred at 1258C (bath
temperature, pre-heated) under air for desired time (usually 10 h)
until complete consumption of starting materials judged by TLC.
Then the reaction mixture was filtered through a short plug of
silica gel, washed with ethyl acetate and concentrated, the residue
was purified by chromatography (petroleum ether/ethyl acetate=
20.5, 120.1, 116.2, 114.5, 110.7, 106.7, 96.2, 86.7, 55.3 ppm. HRMS
+
(
ESI) Calcd for C H N O [M+H ]: 375.1492, found: 375.1490.
2
6
19
2
Methyl 2-((9-(pyridin-2-yl)-9H-carbazol-1-yl)ethynyl)benzoate (5j):
Yellow solid; 41 mg, 51% yield; m.p.: 113–1158C; H NMR
1
(
500 MHz, CDCl ): d=8.70 (dd, J=4.8 Hz, J=1.3 Hz, 1H), 8.19 (d,
3
J=7.8 Hz, 1H), 8.15 (d, J=7.8 Hz, 1H), 7.93 (d, J=7.8 Hz, 1H), 7.57
m, 2H), 7.56 (d, J=7.8 Hz, 1H), 7.52 (d, J=7.8 Hz, 1H), 7.45 (t, J=
1
00:1 to 30:1) to afford the desired products 3.
(
7
1
.8 Hz, 1H)„ 7.38–7.30 (m, 4H), 7.25 (m, 1H), 6.78 (d, J=7.8 Hz,
1
3
H), 3.96 ppm (s, 3H). C NMR (125 MHz, CDCl ): d=166.59,
3
Acknowledgements
1
1
1
5
51.25, 148.99, 141.69, 139.13, 137.58, 133.69, 131.80, 131.52,
31.20, 130.36, 127.64, 126.68, 125.26, 123.54, 123.49, 122.99,
22.50, 121.12, 121.07, 120.56, 120.16, 110.86, 106.82, 95.49, 91.93,
We thank the National Basic Research Program of China (973
Program 2012CB821600), and Program for Changjiang Scholars
and Innovative Research Team in University (PCSIRT) for financial
support.
+
2.22 ppm. HRMS (ESI) Calcd for C H N O [M+H ]: 403.1441,
2
7
19
2
2
found: 403.1441.
9
-(Pyridin-2-yl)-1-(thiophen-3-ylethynyl)-9H-carbazole (5k): Yellow
1
solid; 34 mg, 48% yield; mp. 115–1178C. H NMR (500 MHz, CDCl ):
3
d=8.62 (m, 1H), 8.00 (m, 2H), 7.73 (td, J=7.7 Hz, J=2.0 Hz, 1H),
Keywords: alkynes · CÀH activation · copper · heterocycles ·
7
1
.53 (dd, J=7.5 Hz, J=1.2 Hz, 1H), 7.41–7.37 (m, 2H), 7.34–7.31 (m,
H), 7.24–7.21 (m, 3H), 7.10 (dd, J=5.0 Hz, J=3.0 Hz, 1H), 6.93
rhodium
(
dd, J=3.0 Hz, J=1.0 Hz, 1H), 6.66 ppm (dd, J=5.0 Hz, J=1.0 Hz,
[
[
1] a) The Chemistry of Heterocyclic Compounds, Vol. 25, Wiley-Interscience,
New York, 1994; b) R. J. Sundberg, Indoles, Academic, New York, 1994.
2] For reviews, see: a) S. Cacchi, G. Fabrizi, Chem. Rev. 2005, 105, 2873;
b) G. R. Humphrey, J. T. Kuethe, Chem. Rev. 2006, 106, 2875.
1
3
1
1
1
H). C NMR (125 MHz, CDCl ): d=151.3, 149.0, 141.7, 139.2, 137.6,
3
31.3, 129.8, 128.2, 126.6, 125.1, 124.9, 123.4, 123.2, 122.6, 122.2,
21.0, 120.7, 120.4, 120.1, 110.7, 106.6, 91.2, 86.3 ppm; HRMS (ESI)
+
Calcd for C H N S [M+H ]: 351.0590, found: 351.0590.
[3] a) B. S. Lane, M. A. Brown, D. Sames, J. Am. Chem. Soc. 2005, 127, 8050;
b) N. P. Grimster, C. Gauntlett, C. R. A. Godfrey, M. J. Gaunt, Angew.
Chem. Int. Ed. 2005, 44, 3125; Angew. Chem. 2005, 117, 3185.
[4] a) L. Ackermann, A. V. Lygin, Org. Lett. 2011, 13, 3332; b) L. Zhang, X.
Xue, C. Xu, X. Pan, G. Zhang, L. Xu, H. Li, Z. Shi, ChemCatChem 2014, 6,
3069; c) S. D. Yang, C. L. Sun, Z. Fang, B. J. Li, Y. Z. Li, Z. J. Shi, Angew.
Chem. Int. Ed. 2008, 47, 1473; Angew. Chem. 2008, 120, 1495; d) R. J.
Phipps, N. P. Grimster, M. J. Gaunt, J. Am. Chem. Soc. 2008, 130, 8172.
2
3
15
2
1
-(Hex-1-yn-1-yl)-9-(pyridin-2-yl)-9H-carbazole (5l): Light yellow
1
solid; 42 mg, 62% yield; m.p.: 89–918C; H NMR (500 MHz, CDCl ):
d=8.62 (m, 1H), 7.99 (m, 2H), 7.77 (td, J=7.8 Hz, J=2.0 Hz, 1H),
7
7
(
1
1
1
3
.38 (dd, J=7.8 Hz, J=1.0 Hz, 1H), 7.34 (m, 2H), 7.30–7.25 (m, 2H),
.18 (m, 1H), 7.14 (d, J=7.8 Hz, 1H), 1.87 (t, J=6.9 Hz, 2H), 1.15
1
3
m, 4H), 0.75 ppm (t, J=7.1 Hz, 3H); C NMR (125 MHz, CDCl ): d=
3
[
5] a) A. García-Rubia, R. G. Arrayµs, J. C. Carretero, Angew. Chem. Int. Ed.
51.4, 148.9, 141.7, 139.3, 137.2, 131.3, 126.4, 124.9, 123.5, 123.4,
22.4, 120.8, 120.3, 120.0, 119.9, 110.6, 107.6, 97.4, 77.7, 30.5, 21.9,
2009, 48, 6511; Angew. Chem. 2009, 121, 6633; b) F. W. Patureau, F. Glo-
+
rius, J. Am. Chem. Soc. 2010, 132, 9982; c) Y. Nakao, K. S. Kanyiva, S. Oda,
T. Hiyama, J. Am. Chem. Soc. 2006, 128, 8146; d) D. J. Schipper, M.
Hutchinson, K. Fagnou, J. Am. Chem. Soc. 2010, 132, 6910.
9.2, 13.6 ppm; HRMS (ESI) Calcd for C H N [M+H ]: 325.1699,
2
3
21
2
found: 325.1698.
ChemCatChem 2016, 8, 2146 – 2154
www.chemcatchem.org
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
[
[
[
6] a) T. Yoshino, H. Ikemoto, S. Matsunaga, M. Kanai, Chem. Eur. J. 2013, 19,
142; b) B. Zhou, Y. Yang, S. Lin, Y. Li, Adv. Synth. Catal. 2013, 355, 360.
7] a) B. Zhou, Y. Yang, Y. Li, Chem. Commun. 2012, 48, 5163; b) J. Shi, B.
Zhou, Y. Yang, Y. Li, Org. Biomol. Chem. 2012, 10, 8953.
8] C2 prefunctionalization of indoles is difficult to accomplish and requires
multistep transformations, for the synthesis of 2-haloindoles, see: J.
Bergman, L. Venemalm, J. Org. Chem. 1992, 57, 2495.
129, 7742; c) Y. Ano, M. Tobisu, N. Chatani, J. Am. Chem. Soc. 2011, 133,
12984; d) J. He, M. Wasa, K. S. L. Chan, J.-Q. Yu, J. Am. Chem. Soc. 2013,
135, 3387; e) Y. Ano, M. Tobisu, N. Chatani, Synlett 2012, 23, 2763.
[17] a) S. H. Kim, S. H. Park, S. Chang, Tetrahedron 2012, 68, 5162; b) Y.-J. Liu,
Y.-H. Liu, X.-S. Yin, W.-J. Gu, B.-F. Shi, Chem. Eur. J. 2015, 21, 205.
[18] a) C. Feng, T.-P. Loh, Angew. Chem. Int. Ed. 2014, 53, 2722; Angew. Chem.
2014, 126, 2760; b) C. Feng, D. Feng, T.-P. Loh, Chem. Commun. 2014,
50, 9865.
9
[
9] L. Yang, L. A. Zhao, C. J. Li, Chem. Commun. 2010, 46, 4184.
[
10] a) G. L. Tolnai, S. Ganss, J. P. Brand, J. Waser, Org. Lett. 2013, 15, 112;
b) J. P. Brand, J. Charpentier, J. Waser, Angew. Chem. Int. Ed. 2009, 48,
[19] K. D. Collins, F. Lied, F. Glorius, Chem. Commun. 2014, 50, 4459.
[20] a) T. Nishimura, H. Ariki, Y. Maeda, S. Uemura, Org. Lett. 2003, 5, 2997;
b) A. Funayama, T. Satoh, M. Miura, J. Am. Chem. Soc. 2005, 127, 15354.
[21] See for selected reviews, see: a) T. Satoh, M. Miura, Chem. Eur. J. 2010,
16, 11212; b) D. A. Colby, R. G. Bergman, J. A. Ellman, Chem. Rev. 2010,
110, 624; c) G. Song, F. Wang, X. Li, Chem. Soc. Rev. 2012, 41, 3651.
[22] T. Li, Z. Wang, M. Zhang, H.-J. Zhang, T.-B. Wen, Chem. Commun. 2015,
51, 6777.
[23] a) For 3ga, 3af, and 3bf, the yields were found to be rather low (<
10%). In each case, the indole starting material was recovered and con-
sumption of the tert-propargyl alcohol substrate, along with formation
of a large amount of Glaser coupling product, were detected; b) 3bj
was given in a low yield of 15% with ~60% of indole substrate 1b re-
covered and consumption of the tert-propargyl alcohol 2j along with
formation of a large amount of Glaser coupling product. Some other
unknown species could be also detected by TLC.
9
346; Angew. Chem. 2009, 121, 9510; c) F. Xie, Z. Qi, S. Yu, X. Li, J. Am.
Chem. Soc. 2014, 136, 4780; d) J. P. Brand, J. Charpentier, R. Scopelliti, J.
Waser, Chem. Eur. J. 2012, 18, 5655.
[
[
11] J. L. García Ruano, J. Alemµn, L. Marzo, C. Alvarado, M. Tortosa, S. Díaz-
Tendero, A. Fraile, Angew. Chem. Int. Ed. 2012, 51, 2712; Angew. Chem.
2012, 124, 2766.
12] During the revision of the manuscript, cobalt(III)-catalyzed C2 CÀH alky-
nylation of indoles was reported by Shi and Ackermann, independently,
see: a) Z.-Z. Zhang, B. Liu, C.-Y. Wang, B.-F. Shi, Org. Lett. 2015, 17, 4094;
b) N. Sauermann, M. J. Gonzalez, L. Ackermann, Org. Lett. 2015, 17,
5
316; Ethynylation of tryptophan-containing peptides and proteins
I
using TIPS-EBX under Au catalysis was reported by Hansen, see:c) M. B.
Hansen, F. Hubµlek, T. Skrydstrup, T. Hoeg-Jensen, Chem. Eur. J. 2016,
2
2, 1572.
[
[
13] Acetylene Chemistry: Chemistry, Biology and Material Science (Eds.: F. Die-
derich, P. J. Stang, R. R. Tykwinski), Wiley-VCH, Weinheim, 2005.
14] For reviews, see: a) R. Giri, B.-F. Shi, K. M. Engle, N. Maugel, J.-Q. Yu,
Chem. Soc. Rev. 2009, 38, 3242; b) C. I. Herrerías, X. Yao, Z. Li, C.-J. Li,
Chem. Rev. 2007, 107, 2546; c) T. W. Lyons, M. S. Sanford, Chem. Rev.
[24] CCDC 1045346 (3ag) contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
[25] a) A. W. Schmidt, K. R. Reddy, H.-J. Knçlker, Chem. Rev. 2012, 112, 3193;
b) S. R. Patpi, L. Pulipati, P. Yogeeswari, D. Sriram, N. Jain, B. Sridhar, R.
Murthy, T. A. Devi, S. V. Kalivendi, S. Kantevari, J. Med. Chem. 2012, 55,
3911; c) J. Roy, A. K. Jana, D. Mal, Tetrahedron 2012, 68, 6099; d) H.
Huang, Y. Wang, B. Pan, X. Yang, L. Wang, J. Chen, D. Ma, C. Yang,
Chem. Eur. J. 2013, 19, 1828.
[26] J.-H. Chu, C.-C. Wu, D.-H. Chang, Y.-M. Lee, M.-J. Wu, Organometallics
2013, 32, 272.
[27] L.-Q. Zhang, S. Yang, X. Huang, J. You, F. Song, Chem. Commun. 2013,
49, 8830.
[28] Y. Wu, Y. Yang, B. Zhou, Y. Li, J. Org. Chem. 2015, 80, 1946.
[29] L. Liang, S. Fu, D. Lin, X.-Q. Zhang, Y. Deng, H. Jiang, W. Zeng, J. Org.
Chem. 2014, 79, 9472.
2010, 110, 1147; d) C. S. Yeung, V. M. Dong, Chem. Rev. 2011, 111, 1215;
e) J. Le Bras, J. Muzart, Chem. Rev. 2011, 111, 1170; f) C.-L. Sun, B.-J. Li,
Z.-J. Shi, Chem. Rev. 2011, 111, 1293; g) J. Wencel-Delord, T. Drge, F. Liu,
F. Glorius, Chem. Soc. Rev. 2011, 40, 4740; h) P. B. Arockiam, C. Bruneau,
P. H. Dixneuf, Chem. Rev. 2012, 112, 5879; i) L. Ackermann, Acc. Chem.
Res. 2014, 47, 281; j) P. Gandeepan, C.-H. Cheng, Chem. Asian J. 2015,
1
0, 824.
15] a) Y. Wei, H. Zhao, J. Kan, W. Su, M. Hong, J. Am. Chem. Soc. 2010, 132,
522; b) N. Matsuyama, M. Kitahara, K. Hirano, T. Satoh, M. Miura, Org.
Lett. 2010, 12, 2358; c) S. H. Kim, J. Yoon, S. Chang, Org. Lett. 2011, 13,
[
2
1
3
474; d) X. Jie, Y. Shang, P. Hu, W. Su, Angew. Chem. Int. Ed. 2013, 52,
630; Angew. Chem. 2013, 125, 3718; e) M. Shang, H.-L. Wang, S.-Z. Sun,
H.-X. Dai, J.-Q. Yu, J. Am. Chem. Soc. 2014, 136, 11590; f) T. d. Haro, C.
Nevado, J. Am. Chem. Soc. 2010, 132, 1512; g) M. Kitahara, K. Hirano, H.
Tsurugi, T. Satoh, M. Miura, Chem. Eur. J. 2010, 16, 1772; h) F. Shibahara,
Y. Dohke, T. Murai, J. Org. Chem. 2012, 77, 5381; i) J. Dong, F. Wang, J.
You, Org. Lett. 2014, 16, 2884; j) Y.-H. Liu, Y.-J. Liu, S.-Y. Yan, B.-F. Shi,
Chem. Commun. 2015, 51, 11650.
[30] Z. Xin, C. Lescot, S. D. Friis, K. Daasbjerg, T. Skrydsrup, Angew. Chem. Int.
Ed. 2015, 54, 6862; Angew. Chem. 2015, 127, 6966.
[
16] a) K. Kobayashi, M. Arisawa, M. Yamaguchi, J. Am. Chem. Soc. 2002, 124,
Received: February 23, 2016
8
528; b) I. V. Seregin, V. Ryabova, V. Gevorgyan, J. Am. Chem. Soc. 2007,
Published online on May 19, 2016
ChemCatChem 2016, 8, 2146 – 2154
www.chemcatchem.org
2154
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