Selective Synthesis of Benzo[a]Carbazoles and Indolo[2,1-a]-Isoquinolines via Rh(III)-Catalyzed C?H Functionalizations of 2-Arylindoles with Sulfoxonium Ylides

Article abstract of DOI:10.1002/adsc.201800622

A highly chem- and regioselective synthesis of diversely substituted benzo[a]carbazoles and indolo[2,1-a]-isoquinolines through Rh(III)-catalyzed cascade reactions of 2-arylindoles with sulfoxonium ylides is presented. To be specific, treatment of 2-arylindoles, 2-arylindole-3-carbaldehydes, 2-arylindole-3-carbonitriles or 2-aryl-3-methylindoles with sulfoxonium ylides under the catalysis of Rh(III) led to the selective formation of 6-aryl/alkyl benzo[a]carbazoles, 5-acylbenzo[a]carbazoles, 6-amino-5-acylbenzo[a]carbazoles or 12-methylindolo[2,1-a]isoquinolines, respectively. Mechanistically, the formation of the title compounds involves a cascade process including metalation of the inert C(sp²)?H bond, migratory insertion of ylide into the carbon-metal bond via an in situ carbenoid formation, protodemetalation, and condensation. To our knowledge, this is the first example in which β-carbonyl sulfoxonium ylides were used as stable carbene precursors and bifunctional C2 synthons to afford benzo[a]carbazoles and indolo[2,1-a]isoquinolines. (Figure presented.).

Full text of DOI:10.1002/adsc.201800622

Title: Selective synthesis of benzo[a]carbazoles and indolo[2,1-
a]isoquinolines via Rh(III)-catalyzed C-H functionalizations of 2-
arylindoles with sulfoxonium ylides
Authors: Guang Chen, Xinying Zhang, Ruixue Jia, Bin Li, and Xuesen
Fan
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201800622
Link to VoR: http://dx.doi.org/10.1002/adsc.201800622

Advanced Synthesis & Catalysis
10.1002/adsc.201800622
UPDATE
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Selective Synthesis of Benzo[a]carbazoles and Indolo[2,1-a]-
isoquinolines via Rh(III)-Catalyzed C−H Functionalizations of
2
-Arylindoles with Sulfoxonium Ylides
a
a,
a
a
a,
Guang Chen, Xinying Zhang, * Ruixue Jia, Bin Li, and Xuesen Fan *
a
Henan Key Laboratory of Organic Functional Molecules and Drug Innovation, Collaborative Innovation Center of
Henan Province for Green Manufacturing of Fine Chemicals, Key Laboratory of Green Chemical Media and Reactions,
Ministry of Education, School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang, Henan
4
53007, China.
E-mail: xuesen.fan@htu.cn; xinyingzhang@htu.cn
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.
Abstract. A highly chem- and regioselective synthesis of
diversely substituted benzo[a]carbazoles and indolo[2,1-a]-
isoquinolines through Rh(III)-catalyzed cascade reactions
of 2-arylindoles with sulfoxonium ylides is presented. To
be specific, treatment of 2-arylindoles, 2-arylindole-3-
carbaldehydes, 2-arylindole-3-carbonitriles or 2-aryl-3-
methylindoles with sulfoxonium ylides under the catalysis
of Rh(III) led to the selective formation of 6-aryl/alkyl
benzo[a]carbazoles, 5-acylbenzo[a]carbazoles, 6-amino-5-
acylbenzo[a]carbazoles or 12-methylindolo[2,1-a]isoquino-
lines, respectively. Mechanistically, the formation of the
title compounds involves a cascade process including
Due to their importance, a number of reliable
methods for the preparation benzo[a]carbazole
[3-17]
derivatives have been developed.
Among them, a
popular approach is to use diazo compounds as metal
carbene precursors to form the required C–C bond(s)
[4,8,17]
in constructing the benzo[a]carbazole scaffold.
While this diazo-related strategy is generally reliable,
the preparation and storage of the unstable and
potentially explosive diazo substrates, especially for
[18]
large-scale procedures, could bring safety issues.
To solve this problem, searching for more stable and
less hazardous reagents to replace diazo compounds
has stimulated intensive research. In this regard,
2
metalation of the inert C(sp )−H bond, migratory insertion
of ylide into the carbon–metal bond via an in situ carbenoid
formation, protodemetalation, and condensation. To our
knowledge, this is the first example in which -carbonyl
sulfoxonium ylides were used as stable carbene precursors
and bifunctional C2 synthons to afford benzo[a]carbazoles
and indolo[2,1-a]isoquinolines.
[19,20]
sulfonium and sulfoxonium ylides
were found to
be ideal alternatives to diazo compounds owing to
their high stability and ready transformation into
[21-23]
carbene intermediates under mild conditions.
Inspired by these elegant pioneering studies and as a
continuation of our recent interest in the development
of novel methods for the preparation of fused N-
heterocycles, we have studied the reactions of 2-
arylindoles with -carbonyl sulfoxonium ylides as
stable carbene precursors and bifunctional C2
synthons with the aim to develop an alternative
synthetic approach toward benzo[a]carbazoles and
indolo[2,1-a]isoquinolines. Herein, we report our
results in this aspect.
Keywords: Benzo[a]carbazole; Indolo[2,1-a]isoquinoline;
C–H Functionalization; 2-Arylindole; Sulfoxonium Ylide
Carbazoles are fused N-heterocycles occuring
ubiquitously in natural products, pharmaceuticals and
functional materials.[ Of them, benzo[a]carbazoles
possess diverse biological activities and unique
photographic properties. As a result, they have found
wide applications in medicinal chemistry and fine
1]
Our study was initiated by treating 2-phenyl-1H-
[2]
6
chemical industry (Figure 1).
indole (1a) with 2-(dimethyl(oxo)- -sulfanylidene)-
1
[
-phenylethan-1-one (2a) in the presence of
o
RhCp*Cl
2
]
2
and AgSbF in DCE at 100 C under air
6
for 12 h. From this reaction, 6-phenyl-11H-benzo[a]-
2
carbazole (3a), formed through an ortho-C(sp )–H
alkylation of the 2-phenyl moiety followed by a C-3
annulation, was obtained in a yield of 19% (Table 1,
entry 1). To improve the efficiency, different additives
such as Cu(OAc) , HOAc, AgOAc and CsOAc were
2
tried (entries 2-5). Among them, CsOAc was the most
efficient (entry 5), and using a combination of CsOAc
Figure 1. Some Important Benzo[a]carbazole Derivatives
with AgSbF
6
as the additive could not improve the
1
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Advanced Synthesis & Catalysis
10.1002/adsc.201800622
efficiency (entry 6). Next, the effect of different
With the establishment of the optimum reaction
solvents such as CH
dioxane and DCM on this reaction was studied
entries 7-13), and THF was found to be the most
3
CN, THF, DME, acetone, toluene, conditions, the scope and the generality of this
benzo[a]carbazole forming reaction was explored.
First, with 2a as a model substrate, several 2-aryl
indoles 1 were tried, and the results were included in
Table 2. It was observed that 1 bearing a fluoro,
chloro or methyl group on the 5-position of the
indolyl moiety underwent this reaction smoothly to
give 3b-3d in good yields. Notably, the halogenated
aromatic moieties survived the reaction conditions to
allow for subsequent structural elaboration. Next, it
was found that 1 with either an electron-donating
group (EDG) (methyl or methoxy) or an electron-
withdrawing group (EWG) (fluoro or trifluoromethyl)
attached on the para-position of the 2-phenyl moiety
took part in this reaction smoothly to give 3e-3i in
yields ranging from 47% to 67%. Moreover, ortho-
substituted 1 gave their corresponding products 3j-3l
in lower yields, most likely due to steric hindrance.
For 1 with a meta-chloro or meta-methyl substituted
(
effective affording 3a in a yield of 73% (entry 8).
Further study showed that carrying out this reaction
under a nitrogen atmosphere instead of air did not
result in an obvious improvement in the yield of 3a,
indicating that this reaction does not require an inert
gas protection (entry 14). Increasing the reaction
o
temperature to 120 C or reducing it to 80 °C had an
adverse effect (entries 15 and 16). When PdCl
Pd(OAc) or RhCl ·3H O was used to replace
RhCp*Cl as the catalyst, the formation of 3a was
2
,
2
3
2
[
2 2
]
not observed (entries 17-19). Control experiments
showed that an absence of either the Rh catalyst or the
additive led to no formation of 3a (entries 20 and 21).
Table 1. Optimization Studies for the Synthesis of 3a [a]
2
-phenyl unit, the reaction underwent regioselectively
on the less hindered ortho-site to give 3n and 3o.
Interestingly, the C−H alkylation occurred exclusively
at the more hindered ortho-site for a meta-fluoro
substituted substrate to give 3m. Notably, the
structure of 3m was confirmed by its single crystal X-
ray diffraction analysis. This is in consistence with
what has been observed by Li et al in a Rh(III)-
catalyzed synthesis of indoles from the reactions of
imidamides with diazo ketoesters via C−H activation
Entry
Catalyst
Additive Solvent T (°C) Yield [b]
1
2
3
4
5
[RhCp*Cl
[RhCp*Cl
[RhCp*Cl
[RhCp*Cl
[RhCp*Cl
2
]
]
]
]
]
2
2
2
2
2
AgSbF
6
DCE
DCE
DCE
DCE
DCE
100
19
[24]
2
2
2
2
Cu(OAc)
HOAc
2
100 trace
100 trace
AgOAc
CsOAc
100
100
12
55
[25]
and C−C/C−N bond cleavage. As a further aspect,
in addition to 2-phenylindoles, 2-(naphthalene-1-yl)
indole was also suitable for this reaction to give 3p in
52% yield.
CsOAc/
AgSbF
6
[RhCp*Cl
2
]
]
2
2
DCE
100
51
6
Table 2. Substrate Scope for the Synthesis of 3 (I) [a,b]
7
8
9
[RhCp*Cl
2
CsOAc CH
3
CN
100
100
100
100
100
100
100
100
80
29
73
32
39
37
33
54
74
63
68
-
[RhCp*Cl
2
]
2
CsOAc
THF
[RhCp*Cl
[RhCp*Cl
[RhCp*Cl
[RhCp*Cl
[RhCp*Cl
2
]
]
]
]
]
]
]
]
2
2
2
2
2
2
2
2
CsOAc
DME
1
1
1
1
0
1
2
3
2
2
2
2
2
2
2
CsOAc acetone
CsOAc toluene
CsOAc dioxane
3
a, 73%
e, 61%
3b, 68%
3f, 67%
3c, 74%
3g, 58%
3d, 72%
3h, 62%
CsOAc
CsOAc
CsOAc
CsOAc
CsOAc
CsOAc
CsOAc
CsOAc
DCM
THF
THF
THF
THF
THF
THF
THF
THF
1
4c [RhCp*Cl
1
5
6
7
8
9
0
1
[RhCp*Cl
[RhCp*Cl
3
1
1
1
1
2
2
120
100
100
100
100
100
PdCl
Pd(OAc)
RhCl ·3H
2
2
-
3
i, 47%
3
j, 39%
3k, 42%
3o, 60%
3l, 51%
3p, 52%
3
2
O
-
-
[RhCp*Cl
2
]
2
-
3
m, 61%
3n, 63%
[
a]
Conditions: 0.5 mmol of 1a, 0.75 mmol of 2a, 0.025
mmol of catalyst, 0.25 mmol of additive, 3 mL of
[
a]
Reaction condition: 1 (0.5 mmol), 2a (0.75 mmol),
[RhCp*Cl ] (0.025 mmol), CsOAc (0.25 mmol), THF (3
[
b]
[c]
solvent, sealed tube, air, 12 h. Isolated yield. Under
atmosphere.
2 2
o
[b]
mL), 100 C, 12 h. Isolated yields.
N
2
2
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Advanced Synthesis & Catalysis
10.1002/adsc.201800622
Next, the scope and generality of sulfoxonium
ylides 2 was evaluated by using 1a as a model
substrate, and the results were included in Table 3. It
was firstly observed that phenyl substituted 2 with
either an EDG (tert-butyl or methoxy) or an EWG
Scheme 1. Formation of 5a from the reaction of 4a with 2a
(
fluoro or trifluoromethyl) attached on the 4-position
of the phenyl unit afforded the corresponding products
q-3u in synthetically useful yields. Second, the
a challenging task in synthetic chemistry.[26]
3
To establish a general protocol for the synthesis of
-acylbenzo[a]carbazoles, the substrate scope of this
reaction was extended to ortho-substituted phenyl
sulfoxonium ylides to give 3v and 3w. In addition,
5
reaction was studied. It turned out that 4 with either a
fluoro or a methyl group attached on the 5-position of
the indole unit or a methyl or trifluoromethyl unit on
the para-site of the 2-phenyl moiety underwent this
cascade reaction with 2a to give 5a-5e in good yields.
Promisingly, the generality of the substrate scope was
further showcased by the participation of phenyl,
thien-2-yl or tert-butyl substituted sulfoxonium ylides
2 to give 5f-5l in moderate to good yields (Table 4).
Notably, the structure of 5e was confirmed by its
3
,5-dimethyl or 3,4,5-trimethoxy groups were well
tolerated as demonstrated in the efficient formation of
x and 3y. As a further aspect, a furan-2-yl moiety
3
was smoothly introduced onto the benzo[a]carbazole
scaffold as shown in the formation of 3z. Next, we
were delighted to find that 2 was not limited to aryl
substituted ylides in that iso-propyl and tert-butyl
substituted sulfoxonium ylides took part in this
reaction to give 3aa and 3bb in good yields.
Table 3. Substrate Scope for the Synthesis of 3 (II) [a,b]
[27]
single crystal X-ray diffraction analysis.
Table 4. Substrate Scope for the Synthesis of 5 [a,b]
3
3
3
q, 52%
u, 54%
y, 60%
3r, 61%
3v, 40%
3s, 65%
3t, 50%
3x, 53%
3bb, 68%
5
a, 85%
5b, 75%
5c, 83%
5g, 81%
5k, 58%
5d, 85%
5h, 67%
5l, 42%
3
w, 45%
5
e, 60%
5
f, 80%
3
z, 62%
3aa 74%
[
a]
Reaction condition: 1a (0.5 mmol), 2 (0.75 mmol),
RhCp*Cl (0.025 mmol), CsOAc (0.25 mmol), THF
3 mL), 100 C, 12 h. Isolated yields.
[
(
2 2
]
o
[b]
5
i, 82%
5j, 86%
Thus far, we have developed an efficient protocol
[
a]
Reaction condition: 4 (0.5 mmol), 2 (0.75 mmol),
RhCp*Cl (0.025 mmol), CsOAc (0.25 mmol), THF
for the construction of benzo[a]carbazole scaffold
with the introduction of an aryl or an alkyl unit onto
the 6-position via the reaction of 2-arylindoles with
aryl/alkyl substituted -carbonyl sulfoxonium ylides
[
(
2 2
]
o
[b]
3 mL), 100 C, 12 h. Isolated yields.
2
In further study, the reactivity of 2-arylindoles
through C(sp )–H alkylation of the 2-aryl moiety
bearing a cyano group on the C-3 position toward 2
was studied. Thus, 3-cyano-2-phenylindole (6a) was
treated with 2a under the optimized reaction
conditions. From this reaction, 7a was obtained in a
yield of 42%. It is worth to be noted that the structure
of 7a features with an amino unit and a benzoyl group
attached on the 6- and 5-position of the benzo[a]-
carbazole scaffold. This structural feature is not only
distinct from that of 3 and 5, but also of high synthetic
significance owing to the rich reactivity of the o-
aminobenzophenone fragment. Encouraged by this
preliminary result, we then explored the substrate
generality of this reaction. Thus, several 3-cyano-2-
phenylindoles 6 and sulfoxonium ylides 2 were tried.
From the corresponding reactions, 6-amino-5-benzoyl
followed by a C-3 annulation. Next, we continued our
study by trying to use 2-arylindole-3-carbaldehydes 4
as the substrates. Since the C-3 position of the indole
moiety in 4 is blocked by a formyl unit, an alternative
N-1 cyclization might take place to afford an indolo-
[
1
2,1-a]isoquinoline derivative A as shown in Scheme
. Thus, 2-phenyl-1H-indole-3-carbaldehyde (4a) was
treated with 2a under the optimal conditions as
described above. From this reaction, to our surprise,
benzo[a]carbazole derivative 5a bearing a 5-benzoyl
group, instead of a 6-aryl/alkyl unit as that embedded
in 3, was obtained in a yield of 85%. Meanwhile, the
proposed N-1 annulation product A was not obtained
(
Scheme 1). This is a promising finding as the
efficient synthesis of 5-acylbenzo[a]carbazoles is still
3
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Advanced Synthesis & Catalysis
10.1002/adsc.201800622
Table 5. Substrate Scope for the Synthesis of 7 [a,b]
Table 6. Substrate Scope for the Synthesis of 9 [a,b]
9
a, 62%
e, 68%
9b, 58%
9f, 55%
9j, 55%
9c, 61%
9g, 45%
9k, 51%
9d, 60%
9h, 60%
9l, 62%
7
a, 42%
7b, 41%
7f, 35%
7c, 44%
7g, 38%
7d, 50%
9
7
e, 45%
[
a]
Reaction condition: 6 (0.5 mmol), 2 (0.75 mmol),
RhCp*Cl (0.025 mmol), CsOAc (0.25 mmol), THF
3 mL), 100 C, 12 h. Isolated yields.
[
(
2 2
]
o
[b]
9i, 44%
m, 65%
benzo[a]carbazole derivatives 7a-7g were obtained in
yields ranging from 35% to 50% (Table 5).
Finally, the reaction of 2-arylindoles with a methyl
group attached on the 3-position of the indole scaffold
was explored. To be specific, 3-methyl-2-phenyl-1H-
indole (8a) was treated with 2a in the presence of
9
a]
9n, 58%
9o, 35%
9p, 40%
[
Reaction condition: 8 (0.5 mmol), 2 (0.75 mmol),
RhCp*Cl (0.025 mmol), CsOAc (0.25 mmol), THF
3 mL), 100 C, 12 h. Isolated yields.
[
(
2 2
]
o
[b]
[
RhCp*Cl
2
] and CsOAc in THF at 100 °C for 12 h.
2
2
under standard reaction conditions for 12 h. From the
resulting mixture, 92% of 10 was recovered, and the
proposed N-methylbenzo[a]carbazole 11 was not
obtained (Scheme 2). These results tell that the
presence of a free NH unit in 1a is indispensible for
the formation of the benzo[a]carbazole scaffold.
From this reaction, 9a, generated via a C(sp )–H
alkylation of the 2-phenyl moiety followed by a N-1
cyclization, was obtained in 62% yield (Table 6). It is
well known that indolo[2,1-a]isoquinolines constitute
an important class of fused N-heterocycles with wide
presence in pharmaceutical molecules and natural
products.[
28,29]
While several elegant methods for the
preparation of indolo[2,1-a]isoquinolines have been
developed,[ new protocols featuring with a profile of
simple procedure and easily obtainable substrates are
still urgently needed. To establish a general synthetic
approach toward indolo[2,1-a]isoquinolines, the
suitability of several 2-aryl-3-methylindoles 8 was
studied by using 2a as a model substrate. It turned out
that 8 bearing either a 5-fluoro or a 5-methyl unit on
the indole scaffold took part in this reaction efficiently
to afford 9b and 9c. In addition, 8 with a 4-fluoro or
29]
Scheme 2. A Control Experiment
Second, an intermolecular kinetic isotopic effect
was measured based on competition reactions between
1
a with 2a and 1a-d
5
with 2a. From this study, a KIE
value (K /K ) of 2.57 was observed (Scheme 3). This
H
D
result indicates that the cleavage of the ortho-C−H
bond is probably involved in the rate-limiting step.
4
-methyl group attached on the 2-phenyl unit could
[30]
also react with 2a to give 9d and 9e. Next, by using
a as a model substrate, the suitability of a number of
8
sulfoxonium ylides 2 was studied. Promisingly, 2
bearing a 4-fluoro, 4-chloro, 4-methyl, 4-tert-butyl, 4-
trifluoromethyl, 4-methoxy, 4-ester, 2-chloro or 2-
Scheme 3. An Intermolecular Kinetic Isotope Effect Study
3
methyl group on the phenyl unit (R ) took part in this
reaction smoothly to give 9f-9n efficiently, and,
Third, competition experiments were performed by
various functional groups were tolerated. Interestingly, using 2-phenylindoles 1 bearing an EWG (fluoro) or
furan-2-yl or isopropyl substituted sulfoxonium ylides
could also react with 8a to give 9o and 9p, albeit the
yields were relatively lower.
To gain some insight into the reaction mechanism,
the following experiments were carried out. First, 1-
methyl-2-phenyl-1H-indole (10) was treated with 2a
an EDG (methyl) on the mata-position of the 2-phenyl
unit (1l vs 1n, Scheme 4). It turned out that 1l reacted
with 2a 4 times faster than 1n. This result suggests
that the acidity of the ortho-proton of the 2-phenyl
moiety in 1 might play a role in dictating the rate and
efficiency of the corresponding C(sp )–H activation
and alkylation of the 2-phenyl unit.
2
4
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Advanced Synthesis & Catalysis
10.1002/adsc.201800622
Finally, to see whether this new method is suitable for
large scale applications, the preparation of 3a was carried
out in a quantity of 5 mmol. Promisingly, the corresponding
reaction proceeded smoothly to afford 3a in a yield of 68%
(
0.991 g, Scheme 7).
Scheme 4. Competition Experiments of 1 with Different
Electronic Characteristics
Based on the above described experimental results
and previous reports,[ a plausible mechanism for the
formation of 3a from the reaction of 1a with 2a is
proposed in Scheme 5. First, 1a reacts with
23]
RhCp*(OAc)
of [RhCp*Cl
2
, generated in situ through ion exchange
with CsOAc, to form intermediate I.
Scheme 7. A Large Scale Synthesis of 3a
2 2
]
The following C–H metalation of I provides a five-
membered rhodacycle II, which then reacts with 2a to
give a rhodium-carbene intermediate III. Next,
migratory insertion of carbene into the rhodium–
carbon bond occurs with III to afford a six membered
rhodacyclic intermediate IV. The following proto-
demetalation of IV affords intermediate V, and
releases rhodium catalyst to allow for the next
catalytic cycle. In the second stage of this cascade
process, the in situ generated V undergoes an
intramolecular condensation to form 3a, most likely
via the formation of intermediate VI.
In conclusion, we have developed a selective
synthesis of diversely substituted benzo[a]carbazoles
and indolo[2,1-a]isoquinolines from the reactions of
2-arylindoles with sulfoxonium ylides via Rh(III)-
2
catalyzed inert C(sp )−H bond alkylation followed by
intramolecular
condensation.
Compared
with
literature methods, this new protocol has advantages
such as high efficiency, easily obtainable and stable
substrates, diverse products, excellent chem- and
regioselectivity. The search for more applications of
sulfoxonium ylides as stable and safe carbene
precursors for the synthesis of fused heterocyclic
compounds is currently underway in our laboratories.
Experimental Section
Typical Procedure for the Synthesis of 6-Phenyl-11H-
benzo[a]carbazole (3a)
To a reaction tube equipped with a stir bar were added 2-
phenyl-1H-indole (1a, 96.6 mg, 0.5 mmol), 2-(dimethyl
6
(
0
oxo)- -sulfanylidene)-1-phenylethan-1-one (2a, 147.2 mg,
.75 mmol), [RhCp*Cl
2 2
] (15.4 mg, 0.025 mmol), CsOAc
(
47.8 mg, 0.25 mmol) and THF (3 mL). The tube was then
Scheme 5. A Plausible Mechanism for the Formation of 3a
sealed, and the mixture was stirred at 100 °C for 12 h. Upon
completion, it was cooled to room temperature, quenched
with saturated brine (5 mL), and extracted with EtOAc (10
mL × 3). The combined organic layers were dried over
Meanwhile, the reaction mechanisms accounting
for the formation of 5a, 7a and 9a should be similar to
that proposed for the formation of 3a as shown in
2 4
anhydrous Na SO , and concentrated under reduced
2
Scheme 5. Firstly, Rh(III)-catalyzed C(sp )−H bond
pressure. The residue was purified by silica gel
chromatography using petroleum ether/ethyl acetate (20:1)
as eluent to afford 3a in 73% yield. 3b-3aa, 5a-5k, 7a-7f
and 9a-9l were obtained in a similar manner.
alkylation of the 2-phenyl unit in 4a, 6a or 8a affords
intermediate VII, VIII or IX, respectively. Then, the
in situ formed VII, VIII and IX undergo different
versions of intramolecular condensation to give the
corresponding products 5a, 7a and 9a (Scheme 6).
Acknowledgements
We are grateful to the National Natural Science Foundation of
China (NSFC) (Grant No. 21572047), Program for Innovative
Research Team in Science and Technology in Universities of
Henan Province (15IRTSTHN003), Program for Science and
Technology Innovation Talents in Universities of Henan Province
(
15HASTIT005), and the Plan for Scientific Innovation Talents of
Henan Province (184200510012) for financial support.
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UPDATE
Selective Synthesis of Benzo[a]carbazoles and
Indolo[2,1-a]isoquinolines via Rh(III)-Catalyzed
C−H Functionalizations of 2-Arylindoles with
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Adv. Synth. Catal. Year, Volume, Page – Page
Guang Chen, Xinying Zhang,* Ruixue Jia, Bin Li,
and Xuesen Fan*
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