Rhodium-catalyzed regioselective C(sp2)–H bond activation reactions of N-(hetero)aryl-7-azaindoles and cross-coupling with α-carbonyl sulfoxonium ylides

Article abstract of DOI:10.1016/j.tetlet.2020.151627

We described a protocol for rhodium-catalyzed C(sp²)–H bond activation reactions of N-(hetero)aryl-7-azaindoles and cross-coupling with α-carbonyl sulfoxonium ylides. In the C–H activation reaction, the 7-azaindole moiety acts as a directing gr

Full text of DOI:10.1016/j.tetlet.2020.151627

Journal Pre-proofs
Rhodium-Catalyzed Regioselective C(sp2)−H Bond Activation Reactions of
N-(Hetero)aryl-7-azaindoles and Cross-Coupling with α-Carbonyl Sulfoxoni-
um Ylides
Yan Tian, Xian-Qiang Kong, Jie Niu, Yi-Bo Huang, Zhao-Hua Wu, Bo Xu
PII:
S0040-4039(20)30039-3
DOI:
https://doi.org/10.1016/j.tetlet.2020.151627
TETL 151627
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
14 November 2019
24 December 2019
10 January 2020
Please cite this article as: Tian, Y., Kong, X-Q., Niu, J., Huang, Y-B., Wu, Z-H., Xu, B., Rhodium-Catalyzed
Regioselective C(sp2)−H Bond Activation Reactions of N-(Hetero)aryl-7-azaindoles and Cross-Coupling with α-
Carbonyl Sulfoxonium Ylides, Tetrahedron Letters (2020), doi: https://doi.org/10.1016/j.tetlet.2020.151627
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Rhodium-Catalyzed Regioselective C(sp2)−H Bond Activation Reactions of N-
(Hetero)aryl-7-azaindoles and Cross-Coupling with α-Carbonyl Sulfoxonium Ylides
Yan Tianab, Xian-Qiang Kongb*, Jie Niua, Yi-Bo Huanga, Zhao-Hua Wua, Bo Xub*
aChangzhou Vocational Institute of Engineering, Changzhou 213164, China
bCollege of Chemistry, Chemical Engineering and Biotechnology, Donghua University, 2999 North Renmin Lu, Shanghai 201620,
China
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
We described a protocol for rhodium-catalyzed C(sp2)−H bond activation reactions of
N-(hetero)aryl-7-azaindoles and cross-coupling with α-carbonyl sulfoxonium ylides.
In the C−H activation reaction, the 7-azaindole moiety acts as a directing group,
which results in high regioselectivity. The protocol features excellent chemical yields
and good functional group tolerance.
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
N‑(Hetero)aryl-7-azaindoles
C−H activation
α-carbonyl sulfoxonium ylides
cross-coupling
Azaindole is one of the most attractive frameworks with a wide
range of biological and pharmacological activities, present in various
biologically active molecules1 and new synthetic materials.2
Compared with indole, 7-azaindole ring system has an additional
nitrogen atom, they can act both as hydrogen donors and as hydrogen
acceptors, and this feature endows azaindole-containing molecules
exhibiting a broad spectrum of biological activities such as antitumor,
antibacterial, and anti-inflammatory activity. Many marketed drugs
contain a 7-azaindole skeleton,3 such as anticancer drug Vemurafenib,
potent anti-melanoma agent PLX4720.4
sulfoxonium ylides, which generates the corresponding
derivative ketones of N-(hetero)aryl-7-azaindoles in high
chemical yields, has broad functional group tolerance, and does
not require a sacrificial oxidizing reagent (Scheme 1f).
Scheme 1: 7-Azaindole-directed C(sp2)−H bond functionalization
Previous works
cat. Rh, Cu(TFA)2
Cl
N
+
(a)
N
Cl
Cl
Li2CO3, t-BuNC, 130 o
C
Despite the importance of 7-azaindoles in medicinal and
materials chemistry, only a few methods for metal-catalyzed
functionalization of the 7-azaindole skeleton have been
Ph
N
cat. Ru
AgOTf, NaOAc, DCE, 110 o
+
N
(b)
N
C
CN
R5
Ts CN
developed. The reported methods have been developed ：
palladium-catalyzed amination,5 C2−C3 arylation,6 C3-
alkenylation,7 and selective C6 arylation.8 Reports of activation
of the C(sp2)−H bonds of the aryl groups of N-aryl-7-azaindoles
with the azaindole moiety acting as a directing group are even
rarer. The few examples include C−H chlorination,9 C−H
cyanation,10 alkynylation,11 and C−C coupling reactions with
vinyl and allyl acetates,12 with catalysis by expensive rhodium or
iridium complexes (Scheme 1a–e). However, 7-azaindole-
directed C(sp2)−C bond-forming cross-coupling reactions
involving sulfoxonium ylides have not been reported.
N
N
H
R5
cat. Rh
, toluene, 120 o
C
N
R4
+
+
(c)
(d)
R4
N
Cu(OAc)2

H2
O
R3
R3
cat. Ir
AgNTf2, DCE, 80 o
I
N
O
N
C
N
O
OAc
O
cat. Rh
dioxane, 130 o
N
N
N
+
(e)
+
O
C
Metal-catalyzed reactions of sulfoxonium ylides have been used
for the construction of C–C, C–N, and C–O bonds.13 For example, α-
carbonyl sulfoxonium ylides undergo efficient rhodium-catalyzed
cross-coupling reactions with C(sp2)–H bonds of both arenes and
This work
R2
O
O
S
N
N
heteroarenes14a-d without the need for
a sacrificial oxidizing
N
N
cat. Rh
AgSbF6, K2CO3
H
+
R2
(f)
O
reagent.14e-f Notably, the use of sulfoxonium ylides can avoid the
potential hazards of the recently reported C(sp2)–H functionalization
reactions involving diazo compounds.15
R1
R1
Herein, we report the development of a protocol for rhodium-
catalyzed regioselective C(sp2)−H bond activation reactions of N-
(hetero)aryl-7-azaindoles and cross-coupling with α-carbonyl
We began our investigation by carrying out C(sp2)−C cross-
coupling reactions between 1-phenyl-7-azaindole (1a) and α-

2
Tetrahedron
carbonyl sulfoxonium ylide 2a as model substrates to optimize
First, we evaluated reactions of various α-carbonyl sulfoxonium
ylides 2 with 1-phenyl-7-azaindole 1a (Table 2). Aryl-group-
bearing ylides with an ortho, meta, or para chlorine atom on the
aromatic ring afforded good yields of the corresponding products
(3b–3d), regardless of the position of the chlorine atom. The
analogous fluorine-substituted compounds gave lower yields (3f–
3h, 68%–77%). Both electron-deficient (–CF3, NO2) and
electron-rich (–OMe, Me) aryl substituents were well-tolerated,
giving excellent yields of the corresponding products (3i–3m).
Replacement of the phenyl ring on the α-carbonyl sulfoxonium ylide
with a furan, thiophene or aliphatic (cyclohexyl or methyl ) ring also
resulted in excellent yields of the target products (3n, 3o, 3p, and
3q, respectively).
the reaction conditions (Table 1). Because [CpRhCl2]2 is known
to catalyze cross-coupling of α-carbonyl sulfoxonium ylides with
C–H bonds,14f we started with a catalyst system comprising
[CpRhCl2]2 and AgSbF6. However, in DCE at 100 °C, the yield
of desired product 3a was only 9% (entry 1). Exploration of
various nonpolar and polar solvents (entries 2–7) revealed that
HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) produced the best
results, giving a 23% yield of 3a (entry 6). In attempts to increase
the yield, we tested various additives (CsOAc, K2CO3, KOAc,
and NaOAc) and found that neither NaOAc and KOAc improved
the yield (entries 10 and 11). However, the addition of CsOAc
increased the yield to 54% (entry 8), and when we used K2CO3 as
an additive, 3a was obtained in 83% yield (entry 9). Variation of
the reaction temperature from 80 to 110 °C failed to produce any
additional improvements (entries 12–14). Shortening the reaction
time to 7 h decreased the yield of 3a to 72% (entry 9). The
reaction did not proceed at all in the absence of [CpRhCl2]2
(entry 15), and although the reaction worked without AgSbF6, the
yield was only 23% (entry 16). In summary, the [CpRhCl2]2
catalyst was indispensable, and AgSbF6 and K2CO3 played
supporting roles in increasing the yield. Also, HFIP, which has
been shown to play a unique role in the activation of C(sp2)–H
bonds,16 was essential for efficient protodemetallation leading to
catalyst turnover and product formation.
Table 2. Scope for α-Carbonyl Sulfoxonium Ylidesa
[CpRhCl2
]2 (4 mmol %)
O
R
O
O
S
AgSbF6 (8 mmol %)
N
N
N
N
R
HFIP , K2CO3, 100o
C
1a
2
3
O
O
O
O
N
N
N
N
N
N
N
N
Cl
Cl
Cl
I
3b
3c
3d
3e
81%
77%
72%
80%
80%
78%
79%
76%
O
O
O
O
N
N
N
N
N
N
N
N
F
Table 1. Optimization of reaction conditions.a
F
[CpRhCl2]2 ( 4 mmol%)
O
F
CF3
O
O
S
AgSbF6 (8 mmol%)
N
N
N
N
3i
3f
3g
73%
3h
68%
Ph
Ph
Solvent , Additive, Temp (oC)
O
O
O
O
N
N
N
N
N
N
N
N
1a
2a
3a
NO2
OMe
3j
3k
3l
3m
75%
75%
Entry
1
Solvent
Additive
—
Temp (°C)
100
Yieldb
9%
DCE
O
N
O
O
O
N
N
N
N
N
N
N
2
DCM
—
100
13%
5%
O
S
3
1,4-dioxane
MeOH
t-AmOH
HFIP
—
100
3q
78%
3n
3o
3p
80%
82%
82%
4
—
100
trace
17%
23%
Trace
54%
5
—
100
a Reaction conditions: 1a (0.2 mmol), 2 (0.4 mmol), [CpRhCl2]2 (4 mmol %),
AgSbF6 (8 mmol %), and K2CO3 (0.2 mmol) were gradually added to the
HFIP (2 mL) with stirring under N2, and then the reaction mixture was heated
at 100 °C for 12 h. Isolated yields are provided.
6
—
100
7
CF3CH2OH
HFIP
—
100
8
CsOAc
K2CO3
KOAc
NaOAc
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
100
9
HFIP
100
100
100
110
90
83% (72%c)
22%
Next, we explored how various substituents on the N-phenyl
ring of N-(hetero)aryl-7-azaindoles 1 affected their reactions with
2a (Table 3). Neither the position of the substituent (meta, para)
nor its electronic properties played a major role; good yields were
obtained in all cases. Specifically, alkyl groups (4b–4d), ethers
(4e), halides (4f and 4g), a trifluoromethyl group (4h), and an
ester group (4i) were all well-tolerated. To further evaluate the
regioselectivity of the reaction, we changed the meta-substituents
from methyl(4b) to other groups, such as methoxy(4j) and
ester(4k). Only a few of the methoxy-substituted products(4j) are
6-substituted regioisomers. Ester-substituted products(4k) have a
single configuration.
10
11
12
13
14
15d
16e
HFIP
HFIP
12%
HFIP
81%
HFIP
75%
HFIP
80
66%
HFIP
100
100
NR
HFIP
23%
a
Reaction conditions, unless otherwise noted: 1a (0.2 mmol), 2a (0.4 mmol),
[CpRhCl2]2 (4 mmol %), AgSbF6 (8 mmol %), and additive (0.2 mmol) were
gradually added to the solvent (2 mL) with stirring under N2, and then the reaction
mixture was heated at 100 °C for 12 h. b Isolated yields are provided. c Reaction
time, 7 h. d [CpRhCl2]2 was omitted. e AgSbF6 was not used.
Table 3. Scope for N‑(hetero)aryl-7-Azaindolesa
With the optimized conditions in hand (Table 1, entry 9), we
explored the substrate scope and functional group tolerance of the
rhodium(III)-catalyzed C–C cross-coupling reactions between N-
(hetero)aryl-7-azaindoles and α-carbonyl sulfoxonium ylides.

[CpRhCl2
] (4 mmol% )
In summary, we have developed a protocol for efficient
rhodium-catalyzed C(sp2)−H bond activation reactions of N-
(hetero)aryl-7-azaindoles and cross-coupling with α-carbonyl
sulfoxonium ylides. This protocol, which shows high
regioselectivity and broad functional group tolerance, provides a
new method for derivatizing 7-azaindoles and represents a novel
application of sulfoxonium ylides. Investigation of other metal-
catalyzed C(sp2)–H activation systems is currently underway in
our laboratories.
2
O
O
O
S
AgSbF6 (8 mmol% )
N
N
N
N
Ph
Ph
HFIP , K2CO3, 100 o
C
R
R
1
2a
4
O
O
O
O
N
N
N
N
N
N
N
N
Ph
Ph
Ph
Ph
OMe
78%
4e
4d
4b
78%
79%
4c
74%
O
O
O
O
Acknowledgments
N
N
N
N
N
N
N
N
Ph
Ph
Ph
Ph
We are grateful to the National Science Foundation of China for
financial support (NSFC-21472018). We are also thankful for the
School research fund of Changzhou Vocational Institute of
Engineering (11130300118013), Doctoral Research Startup Fund of
Changzhou Vocational Institute of Engineering for financial support.
O
CF3
Cl
F
O
4h
4i 74%
4g
74%
4f
73%
80%
O
O
N
N
N
N
2
Ph
Ph
6
References and notes
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MeOOC
4k 75%
MeO
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[CpRhCl2]2
AgSbF6/K2CO3
+
O
2
N
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3
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mechanism outlined in Scheme 2 for the reaction between 1-
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[CpRh(SbF6)2] or [CpRhCO3], by reaction of [CpRhCl2]2 with
AgSbF6/K2CO3. Then [CpRh(SbF6)2] or [CpRhCO3], activates
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Declaration of interests
☒ The authors declare that they have no known
competing financial interests or personal
relationships that could have appeared to influence
the work reported in this paper.
☐The authors declare the following financial
interests/personal relationships which may be
considered as potential competing interests:

6
Tetrahedron
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Rhodium-Catalyzed Regioselective C(sp2)−H Bond
Activation Reactions of N-(Hetero)aryl-7-azaindoles
and Cross-Coupling with α-Carbonyl Sulfoxonium Ylides
Leave this area blank for abstract info.
Yan Tian, Xian-Qiang Kong, Jie Niu, Yi-Bo Huang, Zhao-Hua Wu, Bo Xu
[CpRhCl2]2 (4 mmol %)
O
O
O
S
AgSbF6 (8 mmol %)
N
H
N
N
N
R2
R2
HFIP , K2CO3, 100 o
C
R1
68-83% yield
R1
Fonts or abstract dimensions should not be changed or altered.

1. C(sp2)−H bond activation reactions of N-(hetero)aryl-
7-azaindoles.
2. Cross-coupling with α-carbonyl sulfoxonium ylides.
3. In the C−H activation reaction, the 7-azaindole moiety
acts as a directing group, which results in high
regioselectivity.
4. Excellent chemical yields and good functional group
tolerance.