Regioselective Direct C2 Arylation of Indole, Benzothiophene and Benzofuran: Utilization of Reusable Pd NPs and NHC-Pd@MNPs Catalyst for C–H Activation Reaction

Article abstract of DOI:10.1007/s10562-020-03390-x

Abstract: A regioselective C2 arylation of indoles, benzothiophene and benzofuran without directing group has been accomplished using economically cheap Pd NPs and NHC-Pd@MNPs catalyst. The reusable catalyst is efficiently employed to access C2 arylated heterocycles in good to excellent yield. The reusability of the catalyst is studied up to five cycles and a gram-scale synthesis has been achieved. The reaction mechanism is well supported by control experiments and literature precedents. Grapic Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-020-03390-x

Catalysis Letters
https://doi.org/10.1007/s10562-020-03390-x
Regioselective Direct C2 Arylation of Indole, Benzothiophene
and Benzofuran: Utilization of Reusable Pd NPs and NHC‑Pd@MNPs
Catalyst for C–H Activation Reaction
1
2
2
1
1
1
Rajeev V. Hegde · Tiow‑Gan Ong · Ram Ambre · Arvind H. Jadhav · Siddappa A. Patil · Ramesh B. Dateer
Received: 23 May 2020 / Accepted: 6 September 2020
©
Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
A regioselective C2 arylation of indoles, benzothiophene and benzofuran without directing group has been accomplished
using economically cheap Pd NPs and NHC-Pd@MNPs catalyst. The reusable catalyst is eꢀciently employed to access C2
arylated heterocycles in good to excellent yield. The reusability of the catalyst is studied up to ꢁve cycles and a gram-scale
synthesis has been achieved. The reaction mechanism is well supported by control experiments and literature precedents.
Grapic Abstract
Keywords Heterogeneous catalysis · C2 arylation · Pd NPs · NHC-Pd@MNPs · Catalyst recyclability
1
Introduction
coupling partners (For selected review, see [1–11]). Nev-
ertheless, indole, benzothiophene and benzofuran are the
heterocyclic core commonly found in natural products and
pharmaceuticals (For selected review, see [12, 13]) for vari-
ous biological activities (Fig. 1) (For selected examples, see
The direct arylation of heteroaryl compounds via C–H bond
activation has emerged as a powerful synthetic strategy, as it
reduces additional steps associated with pre-functionalized
[
14–17]).
Therefore, the formation of aryl-heteroaryl bonds has
Electronic supplementary material The online version of
this article (doi:https://doi.org/10.1007/s10562-020-03390-x)
contains supplementary material, which is available to authorized
users.
been focus of intensive research for developing numerous
methodologies and depicts several known synthetic strat-
egies used for constructing the heterocyclic molecules
(
Scheme 1a). For instance, coupling of aryl metal with heter-
*
Ramesh B. Dateer
d.ramesh@jainuniversity.ac.in
oaryl or arene with heteroaryl metal reagent [18–25] (Route
I); cross-coupling of heteroaryl and arene (Route II) [26–29]
coupling of aryl halide with heteroaryl metal reagent or aryl
metal with heteroaryl halide (For reviews, see [30–33])
1
Centre for Nano and Material Sciences, JAIN (Deemed-
to-be University), Jain Global Campus, Bangalore,
Karnataka 562112, India
(
Route III) and coupling of aryl halide with heteroaryl or
2
Institute of Chemistry, Academia Sinica, Nangang,
Taipei 11529, Taiwan, Republic of China
arene with heteroaryl halide (Route IV) [34–43].
Vol.:(0
1
123456789)
3

R. V. Hegde et al.
Fig. 1 Selected examples of
natural products and biologi-
cally active molecules
Scheme 1 Evolution of aryl-
heteroaryl coupling reaction
Despite of the significant advantages, these reported
methods are still suꢂering from several issues of employ-
ing stoichiometric metallic reagents, expensive catalyst (e.g.
Pd, Rh, and Ru etc.) and ligands. Importantly, all of these
reactions are performed in homogenous manner, which suf-
fered from the recyclability of catalyst and metallic con-
tamination. Our extensive literature search shows that the
development of transition metal-catalysed C–H activation,
particularly C2-selective arylation of indole, benzothiophene
and benzofuranis is developed preferably with homogeneous
catalysis ([44–46, For electrophilic metalation–migration
see 47, For directing groups assisted reaction see 48–53].
However, despite of several reports (For C2 arylation of
indole by Pd NPs see [54–61]), the heterogeneous catalyst
for such a transformation are comparitively less explored.
Therefore,the new paradigm for the development of het-
erogeneous catalyst to address the C2 functionalization at
heterocycles would be highly desirable from the perspective
of synthesis. In this context, we are particularly interested
into developing heterogeneous support (For examples, see
[62–67]) in a greener set-up (For C2 arylation with under
green condition, see [68–72]) as possible contemporary
1
3

Regioselective Direct C2 Arylation of Indole, Benzothiophene and Benzofuran: Utilization…
method to address C–H arylation of heterocycles. Along
this line, we successfully discloseregioselective C–H aryla-
tion of (N–H free) indole, benzothiophene and benzofuran
with iodoarenes using economically cheap palladium nano-
particles (Pd NPs) and N-heterocyclic carbene-palladium
magnetic nanoparticles (NHC-Pd@MNPs) catalyst [73–78].
It is worth mentioning that, the phytochemicals present in
3 Results and Discussion
3.1 Table 1
We started our exploration in accessing the regioselective
C–H arylation of 1-methyl-1H-indole (1a) with
iodobenzene (2a). We selected Pd NPs [73] (Pd content:
II
black pepper extract plays a dual role for reducing the Pd
44.48 w/w, analysed by ICP-OES) as a catalyst and K CO
2
3
0
to Pd and also act as stabilizing agents for Pd NPs (See
as a base (Table 1, condition A). At room temperature, no
the SI for schematic representation). The wide range of C2
substituted indoles, benzothiophene and benzofuran can be
transformed eꢂectively to the corresponding coupling prod-
ucts without installing additional auxiliary directing group
onto substrates. Importantly, the concept on the recyclability
of nano-catalyst is demonstrated in this work.
reaction was observed even at longer reaction time (entry
1). Increasing the reaction temperature to 70 °C in 18 h led
to formation the product 3 in 35% yield, which is puriꢁed
by column chromatography and its identity was further
1
conꢁrmed by H NMR spectroscopy with singlet signal
appeared at 7.20 ppm, indicative of C2-arylation over C3
[
73, 75] (entry 2). Bases such as sodium carbonate, cesium
carbonate, sodium acetate and potassium acetate furnished
low to moderate yield (entries 3–6), while sodium
2
Experimental Section
hydroxide and potassium hydroxide were not eꢂective (See
the SI for more details). Keeping sodium acetate as an
optimum base, we have screened numerous solvents and
2
.1 Experimental Procedure for the Synthesis
of 2‑Phenyl‑1H‑indole (3a)
Condition A The DMSO (3 mL) were added in to the oven
dried 25 mL R.B.F containing compound 1a (58.57 mg,
found the signiꢁcant improvement in the reaction eꢀciency
with DMSO (entries 9 and 10). Other high boiling solvents
such as DMF, DMA and toluene are ineꢂective in this
methodology (See the SI for more details). Encouragingly,
such high eꢀciency and C2 selectivity can still be
0
.5 mmol, 1 equiv), followed by addition of NaOAc
(
45.11 mg, 1.1 equiv), Pd NPs (2.39 mg, 2 mol% Pd content:
4
4.48 w/w), iodobenzene 2a (408.02 mg, 2 mmol, 4 equiv).
The reaction mixture was stirred at 120 °C for 24 h, after
complete conversion of starting material (indicated by TLC),
the reaction was quenched with water and the organic layer
was extracted with EtOAc (25 × 3) the combined organic
layer was dried over anhydrous Na SO the solvent was
maintained when the catalyst loading was further reduced
to 2 mol % and desired product obtained in 92% yield,
albeit in longer reaction time at 120 °C (entry 11). The
blank reaction indicated that the coupling reaction failed to
proceed in an absence of catalyst (entry 12). Other halide
sources such as bromobenzene or chlorobenzene is not
suitable in this Pd NPs mediated reaction (See the SI for
more details). Whereas this C2-arylation method could be
applied to other precursors such as, benzothiophene (1b)
and benzofuran (1c) under the similar reaction condition in
86 and 87% yield, respectively (entries 13 and 14).
2
4
evaporated by rotary evaporator and crude compound was
puriꢁed by column chromatography (eluent: 2% EA/Hex-
ane) to get the compound 2-phenyl-1H-indole (3a, 88.01 mg,
9
2%).
Condition B The similar experimental procedure was fol-
lowed for condition B using NHC-Pd@MNPs (17.62 mg,
2
2
mol%, Pd content: 6.04 w/w) catalyst to get the compound
-phenyl-1H-indole (3a, 85.14 mg, 89%).
1
3

R. V. Hegde et al.
Table 1 Optimization of reaction condition
S.No
1 ( X)
Solvent
Base
T (°C)/t (h)
Yield % (3)a
Condition A
Condition B
1
2
3
4
5
6
7
8
9
=NH (1a)
=NH (1a)
=NH (1a)
=NH (1a)
=NH (1a)
=NH (1a)
=NH (1a)
=NH (1a)
=NH (1a)
=NH (1a)
=NH (1a)
=NH (1a)
=S (1b)
THF
THF
THF
THF
THF
THF
K CO
25/36
70/18
70/18
70/18
70/18
70/18
70/18
70/18
70/18
120/18
120/24
120/24
120/24
120/24
Trace
35
33
29
57
61
47
38
71
80
92
0
Trace
23
31
32
55
62
30
31
68
77
89
0
2
3
K CO
2
3
Na CO
2
3
Cs CO
2
3
NaOAc
KOAc
CH CN
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
3
EtOH
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
10
11
12
13
14
b
86
87
74
80
=O (1c)
Reaction condition: condition A: 1 (0.5 mmol), 2a (4.0 equiv), Pd NPs (0–4.0 mol%, 44.48 w/w), NaOAc (0–1.1 equiv) solvent, 25–120 °C,
1
2-32 h. Condition B: 1a (0.5 mmol), 2a (4.0 equiv), NHC-Pd@MNPs (0–4 mol%, 6.04 w/w), NaOAc (0–1.1 equiv), solvent, 12–36 h
a
Yields after puriꢁcation from silica gel column chromatography (average of two run)
No catalyst used
b
3
.2 Table 2
withdrawing substituents such as, 2-ꢃuoro (3e), 4-triꢃuoro-
methyl (3f), 4-chloro (3g), 4-bromo (3h), 3-chloro 4-methyl
(3i) reacted smoothly, aꢂording C2 arylation product in sat-
isfactory yield of 68–80% (condition A) and 61–78% (condi-
tion B). In addition, N-methylindole also reacted smoothly
that alkyl-substitution does not aꢂect yield and regioselec-
tivity of this synthetic methodolgy. The heteroaryl halide
such as 3-iodopyridine are not reactive under both condition,
which would be used as precursor to synthesize INF55 NorA
efux pump inhibitor3l.
We also examined the viability of this protocol with other
heterogeneous catalyst, NHC-Pd@MNPs [78] (Pd con-
tent: 6.04 w/w, analyzed by ICP-AES) for similar reaction
(
Table 1 condition B), which gave a comparable reactiv-
ity to the condition A. Thus, optimized reaction condition
for (NH-free) indole, benzothiophene and benzofuran is:
Pd NPs (2.0 mol%, Pd content: 44.48 w/w, for condition
A) and NHC-Pd@MNPs (2.0 mol%, Pd content: 6.04 w/w,
for condition B) as a catalyst, iodobenzene (4.0 equiv) as a
halide precursor, NaOAc (1.1 equiv) as a base, DMSO as
solvent at 120 °C for 24 h.
3.3 Table 3
Having gained preliminary insights in to the novel reac-
tion and identiꢁed the optimized reaction conditions, we ꢁrst
explored the scope and generality of this process against dif-
ferent aryl iodide 2 with (N–H free) indole (see Table 2 for
condition A and B). The aryl iodides bearing electron donat-
ing 4-methoxy, 4-methyl and 2-methyl substituents furnishes
C-2 arylated products (3b–3d) in high yield of 85–90%
Next, the generality of Pd NPs mediated selective C-H acti-
vation of benzothiophenes were also evaluated by exploring
diꢂerent substrates (Table 3). For instance, the benzothio-
phene reacted with aryl iodides to furnish desired products
3m–3t in 69–85% yield (under condition A) and 58–81%
yield. (Under condition B). Similarly, reaction of benzofuran
with iodobenzenes bearing diꢂerent functionality handles
achieved expected coupling product 3u–3y in moderate to
(
condition A) and 83–87% (condition B). While, electron
1
3

Regioselective Direct C2 Arylation of Indole, Benzothiophene and Benzofuran: Utilization…
Table 2 Scope with aryl halides
a c
b c
b
Reaction condition: condition A: 1a (0.5 mmol), 2a (4.0 equiv), Pd NPs (2.0 mol%, 44.48 w/w), NaOAc (1.1 equiv.) DMSO at 120 °C in 24 h.
a
Condition B: 1a (0.5 mmol), 2a (4.0 equiv), NHC-Pd@MNPs (2.0 mol%, 6.04 w/w), NaOAc (1.1 equiv), DMSO at 120 °C in 24 h. Yields/TON
b
c
using condition A; yields/TON using condition B; yields after puriꢁcation form silica gel column chromatography (average of two run)
good yields. The use of 3-iodopyridine as coupling partner
resulted in no product formation (3z).
Finally, to test the reaction potential for practical indus-
trial applications, our protocol can be successfully scaled up
using indole substrate without aꢂecting the chemical yield
and regioselectivity (Eq. 1). To get a better insight about
the substituent eꢂect on the rate of the reaction and product
formation competitive experiments were performed with
Notably, the catalyst recyclability [73–78] of Pd NPs was
found to be more than ꢁve times with a signiꢁcant decreas-
ing in the reaction eꢀciency for each following reaction,
We believed that the decrease in activity of Pd NPs might
suꢂer from the possible particles aggregation caused poor
solubility of catalyst in organic solution (See SI for FESEM
images). It should be noted that, we are failed to recycle
NHC-Pd@MNPs due to its high solubility in organic solu-
tion (Fig. 2).
electronically biased iodoarenes (OMe and CF ) with indole
3
(Eq. 2). The competing substrates were taken into account
by using equal stoichiometric amounts of substrates in 10 h.
1
3

R. V. Hegde et al.
Table 3 Scope with
benzothiophene and benzofuran
a c
b c
a
b
Reaction condition: condition A: 1 (0.5 mmol), 2a (4.0 equiv), Pd NPs (2.0 mol%, 44.48
w/w), NaOAc (1.1 equiv.) DMSO at 120 °C in 24 h. Condition B: 1a (0.5 mmol), 2a (4.0
equiv), NHC-Pd@MNPs (2.0 mol%, 6.04% w/w), NaOAc (1.1 equiv), DMSO at 120 °C in
a
b
c
2
4 h. Yields/ TON using condition A; yields/TON using condition B; yields after puriꢁ-
cation form silica column chromatography (average of two run)
The desired products and un-reacted starting materials
analysed by TLC revealing the complete conversion of the
limiting substrates. It is then separated by ꢃash chromatog-
raphy and the isolated yields of products indicates that the
substituent eꢂect has no signiꢁcant consequence over the
nominal product selectivity, ruling out oxidative addition is
the rate-determining step in this reaction [79, 80]. Further-
more, the existence of Pd (0) along with a traces of Pd (II) is
clearly investigated in XPS analysis performed in our recent
study [77]. It reveals that, phytochemicals inside black pep-
per extract serves as a ligand for reduction of Pd(II) to Pd(0)
and thus, avoiding the need of external ligand [73].
In fact, the traditional mechanistic investigation in C–H
functionalization reactions catalyzed by homogeneous pal-
ladium catalysts [44–53] were not directly applicable in
case of heterogeneous catalysis. Thus, detailed mechanis-
tic understanding for heterogeneous reaction pathways is
not completely known. Nevertheless, based on the control
1
3

Regioselective Direct C2 Arylation of Indole, Benzothiophene and Benzofuran: Utilization…
Fig. 2 a Recycling eꢀciency
of Pd NPs in C–H arylation.
FESEM Images: b Fresh Pd
NPs, c Pd NPs after ꢁve cycles
intermediate II [82]. The base mediated regioselective
2
C(sp )–H bond cleavage/activation occurs heterolytically
leading to the formation of III in which basic nitrogen of
indole is further coordinated to the re-oxidised palladium
surface [83]. The subsequent formation of intermediate IV
followed by reductive elimination liberates the product 3a
with the regeneration of Pd(0) to complete catalytic cycle.
The similar reaction pathwaysmay operates for the catalytic
cycles in the case of NHC-Pd@MNPs catalyst.
84
85
4
Conclusion
In summary, without resorting to directing group instalment
on the substrate, we have developed a new catalytic system
for the regioselective C2 arylation of indoles, benzothio-
phene and benzofuran with aryl iodides. This transformation
represents practicality of environmental friendly and eco-
nomically cheap Pd NPs and NHC-Pd@MNPs as a reusable
heterogeneous catalyst for regioselective C–H activation
reaction. The catalytic method features the complimentry
reaction pathways oparating for both the the catalysts high-
lights an important milestone toward the development of
industrially relevant strategy. Ongoing work seeks to gain
a detailed mechanistic understanding of the resemblance
Scheme 2 Plausible reaction mechanism
experiment and literature precedents [37, 54–61, 81–83]
plausible mechanism for the regioselective C2 arylation
is depicted in Scheme 2. First, oxidative addition of het-
erogeneous palladium catalyst across aryl iodide forms
1
3

R. V. Hegde et al.
oꢂered by Pd NPs and NHC-Pd@MNPs catalysts. In addi-
tion, the possibilities to functionalize the C5 position of
indoles, benzothiophene and benzofuran are currently under
exploration in our laboratory.
29. Dwight TA, Rue NR, Charyk D, Josselyn R, DeBoef B (2007) Org
Lett 9:3137–3139
3
3
0. Suzuki A (2005) Chem Commun 38:4759–4763
1. Nicolaou KC, Bulger PG, Sarlah D (2005) Angew Chem Int Ed
44:4442–4489
3
2. Miura M (2004) Angew Chem Int Ed 43:2201–2203
Acknowledgements Author thank to, SERB-DST, Government of
India, for the ꢁnancial support through the research Grant: File Nos.
SB/S2/RJN-042/2017 and ECR/2017/002207. Author also thanks to
Jain University, India, for ꢁnancial support.
33. Stanforth SP (1998) Tetrahedron 54:263–303
34. Art SP, Satoh T, Kawamura Y, Miura M, Nomura M (1998) Bull
Chem Soc Jpn 71:467–473
35. Rieth RD, Mankad NP, Calimano E, Sadighi JP (2004) Org Lett
6
3:981–3983
3
3
3
6. Chiong HA, Daugulis O (2007) Org Lett 9:1449–1451
7. Lebrasseur N, Larrosa I (2008) J Am Chem Soc 130:2926–2927
8. Lane BS, Sames D (2004) Org Lett 6:2897–2900
Compliance with Ethical Standards
Conflicts of interest There are no conꢃicts to declare.
39. Deprez NR, Kalyani D, Krause A, Sanford MS (2006) J Am Chem
Soc 128:4972–4973
4
0. Gryko DT, Vakuliuk O, Gryko D, Koszarna B (2009) J Org Chem
7
4:9517–9520
References
4
4
1. Ca ND, Maestri G, Catellani M (2009) Chem. Eur. J 15:7850–7853
2. Gracia S, Cazorla C, Metay E, Rostaing P, Lemaire M (2009) J
Org Chem 74:3160–3163
1
2
3
.
.
.
Wang D-H, Engle KM, Shi B-F, Yu J-Q (2010) Science
27:315–319
Daugulis O, Do H-Q, Shabashov D (2009) Acc Chem Res
2:1074–1086
Ackermann L, Vicente R, Kapdi AR (2009) Angew Chem Int Ed
3
43. Battace A, Lemhadri M, Zair T, Doucet H, Santelli M (2007)
Organometallics 26:472–474
4
44. Yang L, Zhao L, Li C-J (2010) Chem Comm 46:4184–4186
45. Sauermann N, González MJ, Ackermann L (2015) Org Lett
17:5316–5319
4
8:9792–9826
4
5
.
.
Lyons TW, Sanford MS (2010) Chem Rev 110:1147–1169
46. Nadres ET, Lazareva A, Daugulis O (2011) J Org Chem
76:471–483
McGlacken GP, Bateman LM (2009) Chem Soc Rev
3
8:2447–2464
47. Tolnai GL, Ganss S, Brand JP, Waser J (2013) Org Lett
15:112–115
6
7
8
.
.
.
Alberico D, Scott ME, Lautens M (2007) Chem Rev 107:174–238
Godula K, Sames D (2006) Science 312:67–72
48. Xie F, Qi Z, Yu S, Li X (2014) J Am Chem Soc 136:4780–4787
49. Zhang ZZ, Liu B, Wang CY, Shi BF (2015) Org Lett
17:4094–4097
Colby DA, Bergman RG, Ellman JA (2010) Chem Rev
1
10:624–655
9
.
Kuhl N, Hopkinson MN, Delord JW, Glorius F (2012) Angew
Chem Int Ed 51:2–21
50 Li T, Wang Z, Qin WB, Wen TB (2016) ChemCatChem
8:2146–2154
1
0. Girard SA, Knauber T, Li CJ (2014) Angew Chem Int Ed
51. Ruan Z, Sauermann N, Manoni E, Ackermann L (2017) Angew
Chem Int Ed 56:1–6
5
3:74–100
1
1
1. Ackermann L (2011) Chem Rev 111:1315–1345
52. Wu W, Fang S, Jiang G, Li M, Jiang H (2019) Org. Chem. Front
6:2200–2204
2. Kochanowska-Karamyan AJ, Hamann MT (2010) Chem Rev
1
10:4489–4497
53. Khake SM, Soni V, Gonnade RG, Punji B (2017) Chem Eur J
23:2907–2916
1
1
3. Somei M, Yamada F (2004) Nat Prod Rep 21:278–311
4. Ambros R, Schneider MR, von Angerer S (1990) J Med Chem
54. Jumn MA, Donia B, Piet WNM, Van L, Baruno C (2020) Chem
Rev 120:1042–1084
3
3:153–160
1
1
1
5. Polossek T, Ambros R, von Angerer S, Brandl G, Mannschreck
A, von Angerer E (1992) J Med Chem 35:3537–3547
55. Yuanbiao H, Zujin L, Rong C (2011) Chem Eur J 17:12706–12712
56. Liang W, Wen-bin Y, Chun C (2011) Chem Commun 47:806–808
57. Joel M, Anuja N, Cheuk-Wai T, Jan-E B, Berit O (2014) Chem
Eur J 20:13531–13535
6. Faust R, Garratt PJ, Jones R, Yeh LK (2000) J Med Chem
4
3:1050–1061
7. Kraus GA, Gupta V, Kohut M, Singh N (2009) Bio Org Med
Chem Lett 19:5539–5542
58. Linlin D, Rao F, Bingsen Z, Wen S, Shangjun C, Ying W (2016)
ACS Catal 6:1062–1074
1
1
8. Zhao J, Zhang Y, Cheng K (2008) J Org Chem 73:7428–7431
9. Yang S-D, Sun C-L, Fang Z, Li B-J, Li Y-Z, Shi Z-J (2008) Angew
Chem Int Ed 47:1473–1476
59. Christophe VD, Rong Y, Walter R, Dean FT, Gabor AS (2017) J
Am Chem Soc 139:18084–18092
60. Yuan BH, Qiang W, Jun L, Xusheng W, Rong C (2016) J Am
Chem Soc 138:10104
2
2
2
2
0. Liang Z, Yao B, Zhang Y (2010) Org Lett 12:3185–3187
1. Cornella J, Lu P, Larrosa I (2009) Org Lett 11:5506–5509
2. Vogler T, Studer A (2008) Org Lett 10:129–131
3. Ban I, Sudo T, Taniguchi T, Itami K (2008) Org Lett
61. Yuan BH, Min S, Xusheng W, Ping H, Ruiping C, Zu JL, Rong C
(2016) J Catal 333:1–7
62. Wang L, Yi WB, Cai C (2011) Chem Commun 47:806–808
63. Huang Y, Ma T, Huang P, Wu D, Lin Z, Cao R (2013) Chem-
CatChem 5:1877–1883
1
0:3607–3609
2
2
4. Hachiya H, Hirano K, Satoh T, Miura M (2010) Angew Chem Int
Ed 49:2202–2205
64. Zhang L, Li P, Liu C, Yang J, Wanga M, Wang L (2014) Catal Sci
Technol 4:1979–1988
5. Xie K, Yang Z, Zhou X, Li X, Wang S, Tan Z, An X, Guo C-C
(
2010) Org Lett 12:1564–1567
65. Huang Y, Lin Z, Cao R (2011) Chem Eur J 17:12706–12712
66. Malmgren J, Nagendiran A, Tai CW, Backvall JE, Olofsson B
(2014) Chem Eur J 20:1–6
2
2
6. Stuart DR, Fagnou K (2007) Science 316:1172–1175
7. Xi P, Yang F, Qin S, Zhao D, Lan J, Gao G, Hu C, You J (2010) J
Am Chem Soc 132:1822–1824
67. Duan L, Fu R, Zhang B, Shi W, Chen S, Wan Y (2016) ACS Catal
6:1062–1074
2
8. Kita Y, Morimoto K, Ito M, Ogawa C, Goto A, Dohi T (2009) J
Am Chem Soc 131:1668–1669
68. Lu GP, Cai C (2012) Synlett 23:2992–2966
1
3

Regioselective Direct C2 Arylation of Indole, Benzothiophene and Benzofuran: Utilization…
6
7
9. Xu Z, Xu Y, Lu H, Yang T, Lin X, Shao L, Ren F (2015) Tetrahe-
dron 71:2616–2621
78. Vishal K, Fahlman BD, Sasidhar BS, Patil SA, Patil SA (2017)
Catal Lett 147:900–918
0. Joucla L, Batail N, Djakovitcha L (2010) Adv Synth Catal
79. Das D, Bhutia ZT, Chatterjee A, Banerjee M (2019) J Org Chem
84:10764–10774
3
52:2929–2936
7
7
1. Islam S, Larrosa I (2013) Chem Eur J 19:15093–15096
2. Moncea O, Poinsot D, Fokin AA, Schreiner PR, Hierso JC (2018)
ChemCatChem 10:2915–2922
80. Colletto C, Panigrahi A, Casado J-F, Larrosa I (2018) J Am Chem
Soc 140:9638–9643
81. Jayarajan R, Kumar R, Gupta J, Dev G, Kadu P, Chatter-
jee D, Bahadur D, Maiti D, Maji SK (2019) J Mater Chem A
7:4486–4493
7
7
7
7
7
3. Kandathil V, Dateer RB, Sasidhar BS, Patil SA, Patil SA (2018)
Catal Lett 148:1562–1578
4. Nasrollahzadeh M, Sajadi SM, Maham M, Ehsani A (2015) RSC
Adv 5:2562–2567
82. Domingo GC, Paula DM, Ataualpa AC, Braga FM, Antonio ME
(2007) J Am Chem Soc 129:6880–6886
5. Kandathil V, Kempasiddaiaha M, Sasidhar BS, Patil SA (2019)
Carbohydr Polym 223:1150
83. Sudha K, Michael B, Stanley EG, Kendra B, Frank B, G, Keith,
CE, (2017) Chem Commun 53:7022–7025
6. Garai C, Hasan SN, Barai AC, Ghorai S, Panja SK, Bag BG
(
2019) J Nanostr Chem 8:462
Publisher’s Note Springer Nature remains neutral with regard to
7. Hegde RV, Ghosh A, Patil SA, Dateer RB (2019) Tetrahedron
5:13077
jurisdictional claims in published maps and institutional aꢀliations.
7
1
3