(E)-N-(pyren-1-ylmethylene)benzenamine: efficient promoter for additive-free palladium catalyzed aerobic oxidative coupling of arylboronic acids and terminal alkynes

Article abstract of DOI:10.1007/s11696-020-01156-8

Abstract: A highly productive protocol for the synthesis of internal alkynes by the carbon–carbon cross-coupling reactions of electronically different arylboronic acids with substituted phenylacetylenes was described by employing (E)-N-(pyren-1-ylmethylene)benzenamine with Pd(OAc)₂. The influence of reaction parameters such as solvent, base and reaction temperature in this carbon–carbon cross-coupling reaction was also investigated. The substrate scope could be expanded to electron-poor alkynes, for which the conventional Sonogashira reaction gives poor yields. Moderate to excellent yield was obtained in the oxidative Sonogashira-type coupling reaction. Graphic abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s11696-020-01156-8

Chemical Papers
https://doi.org/10.1007/s11696-020-01156-8
SHORT COMMUNICATION
(E)‑N‑(pyren‑1‑ylmethylene)benzenamine: efcient promoter
for additive‑free palladium catalyzed aerobic oxidative coupling
of arylboronic acids and terminal alkynes
Jagadeesan Lakshmipraba1 · Rupesh Narayana Prabhu1 · Victor Violet Dhayabaran1
Received: 6 December 2019 / Accepted: 2 April 2020
© Institute of Chemistry, Slovak Academy of Sciences 2020
Abstract
A highly productive protocol for the synthesis of internal alkynes by the carbon–carbon cross-coupling reactions of electroni-
cally diferent arylboronic acids with substituted phenylacetylenes was described by employing (E)-N-(pyren-1-ylmethylene)
benzenamine with Pd(OAc)2. The infuence of reaction parameters such as solvent, base and reaction temperature in this
carbon–carbon cross-coupling reaction was also investigated. The substrate scope could be expanded to electron-poor alkynes,
for which the conventional Sonogashira reaction gives poor yields. Moderate to excellent yield was obtained in the oxidative
Sonogashira-type coupling reaction.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11696-020-01156-8) contains
supplementary material, which is available to authorized users.
* Jagadeesan Lakshmipraba
lakshmiprabachem@gmail.com
1
Post Graduate and Research Department of Chemistry,
Bishop Heber College, Tiruchirappalli 620 017, Tamil Nadu,
India
Vol.:(0123456789)
1 3

Chemical Papers
Graphic abstract
Keywords Schif base · Palladium-catalyzed · Oxidative Sonogashira-type · C–C coupling · Diaryl acetylenes
Internal alkynes moiety has wide application in daily life and
is encountered as building blocks in numerous medicines,
natural products, dendrimers (Agou et al. 2009), macrocy-
cles (Liu et al. 2009), optoelectronic materials (Balsukuri
et al. 2015), fne chemicals (Dasaradhan et al. 2015; Prabhu
and Ramesh 2016), etc. Hence, reaction protocols that pro-
vide an efcient access to internal alkynes are greatly desir-
able. Many synthetic protocols are reported for the genera-
tion of diaryl acetylenes. The palladium-catalyzed and CuI
co-catalyzed coupling reaction of aryl halides and terminal
acetylenes, also known as the Sonogashira reaction, is com-
petent and unequivocal methodology for the construction of
C(sp2)–C(sp) bond (Chinchilla and Nájera 2011; Karak et al.
2014). However, from literature reports it is inferred that the
use of copper salts which can yield undesired diynes in air
or O2 by the Glaser–Hay-type homo-coupling of alkynes. In
addition, highly sensitive and potentially explosive copper
acetylides can also form, thereby decreasing the productivity
of the reaction. Though diferent ligand systems have been
used for the palladium-catalyzed Sonogashira reaction under
copper free conditions (Chinchilla and Nájera 2007; Fort-
man and Nolan 2011; Singh and Verma 2011; Sabounchei
et al. 2013; Yang et al. 2014; Prabhu and Pal 2015a), some
of the main drawbacks of these systems include their avail-
ability, high price, laborious and time consuming strate-
gies for synthesis of ligands and corresponding palladium
complexes, unstability of ligands, use of inert atmosphere
and Schlenk-line techniques, etc. Further, electron-defcient
alkynes are not efective substrates in Sonogashira reaction
as poor yields are generally observed. These enforce the
researchers to develop new, stable, cost-efective and ef-
cient catalytic systems as modifcations of the traditional
Sonogashira protocol. In recent years, oxidative coupling of
terminal alkynes with arylboronic acids mediated by tran-
sition metals has transpired as an alternate option for the
traditional Sonogashira coupling reaction. This oxidative
cross-coupling reaction ofers copious superiority, such as
mild reaction conditions, carrying out the reaction in the
absence of inert atmosphere and high functional group toler-
ance, many air- and water-stable boronic acid derivatives are
1 3

Chemical Papers
commercial available or can be easily prepared, boron resi-
dues can be easily removed after the reaction, the reagents
and by-products are generally non-toxic, thus explaining the
growing attraction in this synthetic methodology. There are
some interesting reports on the oxidative coupling between
terminal acetylenes with arylboronic acids catalyzed by iron
(You et al. 2012), copper (Mao et al. 2008; Pan et al. 2009;
Rao et al. 2010; Yasukawa et al. 2011; Li et al. 2012) nickel
(Troung et al. 2014; Prabhu and Lakshmipraba 2017) pal-
ladium (Zou et al. 2003; Mitsudo et al. 2010; Zhou et al.
2010; Nie et al. 2011; Li et al. 2013; Lu et al. 2014; Xu
et al. 2016) or gold (Qian and Zhang 2011) as an alternative
to the traditional Sonogashira reaction. However, in most
of these reports, additives were required for good yields of
the desired product. Although compelling results have been
obtained, the development of a milder protocol for this trans-
formation, especially under additive-free conditions, con-
tinues to be a central goal of current research in chemistry.
Schif bases draw considerable attention as ligands due
to their ease in preparation, stability and high coordination
capacity towards various transition metals (Das and Linert
2016). Further, the steric and electronic properties of Schif
bases could be tuned easily by selecting appropriate sub-
stituents on the aldehyde or amine (Abu-Dief and Mohamed
2015). In this paper, we report a straightforward and efec-
tual protocol for the aerobic oxidative Sonogashira reaction
of substituted arylboronic acids and electronically diferent
phenylacetylenes by utilizing Pd(OAc)2/(E)-N-(pyren-1-yl-
methylene)benzenamine system in the absence of any silver
additive. Diverse reaction parameters such as solvent, base
and reaction temperature were sequentially optimized for
this C(sp2)–C(sp) coupling reaction before evaluating the
scope of the coupling partners. Though there are reports on
the synthesis and characterization of Schif bases derived
from 1-pyrenecarboxaldehyde (Shree et al. 2019; Shellaiah
et al. 2013), our screening on the literature has revealed
that no attention has been paid to explore the Pd-catalyzed
synthesis of diaryl acetylenes by the oxidative Sonogashira
coupling reaction using (E)-N-(pyren-1-ylmethylene)ben-
zenamine (L).
mass spectra were recorded on Elmer Clarus 900 C GC–MS
spectrometer.
The Schif base, L, was readily accessible in good yields
by the condensation of 1-pyrenecarboxaldehyde with aniline
in ethanol (Scheme 1). FT-IR, NMR (1H and 13C) and MS
techniques were used to authenticate the purity and identity
of L.
The FT-IR of free 1-pyrenecarboxaldehyde and aniline
displayed bands due to the free aldehydic group (1700 cm−1)
and free –NH2 group (3200 cm−1), respectively. Disappear-
ance of these bands in L indicated the formation of Schif
base. This was further confrmed by the appearance of a new
stretching frequency at 1583 cm−1 in L. In the 1H NMR spec-
tra of L, the sharp singlet resonance at δ 9.65 ppm indicated
the presence of azomethine proton and formation of the
Schif base (Kathiravan et al. 2014, Prabhu and Pal 2015b).
This was further confrmed by the absence of the aldehy-
dic proton of 1-pyrenecarboxaldehyde and –NH2 protons of
aniline in the 1H NMR spectrum of L. The chemical shifts
of the other aromatic protons of L are unexceptional. The
13C NMR spectrum of L, the resonance at δ 158.97 ppm is
attributed to the azomethine carbon (Kathiravan et al. 2014).
Other carbons of the aromatic group resonate at expected
regions. The GC–MS of L exhibited the molecular ion peak
at m/z 339.
The unceasing procedure to discover diferent routes
has made us interested in searching for a new methodology
for the silver-free Pd(OAc)2-L mediated aerobic oxidative
Sonogashira coupling reaction. The generation of catalyst
in situ is considered to be appealing because it eliminates
the need for the additional tasks of prior synthesis and sub-
sequent characterization of the corresponding metal-com-
plex. In addition, it also provides the fexibility of selecting
ligand to partner the available palladium salts based on the
requirement of a specifc cross-coupling catalysis reaction.
The synthesis of 1-methoxy-4-(phenylethynyl)benzene by
the coupling between phenylboronic acid and 4-ethynylani-
sole mediated by Pd(OAc)2/L in air and in the absence of
silver salts was frst selected as a model system to establish
the practical efcacy of the system. The solvent, base and
reaction temperature were varied sequentially in order to
determine the best reaction conditions. In order to identify a
solvent which can enhance the yield of the desired product,
initial investigation was implemented on the evaluation of
diferent solvents (Fig. 1). It was inferred that the extent
of product formation depended on the solvent used and
All the chemicals used in this work were of analytical
grade, available commercially and were used as received.
Infrared spectra of ligands were recorded as KBr pellets
on Perkin Elmer Spectrum RX I spectrophotometer. The
NMR spectra were obtained on a Bruker Avance III NMR
400 MHz spectrometer operating at room temperature. ESI
Scheme 1 Preparation of Schif
NH2
base
N
O
+
EtOH, AcOH
Reflux, 3 h
L
1 3

Chemical Papers
Other organic bases (Et3N, Bu3N, pyridine) and inorganic
bases (K2CO3, KHCO3, K3PO4) were found to less efcient
in this cross-coupling reaction.
The efect of temperature on the cross-coupling reaction
was then probed. As the temperature of the reaction was
decreased from 100 °C to 35 °C, a drop in the isolated yield
of the product was observed (Fig. 3). At 100 °C, almost quan-
titative yield of the desired product was observed, whereas
at 35 °C only < 10% of the desired product was obtained.
Hence, for consequent experiments, DMF–DBU at 100 °C
was considered to be optimal condition. Controlled experi-
ments were also carried out in DMF at 100 °C. It was ascer-
tained that in the absence of Pd(OAc)2 or base, the desired
product was not formed. Further, though Pd(OAc)2–DBU
in DMF could catalyze the oxidative Sonogashira coupling
reaction in the absence of L, the efciency was poor with
only 30% yield of the product indicating that L acts as a pro-
moter in this conversion. It is gratifying to say that under the
given conditions the homo-coupling by-products of neither
the internal alkyne nor the arylboronic acid were detected.
After authenticating the optimal reaction conditions
(DMF, DBU, 100 °C, 3 h, in air), in order to comprehend
the scope and feasibility of the oxidative Sonogashira reac-
tion, the reaction of phenylboronic acid (as a representa-
tive arylboronic acid derivative) with a wide range of sub-
stituted phenylacetylenes with diverse electronic efects
were surveyed (Table 1). For the ease of correlation of the
results, all the coupling reactions were efectuated under
identical reaction conditions. It was inferred that the proto-
col tolerated diferent functional groups giving the desired
internal alkynes in good to excellent isolated yields when
electron-donating, electron-neutral and electron-with-
drawing substituents were present on the aromatic ring.
Fig. 1 Efect of solvent on product yield at 100 °C
among the various solvents screened, dimethylformamide
(DMF) gave better results. When the reaction was carried
out in other solvents such as dimethylsulphoxide (DMSO),
N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMA),
toluene and xylene, relatively low but promising isolated
yield of the desired internal alkyne was obtained. Therefore,
DMF was chosen as relevant solvent for further coupling
reactions.
In carbon–carbon cross-coupling reactions, base is known
to infuence the yield of the product and the efects of vari-
ous bases were then probed. Evident sensitivity to base used
was noted in DMF. The results from the optimization of
bases (Fig. 2) revealed that 1,8-diazabicycloundec-7-ene
(DBU) had ranked the highest yield (99%) of the desired
internal alkyne and was the best choice among other bases.
Fig. 3 Efect of reaction temperature on product yield in DMF at
Fig. 2 Efect of base on product yield in DMF at 100 °C
100 °C
1 3

Chemical Papers
Table 1 C–C coupling reactions
of phenylboronic acid with
substituted phenylacetylene
Pd(OAc)2, L
DMF, DBU
100 oC, 3h
+
(HO)2B
R
R
Entry
1
Product
Yield (%)a
99
O
H3C
2
3
4
97
94
90
H3C
H
H
O
H3C
5
87
O
6
7
83
93
O2N
H3C O
8
9
85
80
O
H
O
H3C
10
76
H
O
Phenylboronic acid (1.0 mmol), arylacetylene (1.2 mmol), Pd(OAc)2 (1 mol%), L (1 mol%), DMF
(5 mL), DBU (2.0 mmol) at 100 °C in air for 3 h
aIsolated yield after column chromatography (average of two independent runs)
Substituted phenylacetylenes bearing electron-donating
groups (such as 4-methoxy or 4-methyl) reacted efort-
lessly with phenylboronic acid to afford greater iso-
lated yield of the desired product when compared to
phenylacetylene (entries 1-3). When electron-withdrawing
groups (such as 4-formyl, 4-acetyl or 4-nitro) were present,
the conversion is less when compared to that of phenyla-
cetylene (entries 3-6). Utilization of 3-ethynylanisole and
1 3

Chemical Papers
Table 2 C–C coupling reactions
of arylboronic acids with
phenylacetylene
Pd(OAc)2, L
(HO)2B
+
DMF, DBU
100 oC, 3h
R
R
Entry
1
Product
Yield (%)a
96
NO2
O
2
3
92
90
CH3
O
H
H
4
5
6
86
82
78
CH3
O
CH3
7
8
76
72
O
H
O
H3C
9
70
64
H
O
10
O
CH3
Arylboronic acid (1.0 mmol), phenylacetylene (1.2 mmol), Pd(OAc)2 (1 mol%), L (1 mol%), DMF
(5 mL), DBU (2.0 mmol) at 100 °C in air for 3 h
aIsolated yield after column chromatography (average of two independent runs)
3-ethynylbenzaldehyde (entries 7,8) as coupling partners,
aforded the desired products with yields comparable to
that of the corresponding para substituted derivatives
(entries 1,4). Ortho substituted derivatives such as 2-ethy-
nylanisole and 2-ethynylbenzaldehyde (entries 9, 10) were
also compatible in the employed protocol. However, they
resulted in slightly inferior yields than the corresponding
para substituted derivatives (entries 1,4) which could be
due to the steric efects as expected.
1 3

Chemical Papers
Additional coupling reactions were then efectuated
in an inverted manner: i.e., with functionalized arylbo-
ronic acids and phenylacetylene (as a representative ter-
minal acetylene derivative) to determine the generality
of this catalytic method towards diferent arylboronic
acids (Table 2). All the coupling reactions were carried
out under identical reaction conditions for the ease of
comparison of results. It was inferred that the substituted
arylboronic acids reacted smoothly with phenylacetylene
to furnish the corresponding internal alkynes in good
to excellent yields, when electron-withdrawing (such as
4-nitro, 4-acetyl or 4-formyl), electron neutral and elec-
tron-donating (such as 4-methyl or 4-methoxy) substitu-
ents were present on the arylboronic acids. Fabulously,
aryl boronic acids bearing electron-withdrawing groups
aforded superior isolated yield of the desired product (up
to 96%) when compared with those having electron donat-
ing groups. Utilization of 3-formylphenylboronic acid and
3-methoxyphenylboronic acid as coupling partners (entries
7,8) in this reaction resulted in the formation of the cor-
responding desired products in good yields. However,
employment of 2-formylphenylboronic acid and 2-meth-
oxyphenylboronic acid (entries 9,10) resulted in slightly
reduced yields than for the corresponding para derivatives
(entries 1,5) which may be due to steric efects.
arylboronic acids with substituted phenylacetylenes under
aerobic conditions. The substrate scope could be extended
to electron-neutral, electron-rich as well as electron-poor
arylboronic acids and substituted phenylacetylenes to yield
the desired products in satisfactory to excellent isolated
yields. The substrate scope can include electron-defcient
alkynes for which the traditional Sonogashira reaction does
not proceed. This protocol provides the frst examples of (E)-
N-(pyren-1-ylmethylene)benzenamine as efective ligand for
this palladium-catalyzed cross-coupling reaction. Further,
such a strategy minimizes preparation and characterization
of a metal complex which generally require specifc condi-
tions, laborious and time-consuming methods of synthesis.
The scope, mechanism and synthetic applications of this
catalytic reaction are under investigation in our laboratory.
Acknowledgements Dr. J. Lakshmipraba gratefully acknowledges the
fnancial support from Department of Science & Technology (DST),
New Delhi, India, for the Women Scientists Scheme-A (WOS-A) (Ref
No. SR/WOS-A/CS-59/2017). The use of the NMR facility at the
School of Chemistry, Bharathidasan University, Tiruchirappalli, Tamil
Nadu, India, is also thankfully acknowledged. We also acknowledge
the Management of Bishop Heber College for the facilities provided
through DST-FIST, DBT-STAR Scheme, UGC-CE and Heber Analyti-
cal Instrumentation Facility (HAIF), Bishop Heber College.
The salient features of this protocol include simple and
convenient reaction procedure, insensitivity towards air and
moisture, non-necessity of any inert atmosphere, absence of
silver additive, ease of handling of the reagents, lower reac-
tion time, broad substrate scope and simple workup proce-
dure. Though we have not carried out any mechanistic inves-
tigation, it is likely that L binds to the Pd-centre resulting in
a cyclometallated complex which acts as the actual catalyst
in this cross-coupling reaction (Han et al. 2011; Rao and Pal
2014). Further, though there are a few reports on the Pd-cat-
alyzed oxidative Sonogashira reactions, a direct comparison
of the present catalytic system with those reported earlier
is difcult due to the diferences in the reaction conditions
such as solvent, base, temperature, reaction time and catalyst
loading. However, in terms of isolated yields, the catalytic
efciency of the present protocol is found to be comparable
or even slightly superior to some of the previously reports
on oxidative Sonogashira cross-coupling reaction (Zou et al.,
2003; Yang and Wu 2007; Lu et al. 2014).
References
Abu-Dief AM, Mohamed IMA (2015) A review on versatile appli-
cations of transition metal complexes incorporating Schiff
bases. Beni-Suef Univ J Basic Appl Sci 4:119–133. https://doi.
org/10.1016/j.bjbas.2015.05.004
Agou T, Kojima T, Kobayashi J, Kawashima T (2009) Synthesis of
π-conjugated dendrimers based on azaborines. Org Lett 11:3534–
3537. https://doi.org/10.1021/ol901035d
Balsukuri N, Das S, Gupta I (2015) Carbazole–corrole and carbazole–
prophyrin dyads: synthesis, fuorescence and electrochemical
studies. New J Chem 39:482–491. https://doi.org/10.1039/C4NJ0
1086H
Chinchilla R, Nájera C (2007) The sonogashira reaction: a booming
methodology in synthetic organic chemistry. Chem Rev 107:874–
922. https://doi.org/10.1021/cr050992x
Chinchilla R, Nájera C (2011) Recent advances in Sonogashira reac-
tions. Chem Soc Rev 40:5084–5121. https://doi.org/10.1039/
C1CS15071E
Das P, Linert W (2016) Schif base-derived homogeneous and het-
erogeneous palladium catalysts for the Suzuki-Miyaura reac-
tion. Coord Chem Rev 311:1–23. https://doi.org/10.1016/j.
ccr.2015.11.010
Dasaradhan C, Kumar YS, Prabakaran K, Khan F-RN, Jeong ED,
Chung EH (2015) Efcient and convenient copper-free Pd(OAc)2/
Ruphos-catalyzed Sonogashira coupling in the preparation of
corfin analogues. Tetrahedron Lett 56:784–788. https://doi.
org/10.1016/j.tetlet.2014.12.059
Conclusions
In conclusion, a new facile protocol was developed using
(E)-N-(pyren-1-ylmethylene)benzenamine as promoter for
the silver-free palladium-catalyzed synthesis of internal
alkynes by the C(sp2)–C(sp) coupling reactions between
Fortman GC, Nolan SP (2011) N-Heterocyclic carbene (NHC) ligands
and palladium in homogeneous cross-coupling catalysis: a perfect
1 3

Chemical Papers
regioselective ruthenation of the 1-pyrenyl group. J Chem Sci
127:589–596. https://doi.org/10.1007/s12039-015-0812-3
Prabhu RN, Ramesh R (2016) Square-planar Ni(II) thiosemicarba-
zonato complex as an easily accessible and convenient cata-
lyst for Sonogashira cross-coupling reaction. Tetrahedron Lett
57:4893–4897. https://doi.org/10.1016/j.tetlet.2016.09.049
Qian D, Zhang J (2011) Au(I)/Au(III)-catalyzed Sonogashira-type
reactions of functionalized terminal alkynes with arylboronic
acids under mild conditions. Beilstein J Org Chem 7:808–812.
https://doi.org/10.3762/bjoc.7.92
union. Chem Soc Rev 40:5151–5169. https://doi.org/10.1039/
C1CS15088J
Han Y-F, Li H, Hu P, Jin G-X (2011) Alkyne Insertion Induced Regio-
specifc C–H Activation with [Cp*MCl2]2 (M=Ir, Rh). Organo-
metallics 30:905–911. https://doi.org/10.1021/om101064v
Karak M, Barbosa LCA, Hargaden GC (2014) Recent mechanistic
developments and next generation catalysts for the Sonoga-
shira coupling reaction. RSC Adv 4:53442–53466. https://doi.
org/10.1039/C4RA09105A
Kathiravan A, Sundaravel K, Jaccob M, Dhinagaran G, Rameshku-
mar A, Ananth DA, Sivasudha T (2014) Pyrene Schif base:
photophysics, aggregation induced emission, and antimicro-
bial properties. J Phys Chem B 118:13573–13581. https://doi.
org/10.1021/jp509697n
Rao ARB, Pal S (2014) Regioselective cyclometallation with some
platinum group metal ions. J Organomet Chem 762:58–66. https
://doi.org/10.1016/j.jorganchem.2014.04.009
Rao H, Fu H, Jiang Y, Zhao Y (2010) Highly efcient copper-cata-
lyzed synthesis of internal alkynes via aerobic oxidative aryla-
tion of terminal alkynes. Adv Synth Catal 352:458–462. https
://doi.org/10.1002/adsc.200900723
Li L, Nan C, Peng Q, Li Y (2012) Selective synthesis of Cu2O
nanocrystals as shape-dependent catalysts for oxidative aryla-
tion of phenylacetylene. Chem Eur J 18:10491–10496. https://
doi.org/10.1002/chem.201200567
Sabounchei SJ, Ahmadi M, Nasri Z, Shams E, Panahimehr M (2013)
Palladium(II) phosphine-ylide complexes as highly efcient pre-
catalysts in additive- and amine-free Sonogashira coupling reac-
tions performed under aerobic and low Pd loading conditions.
Tetrahedron Lett 54:4656–4660. https://doi.org/10.1016/j.tetle
t.2013.06.064
Li H-M, Xu C, Duan L-M, Lou X-H, Wang Z-Q, Li Z, Fan Y-T
(2013) N-heterocyclic carbene adducts of cyclopalladated fer-
rocenylpyridine containing chloride or iodide anions: synthesis,
crystal structures and application in the coupling of terminal
alkynes with arylboronic acids. Transit Met Chem 38:313–318.
https://doi.org/10.1007/s11243-013-9695-7
Shellaiah M, Wu Y-H, Singh A, Raju MVR, Lin H-C (2013) Novel
pyrene- and anthracene-based Schif base derivatives as Cu2+
and Fe3+ fluorescence turn-on sensors and for aggregation
induced emissions. J Mater Chem A 1:1310–1318. https://doi.
org/10.1039/C2TA00574C
Liu J, Lam JWY, Tang BZ (2009) Acetylenic polymers: syntheses,
structures, and functions. Chem Rev 109:5799–5867. https://
doi.org/10.1021/cr900149d
Lu L, Chellan P, Smith GS, Zhang X, Yan H, Mao J (2014) Thio-
semicarbazone salicylaldiminato palladium(II)-catalyzed alky-
nylation couplings between arylboronic acids and alkynes or
alkynyl carboxylic acids. Tetrahedron 70:5980–5985. https://
doi.org/10.1016/j.tet.2014.05.087
Shree GJ, Sivaraman G, Siva A, Chellappa D (2019) Anthracene- and
pyrene-bearing imidazoles as turn-on fuorescent chemosensor
for aluminum ion in living cell. Dyes Pigm 163:204–212. https
://doi.org/10.1016/j.dyepig.2018.11.061
Mao J, Guo J, Ji S-J (2008) CuBr/rac-BINOL-catalyzed Sonogashira
reaction of terminal alkynes with aryl halides or arylboronic
acids. J Mol Catal A Chem 284:85–88. https://doi.org/10.1016/j.
molcata.2008.01.006
Singh J, Verma AK (2011) Di(1H-benzo[d][1,2,3]triazol-1-yl)meth-
ane: an efcient ligand for copper and amine-free palladium-cat-
alysed Sonogashira coupling reaction. J Chem Sci 6:937–942.
https://doi.org/10.1007/s12039-011-0174-4
Mitsudo K, Shiraga K, Mizukawa J-i, Suga S, Tanaka H (2010)
Electrochemical generation of silver acetylides from terminal
alkynes with a Ag anode and integration into sequential Pd-
catalysed coupling with arylboronic acids. Chem Commun
46:9256–9258. https://doi.org/10.1039/C0CC02633F
Nie X, Liu S, Zong Y, Sun P, Bao J (2011) Facile synthesis of sub-
stituted alkynes by nano-palladium catalyzed oxidative cross-
coupling reaction of arylboronic acids with terminal alkynes.
J Organomet Chem 696:1570–1573. https://doi.org/10.1016/j.
jorganchem.2010.12.038
Troung T, Nguyen CK, Tran TV, Nguyen TT, Phan NTS (2014)
Nickel-catalyzed oxidative coupling of alkynes and arylboronic
acids using the metal–organic framework Ni2(BDC)2(DABCO)
as an efficient heterogeneous catalyst. Catal Sci Technol
4:1276–1285. https://doi.org/10.1039/C3CY01053H
Xu C, Li H-M, Wang Z-Q, Fu W-J (2016) Synthesis, crystal struc-
tures, and catalytic application of two triphenylphosphine-
cyclopalladated ferrocenylpyrazine complexes containing chlo-
rine/iodine anion. Synth React Inorg M 46:872–876. https://doi.
org/10.1080/15533174.2014.989614
Pan C, Luo F, Wang W, Ye Z, Cheng J (2009) Ligand-free copper(I)-
catalyzed Sonogashira-type coupling of arylboronic acids with
terminal alkynes. Tetrahedron Lett 50:5044–5046. https://doi.
org/10.1016/j.tetlet.2009.06.093
Yang F, Wu Y (2007) Facile synthesis of substituted alkynes by
cyclopalladated ferrocenylimine catalyzed cross-coupling of
arylboronic acids/esters with terminal alkynes. Eur J Org Chem
2007:3476–3479. https://doi.org/10.1002/ejoc.200700065
Yang Y, Chew X, Johannes CW, Robins EG, Jong H, Lim YH (2014)
A versatile and efcient palladium–meta-terarylphosphine cata-
lyst for the copper-free Sonogashira coupling of (hetero-)aryl
chlorides and alkynes. Eur J Org Chem 2014:7184–7192. https
://doi.org/10.1002/ejoc.201402699
Prabhu RN, Lakshmipraba J (2017) A nickel(II) thiosemicarbazonato
complex: synthesis, structure, electrochemistry, and application
in catalytic coupling of terminal alkynes with arylboronic acids.
Transit Met Chem 42:579–585. https://doi.org/10.1007/s1124
3-017-0162-8
Prabhu RN, Pal S (2015a) Copper-free Sonogashira reactions cata-
lyzed by a palladium(II) complex bearing pyrenealdehyde thio-
semicarbazonate under ambient conditions. Tetrahedron Lett
56:5252–5256. https://doi.org/10.1016/j.tetlet.2015.07.076
Prabhu RN, Pal S (2015b) Cyclometallated ruthenium(II) carbonyl
complexes with 1-pyrenaldehyde 4-R-3-thiosemicarbazones:
Yasukawa T, Miyamura H, Kobayashi S (2011) Copper-catalyzed,
aerobic oxidative cross-coupling of alkynes with arylboronic
acids: remarkable selectivity in 2,6-lutidine media. Org Biomol
Chem 9:6208–6210. https://doi.org/10.1039/C1OB05915G
1 3

Chemical Papers
You XL, Xu L, Hu T (2012) Iron-catalyzed oxidative coupling of
terminal alkynes with arylboronic acids. Lett Org Chem 9:300–
304. https://doi.org/10.2174/157017812800233688
Zou G, Zhu J, Tang J (2003) Cross-coupling of arylboronic acids with
terminal alkynes in air. Tetrahedron Lett 44:8709–8871. https://
doi.org/10.1016/j.tetlet.2003.09.173
Zhou M-B, Wei W-T, Xie Y-X, Lei Y, Li J-H (2010) Palladium-
catalyzed cross-coupling of electron-poor terminal alkynes with
arylboronic acids under ligand-free and aerobic conditions. J
Org Chem 75:5635–5642. https://doi.org/10.1021/jo101063p
Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional afliations.
1 3