Cobalt(III)-Catalyzed Direct ortho-Alkenylation of Arylpyrazoles: A Comparative Study on Decarboxylation and Desilylation

Article abstract of DOI:10.1002/ejoc.201900270

A comparative study on Co^III-catalyzed direct C–H bond alkenylation of 1-phenylpyrazole derivatives with alkynyl carboxylic acids and arylalkynylsilanes under redox-neutral conditions has been disclosed. These methods show excellent selectivity with good to excellent yields. Trimethylsilylacetylene has been utilized as a vinyl source to obtain the corresponding styrene derivatives. The major differences between these two reactions are the decarboxylation proceeds in the presence of a base additive whereas the desilylation takes place in the presence of an acid additive. The developed methodologies are compatible with a variety of functional groups.

Full text of DOI:10.1002/ejoc.201900270

A Journal of
Accepted Article
Title: Cobalt(III)-Catalyzed Direct ortho-Alkenylation of Arylpyrazoles: A
Comparative Study on Decarboxylation and Desilylation
Authors: Anil Kumar, Nachimuthu Muniraj, and Kandikere Ramaiah
Prabhu
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201900270
Link to VoR: http://dx.doi.org/10.1002/ejoc.201900270
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10.1002/ejoc.201900270
European Journal of Organic Chemistry
COMMUNICATION
Cobalt(III)-Catalyzed Direct ortho-Alkenylation of Arylpyrazoles: A
Comparative Study on Decarboxylation and Desilylation
Anil Kumar,[a] Nachimuthu Muniraj,[a] and Kandikere Ramaiah Prabhu*[a]
Dedication ((optional))
Abstract: A comparative study on Co(III)-catalyzed direct C-H bond
alkenylation of 1-phenylpyrazole derivatives with alkynyl carboxylic
acids and arylalkynyl silanes under redox-neutral conditions has
been disclosed. These methods show excellent selectivity with good
to excellent yields. Trimethylsilylacetylene has been utilized as a
vinyl source to obtain the corresponding styrene derivatives. The
major differences between these two reactions are the
decarboxylation proceeds in the presence of a base additive
whereas the desilylation takes place in the presence of an acid
additive. The developed methodologies are compatible with a variety
of functional groups.
reactivity.[10] Surprisingly, arylalkynyl silanes were rarely studied
as a coupling partner in the transition-metal catalyzed C-H
activation reactions.[11] Moreover, one of the easiest ways of
obtaining aryl acetylene derivatives (terminal alkynes) are by
either
decarboxylation
of
the
corresponding
aryl
alkynylcarboxylic acids or deprotection(desilylation) of aryl
alkynyl silanes.[9c] Therefore, developing alkenylation reactions
using alkynyl carboxylic acids or alkynyl silanes instead of
terminal alkynes could be a step economical process. Inspired
by our previous results on alkenylation reactions[10b,11c] and
continued interest on Co(III)-catalyzed directed reactions,[12]
herein, we report a comparative study on the decarboxylative
and the desilylative ortho-alkenylation of 1-phenylpyrazole
derivatives using Co(III)-catalyst (Scheme 1b).
Introduction
Transition metal-catalyzed C-H activation leading to the
functionalization of organic molecules has emerged as a
powerful synthetic tool for installing desired functional groups of
interest.[1] There is significant progress employing a directing
group assisted C-H activation using second- and third-row
transition metal-catalysts.[2] However, the first-row transition
metal-catalysts, such as cobalt(III) has received great attention
in recent years.[3] C-H bond activation strategy is an efficient
method for incorporating the olefins into the substituted
aromatics. Alkynes are the preferred precursors for the
alkenylation reaction as they offer external oxidant-free
conditions. In most of the studies, internal alkynes
(diphenylacetylene derivatives) are widely used as coupling
partners to obtain the trisubstituted olefin derivatives (Scheme
1a).[4-7] As compared to internal alkynes, the utility of terminal
Scheme 1.Comparision of previous works with this work.
alkynes
(phenylacetylene
derivatives)
to
obtain
the
Results and Discussion
corresponding disubstituted olefin derivatives are limited.[8]
However, recently Chen and Yu have reported Co(III)-catalyzed
ortho-alkenylation of arenes and 6-arylpurines with terminal
alkynes.[8a]
The optimization studies were started by treating 1-
phenylpyrazole 1a with phenylpropiolic acid 2a in the presence
of MnBr(CO)5 as a catalyst, using various additives, and
solvents (see the Supporting Information, Table-S-1). After
several trials, we found that the corresponding ortho-alkenylated
product 3aa could be obtained in 34% yield. Since MnBr(CO)5
catalyst is not effective for this transformation, we turned our
attention to cobalt(III)-catalyst for the same transformation. The
reaction of 1a with 2a in the presence of Cp*Co(CO)I2 (5 mol%)
as a catalyst, AgSbF6 (20 mol%) as an activator and NaOAc (20
Transition metal catalyzed traditional decarboxylative cross
coupling reactions of alkynylcarboxylic acids are well explored
area in organic synthesis.[9] Recently, alkynyl carboxylic acids
are getting considerable attention in C-H activation reactions as
they are bench stable, readily synthesized, and have unique
o
mol%) as an additive in DCE solvent (2 mL) at 100 C for 3 h
furnished the corresponding alkenylated product 3aa in 78%
yield (entry 1, Table 1). The solvent screening studies revealed
that TFE is the bestsuited solvent as it afforded the product 3aa
in 88% yield (entries 2-5). Changing the activators to AgBF4 and
AgNTf2 rendered the product 3aa in 80 and 87% yields,
respectively (entries 6 and 7), whereas AgOAc provided the
product 3aa in low yield (45%, entry 8). Among the additives,
NaOAc was found to be an effective additive (entries 9-11).
Lowering the catalyst loading, increasing or decreasing the
[a]
Mr. Anil kumar, Mr. Nachimuthu Muniraj and
Prof. Dr. Kandikere Ramaiah Prabhu
Department of Organic Chemistry, Indian Institute of Science,
Bangalore 560 012, Karnataka, India.
Telephone: +91-80-22932887; Fax: +91-80-23600529;
E-mail: prabhu@iisc.ac.in
http://www.orgchem.iisc.ac.in/kr-prabhu/
Supporting information for this article is given via a link at the end
of the document.
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10.1002/ejoc.201900270
European Journal of Organic Chemistry
COMMUNICATION
reaction temperature did not enhance the yield of 3aa (entries
12-14). Reactions in the absence of Cp*Co(CO)I2 catalyst or
AgSbF6 did not furnish the expected product 3aa (entry 15 and
16), while the reaction in the absence of additive decreased the
yield of 3aa to 50% (entry 17). Reaction in the presence of Ru(II)
was not useful, whereas reaction using Rh(III)-catalyst furnished
the product 3aa in 51% yield (entries 18 and 19).Next, we
yield. Electron withdrawing groups such as acetyl and nitro
groups on 1-phenylpyrazole were compatible under both the
reaction conditions furnishing the products 3ja and 3ka in
moderate to good yields. The reaction of 2-phenylpyridine with
the phenylpropiolic acid and 1-phenyl-2-trimethylsilylacetylene
furnished the product 3la in 37 and 15% yields, respectively.
Table 2.Scope for 1-phenylpyrazole derivatives.
examined
the
reaction
of
1a
with
1-phenyl-2-
trimethylsilylacetylene 2a' for the alkenylation reaction as 2a'
can be used as alternate for terminal alkynes. To our delight, the
reaction of 1a (0.2 mmol) with 1-phenyl-2-trimethylsilylacetylene
2a' (0.24 mmol), Cp*Co(CO)I2 (5 mol%) as a catalyst, AgSbF6
(20 mol%) as an activator and Cl3CCOOH (1.0 equiv) as an
o
additive in TFE solvent (2 mL) at 100 C for 3 h furnished the
corresponding alkenylated product 3aa in 83% isolated yield
(entry 20, Table 1 and for detail optimization studies see the
Supporting Information, Table-S-2).
Table 1. Optimization studies.[a]
entry
activator
additive
solvent
time (h)
NMR yield
6aa (%)b
78
1
2
3
4
5
6
7
8
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgBF4
AgNTf2
AgOAc
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
none
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
KOAc
DCE
THF
TFE
toluene
dioxane
TFE
TFE
TFE
TFE
TFE
TFE
TFE
TFE
TFE
TFE
TFE
TFE
TFE
TFE
TFE
3
3
3
3
3
3
3
3
3
3
3
3
12
12
3
3
3
3
3
3
53
88 (85)c
78
67
80
87
45
86
85
80
69
73
88
nd
nd
50
nd
9
Condition A: 1a (0.2 mmol), 2a (0.24 mmol), [Cp*Co(CO)I2] (5 mol%), AgSbF6
(20 mol%), NaOAc (20 mol %), TFE (2 mL), at 100 oC for 3 h. Condition B: 1a
(0.2 mmol), 2a' (0.24 mmol), [Cp*Co(CO)I2] (5 mol%), AgSbF6 (20 mol%),
Cl3CCO2H (1.0 equiv), TFE (2 mL), at 100 oC for 3 h. [a] Isolated yield. [b]1H
NMR yield using terephthaldehyde as an internal standard.
10
11
12d
13e
14f
15g
16
17
18h
19i
20j
CH3CO2H
PivOH
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
none
NaOAc
NaOAc
Cl3CCOOH
The scope of the reaction has been extended by reacting
1a with various arylalkynyl carboxylic acid derivatives2 (Table 3).
Thus, alkyl, methoxy and halo-substituted arylalkynyl carboxylic
acids reacted smoothly with 1a furnishing the corresponding
ortho-alkenylated products 4aa-4agin good yields. Synthetically
useful functional groups such as cyano, nitro, acetyl and ester
groups at the para-position of arylalkynyl carboxylic acid are
well-tolerated affording the products 4ah-4ak in good to
excellent yields. Thiophene derived alkynyl carboxylic acid
underwent a smooth reaction with 1a yielding the product 4al in
62% yield. Alkylalkynyl carboxylic acids such as 2-butynoic acid
reacted with 1a furnishing the mono-alkenylated product 4am in
65% yield. The reaction of 1a with 2-hexynoic acid furnished a
mixture of mono- and di-alkenylated products 4an and 4an' in 29
and 14% yields, respectively.
The scope of the reaction was further explored by the
reaction of 1a with a few arylalkynyl silane derivatives2' (Table
4). The reaction of 1a with arylalkynyl silane derivatives having
alkyl, methoxy, and halo substitution at the para-position
furnished the corresponding ortho-alkenylatedproducts 4aa-4ac
in good to excellent yields. A methyl substituent at the ortho-
position or a bulky group tert-butyl group at the para-position
afforded the corresponding alkenylated products 4af and 4ag in
80 and 73% yields, respectively. Different functional groups like
AgSbF6
AgSbF6
AgSbF6
AgSbF6
51
86 (83)c
[a] Reaction conditions: 1a (0.2 mmol), 2a (0.24 mmol), [Cp*Co(CO)I2] (5
mol%), activator (20 mol%), additive (20 mol%), solvent (2 mL), at 100
oC for 3 h. [b]1H NMR yield using terephthaldehyde as an internal
standard. [c] Isolated yield. [d] 2.5 mol% [Co(III)] catalyst was used. [e]
Reaction at 80 oC. [f] Reaction at 120 oC. [g] in absence of Co(III)
catalyst. [h] [Ru(p-cymene)Cl2]2 was used. [i] [RhCp*Cl2]2 was used. [j]
reaction with 2a'. nd = not detected. PivOH = pivalic acid.
Having two different methods in hand (entries 3 and 20,
Table 1) for ortho-alkenylation of 1-phenylpyrazole 1a, we
started a comparative study on decarboxylative and desilylative
alkenylation of 1-phenylpyrazolederivatives 1 (Table 2). Thus,
precursors having alkyl, halogen, and methoxy substitution on
the various positions of the phenyl ring of 1, reacted smoothly
with
phenylpropiolic
acid
2a
as
well
1-phenyl-2-
trimethylsilylacetylene 2a' furnishing the corresponding
alkenylated products 3aa-3ha in good to excellent yields. The
reaction of 4-(1H-tyrazol-1-yl)benzonitrile1i with phenylpropiolic
acid was not successful while the same reaction of 1i with 1-
phenyl-2-trimethylsilylacetylene furnished the product 3ia in 83%
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10.1002/ejoc.201900270
European Journal of Organic Chemistry
COMMUNICATION
cyano, nitro, and ester groups at para-position on the phenyl ring
are also well tolerated forming the products 4ah, 4ai, and 4ak in
89, 81, and 85% yields, respectively. The thiophene derived
alkynyl silane furnished the corresponding alkenylated product
4al in moderate yield of 53%.
[a]Reaction conditions: 1a (0.2 mmol), 2' (0.24 mmol), [Cp*Co(CO)I2] (5
mol%), [AgSbF6] (20 mol%), Cl3CCO2H (1.0 equiv), TFE (2 mL), at 100
oC for 3 h. [b] Isolated yields.
acid 5a and trimethylsilyl acetylene 5a'to obtain the
corresponding styrene derivatives. The reaction of propiolic acid
5a with 1a under the optimal reaction conditions furnished the
product 6aa in low yield of 25% (see Supporting Information,
Table-S-3), whereas the reaction of trimethylsilylacetylene
5a'with 1a under the optimal conditions furnished the product
6aa in moderate yield of 58%(see Supporting Information,
Table-S-4).
Table 3. Scope for alkynyl carboxylic acid derivatives.[a,b]
Table 5. Substrate scope for 1-phenylpyrazole derivatives.[a]
[a]Reaction conditions: 1a (0.3 mmol), 5a' (0.36 mmol), [Cp*Co(CO)I2] (5
mol%), [AgSbF6] (20 mol%), Cl3CCO2H (1.0 equiv), TFE (3 mL), at 100
oC for 3 h. [b] Isolated yield. [c] NMR yield using terephthaldehyde as an
internal standard.
Further optimization of reaction conditions was not helpful in
improving the yield of 6aa (see Supporting Information, Table-S-
4). This protocol was useful for halogen substituted 1-
phenylpyrazole derivatives, which gave moderate to good yields
6aa-6fa (Table 5).However, 1-phenylpyrazoles having
substituents such as methoxy, nitro, cyano, and keto groups on
phenyl ring also furnished a good yield of the ortho-alkenylated
products 6ga-6ka as inseparable mixture with their
corresponding 1-phenylpyrazole derivatives (See Supporting
Information, Scheme-S-1). A few unsuccessful substrates for the
ortho-alkenylation reactions are also listed in the supporting
information (see SI, Scheme-S-2).
[a]Reaction conditions: 1a (0.2 mmol), 2 (0.24 mmol), [Cp*Co(CO)I2] (5 mol%),
[AgSbF6] (20 mol%), NaOAc (20 mol%), TFE (2 mL), at 100 oC for 3 h. [b]
Isolated yields.
From this experimental study, we found that the reactivity of both
arylalkynyl carboxylic acid derivatives and arylalkynyl silane
derivatives are similar and complimentary to each other. Next,
we attempted to extend the scope of the reaction using propiolic
Table 4. Scope for alkynyl silane derivatives.[a,b]
Scheme 2. Synthetic utility and scaling-up reaction.
Further, to demonstrate the usefulness of the alkenylated
products, ortho-alkenylated product 3aa was subjected to
ozonolysis to obtain the corresponding aldehyde 7 in 74% yield
(Scheme 2). A scaling-up experiment of 1a (3 mmol, 432 mg)
with phenylpropiolic acid 2a under the optimum reaction
conditions afforded the corresponding product 3aa in 82%
isolated yield (Scheme 2).
To probe the reaction mechanism,
a few control
experiments were performed (Scheme 3). 1-(p-Tolyl)-1H-
pyrazole 1c on treatment with D2O under optimal reaction
conditions did not lead to the deuteration of ortho-hydrogens of
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10.1002/ejoc.201900270
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COMMUNICATION
1c, whereas the same deuteration experiment, using DCE as a
solvent, showed 81% deuteration at the ortho-positions of 1c
(see SI and Scheme 3a). Since, DCE was also found to be an
effective solvent for this transformation, further control
experiments were carried out in DCE solvent. The reaction of 1c
with 1-phenyl-2-trimethylsilylacetylene 2a' using CD3CO2D as an
acid additive led to the deuteriumin corporation on the olefinic
carbon of the product 3ca (10% D, Scheme 3b) indicating the
involvement of the acid additive in the protodemetallation step.
To find out whether silver phenylacetylide 8 is an intermediate,
we performed a reaction of 1c with silver phenylacetylide 8,
which failed to give the product 3ca (Scheme 3c). This
experiment rules out the intermediacy of silver phenylacetylide.
The Kinetic Isotopic Effect (KIE) value of 2.45 observed in the
reaction of 1c and 1c-d2 with 2a suggested that the C-H
activation step could be a rate-determining step (Scheme 3d). A
generated catalytically active species A reacts with 1a leading to
the cobaltacycle B. Insertion of alkyne 2a or 2a' to the B forms
the 7-membered intermediate C. From intermediate C the
decarboxylation[10b] or desilylation[11c] takes place in the presence
of AgSbF6/additive followed by subsequent protodemetallation
with the help of acid allows the desired product 3aa along with
the active catalyst A.
Scheme 4. Plausible Mechanism
Scheme 3. Control experiments for mechanistic studies.
H/D Exchange
D
(59% D)
D
Cp*CoCOI2 (5 mol%)
AgSbF6 (20 mol%)
NaOAc (20 mol%)
DCE, 100 oC, 24 h
N
N
(a)
(b)
N
D
N
+
D2O
1c
(81% D)
(10 equiv)
(10 mmol)
deuterio-1c
SiMe3
Cp*CoCOI2 (5 mol%)
AgSbF6 (20 mol%)
CD3CO2D (1.0 equiv)
DCE, 100 oC, 3 h
N
N
H
N
N
+
Ph
1c
2a'
10% D
H
(0.2 mmol)
Ph
Conclusions
deuterio-3ca, 68%
Finding intermediate
Ag
Cp*CoCOI2 (5 mol%)
AgSbF6 (20 mol%)
NaOAc (20 mol%)
DCE, 100 oC, 3 h
In conclusion,
a Co(III)-catalyzed ortho-alkenylation of 1-
N
N
+
(c)
phenylpyrazole derivatives using arylalkynyl carboxylic acid
derivatives and arylalkynyl silane derivatives as a coupling
partner through decarboxylation and desilylation routes have
been studied. In this study, we found that the alkynylcarboxylic
acids and arylalkynylsilanes, which have electronically different
environment, furnished the same products in excellent selectivity
with high yields. Both the coupling partners can serve as
alternate to terminal alkynes in C-H activation reactions, which
are complementary to each other. Additionally, trimethylsilyl
acetylenes have also been utilized as a vinyl source to obtain
the corresponding styrene derivatives.
no reaction
Ph
1c
8
(0.2 mmol)
KIE Experiment
D
D
Cp*CoCOI2 (5 mol%)
AgSbF6 (20 mol%)
NaOAc (20 mol%)
DCE, 100 oC, 3 h
N
N
D
N
N
H
N
N
H
1c
+
+
2a
+
(d)
(1.2 equiv)
1c-d2
H
Ph
H
Ph
(0.2 mmol)
3ca
combined yield = 63%
3ca deuterio-3ca
) - 2.45
deuterio-3ca
KIE (
/
Competitive Experiment
Cp*CoCOI2 (5 mol%)
AgSbF6 (20 mol%)
Cl3CCO2H (1.0 equiv)
TFE, 100 oC, 3 h
N
N
N
N
Experimental Section
N
N
3ha
, 48% + 3ja, 46%
(e)
+
+ 2a'
O
O
(a) Procedure for ortho-alkenylation of arylpyrazole derivatives with
arylalkynyl carboxylic acids derivatives
3j
3h
Cp*CoCOI2 (5 mol%)
AgSbF6 (20 mol%)
NaOAc (20 mol%)
TFE, 100 oC, 3 h
N
In a 8-mL screw-cap reaction vial, arylpyrazole derivative (0.2 mmol),
arylalkynyl carboxylic acid (0.24 mmol), cobalt catalyst [Cp*CoCOI2], (4.8
mg, 5 mol%), NaOAc (3.3 mg, 20 mol%), AgSbF6 (13.4 mg, 20 mol%) in
TFE solvent (2 mL) were taken. The vial was sealed with a screw cap
and placed on a pre-heated metal block at 100 °C and the reaction
mixture was stirred at the same temperature for 3 h. After completion of
the reaction (monitored by TLC), the reaction mixture was cooled to room
temperature, filtered through a silica pad using a mixture of EtOAc and
petroleum ether (1:1, 100 mL), and concentrated under vacuum. The
crude products were submitted directly for 1H NMR analysis for
calculating the 1H NMR yields, terephthalaldehyde (0.1 mmol, 13.4 mg)
has been used as an internal standard. The crude products were purified
on a silica gel column using EtOAc/petroleum ether mixture.
N
O
(f)
+ 3ja, 53%
3ha
, 29%
+
+
2a
O
3h
3j
competitive reaction of electronically different pyrazole
derivatives 3h and 3j with alkynyl silane 2a' exhibited an almost
equal reactivity (Scheme 3e). However, the similar reaction of
pyrazole derivatives 3h and 3j with alkynylcarboxylic acid 2a
favors the electron poor 3j (Scheme 3f).
Based on the control experiments, our previous
studies,[10b,11c] and the literature precedence,[5-8] a plausible
mechanism has been proposed (Scheme 4). An in situ
(b) Procedure for ortho-alkenylation of arylpyrazole derivatives with
1-phenyl-2-trimethylsilylacetylene derivatives
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10.1002/ejoc.201900270
European Journal of Organic Chemistry
COMMUNICATION
In a 8-mL screw cap reaction vial, arylpyrazole derivative (0.2 mmol), 1-
Phenyl-2-trimethylsilylacetylene derivative (0.24 mmol), cobalt catalyst
[Cp*CoCOI2],(4.8 mg, 5 mol%), Cl3CCO2H (33.0 mg, 100 mol%), AgSbF6
(13.4 mg, 20 mol%) in TFE solvent (2 mL) were taken. The vial was
sealed with a screw cap and placed on a pre-heated metal block at
100 °C and the reaction mixture was stirred at the same temperature for
3 h. After completion of the reaction (monitored by TLC), the reaction
mixture was cooled to room temperature, filtered through a silica pad
using a mixture of EtOAc and petroleum ether (1:1, 100 mL), and
concentrated under vacuum. The crude products were submitted directly
for 1H NMR analysis for calculating the NMR yields, terephthalaldehyde
(0.1 mmol, 13.4 mg) has been used as an internal standard. The crude
products were purified on a silica gel column using EtOAc/petroleum
ether mixture.
[2]
(a) M. Moselage, L. Ackermann, ACS Catal. 2016, 6, 498; (b) J. Li, K.
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(c) Procedure for ortho-alkenylation of arylpyrazole derivatives with
trimethylsilylacetylene
In a 8-mL screw cap reaction vial, aryl pyrazole derivative (0.3 mmol),
trimethylsilylacetylene (0.36 mmol), cobalt catalyst [Cp*CoCOI2],(7.2 mg,
5 mol%), Cl3CCO2H (49.5 mg, 100 mol%), AgSbF6 (20.1 mg, 20 mol%) in
TFE solvent (3 mL) were taken. The vial was sealed with a screw cap
and placed on a pre-heated metal block at 100 °C and the reaction
mixture was stirred at the same temperature for 3 h. After completion of
the reaction (monitored by TLC), the reaction mixture was cooled to room
temperature, filtered through a silica pad using a mixture of EtOAc and
petroleum ether (1:1, 100 mL), and concentrated under vacuum. The
crude products were submitted directly for 1H NMR analysis for
calculating the NMR yields, terephthalaldehyde (0.15 mmol, 13.4 mg)
has been used as an internal standard. The crude products were purified
on a silica gel column using DCM/petroleum ether mixture.
[7]
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mL). The reaction mixture was warmed to 0 °C and stirred at the same
temperature for 2 h. The reaction mixture was concentrated under
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column using EtOAc/petroleum ether mixture to afforded the product 7 in
74% yield.
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Acknowledgements
This work was supported by SERB (EMR/2016/006358),
New-Delhi, CSIR (No. 02(0226)15/EMR-II), New-Delhi, Indian
Institute of Science and R. L. Fine Chem. We thank Dr. A. R.
Ramesha (R. L. Fine Chem) for useful discussion. A. K. and N.
M. thank UGC, New Delhi for fellowships.
Keywords: arylpyrazole; arylalkynyl carboxylic acids; 1-phenyl-
2-trimethylsilylacetylene; C-H Activation.
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This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900270
European Journal of Organic Chemistry
COMMUNICATION
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COMMUNICATION
Decarboxylation and Desilylation*
Anil Kumar, Nachimuthu Muniraj,
and Kandikere Ramaiah Prabhu*
Page No. – Page No.
Cobalt(III)-Catalyzed Direct ortho-
Alkenylation of Arylpyrazoles: A
Comparative Study on
Decarboxylation and Desilylation
A comparative study on Co(III)-catalyzed direct C-H bond alkenylation of 1-phenylpyrazole derivatives with alkynyl carboxylic acids
and arylalkynyl silanes under redox-neutral conditions has been studied. Trimethylsilylacetylene has been utilized as a vinyl source to
obtain the corresponding styrene derivatives. The developed methodologies are compatible with a variety of functional groups.
This article is protected by copyright. All rights reserved.