Pd(NHC)PEPPSI-diazonium salts: An efficient blend for the decarboxylative Sonogashira cross coupling reaction

Article abstract of DOI:10.1039/c7nj00877e

An efficient N-heterocyclic carbene based Pd complex is described for the de-carboxylative Sonogashira coupling reaction with diazonium salts under ligand and co-catalyst free conditions. Pd(NHC)PEPPSI not only offers an air and moisture stable pre-cataly

Full text of DOI:10.1039/c7nj00877e

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
rsc.li/njc

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ARTICLE
Pd(NHC)PEPPSI- diazonium salts: An efficient blend for
decarboxylative Sonogashira cross coupling reaction
a
a
a
Jeevan Manohar Bhojane, Vilas Gangadhar Jadhav, and Jayashree Milind Nagarkar *
Received 00th January
20xx,
Accepted 00th January
0xx
An efficient N-heterocyclic carbene based Pd complex is described for de-carboxylative Sonogashira coupling reaction with
diazonium salts under ligand and co-catalyst free conditions. The Pd( NHC)PEPPSI not only offer an air and moisture stable
pre-catalyst but also efficiently catalyzes the reaction with lower loading. Various aryl and hetero aryl diazonium salts
2
DOI: 10.1039/x0xx00000x
2
undergo sp-sp cross coupling reaction with alkynyl acid to give good to excellent yield of substituted acetylene
www.rsc.org/
derivatives. The diazonium salts serve as an efficient, easily available, and inexpensive aryl surrogates over conventional
aryl halides, triflates, oxalate, and sulphamate.
Keywards: Pd(NHC)PEPPSI, Ligand free, Decarboxylative coupling, Alkynyl propiolic acid, Propiolic acid, Aryl
diazonium salts.
Introduction
Sonogashira cross coupling reaction is an important and cost effective. The uses of alkynyl acid is circumventing the
2
reliable tool to construct sp-sp bond which has broad homo-coupling of alkyne group and serve as an easily.
1
9,38–49
applications in the synthesis of natural products and bioactive available, source for alkyne
. It is also very stable and
typical Sonogashira coupling reaction easy to store and handle. Moreover, carboxylic acid is
comprises reaction of terminal alkynes with alkyl or aryl environmentally friendly as it releases carbon dioxide during
1–6
compound
. A
50
halides in the presence of Pd catalysts, ligands, co-catalyst reaction instead of creating metal waste . Additionally,
7–9
such as Cu (I) salts, and base to give substituted acetylene
.
Pd(NHC)PEPPSI complex demonstrates excellent functional
The major shortcoming of this traditional approach is group tolerance with good efficiency. They posses thermal
10,11
formation of homo-coupling product of acetylene
. Apart stability as well as are stable in air and moisture due to the
from homo coupling, another major drawback of this
conventional process is the necessity of expensive phosphine
12
ligands which are highly air and moisture sensitive . The
various coupling partners used in this reaction are aryl
1
3–20
21–23
24,25
halides
siloxanes
phospnonium salt
, aryl boronic acid
, diaryliodonium salts
, aryl
26,27
28
29–33
,
aryl mesylates , aryl sulphonate
, and aryl
34–36
. These arylating agents are costly and
also require tedious procedures for their synthesis. Thus, the
improved protocol is still in demand for this cross coupling
reaction (Scheme 1).
Previously we reported decarboxylative cross coupling of
alkynyl acids with aryl diazonium salts in presence of
37
Palladium nano particles supported on manganese ferrite .
Here in we report an efficient and effective protocol for
improved decarboxylative Sonogashira reaction in presence of
Pd(NHC)PEPPSI as pre-catalyst. The present protocol has
additional advantages. It shows tolerance towards some of the
sterically hindered substrates. It is also applicable to
heterocyclic diazonium salts which are very unstable.
Moreover, the palladium content in the Pd(NHC)PEPPSI is
lower than that in Pd MnFe O , which makes this protocol Scheme1 General scheme for Sonogashira cross coupling
2
4
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electron donating nature of NHC and thus serve as efficient increased from 2 mol% to 4 mol% (Table 1, entries 5, 6).
View Article Online
51–57
alternative to phosphine ligands
. The most important Further increase in pre-catalyst loadingDOdoI:e10s.1n03o9t/Cs7hNoJw008a7n7yE
feature of the present work is the application of aryl diazonium significant influence on time required for the coupling reaction
5
8–61
salts as the coupling partner
. These aryl diazonium salts as well as yield of the product (Table 1, entry 7). The
are more reactive, easy to synthesize, inexpensive and offers inevitability of pre-catalyst was clearly established when the
wide substrate range and thus serves as effective and reaction was performed in the absence of ‘C’. Without pre-
6
2–69
prominent alternative to conventional arylating agents
.
catalyst C, only 5% yield of 3a was obtained in 12 h (Table 1,
entry 8). After the pre-catalyst study, other reaction
parameters such as effect of base, solvent, additive,
temperature and reaction time were optimized (Table 2). To
study effect of base on coupling reaction, both inorganic and
organic bases were used by keeping other parameters
constant. The inorganic base Cs CO gave only 22% yield of 3a
Result and Discussion
Initially the optimization of reaction conditions was carried out
by taking diazonium salt of aniline (1a, 1.2 mmol), phenyl
propiyalic acid (2a, 1 mmol), TBAI as iodine source (1.4 mmol),
K CO (3 mmol) in DMSO (2mL) at temperature 120 °C. We
2
3
2
3
(Table 2, entry 1), on the other hand with K-OtBu 78% yield of
started this work with four Pd-NHC complexes which are
depicted in scheme 1. The decarboxylative Sonogashira cross
coupling reaction of 1a with 2a was tested for all four
complexes under identical conditions and the results obtained
are presented in Table 1. Among them, pre-catalyst C was
found to be the most efficient to give 85% yield of the desired
product (3a) in 12 h (Table 1, entry 3). Therefore, further
optimization of reaction parameters was carried out by taking
C as the pre-catalyst.
3
a
was obtained (Table 2, entry 2). We also employed various
bases such as K-OtBu, DIPEA, TEA, and DBU. Among these
organic bases only K-OtBu gave 78% yield of 3a whereas others
gave good to moderate yield except DIPEA which gave only 8%
yield. We have also tested effect of the solvent on the yield of
3
a. DMF gave 79% where as acetonitrile gave 52% and 1, 4
Dioxane gave 42% yield. The reaction does not proceed in
NMP. This shows that DMSO is the suitable solvent for this
protocol (Table 2, entries 6-9). It was noticeable that, additive
also plays vital role in the cross coupling reaction. When the
iodide was replaced by bromide and chloride analog, reaction
rate was greatly reduced affording poor yield of 3a (Table 2,
entries 10, 11). In the absence of additive, instead of 3a, homo
coupled product of diazonium salt was formed as major
product (Table 2, entry 12). When the reaction temperature
was reduced to 110 °C yield of 3a was also reduced to 73%
from 85% in 12 h (Table 2, entry 13) whereas increasing the
temperature to 130 °C, did not show any significant
improvement in the reaction time (Table 1, entry 14). The yield
of 3a was rather decreased to 71% with decreasing the
reaction time to 8 h (Table 2, entry 15).
a
Table1. Screening and optimization of pre-catalyst
Pre-catalyst
Pre-
catalyst
3a Isolated yield
(%)
Entry
loading
mol %)
(
1
2
3
A
B
C
D
5
5
5
78
72
85
a
Table2 Optimization of reaction parameters
4
5
6
7
8
5
2
4
6
-
74
67
79
86
5
C
3
a Isolated
[
a] Reaction conditions: 1a (1mmol), 2a (1.2mmol), K CO
2 3
Entry Additive
Base
Solvent
yield (%)
(3mmol), TBAI (1.4mmol), DMSO (2mL); time: 12 h;
temperature: 120 °C.
1
2
3
4
5
6
7
8
9
1
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAB
TBACl
-
CsCO
K-OtBu
DIPEA
3
DMSO
DMSO
DMSO
DMSO
DMSO
ACN
DMF
1,4 Dioxane 42
NMP
DMSO
DMSO
DMSO
DMSO
22
78
8
20
65
52
79
Et
DBU
N
3
K
K
K
K
K
K
K
K
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
3
3
3
3
3
3
3
3
Figure 1. Selected Pd−NHC catalysts.
Trace
18
Trace
NR
73
0
The effect of pre-catalyst loading was investigated by varying
its amount from 2 to 6 mol% (Table 1, entries 5-7). The yield of
11
12
13
b
3
a
was increased from 67% to 79% as the loading of C was
TBAI
2
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c
1
1
4
5
TBAI
TBAI
K2CO3
K2CO3
DMSO
DMSO
86
71
diazonium salt of ester furnished good yield of desired
product(Table 3, entry 3j). Good chemo selectivity was
View Article Online
DOI: 10.1039/C7NJ00877E
d
a
Reaction conditions: 1a (1.2mmol); 2a (1 mmol), C (5 mol%), observed, in case of halogen bearing diazonium salts, such as
additive ( 1.4 mmol), base (3 mmol) Solvent (2 mL); 3-Cl, 4-Cl, and 4-Br. The cross coupled products were obtained
b
c
Temperature 120 °C, Temperature 110 °C; Temperature 130 in good to excellent yield (Table 3, entries 3l
°
-
3n).
d
C; Time 8 h.
The present methodology was proficiently applied to hetero
All these experiments revealed that the maximum product aryl diazonium salts of 4-amino pyridine, 3-amino pyridine, and
yield is obtained, when aryl diazonium salt (1.2mmol) reacted benzo[d]thiazol-2-amine to give corresponding hetero aryl
with (1 mmol) of phenyl propylic acid in presence of 5mol% of substituted acetylene products in good yields (Table 3, entries
Cat. C, (3 mmol) of K2CO3 and (1.4 mmol) TBAI additive in (2 3o,3p). After successfully utilizing the optimized conditions for
mL) DMSO solvent at 120°C for 12h. Various aryl and the synthesis of asymmetrical alkynes we have extended our
heteroaryl diazonium salts were screened under optimized work to synthesize symmetrical alkynes. For this purpose we
conditions and the obtained results are summarized in Table 3. replaced phenylpropiolic acid by propiolic acid (4a) keeping
The diazonium salt of aniline gave maximum yield of other parameters constant. Interestingly, no coupling product
corresponding alkyne product. (Table 3, entry 3a).
was formed under the optimized conditions for the synthesis
of asymmetrical alkynes. Therefore we further optimized the
Table3. Asymmetrical decarboxylative Sonogashira cross reaction conditions for symmetrical cross coupling reaction
a
coupling reaction
Table4. Symmetrical decarboxylative Sonogashira cross
a
coupling reaction
a
Reaction conditions: 1a (2mmol); 4a (1 mmol), C (5 mol%),
a
Reaction conditions: 1a (1mmol); 2a (1.2 mmol), C (5 mol%), TBAI ( 2.5 mmol), DBU (3 mmol) DMSO(2 mL); Temperature 90
TBAI ( 1.4 mmol), K CO (3 mmol) DMSO(2 mL); Temperature °C, Time 12h.
2
3
1
20 °C, Time 12h.
and finalised as 1a (2 mmol), 4a (1mmol), Pd(NHC) (5 mol%),
The aryl diazonium salts bearing electron donating and TBAI (2.5 mmol), DBU as base (3 mmol) in DMSO (2 mL) at 90
withdrawing substituents efficiently undergo decarboxylic °C for 12 h. It was observed that though the inorganic bases
cross coupling reaction to give respective substituted such as K
acetylene derivative in good to excellent yield (Table 3, entries coupling product, the reaction proceeds effectively with DBU,
3n). It was observed that, though the electronic effect does an organic base to give 83% yield of 5a (Table 4, entry 5a).
CO and CsCO failed to give desired symmetrical
2
3 3
3b-
not influence the yield of product, the steric factor plays an Unlike, asymmetrical coupling, the electronic effect played
important role. The substituents such as alkyl, -NO , and –Cl vital role in symmetrical coupling than steric hindrance as the
2
present at ortho position with respect to diazo functionality diazonium salts with electron donating substituents such as 2-
exert steric hindrance during cross coupling reaction. methyl, 2,6-dimethyl, and 4-methyl straightforwardly undergo
Comparatively lower yields of corresponding alkynes (Table 3, coupling reaction to give corresponding product in excellent
entries 3b-3e, 3g,
3k) than that with substituents at meta and yield (Table 4, entries 5a-5d). Similarly, diazonium salts bearing
para position are obtained (Table 3, entries 3f, 3h, 3i). A mild electron withdrawing group such as halides also undergo
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coupling reaction to give good yield of corresponding General procedure for Unsymmetrical Sonogashira cross
View Article Online
DOI: 10.1039/C7NJ00877E
substituted acetylene (Table 4, entries 5e, 5f). However coupling reaction
diazonium salts bearing electron withdrawing substituents An oven-dried Schlenk tube equipped with a magnetic stirring
such as 2-nitro and 4-nitro failed to give coupling product bar was charged phenyl propylic acid (1 mmol),
(
Table 4, entry 5g
unsuccessful for heteroaryl diazonium salts (Table 4, entry 5i
).
, 5h). The protocol was also found to be arenediazonium salt (1.2 mmol), Cat. C (5mol%), K CO3 (3
2
,
mmol) and TBAI (1.4 mmol) followed by anhydrous DMSO (2
mL). Reaction mixture was heated in an oil bath at 120°C and
was stirred for 12 h. The reaction was monitored by GC and
TLC. After completion of the reaction, the reaction mixture
was cooled to room temperature and the reaction mass was
diluted with ethyl acetate and filtered through plug of celite.
The resulting filtrate was washed with HCl (1N) and 20% brine
solutions. The organic layer was separated and dried over
anhydrous sodium sulphate. The solvent was removed under
vacuum to get the crude product, which was purified by
column chromatography on silica gel eluting with the mixture
5
j
Scheme2 Controlled experiments
In order to understand the essence of Pd(NHC) catalytic of pet ether/ EtOAc (90:10) mixture to afford the pure
system, some control experiments were conducted. Reaction product. The purity and identity of known products are
1
was carried out with Pd(OAc) , Pd(PPh ) and PdCl (dppf) conformed by H NMR and GC-MS Spectroscopic techniques.
2
3 4
2
under standard reaction conditions. We observed that
Pd(OAc) gave very low yield of the desired product. Whereas General procedure for Symmetrical Sonogashira cross
2
Pd(PPh3)4 and PdCl (dppf) gave 62% and 56% yield coupling reaction
2
respectively. These results suggest that there is need of more
complex catalyst such as Pd(NHC)PEPPSI is more active than An oven-dried Schlenk tube equipped with a magnetic stirring
other palladium sources.
bar was charged propylic acid (1.0mmol), arenediazonium salt
2.2 mmol), Cat. C (5mol %), DBU (3 mmol) and TBAI (2.4
(
mmol) followed by anhydrous DMSO (2 mL). Reaction mixture
was heated in an oil bath at 90°C and was stirred for 12 h. The
reaction was monitored by GC and TLC. After completion of
the reaction, the reaction mixture was cooled to room
temperature and the reaction mass was diluted with ethyl
acetate and filtered through plug of celite. The resulting
filtrate was washed with HCl (1N) and 20% brine solutions. The
organic layer was separated and dried over anhydrous sodium
sulphate. The solvent was removed under vacuum to get the
crude product, which was purified by column chromatography
on silica gel eluting with the mixture of pet ether / EtOAc
Conclusion
In summary, we have developed a novel protocol for
decarboxylative Sonogashira cross coupling reaction by using
inexpensive diazonium salts as arylating agent. Pd(NHC)
catalyst is proved to be robust and effective for various
electron donating, withdrawing as well as sterically hindered
aryl diazonium salts and gave the desired products in
acceptable to higher yields. This catalytic system is also
applicable to heteroaryl diazonium salts and also afforded
desired products with good yields. . The NHC-Pd(II) complex
catalyzed reaction between alkynyl carboxylic acid and aryl
(
90:10) mixture to afford the pure product. The purity and
1
2
identity of known products are conformed by H NMR and GC-
MS Spectroscopic techniques.
diazonium salt to form sp-sp bond demonstrates a good,
alternative to the traditional methods.
Spectral data for the representative compounds
Experimental section
1
3
Diphenylethyne (3a) : White solid; yield: 0.15 g (85%); mp 61-
6
(
All chemicals were purchased from Loba chemi, Avra, S.D Fine
Chemical, Spectrochem Ltd and used without further
purifications. The progress of reaction was monitored by GC
analysis performed on PerkinElmer Clarus 480. GC equipped
with flame ionized detector with capillary column (Elite- 1701,
1
3°C; H NMR (400 MHz, cdcl ) δ 7.53 (d, J = 4.8 Hz, 4H), 7.34
3
d, J = 5.0 Hz, 6H); GC-MS m/z (% relative intensity): 178(M+,
00), 152(8), 89(15), 76(16)
,4-dimethyl-1-(phenylethynyl)benzene (3d) : Light yellow
solid; yield: 0.146 g (71%); mp 38-40°C; H NMR (400 MHz,
cdcl ) δ 7.56 – 7.49 (m, 2H), 7.38 (d, J = 7.8 Hz, 1H), 7.33 (d, J =
.0 Hz, 3H), 7.05 (s, 1H), 6.97 (d, J = 7.7 Hz, 1H), 2.47 (s, 3H),
.33 (s, 3H).; GC-MS m/z (% relative intensity): 206(M+, 100),
91(75), 189(20), 165(17), 128(20), 91(18)
1
2
16
1
3
0m X 0.32 X 0.25). The GC–MS-QP 2010 instrument (Rtx-17,
3
0 m_25 mm ID, film thickness 0.25 μm, column flow: 2 mL
3
–
1
1
7
2
1
1
min–1, 80–240 °C at 10 °Cmin rise). H NMR Spectroscopic
data of compound were recorded on Agilent- 400
a
spectometer using CDCl3 as a solvent and TMS as internal
standard. The products were purified by column
chromatography using (60-120 mesh) silica gel with pet ether
and ethyl acetate (90:10) as eluents
1
5
,3-dimethyl-2-(phenylethynyl)benzene (3e) : Yellow liquid;
1
yield: 0.148 g (72%); H NMR (400 MHz, cdcl ) δ 7.57 (d, J = 6.2
3
Hz, 2H), 7.37 (d, J = 6.8 Hz, 3H), 7.20 – 7.12 (m, 1H), 7.09 (d, J =
4
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2
1
.0 Hz, 2H), 2.54 (s, 6H). GC-MS m/z (% relative intensity): 3H); GC-MS m/z (% relative intensity): 256(M+, 100), 257(16),
View Article Online
DOI: 10.1039/C7NJ00877E
06(M+, 100), 191(67), 101(13), 95(11), 89(16)
258(98), 178(9), 177(62), 176(65), 151(20), 128(12), 88(49),
1
8
-methyl-4-(phenylethynyl)benzene (3f) : Off white solid; 75(18)
1
42
yield: 0.151 g (79%); mp 68-70°C; H NMR (400 MHz, cdcl ) δ 4-(phenylethynyl)pyridine (3o) : Off white solid; yield: 0.141
7
3
3
1
.56 – 7.48 (m, 2H), 7.43 (d, J = 7.9 Hz, 2H), 7.33 (d, J = 6.2 Hz, g (79%); mp 93-94°C; H NMR (400 MHz, cdcl ) δ 8.58 (d, J =
3
H), 7.15 (d, J = 7.8 Hz, 2H), 2.37 (s, 3H); GC-MS m/z (% relative 4.6 Hz, 2H), 7.58 – 7.49 (m, 2H), 7.41 – 7.29 (m, 5H); GC-MS
intensity): 192(M+, 100), 165(16)
m/z (% relative intensity): 179(M+, 100), 152 (13), 151(17),
1
7
1
0
-nitro-2-(phenylethynyl)benzene (3g) : Yellow solid; yield: 76(14)
.153 g (69%); mp 50-52°C; H NMR (400 MHz, cdcl ) δ 8.07 (d, 3-(phenylethynyl)pyridine (3p) : Yellow solid; yield: 0.144 g
3
1
19
1
J = 8.2 Hz, 1H), 7.71 (d, J = 7.7 Hz, 1H), 7.59 (d, J = 4.1 Hz, 3H), (81%); mp 47-49°C; H NMR (400 MHz, cdcl ) δ 8.76 (s, 1H),
3
7
1
0
1
=
.45 (t, J = 7.8 Hz, 1H), 7.37 (dd, J = 8.2, 5.1 Hz, 3H)
8.53 (d, J = 4.0 Hz, 1H), 7.79 (d, J = 7.8 Hz, 1H), 7.58 – 7.44 (m,
65
-nitro-3-(phenylethynyl)benzene (3h) : Yellow solid; yield: 2H), 7.40 – 7.32 (m, 3H), 7.26 (dd, J = 7.7, 4.9 Hz, 1H); GC-MS
1
.162 g (73%); mp 65-67°C; H NMR (400 MHz, cdcl ) δ 8.37 (s, m/z (% relative intensity): 179(M+, 100), 152 (13), 151(17),
3
H), 8.17 (d, J = 8.4 Hz, 1H), 7.82 (d, J = 7.7 Hz, 1H), 7.53 (dd, J 76(14)
10.6, 5.5 Hz, 3H), 7.42 – 7.33 (m, 3H); GC-MS m/z (% relative 1,2-di-o-tolylethyne (5b) : Yellow liquid; yield: 0.157 g (76%);
4
6
1
intensity): 223(M+, 100), 176 (49), 165 (18),151(15),88(11)
1
0
H NMR (400 MHz, cdcl ) δ 7.51 (d, J = 7.5 Hz, 2H), 7.24 (d, J =
3
1
7
-nitro-4-(phenylethynyl)benzene (3i) : Yellow solid; yield: 3.9 Hz, 4H), 7.18 (dd, J = 7.6, 4.6 Hz, 2H), 2.53 (s, 6H); GC-MS
1
.172 g (77%); mp 112-114°C; H NMR (400 MHz, cdcl ) δ 8.21 m/z (% relative intensity): 206(M+, 100),207(16.2), 191(20),
3
(
d, J = 8.2 Hz, 2H), 7.66 (d, J = 8.3 Hz, 1H), 7.60 – 7.48 (m, 2H), 189(10), 178(14), 101(11), 91(30).
.38 (d, J = 4.2 Hz, 3H); GC-MS m/z (% relative intensity): 1,2-bis(2,6-dimethylphenyl)ethyne (5c) : Off white solid;
23(M+, 100), 193(40), 176(62), 177(58), 165(47), 151(22), yield: 0.168 g (72%); mp 112-114°C; H NMR (400 MHz, cdcl ) δ
46
7
2
8
1
3
8(34)
7.10 (s, 6H), 2.55 (s, 12H); GC-MS m/z (% relative intensity):
1
7
methyl 4-(phenylethynyl)benzoate (3j) : Yellow solid; yield: 234(M+, 100), 235(22), 219(86), 218(12), 217(10), 204(33),
0
1
.184 g (78%); mp 116-117°C; H NMR (400 MHz, cdcl3) δ 8.01 203(17), 202(13), 142(20), 141(20), 128(21), 105(52), 91(18).
4
6
(d, J = 8.0 Hz, 2H), 7.58 (d, J = 8.0 Hz, 2H), 7.53 (d, J = 3.5 Hz, 1,2-di-p-tolylethyne (5d) : Off white solid; yield: 0.161 g
1
2
1
H), 7.36 (d, J = 2.8 Hz, 3H), 3.92 (s, 3H).
(78%); mp 131-133°C; H NMR (400 MHz, cdcl ) δ 7.40 (d, J =
3
6
6
-chloro-3-(phenylethynyl)benzene (3l) : Colourless liquid; 7.6 Hz, 4H), 7.14 (d, J = 7.7 Hz, 4H), 2.35 (s, 6H); GC-MS m/z (%
1
yield: 0.166 g (78%); H NMR (400 MHz, cdcl ) δ 7.52 (s, 3H), relative intensity): 206(M+, 100), 205(20), 191(38), 189(12).
3
7
1
1
1
.40 (d, J = 6.1 Hz, 1H), 7.35 (d, J = 3.2 Hz, 3H), 7.29 (dd, J = 1,2-bis(2-chlorophenyl)ethyne (5e): Light yellow solid; yield:
0.6, 8.1 Hz, 2H); GC-MS m/z (% relative intensity): 212(M+, 0.20 g (80%); mp 82-83°C; GC-MS m/z (% relative intensity):
00), 176 (36),150(10), 106 (12), 88 (15)
246(M+, 100), 247(15), 248(62), 210(8), 211(9), 177(11),
18
-chloro-4-(phenylethynyl)benzene (3m) : Off white solid; 176(79), 175(18), 150(7), 123(13)
1
46
yield: 0.168 g (79%); mp 81-82°C; H NMR (400 MHz, cdcl ) δ 1,2-bis(3-chlorophenyl)ethyne (5f) : White solid; yield: 0.192
3
1
7
1
1
1
0
2
.52 (d, J = 3.5 Hz, 2H), 7.45 (d, J = 8.1 Hz, 2H), 7.33 (dd, J = g (78%); mp 79-80°C; H NMR (400 MHz, cdcl ) δ 7.48 (d, J = 8.3
3
0.9, 5.8 Hz, 5H); GC-MS m/z (% relative intensity): 212(M+, Hz, 4H), 7.37 (d, J = 8.3 Hz, 4H); GC-MS m/z (% relative
00), 176 (36),150(10), 106 (12), 88 (15)
intensity): 246(M+, 100),247(16),248 (63), 176(52), 175(17),
17
-bromo-4-(phenylethynyl)benzene (3n) : White solid; yield: 174(18),149(6), 150(9), 123(15), 87(20)
1
.21 g (81%); mp 82-84°C; H NMR (400 MHz, cdcl ) δ 7.52 (s,
3
H), 7.48 (d, J = 7.7 Hz, 2H), 7.38 (d, J = 8.1 Hz, 2H), 7.35 (s,
Acknowledgements
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The authors are thankful to UGC-SAP New Delhi (India) for
providing financial assistance and Dr. Vinod Parab Loba
chemie, India for providing a gift samples aniline derivatives.
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