Thiosemicarbazone salicylaldiminato palladium(II)-catalyzed alkynylation couplings between arylboronic acids and alkynes or alkynyl carboxylic acids

Article abstract of DOI:10.1016/j.tet.2014.05.087

An efficient catalytic system has been developed for the synthesis of unsymmetrical substituted alkynes via the thiosemicarbazone salicylaldiminato palladium(II)-catalyzed alkynylation couplings between arylboronic acids and alkynes or alkynyl carboxylic acids under mild conditions.

Full text of DOI:10.1016/j.tet.2014.05.087

Accepted Manuscript
Thiosemicarbazone Salicylaldiminato Palladium(II)-Catalyzed Alkynylation Couplings
between Arylboronic Acids and Alkynes or Alkynyl Carboxylic Acids
Linhua Lu , Prinessa Chellan , Gregory S. Smith , Xiang Zhang , Hong Yan , Jincheng
Mao
PII:
S0040-4020(14)00793-5
10.1016/j.tet.2014.05.087
TET 25636
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 29 March 2014
Revised Date: 14 May 2014
Accepted Date: 22 May 2014
Please cite this article as: Lu L, Chellan P, Smith GS, Zhang X, Yan H, Mao J, Thiosemicarbazone
Salicylaldiminato Palladium(II)-Catalyzed Alkynylation Couplings between Arylboronic Acids and Alkynes
or Alkynyl Carboxylic Acids, Tetrahedron (2014), doi: 10.1016/j.tet.2014.05.087.
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Thiosemicarbazone Salicylaldiminato
Palladium(II)-Catalyzed Alkynylation
Couplings between Arylboronic Acids and
Alkynes or Alkynyl Carboxylic Acids
Leave this area blank for abstract info.
Linhua Lu,[a] Prinessa Chellan,[b] Gregory S. Smith, *[b] Xiang Zhang,[a] Hong Yan,[a] and Jincheng Mao*[a]
[a]Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and
Materials Science, Soochow University, Suzhou 215123, P. R. China
[b]Department of Chemistry, University of Cape Town, Rondebosch 7701, Cape Town, South Africa
R
H
N
NH2
N
Cat. 3 (2 mol%)
R
Ar
Pd
S
Ar
Ag2O, KOAc
B(OH)2
O
CH2Cl2, 35 oC, 24 h, Ar
PPh3
Catalyst 3
30 examples
up to 99% yield
R
COOH

1
ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
Thiosemicarbazone Salicylaldiminato Palladium(II)-Catalyzed Alkynylation
Couplings between Arylboronic Acids and Alkynes or Alkynyl Carboxylic Acids
Linhua Lu,[a] Prinessa Chellan,[b] Gregory S. Smith, *[b] Xiang Zhang,[a] Hong Yan,[a] and Jincheng Mao*[a]
[a]Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou
215123, P. R. China
[b]Department of Chemistry, University of Cape Town, Rondebosch 7701, Cape Town, South Africa
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
An efficient catalytic system has been developed for the synthesis of unsymmetrical substituted
alkynes via the thiosemicarbazone salicylaldiminato palladium(II)-catalyzed alkynylation
couplings between arylboronic acids and alkynes or alkynyl carboxylic acids under mild
conditions.
Available online
Keywords:
Alkynylation
Thiosemicarbazone
Palladium
2009 Elsevier Ltd. All rights reserved
.
Carboxylic acids
Boronic acids
1. Introduction
type Pd(II) complexes which have shown high efficiency as
precatalysts for coupling reactions24-27 and their high thermal
stability in solution and in the solid state makes them ideal for
high temperature homogenous catalysis.
Cross-coupling reactions are set of palladium catalyzed
reactions that have proven useful for
the syntheses of
and
polymers,1,2 products,3 agrochemicals4,5
natural
pharmaceuticals.6,7 Generally, a Pd(II) complex is employed from
which the active Pd(0) species is generated in situ. A drawback
of many currently used palladium catalyst systems is
decomposition of the catalyst giving rise to poor recyclability and
impurities in the products.8 Thus, it is of great importance to find
a catalytic system that is stable while maintaining high chemo-
and regio-selectivity and recyclability.
It is well known that the Sonogashira reaction of terminal
alkynes with aryl or alkenyl halides is the most powerful and
straightforward approach for the formation of C(sp)–C(sp2)
bonds. In the past decades, various modifications on this
coupling have been developed. For example, Pd-catalyzed cross-
coupling reaction of arylboronic reagents with terminal alkynes
was disclosed by several groups.28-30 Very recently, Loh and co-
workers successfully reported the first example of Pd-catalyzed
decarboxylative cross-coupling of arylboronic acids and alkynyl
carboxylic acids for the synthesis of unsymmetrical substituted
alkynes.31 Although the great progress has been made on
alkynylations, the development of a general and efficient
catalytic system remains highly desirable.
The study of thiosemicarbazone metal complexes has been
mainly concerned with their biological activities
last two decades increasing interest in their catalytic applications
has arisen. Recent examples of their catalytic evaluations include
a hydroxyquinoline thiosemicarbazone Ru(II) complex for the
9-11
but in the
conversion of aldehydes to amides and oxidation of alkanes to
12
alcohols and ketones
and dioxomolybdenum(VI)
We have shown that the [O,N,S] tridentate salicylaldiminato
thiosemicarbazone palladium catalysts 1-4 (Figure 1) were able
to catalyse the Mizoroki-Heck coupling of methylacrylate and
iodobenzene.18 The best activity was observed for catalyst 2 and
its use for the Heck coupling of other aryl halides and olefins
gave yields of between 90 and 100%. Herein, we report the
further evaluation of 1-4 as catalyst precursors for the
thiosemicarbazone complexes demonstrated activity in the
epoxidation of olefins using tert.-butyl hydrogen peroxide.13
Several mononuclear Pd(II) tridentate thiosemicarbazone
complexes have been studied as pre-catalysts for a variety of
cross-coupling reactions.14-23 There are several factors that have
contributed to this burgeoning interest including, the tridentate
coordination of the thiosemicarbazone ligand is similar to pincer
———
*
Corresponding author. Tel (Fax): +86 512 65880403; +27-21-6505195; E-mail address: jcmao@suda.edu.cn (J. Mao); gregory.smith@uct.ac.za (G. S. Smith)

2
Tetrahedron
alkynylation coupling of different various boronic acids and
46 % was obtained. A product yield of 70% is observed when
ACCEPTED MANUSCRIPT
alkynes.
silver carbonate was used (Entry 3) but this yield was still lower
than that obtained for the catalytic reaction using silver oxide
(Entry 1). Thus, silver oxide was identified as the best oxidant
and the catalytic reaction was repeated using a 1 mol equivalent
(Entry 8) to see if a decrease in oxidant effects the catalyst
activity.
N
NH2
N
NH2
N
N
Pd
S
Pd
S
O
O
PPh3
PPh3
O
Catalyst 1
Catalyst 2
N
N
NH2
Cl
N
N
NH2
Pd
S
Pd
O
S
O
PPh3
PPh3
Catalyst 3
Catalyst 4
Figure 1. Pd(II) thiosemicarbazone catalysts 1-4.
2. Results and discussion
Catalysts 1-4 were first evaluated for activity for the
alkynylation coupling of 4-methoxy-phenylboronic acid and
phenylacetylene in air (Entries 1-4, Figure 2) in order to
determine the most active catalyst for further study. Catalysts 1
and 2, which contain electron donating groups in the 3’-position,
yielded moderate product yields of 47 and 45% respectively.
Catalyst 4 gave a higher yield of 59% and catalyst 3 showed the
best activity. The coupling reaction was repeated using catalyst 3
but under argon (Entry 5) and this led to a significant increase in
the product yield to 76%. Thus, catalyst 3 was chosen for further
analysis. Figure 3 contains the percent yields obtained while
investigating different catalytic condition for catalyst 3.
Figure 3. Screening of various bases and additives for the alkynylation
coupling of phenylacetylene and 4-methoxy(phenylacetylene). Reaction
conditions: boronic acid (0.5 mmol), alkyne (0.6 mmol), Pd cat.3 (2 mol%),
additive (2 equiv), base (2 equiv), CH2Cl2 (2 mL), 35 °C, 24 h. Isolated yield
based on arylboronic acid.
Only 40% of product was obtained, less than half of what is
obtained using 2 mol equivalents (Entry 1). Varying the base led
to no product formation when cesium carbonate was used (Entry
9) and only moderate yields were obtained for potassium tert-
butoxide, triethylamine and lithium acetate (Entries 10-12).
When potassium acetate was used as base, the product yield
increased to 94%. Overall, the best activity was observed when a
2 mol% catalyst loading was used with 2 mol equivalents of
silver oxide and potassium acetate.
Table 1. Yields obtained for the alkynylation coupling reaction between
a
phenylacetylene and different aryl boronic acids using catalyst 3.
Cat. 3 (2 mol%)
Ag2O, KOAc
+
ArB(OH)2
Ar
CH2Cl2, 35 oC, 24 h, Ar
Yield
(%)b
Entry
1
Arylboronic acid
Product
MeO
B(OH)2
MeO
94
Figure 2. Screening of catalysts 1-4 for the alkynylation coupling of
phenylacetylene and 4-methoxy(phenylacetylene). Reaction conditions:
boronic acid (0.5 mmol), alkyne (0.6 mmol), Pd cat. (1 mol%), Ag2O (2
equiv), NaOAc (2 equiv), CH2Cl2 (2 mL), 35 °C, 24 h, air (Entries 1-4) or
argon (Entry 5). Isolated yield based on arylboronic acid.
2
3
90
63
4
5
6
99
85
64
A 2 mol% loading of catalyst was used and the reaction was
carried out in DCM at 35 °C. When the catalyst loading of 3 was
increased from 1 mol % (Entry 5, Figure 2) to 2 mol% (Entry 1,
Figure 3) the total yield of product increases to 82%. Changing
the oxidant (Entries 2-7) for the catalytic reactions revealed that
no product was formed when silver nitrate, 1,4-benzoquinone
(BQ), K2S2O4 or tert-butyl hydroperoxide (TBHP) were used.
When silver acetate (Entry 4) was used as oxidant a low yield of
7
92

3
ACCEPTED MANUSCRIPT
8
9
96
93
73
96
10
11
12
93
83
13
14
15
16
Figure 4. Yields obtained for alkynylation coupling of 4-
methoxy(phenylboronic acid) with different terminal alkynes using catalyst 3.
Reaction conditions: 4-methoxyphenylboronic acid (0.5 mmol), terminal
alkyne (0.6mmol), Pd cat. (2 mol%), Ag2O (2 equiv), KOAc (2 equiv), DCM
(2 mL), 35 °C, 24 h, argon, isolated yield based on arylboronic acid.
92
30
40
Evaluation of catalyst 3 for the coupling of 4-methoxy phenyl
boronic acid and different alkynes revealed the best product yield
was obtained for the substrate 4-ethynyl-toluene (Entry 9, Figure 4).
Moderate to high yields were observed of all of the alkynylation
reactions. A slightly lower yield is obtained when there is no
substituent on the aromatic ring of the alkyne substrate (Entry 1)
and increasing the chain length between the phenyl ring and the
alkyne bond leads to a decrease in activity (Entry 10), a similar
yield is observed when 1-octyne is the substrate. This suggests that
the presence and proximity of the phenyl ring influences the
catalytic activity of 3. The reactions using halo-aryl-alkynes
(Entries 2-4) gave yields ranging from 70 – 90%. A similar range
in activity was obtained for the alkynyl substrates containing
electron donating substituents (Entries 5-7). This observation
proposes that catalyst 3 displays no selectivity toward electron-
donating or withdrawing substituents.
a
Catalytic conditions: arylboronic acid (0.5 mmol), phenylacetylene (0.6
mmol), Pd cat. (2 mol%), Ag2O (2 equiv), KOAc (2 equiv), DCM (2 mL),
35 °C, 24 h, Ar. b Isolated yield based on arylboronic acid.
The optimal reactions conditions and reagents were then
applied to the alkynylation coupling of phenylacetylene and
different aryl bromides using catalyst 3 (Table 1). Similar
product yields were obtained when 4-methoxyphenyl boronic
acid or 3-methoxyphenylboronic acid was used (Entries 1 and 2),
however when the methoxy substituent is in the 2’-position
(Entry 3) a significant decrease in the yield was evident. A
similar observation was noted for the coupling reactions using
methylphenyl boronic acid, the yields decreased when the methyl
substituent is in the 2’-position of the ring compared to the 4’-
position (Entries 5 and 6). This large decrease in activity may be
a consequence of steric effects imposed by the substituents in the
2’-positon hindering coordination of the boronic acid substrate to
palladium. A decrease in percent yield from 96 to 92% was
observed with an increase in electronegativity of the halide
substituent (Entries 7 and 8). The trifluoromethyl substituent is a
highly electron withdrawing group and a product yield of only
73% is observed for 4-trifluoromethyl-phenyl boronic acid (Entry
10). High product yields were also observed for the coupling
reactions using formylphenyl boronic acid (Entries 11 and 12).
For the two reactions using naphthyl boronic acid, large differences
in the yields were noted depending on the position of the boronic
acid substituent. A yield of 92% is obtained when the acid is in the
2’-position (Entry 14) and this decreases to 30% when it is in the
1’-position (Entry 15). When pyridin-3-yl-3-boronic acid was used
as the substrate, the desired product was obtained in 40% yield
(Entry 16).
Table 2. Yields obtained for the alkynylation coupling of 4-
methoxy(phenylboronic acid) and different alkynyl carboxylic acids using
catalyst 3 a
Cat. 3 (2 mol%)
Ag2O, KOAc
+
MeO
B(OH)2
R
COOH
MeO
R
CH2Cl2, 35 oC, 24 h, Ar
alkynyl carboxylic
acid
Entry
1
product
Yield (%)b
80
2
3
MeO
OMe
95
70
COOH
4
81
a
Catalytic conditions: 4-methoxyphenylboronic acid (0.5 mmol), terminal
alkynyl carboxylic acid (0.6mmol), Ag2O (2 equiv), KOAc (2 equiv), DCM
(2 mL), 35 °C, 24h, Ar. b Isolated yield based on 4-methoxyphenylboronic
acid.

4
Tetrahedron
ACCEPTED MANUSCRIPT
1-Methoxy-3-(phenylethynyl)benzene31 (Table 1, entry 2) (94
o
1
mg, 90% yield): White solid, mp: 77–78 C; H NMR (400
MHz, CDCl3) δ 7.58 (dd, J = 4.6, 2.8 Hz, 2H), 7.38 (d, J = 5.2
Hz, 3H), 7.29 (t, J = 7.9 Hz, 1H), 7.18 (d, J = 7.6 Hz, 1H), 7.11
(s, 1H), 6.93 (d, J = 8.3 Hz, 1H), 3.84 (s, 3H). 13C NMR (100
MHz, CDCl3) δ 159.3, 131.6, 129.4, 128.3, 128.3, 124.2, 124.2,
123.2, 116.3, 114.9, 89.3, 89.2, 55.2.
The encouraging results obtained for the coupling reactions
using boronic acids and alkynes led us to carry out a preliminary
screen of catalyst 3 for the decarboxylative cross-coupling of
several alkynyl carboxylic acids with arylboronic acids (Table 2).
The results obtained show that catalyst 3 is able to catalyze these
reactions with high product yields, particularly for the reactions
using alkynyl carboxylic acids containing electron-donating
substituents.
1-Methoxy-2-(phenylethynyl)benzene32a (Table 1, entry 3) (66
mg, 63% yield): Pale yellow oil; H NMR (400 MHz, CDCl3) δ
1
7.56 (dd, J = 24.5, 6.8 Hz, 3H), 7.33 (dd, J = 14.0, 6.0 Hz, 4H),
6.99–6.89 (m, 2H), 3.93 (s, 3H). 13C NMR (100 MHz, CDCl3) δ
159.9, 133.6, 131.7, 129.8, 128.2, 128.0, 123.5, 120.4, 112.4,
110.6, 93.4, 85.7, 55.8.
3. Conclusions
In summary, we have demonstrated that tridentate Pd(II)
salicylaldiminato-thiosemicarbazone complexes are able to
efficiently catalyze the alkynylation couplings of a variety of aryl
boronic acids with alkynes or alkynyl carboxylic acids under
mild conditions. In addition, this catalytic system is also suitable
for the decarboxylative coupling of alkynyl carboxylic acids with
arylboronic acids. This will result in this method for the speical
application in some cases. These preliminary studies suggest that
the easily prepared and stable Pd(II) catalysts of this type may be
efficient for the synthesis of substituted alkynes. We are currently
exploring these complexes’ use for other palladium catalyzed
coupling reactions.
Diphenyl acetylene31 (Table 1, entry 4) (88 mg, 99% yield):
o
1
White solid, mp: 60–61 C; H NMR (400 MHz, CDCl3) δ 7.65–
7.58 (m, 4H), 7.44–7.36 (m, 6H).13C NMR (100 MHz, CDCl3) δ
131.6, 128.4, 128.3, 123.3, 89.5.
1-(2-p-Tolylethynyl)benzene31 (Table 1, entry 5) (82 mg, 85%
yield): White solid, mp: 73–74 oC; 1H NMR (400 MHz, CDCl3) δ
7.59 (s, 2H), 7.51 (d, J = 7.3 Hz, 2H), 7.39 (s, 3H), 7.21 (d, J =
6.7 Hz, 2H), 2.42 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 138.4,
131.5, 131.5, 129.1, 128.3, 128.1, 123.5, 120.2, 89.6, 88.8, 21.5.
1-(2-o-Tolylethynyl)benzene31 (Table 1, entry 6) (61 mg, 64%
yield): Colorless oil; 1H NMR (400 MHz, CDCl3) δ 7.58 (dd, J =
15.1, 7.2 Hz, 3H), 7.44–7.35 (m, 3H), 7.28 (d, J = 3.7 Hz, 2H),
7.23 (dd, J = 6.8, 4.7 Hz, 1H), 2.58 (s, 3H). 13C NMR (100 MHz,
CDCl3) δ 140.2, 131.9, 131.5, 129.5, 128.4, 128.3, 128.2, 125.6,
123.6, 123.1, 93.4, 88.4, 20.8.
4. Experiment
4.1 General information
1-(2-(4-Fluorophenyl)ethynyl)benzene31 (Table 1, entry 7) (90
All manipulations were carried out under argon atmosphere.
Terminal alkynes were purchased from Acros Organics and used
without further purification. Palladium complexes were prepared
according to the literature.18 Column chromatography was
generally performed on silica gel (300-400 mesh) and reactions
were monitored by thin layer chromatography (TLC) using UV
o
1
mg, 92% yield): White solid, mp: 109–111 C; H NMR (400
MHz, CDCl3) δ 7.58–7.53 (m, J = 11.7, 5.9, 3.2 Hz, 4H), 7.37
(dd, J = 12.0 Hz, 10.0Hz, 3H), 7.07 (dd, J = 8.6, 7.8 Hz, 2H).;13C
NMR (75 MHz, CDCl3) δ 161.5 (d, J = 248.2 Hz), 132.5 (d, J =
8.3 Hz), 130.6, 127.4, 127.4, 122.1, 118.4 (d, J = 3.0 Hz), 114.7
(d, J = 22.5 Hz), 88.1, 87.3.
1
light to monitor the course of the reactions. The H (400 MHz)
and 13C NMR (100 MHz) data were recorded on Varian 400 M
1-Bromo-4-(phenylethynyl)benzen32b (Table 1, entry 8) (123
o
1
spectrometers using CDCl3 as solvent. The chemical shifts (δ) are
reported in ppm and coupling constants (J) in Hz. H NMR
spectra was recorded with tetramethylsilane (δ= 0.00 ppm) as
internal reference; 13C NMR spectra was recorded with CDCl3 (δ
= 77.00 ppm) as internal reference. MS were performed by the
State-authorized Analytical Center in Soochow University.
mg, 96% yield): White solid, mp: 82–83 C; H NMR (400
MHz, CDCl3) δ 7.56–7.50 (m, 2H), 7.48 (d, J = 8.1 Hz, 2H),
7.42–7.31 (m, 5H); 13C NMR (100 MHz, CDCl3) δ 133.1, 131.6,
131.6, 128.5, 128.4, 122.9, 122.5, 122.3, 90.5, 88.3.
1
1-Chloro-4(phenylethynyl)benzene32c (Table 1, entry 9) (99
o
1
mg, 93% yield): White solid, mp: 81–82 C; H NMR (400
MHz, CDCl3) δ 7.55 (dd, J = 6.1, 2.6 Hz, 2H), 7.48 (d, J = 8.3
Hz, 2H), 7.41–7.30 (m, 5H).13C NMR (100 MHz, CDCl3) δ
134.2, 132.8, 131.6, 128.7, 128.5, 128.4, 122.9, 121.7, 90.3, 88.2.
4.2 General procedure for Pd-catalyzed coupling reaction
between arylboronic acid and terminal alkyne or alkynyl
carboxylic acid:
1-(Phenylethynyl)-4-(trifluoromethyl)benzene32b (Table 1,
entry 10) (90 mg, 73% yield): White solid, mp: 101–103 oC; 1H
NMR (400 MHz, CDCl3) δ 7.67–7.59 (m, 4H), 7.56 (dd, J = 4.4,
1.9 Hz, 2H), 7.42–7.31 (m, 3H).13C NMR (75 MHz, CDCl3)) δ
131.8, 131.7, 130.0 (d, J = 33.0 Hz), 128.8, 128.4, 127.1 (d, J =
1.5 Hz), 125.3 (q, J = 3.8 Hz), 123.9 (d, J = 270. 0 Hz), 122.5,
91.7, 88.0.
A mixture of arylboronic acid (0.5 mmol), terminal alkyne or
alkynyl carboxylic acid (0.6 mmol), DCM (2 mL), catalyst 3 (2
mol%), Ag2O (1.0 mmol), KOAc (1.0 mmol) in a Schlenk tube
was stirred under an argon atmosphere at 35oC for 24 h. The
excess DCM was then removed by rotary evaporation and the
residue was directly purified by flash column chromatography
(petroleum ether or petroleum ether/ethyl acetate) to afford the
corresponding coupling products.
4-(Phenylethynyl)benzaldehyde32d (Table 1, entry 11) (99 mg,
o
1
96% yield): White solid, mp: 98–100 C; H NMR (400 MHz,
CDCl3) δ 9.99 (s, 1H), 7.84 (d, J = 7.8 Hz, 2H), 7.66 (d, J = 8.0
Hz, 2H), 7.56 (dd, J = 3.4, 2.9 Hz, 2H), 7.37 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 191.6, 135.3, 132.0, 131.7, 129.6, 128.9,
128.43, 128.41, 122.4, 93.5, 88.5.
1-Methoxy-4-(phenylethynyl)benzene31 (Table 1, entry 1) (98
1
mg, 94% yield): White solid, mp: 80-81oC; H NMR (400 MHz,
CDCl3) δ 7.53 (d, J = 6.2 Hz, 2H), 7.49 (d, J = 8.7 Hz, 2H), 7.34
(d, J = 6.9 Hz, 3H), 6.89 (d, J = 8.4 Hz, 2H), 3.84 (s, 3H). 13C
NMR (100 MHz, CDCl3) δ 159.6, 133.0, 131.4, 128.3, 127.9,
123.6, 115.3, 114.0, 89.4, 88.1, 55.2.
3-(Phenylethynyl)benzaldehyde32b (Table 1, entry 12) (96 mg,
1
93% yield): yellow oil; H NMR (400 MHz, CDCl3) δ 10.00 (s,

5
+
+
+
1H), 8.02 (s, 1H), 7.82 (d, J = 7.7 Hz, 1H), 7.76 (d, J = 7.7 Hz,
ACCEPTED MANUSCRIPT
15.4. MS ESI (m/z): [M+H] calcd for [C17H17O] requires
1H), 7.55 (dd, J = 4.0, 1.8 Hz, 2H), 7.50 (t, J = 7.7 Hz, 1H),
7.39–7.34 (m, 3H); 13C NMR (100 MHz, CDCl3) δ 191.5, 137.0,
136.4, 132.9, 131.6, 129.0, 128.8, 128.6, 128.4, 124.4, 122.6,
90.9, 87.8.
237.1, found 237.1.
1-Ethoxy-4-((4-methoxyphenyl)ethynyl)benzene (Figure 4,
o
1
entry 7) (93 mg, 74% yield): White solid, mp: 138–139 C; H
NMR (400 MHz, CDCl3) δ 7.53–7.39 (m, 4H), 6.87 (dd, J = 8.8,
5.3 Hz, 4H), 4.03 (q, J = 7.0 Hz, 2H), 3.81 (s, 3H), 1.42 (t, J =
7.0 Hz, 3H).13C NMR (75 MHz, CDCl3) δ 158.3, 157.8, 133.0,
131.9, 114.7, 114.5, 113.5, 112.9, 87.0, 86.9, 62.5, 54.3, 13.8.
MS (ESI+): calcd. for [C17H17O2]+ requires m/z 253.1, found
[M+H]+: 253.2.
1-(4-(Phenylethynyl)phenyl)ethanone32d (Table 1, entry 13)
o
1
(91 mg, 83% yield): White solid, mp: 98–99 C; H NMR (400
MHz, CDCl3) δ 7.92 (d, J = 7.9 Hz, 2H), 7.63–7.51 (m, 4H), 7.36
(s, 3H), 2.59 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 197.2, 136.1,
131.7, 131.6, 128.8, 128.4, 128.2, 128.1, 122.6, 92.7, 88.6, 26.5.
1-Methoxy-4-((4-pentylphenyl)ethynyl)benzene32g (Figure 4,
2-(2-Phenylethynyl)naphthalene31 (Table 1, entry 14) (105
entry 8) (113 mg, 81% yield): White solid, mp: 44–45oC; H
1
o
1
mg, 92% yield): White solid, mp: 113–115 C; H NMR (400
MHz, CDCl3) δ 8.13 (s, 1H), 7.86 (dd, J = 8.6, 4.5 Hz, 3H), 7.66
(d, J = 7.0 Hz, 3H), 7.59–7.49 (m, 2H), 7.42 (d, J = 6.6 Hz, 3H);
13C NMR (100 MHz, CDCl3) δ 133.0, 132.8, 131.7, 131.5,
128.43, 128.41, 128.3, 128.0, 127.8, 126.7, 126.6, 123.3, 120.6,
89.9, 89.8.
NMR (400 MHz, CDCl3) δ 7.47 (dd, J = 13.4, 8.2 Hz, 4H), 7.17
(d, J = 7.9 Hz, 2H), 6.89 (d, J = 8.5 Hz, 2H), 3.83 (s, 3H), 2.66 –
2.58 (m, 2H), 1.68–1.58 (m, 2H), 1.42–1.28 (m, 4H), 0.92 (t, J =
6.8 Hz, 3H).13C NMR (100 MHz, CDCl3) δ 159.4, 143.0, 132.9,
131.3, 128.4, 120.7, 115.6, 113.9, 88.7, 88.2, 55.2, 35.8, 31.4,
30.9, 22.5, 14.0.
1-(2-Phenylethynyl)naphthalene31 (Table 1, entry 15) (34 mg,
30% yield): Colorless oil; 1H NMR (400 MHz, CDCl3) δ 8.50 (d,
J = 8.3 Hz, 1H), 7.89 (t, J = 9.0 Hz, 2H), 7.81 (dd, J = 7.1, 1.1 Hz,
1H), 7.73–7.67 (m, 2H), 7.64 (dd, J = 8.2, 6.9 Hz, 1H), 7.60 –
7.55 (m, 1H), 7.50 (d, J = 8.2 Hz, 1H), 7.46–7.37 (m, 3H); 13C
NMR (100 MHz, CDCl3) δ 133.23, 133.18, 131.6, 130.3, 128.7,
128.41, 128.37, 128.3, 126.8, 126.4, 126.2, 125.3, 123.4, 120.9,
94.3, 87.5.
4-Phenylethynylpyridine32c (Table 1, entry 16) (36 mg, 40%
yield): Yellow solid, mp: 50–51 oC; 1H NMR (400 MHz, CDCl3)
δ 8.77 (s, 1H), 8.54 (d, J = 4.3 Hz, 1H), 7.80 (d, J = 7.7 Hz, 1H),
7.54 (d, J = 2.8 Hz, 2H), 7.36 (s, 3H), 7.31–7.23 (m, 1H);13C
NMR (75 MHz, CDCl3) δ 151.2, 147.5, 137.5, 130.7, 128.0,
127.4, 122.0, 121.5, 119.5, 91.7, 84.9.
1-Bromo-4-(2-(4-methoxyphenyl)ethynyl)benzene31 (Figure 4,
entry 2) (114 mg, 80% yield): White solid, mp: 154–156 oC; 1H
NMR (400 MHz, CDCl3) δ 7.47 (d, J = 8.8 Hz, 4H), 7.37 (d, J =
8.4 Hz, 2H), 6.88 (d, J = 8.5 Hz, 2H), 3.82 (s, 3H). 13C NMR
(100 MHz, CDCl3) δ 159.8, 133.1, 132.9, 131.6, 122.6, 122.1,
115.0, 114.1, 90.6, 87.1, 55.3.
1-Chloro-4-((4-methoxyphenyl)ethynyl)benzene32e (Figure 4,
entry 3) (85 mg, 70% yield): White solid, mp: 114–116 oC; 1H
NMR (400 MHz, CDCl3) δ 7.46 (dd, J = 13.6, 8.5 Hz, 4H), 7.31
(d, J = 8.5 Hz, 2H), 6.89 (d, J = 8.7 Hz, 2H), 3.82 (s, 3H).13C
NMR (75 MHz, CDCl3) δ 158.8, 132.8, 132.1, 131.6, 127.6,
121.1, 114.0, 113.1, 89.4, 86.0, 54.3.
1-Methoxy-4-(p-tolylethynyl)benzene32e (Figure 4, entry 9)
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(109 mg, 98% yield): White solid, mp: 126–130 C; H NMR
(400 MHz, CDCl3) δ 7.46 (d, J = 8.8 Hz, 2H), 7.41 (d, J = 8.1 Hz,
2H), 7.14 (d, J = 7.9 Hz, 2H), 6.87 (d, J = 8.8 Hz, 2H), 3.82 (s,
3H), 2.17 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 158.4, 137.1,
131.9, 130.3, 128.0, 119.4, 114.6, 112.9, 87.6, 87.2, 54.3, 20.5.
1-Methoxy-4-(4-phenylbut-1-yn-1-yl)benzene32e (Figure 4,
entry 10) (71 mg, 60% yield): Yellow oil; 1H NMR (400 MHz,
CDCl3) δ 7.44–7.25 (m, 7H), 6.86 (d, J = 8.6 Hz, 2H), 3.82 (d, J
= 1.0 Hz, 3H), 2.97 (t, J = 7.5 Hz, 2H), 2.73 (t, J = 7.6 Hz,
2H).13C NMR (100 MHz, CDCl3) δ 159.1, 140.8, 132.8, 128.5,
128.3, 126.3, 116.0, 113.8, 87.9, 81.0, 55.2, 35.3, 21.7.
1-Hexyl-4-((4-methoxyphenyl)ethynyl)benzene32f (Figure 4,
entry 11) (65 mg, 60% yield): Yellow oil; 1H NMR (400 MHz,
CDCl3) δ 7.34 (d, J = 8.6 Hz, 2H), 6.82 (d, J = 8.6 Hz, 2H), 3.79
(s, 3H), 2.39 (t, J = 7.1 Hz, 2H), 1.65–1.55 (m, 2H), 1.51–1.42
(m, 2H), 1.39–1.26 (m, 4H), 0.92 (t, J = 6.9 Hz, 3H).13C NMR
(100 MHz, CDCl3) δ 158.9, 132.7, 116.2, 113.7, 88.7, 80.2, 55.1,
31.3, 28.8, 28.6, 22.5, 19.34, 14.0.
1-(Hept-1-ynyl)-4-methoxybenzene31 (Table 3, entry 4) (82
mg, 81% yield): Colorless oil; H NMR (400 MHz, CDCl3) δ
7.34 (d, J = 8.7 Hz, 2H), 6.81 (d, J = 8.7 Hz, 2H), 3.78 (s, 3H),
2.39 (t, J = 7.1 Hz, 2H), 1.67–1.56 (m, 2H), 1.49–1.31 (m, 4H),
0.94 (t, J = 7.1 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 158.9,
132.8, 116.2, 113.7, 88.7, 80.2, 55.1, 31.1, 28.5, 22.2, 19.3, 13.9.
1
1-Fluoro-4-((4-methoxyphenyl)ethynyl)benzene32e (Figure 4,
Acknowledgments
o
1
entry 4) (102 mg, 90% yield): White solid, mp: 83–85 C; H
NMR (400 MHz, CDCl3) δ 7.55–7.45 (m, 4H), 7.04 (t, J = 8.6
Hz, 2H), 6.89 (d, J = 8.6 Hz, 2H), 3.81 (s, 3H).13C NMR (75
MHz, CDCl3) δ 161.3 (d, 1J = 247.5 Hz), 158.7, 132.3 (d, 3J = 8.3
Hz), 132.0, 118.7 (d, 4J = 3.0 Hz), 114.7, 114.3 (d, 2J = 20.3 Hz),
113.0, 88.1, 86.0, 54.2.
We gratefully acknowledge the grants from the Research
Grant under the SA/China Agreement on Cooperation in Science
and Technology, the Scientific Research Foundation for the
Returned Overseas Chinese Scholars, State Education Ministry,
the Priority Academic Program Development of Jiangsu Higher
Education Institutions, The Project of Scientific and Technologic
Infrastructure of Suzhou (SZS201207), and the Key Laboratory
of Organic Synthesis of Jiangsu Province. Financial support from
the University of Cape Town and the National Research
Foundation (NRF) of South Africa is gratefully acknowledged.
Johnson-Matthey/Anglo American Platinum Limited is kindly
acknowledged for donation of metal salts.
1,2-Bis(4-methoxyphenyl)ethyne31 (Figure 4, entry 5) (107 mg,
o
1
90% yield): White solid, mp: 140–142 C; H NMR (400 MHz,
CDCl3) δ 7.46 (d, J = 8.5 Hz, 4H), 6.87 (d, J = 8.6 Hz, 4H), 3.82
(s, 6H). 13C NMR (101 MHz, CDCl3) δ 159.3, 134.0, 115.6,
113.9, 87.9, 55.2.
1-Ethyl-4-((4-methoxyphenyl)ethynyl)benzene (Figure 4,
1
entry 6) (89 mg, 75% yield): Yellow oil; H NMR (400 MHz,
CDCl3) δ 7.49 (t, J = 8.8 Hz, 4H), 7.20 (d, J = 7.6 Hz, 2H), 6.90
(d, J = 8.6 Hz, 2H), 3.82 (s, 3H), 2.68 (q, J = 7.4 Hz, 2H), 1.27 (t,
J = 7.6 Hz, 3H).13C NMR (100 MHz, CDCl3) δ 159.4, 144.3,
132.9, 131.4, 127.9, 120.7, 115.5, 113.9, 88.7, 88.2, 55.2, 28.8,
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Supporting Information
Thiosemicarbazone Salicylaldiminato
Palladium(II)-Catalyzed Alkynylation Couplings between
Arylboronic Acids and Alkynes or Alkynyl Carboxylic Acids
Linhua Lu,a Prinessa Chellan,b Gregory S. Smith,b* Xiang Zhang,a Hong
Yan,a Jincheng Maoa*
a Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry,
Chemical Engineering and Materials Science, Suzhou University, Suzhou 215123, P.
R. China
(Fax: +86-512-65880403, e-mail: jcmao@suda.edu.cn)
b Department of Chemistry, University of Cape Town, Rondebosch 7701, Cape Town,
South Africa (Fax:+27-21-6505195, e-mail: gregory.smith@uct.ac.za)
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