Iron-catalysed Sonogashira reactions

Article abstract of DOI:10.3184/030823409X465295

A catalytic system has been developed that used an iron/ligand combination for the Sonogashira cross coupling of terminal alkynes with aryl iodides, which affords products in good to excellent yields.

Full text of DOI:10.3184/030823409X465295

478 RESEARCH PAPER
AUGUST, 478–481
JOURNAL OF CHEMICAL RESEARCH 2009
Iron-catalysed Sonogashira reactions
Changduo Pan, Fang Luo, Wenhui Wang, Zhishi Ye and Miaochang Liu*
College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325027, P.R. China
A catalytic system has been developed that used an iron/ligand combination for the Sonogashira cross coupling of
terminal alkynes with aryl iodides, which affords products in good to excellent yields.
Keywords: iron-catalysis, terminal alkynes, aryl iodides, sonogashira reaction
The Sonogashira reaction of aryl halides with terminal
acetylenes, which provides a powerful tool for the formation
of alkynes, has been widely applied to such diverse areas as
natural product syntheses and material science.1,2 The existing
protocols for these reactions involve the use of palladium,
copper, nickel and ruthenium catalysts.3,4 Despite remarkable
advances in both palladium and copper-catalysed reactions,
the development of alternative catalysts involving more
cost-efficient, nontoxic, and environmentally friendly metals
to effect this reaction remains an issue of scientific interest
and paramount industrial significance. In this respect, iron is
an ideal metal that offers significant advantages in terms of
its low cost, ready availability, and environmentally benign
character.5,6
salts to the Sonogashira reaction.19 Although their results
were encouraging, a long reaction time was required. Thus,
the development of a new procedure for the iron-catalysed
Sonogashira reaction is still a desirable goal. Here, we report
an iron-catalysed system for the Sonogashira cross-coupling
reaction of aryl iodides with alkynes.
We initially studied the iron-catalysed Sonogashira reaction
of phenylacetylene with 1-iodobenzene in toluene as a model
reaction at 135°C in the presence of a series of ligands
(Scheme 1) and 2 equiv of K2CO3. The results are summarised
in Table 1.
The ligands used had dramatic effects on the yields of cross-
coupling products in the Sonogashira reaction (Table 1, entries
1–5). L1 is a highly effective ligand in this reaction (Table 1,
entry 1), while L3, L4 and L5 were inferior. L2 resulted in no
coupled product (Table 1, entry 2).Then we turned our attention
to screening bases and Cs2CO3 was shown to be the best.
We also studied the effect of the iron sources. Fe(acac)3 was
the best, while the use of FeCl3 resulted in only 13%
Recently, the application of iron salts to C–C,7-19 C–N,20-21
C–O,22 C–S23 bond formation has been developed. Iron salts
as catalysts have attracted particular attention and are widely
used in C–C cross-coupling reactions. Very recently, Bolm
and co-workers were the first to successfully apply iron
N
N
N
N
N
N
L1
L2
L3
N
N
N
N
L5
L4
Scheme 1
Table 1 Selected results of iron sources, ligands, bases, and solvents screeninga
iron source / L
I
base, toluene
Entry
Iron source
Ligand
Base
t/h
Yield/%b
1
2
Fe(acac)3
Fe(acac)3
Fe(acac)3
Fe(acac)3
Fe(acac)3
Fe(acac)3
Fe(acac)3
Fe(acac)3
FeCl3
L1
L2
L3
L4
L5
L1
L1
L1
L1
L1
L1
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Cs2CO3
Na2CO3
K3PO4
42
42
42
42
42
42
42
42
42
42
28
85
<5
15
10
<5
90
<5
37
13
86
41
3
4
5
6
7
8
9
Cs2CO3
Cs2CO3
Cs2CO3
9
Fe(CH2 =CHCOO)3
Fe(acac)3
10
aReaction conditions: 1 (0.5 mmol), 2 (1.5 equiv), iron source (0.1 equiv), ligand (0.20 equiv), base (2.0 equiv), toluene (2 mL),
135°C, under N2.
bIsolated yield.
* Correspondent. E-mail: mcl_wzu@yahoo.com.cn

JOURNAL OF CHEMICAL RESEARCH 2009 479
yield (Table 1, entry 9). Moreover, the solvents played an
important role in the reaction.Acetonitrile, 1, 2-dichloroethane,
or dioxane had a detrimental effect on the outcome of the
reaction.
It should be noted that the reaction time and temperature
were key parameters in the process. When the coupling
reaction between 1 and 2 was allowed to proceed for short
time, the target acetylene 3 was obtained only in 41% yield
(Table 1, entry 11). In addition, no product was obtained
when the reaction temperature was lower than 135°C. Hence,
it was concluded that the best conditions involved 10 mol%
Fe(acac)3, 20 mol% L1, and 2 equivalents of Cs2CO3 in
toluene at 135°C for 42 h.
Next, we explored the scope of this new method. By using
the conditions optimised in the model reaction, we were able
to apply this new method to a broad range of substrates,
including terminal alkynes and aryl iodides substituted by
both electron-withdrawing and electron-donating groups
(Table 2). In general, electron-rich aryl iodides provided
products in higher yield than electron-deficient aryl
iodides. 2-Thiophenyl iodide led to the corresponding
arylated alkynes in good yields (Table 2, entries 5, 10, 15,
19 and 24). In regard to the alkynes, electron-deficient aryl
alkynes proved less reactive. Fortunately, both 1-chloro-4-
ethynylbenzene 1c and 1-bromo-4-ethynylbenzene 1d were
suitable substrates. It is noteworthy that alkyne homocoupling
products were not detected in any reaction.
In summary, we have developed an iron-catalysed system
for the Sonogashira reaction, which affords products in good
to excellent yields. Our system needs less time than the Bolm's
procedure.
Experimental
Melting points were determined with an X4 micro hot-stage
apparatus. IR spectra were determined as KBr pellets on a Bruker
model EQUINOX55 spectrophotometer. 1H NMR and 13C NMR
spectra were determined in a CDCl3 solution with a BrukerAvance300
(300 MHz) spectrometer using tetramethylsilane as the internal
standard. All chemical shifts (d) were expressed in parts per
million, and coupling constants (J) were given in Hertz. Column
chromatography was performed using EM Silica gel 60 (300-
400 mesh).
General procedure for the Sonogashira cross coupling of terminal
alkynes with aryl iodides
A sealable tube was charged with alkyne (0.5 mmol), aryl iodide
(0.75 mmol), Fe(acac)3 (17.6 mg, 10 mol%), L1 (15.6 mg, 20 mol%),
Cs2CO3 (325.8 mg, 1.0 mmol) and toluene (2 mL) under nitrogen.
After the mixture was heated to 135°C for 42 h, it was cooled to
room temperature and then the solvent was evaporated under reduced
pressure and the residue was purified by flash column chromatography
on a silica gel to give the product. The physical and spectra data of all
compounds are as follows.
Table 2 Fe(acac)3-catalysed Sonogashira coupling of terminal alkynes with aryl iodidesa
Fe(acac)3 / L1
Ar2
I
Ar1
Ar2
Ar1
H
Cs2CO3, toluene,135°C
1
2
3
Entry
1
1
2
Yield/%b
90
Entry
12
1
2
Yield/%b
89
1c
1c
2c
I
2a
1a
I
2
3
4
1a
1a
1a
1a
96
94
86
13
14
15
2e
2a
2b
90
84
88
2b
MeO
I
2c
Br
1d
1d
Br
I
2d
5
6
7
8
9
87
89
90
93
89
16
17
18
19
20
1d
1d
2c
2d
2a
2b
2c
86
81
86
93
90
I
2e
S
2a
2b
2c
2e
1b
1b
1b
1b
1e
1e
1e
10
11
2a
2b
85
90
21
22
1e
1e
2d
2e
80
87
Cl
1c
1c
aReaction conditions: 1 (0.5 mmol), 2 (0.75 mmol), Fe(acac)3 (17.6 mg, 10 mol%), L1 (15.6 mg, 20 mol%), Cs2CO3 (325.8 mg,
1.0 mmol), toluene (2 mL), 135°C, 42 h, under N2.
bIsolated yield.

480 JOURNAL OF CHEMICAL RESEARCH 2009
Diphenylacetylene (3aa): M.p. 54–55°C. IR (KBr, cm-1): 2214
(C≡C). 1H NMR (CDCl3, 300 MHz): d 7.75–7.52 (m, 4H), 7.36–7.33
(m, 6H). 13C NMR (75 MHz): d 131.6, 128.4, 128.3, 123.3, 89.4. MS
(ESI) m/z 179 (M + H+). Anal. Calcd for C10H14: C, 94.34; H, 5.66.
Found: C, 94.16; H, 5.84%.
1-bromo-4-(2-phenylethynyl)benzene (3da): M.p. 82–84°C. IR (KBr,
cm-1): 2208 (C≡C). 1H NMR (CDCl3, 300 MHz): d 7.52–7.46 (m, 4H),
7.38–7.32 (m, 5H). 13C NMR (75 MHz): d 133.0, 131.6, 128.5, 128.4,
122.9, 122.5, 122.2, 90.5, 88.3. MS (ESI) m/z 258 (M + H+). Anal.
Calcd for C14H9Br: C, 65.40; H, 3.53. Found: C, 65.24; H, 3.67%.
1-(2-(4-bromophenyl)ethynyl)-4-methylbenzene (3db): M.p. 156–
4-(phenylethynyl)toluene (3ab): M.p.71–72°C. IR (KBr, cm-1): 2216
1
o
1
158 C. IR (KBr, cm-1): 2216 (C≡C). H NMR (CDCl3, 300 MHz):
d 7.47–7.35 (m, 6H), 7.15 (d, J = 8.2 Hz, 2H), 2.36 (s, 3H). 13C
NMR (75 MHz): d 138.6, 132.9, 131.5, 131.4, 129.1, 122.4, 122.2,
119.8, 90.7, 87.7, 21.5. MS (ESI) m/z 272 (M + H+). Anal. Calcd for
C15H11Br: C, 66.44; H, 4.09. Found: C, 66.31; H, 4.23%.
(C≡C). H NMR (CDCl3, 300 MHz): d 7.55–7.52 (m, 2H), 7.44 (d,
J = 8.1 Hz, 2H), 7.36–7.32 (m, 3H), 7.16 (d, J = 8.0 Hz, 2H), 2.38 (s,
3H). 13C NMR (75 MHz): d 138.4, 131.5, 131.4, 129.1, 128.3, 128.0,
123.5, 120.2, 89.5, 88.7, 21.5. MS (ESI) m/z 193 (M + H+). Anal. Calcd
for C15H12: C, 93.71; H, 6.29. Found: C, 93.52; H, 6.48%.
4-(phenylethynyl)anisole (3ac): M.p. 58–60°C. IR (KBr, cm-1):
2220 (C≡C). 1H NMR (CDCl3, 300 MHz): d 7.55–7.48 (m, 4H),
7.37–7.33 (m, 3H), 6.90 (d, J = 8.7 Hz, 2H), 3.83 (s, 3H). 13C NMR
(75 MHz): d 159.6, 133.0, 131.4, 128.3, 127.9, 123.6, 115.4, 114.0,
89.4, 88.1, 55.3. MS (ESI) m/z 209 (M + H+). Anal. Calcd for
C15H12O: C, 86.51; H, 5.81. Found: C, 86.74; H, 5.69%.
1-bromo-4-(2-(4-methoxyphenyl)ethynyl)benzene (3dc): M.p. 234–
1
236°C. IR (KBr, cm-1): 2210 (C≡C). H NMR (CDCl3, 300 MHz):
7.49–7.44 (m, 4H), 7.35 (d, J = 8.4 Hz, 2H), 6.87 (d, J = 8.7 Hz, 2H),
3.82 (s, 3H). 13C NMR (75 MHz): 159.8, 133.0, 132.8, 131.5, 122.6,
122.0, 114.9, 114.0, 90.5, 87.0, 55.3. MS (ESI) m/z 288 (M + H+). Anal.
Calcd for C15H11BrO: C, 62.74; H, 3.86. Found: C, 62.90; H, 3.72%.
1,2-bis(4-bromophenyl)ethyne (3dd): M.p. 182–184°C. IR
(KBr, cm-1): 2204 (C≡C). 1H NMR (CDCl3, 300 MHz): 7.48 (d,
J = 8.3 Hz, 4H), 7.36 (d, J = 8.3 Hz, 2H). 13C NMR (75 MHz): 132.9,
131.6, 122.7, 121.8, 89.4. MS (ESI) m/z 334 (M + H+). Anal. Calcd
for C14H8Br2: C, 50.04; H, 2.40. Found: C, 50.20; H, 2.26%.
2-(2-phenylethynyl)naphthalene (3ea): M.p. 113–115°C. IR
(KBr, cm-1): 2218 (C≡C). 1H NMR (CDCl3, 300 MHz): d 8.05
(s, 1H), 7.83–7.78 (m, 3H), 7.59–7.56 (m, 3H), 7.49–7.46 (m, 2H),
7.36–7.34(m, 3H). 13C NMR (75 MHz): 133.0, 132.8, 131.7, 131.6,
131.4, 128.4, 128.38, 128.30, 127.9, 127.7, 126.6, 126.5, 123.3,
120.6, 89.8, 89.7. MS (ESI) m/z 229 (M + H+); Anal. Calcd for
C18H12: C, 94.70; H, 5.30. Found: C, 94.52; H, 5.48%.
2-(2-4-tolylethynyl)naphthalene (3eb): M.p. 150–152°C. IR
(KBr, cm-1): 2220 (C≡C). 1H NMR (CDCl3, 300 MHz): 8.03 (s,
1H), 7.81–7.77 (m, 3H), 7.58–7.55 (m, 1H), 7.50–7.45 (m, 4H), 7.16
(d, J = 7.8 Hz, 2H), 2.37 (s, 3H). 13C NMR (75 MHz): 138.4, 133.0,
132.7, 131.5, 131.3, 129.1, 128.4, 127.9, 127.7, 126.6, 126.5, 120.8,
120.2, 89.9, 89.2, 21.5. MS (ESI): m/z 243 (M + H+), Anal. Calcd for
C19H14: C, 94.18; H, 5.82; Found: C, 94.34; H, 5.66%.
1-bromo-4-(2-phenylethynyl)benzene (3ad): M.p. 83–84°C. IR
(KBr, cm-1): 2212 (C≡C). 1H NMR (CDCl3, 300 MHz): d 7.54–7.47
(m, 4H), 7.41–7.34 (m, 5H). 13C NMR (75 MHz): d 132.9, 131.6,
128.5, 128.3, 122.9, 122.4, 122.2, 90.5, 88.3. MS (ESI) m/z 256
(M + H+). Anal. Calcd for C14H9Br: C, 65.40; H, 3.53. Found: C,
65.26; H, 3.71%.
2-(2-phenylethynyl)thiophene (3ae): M.p. 49–50°C. IR (KBr, cm-1):
2205 (C≡C). 1H NMR (CDCl3, 300 MHz): d 7.54 (d, J = 8.0 Hz, 2H),
7.39–7.30 (m, 5H), 7.04–7.01 (m, 1H). 13C NMR (75 MHz): d 131.9,
131.4, 128.4, 128.3, 127.2, 127.1, 123.3, 122.9, 93.0, 82.6. MS (ESI)
m/z 185 (M + H+). Anal. Calcd for C12H8S: C, 78.22; H, 4.38. Found:
C, 78.08; H, 4.46%.
4-(phenylethynyl)toluene (3ba): M.p. 71–72°C. IR (KBr, cm-1):
2214 (C≡C). 1H NMR (CDCl3, 300 MHz): d 7.52 (d, J = 7.9 Hz,
2H), 7.42 (d, J = 7.8 Hz, 2H), 7.34–7.30 (m, 3H), 7.14 (d, J = 8.0 Hz,
2H), 2.36 (s, 3H). 13C NMR (75 MHz): d 138.4, 131.5, 131.4, 129.1,
128.3, 128.0, 123.5, 120.1, 89.5, 88.7. MS (ESI) m/z 193 (M + H+).
Anal. Calcd for C15H12: C, 93.71; H, 6.29. Found: C, 93.53; H, 6.47%.
1, 2-di-4-tolylethyne (3bb): M.p. 132–134°C. IR (KBr, cm-1):
2208 (C≡C). 1H NMR (CDCl3, 300 MHz): d 7.41 (d, J = 8.1 Hz, 4H),
7.14 (d, J = 8.1 Hz, 4H), 2.35 (s, 6H). 13C NMR (75 MHz): d 138.1,
131.4, 129.1, 120.4, 88.8. MS (ESI) m/z 207 (M + H+). Anal. Calcd
for C16H14: C, 93.16; H, 6.84. Found: C, 93.35; H, 6.65%.
2-(2-(4-methoxyphenyl)ethynyl)naphthalene (3ec): M.p. 122–
1
124°C. IR (KBr, cm-1): 2214 (C≡C). H NMR (CDCl3, 300 MHz):
8.02 (s, 1H), 7.81–7.77 (m, 3H), 7.57–7.45 (m, 5H), 6.88 (d, J = 8.7 Hz,
2H), 3.82 (s, 3H). 13C NMR (75 MHz): 159.7, 133.1, 133.0, 132.6,
131.1, 128.4, 127.9, 127.74, 127.71, 126.5, 120.9, 115.4, 114.04,
114.01, 89.8, 88.5, 55.3. MS (ESI) m/z 259 (M + H+); Anal. Calcd for
C19H14O: C, 88.34; H, 5.46. Found: C, 88.12; H, 5.62%.
1-(2-(4-methoxyphenyl)ethynyl)-4-methylbenzene (3bc): M.p. 125–
1
126°C. IR (KBr, cm-1): 2226 (C≡C). H NMR (CDCl3, 300 MHz):
d 7.47–7.39 (m, 4H), 7.14 (d, J = 7.9 Hz, 2H), 6.87 (d, J = 8.7 Hz,
2H), 3.82 (s, 3H), 2.36 (s, 3H). 13C NMR (75 MHz): d 159.5, 137.9,
132.9, 131.3, 129.0, 120.5, 115.6, 113.9, 88.6, 88.2, 55.3, 29.7. MS
(ESI) m/z 223 (M + H+). Anal. Calcd for C16H14O: C, 86.45; H, 6.35.
Found: C, 86.31; H, 6.50%.
2-(2-(4-bromophenyl)ethynyl)naphthalene (3ed): M.p. 146–147°C.
1
IR (KBr, cm-1): 2210 (C≡C). H NMR (CDCl3, 300 MHz): 8.0 (s,
1H), 7.82–7.80 (m, 3H), 7.57–7.41 (m, 7H). 13C NMR (75 MHz):
133.0. 132.9, 132.8, 131.6, 131.5, 128.2, 128.0, 127.8, 126.8, 126.6,
122.5, 120.2, 90.9, 88.6. MS (ESI): m/z 308 (M + H+), Anal. Calcd
for C18H11Br: C, 70.38; H, 3.61; Found: C, 70.20; H, 3.75%.
2-(2-p-tolylethynyl)thiophene (3be): M.p. 68–70°C. IR (KBr, cm-1):
2202 (C≡C). 1H NMR (CDCl3, 300 MHz): d 7.40(d, J = 8.1 Hz,
2H), 7.26–7.24 (d, J = 8.0 Hz, 2H), 7.14 (d, J = 8.1 Hz, 2H), 6.99–
6.97 (m, 1H), 2.35 (s, 3H). 13C NMR (75 MHz): d 138.6, 131.6,
131.3, 129.1, 127.0, 126.9, 123.6, 119.8, 93.2, 81.9, 21.5. MS (ESI)
m/z 199 (M + H+). Anal. Calcd for C13H10S: C, 78.75; H, 5.08. Found:
C, 78.58; H, 5.21%.
2-(2-(naphthalen-2-yl)ethynyl)thiophene (3ee): M.p. 126–128°C.
1
IR (KBr, cm-1): 2192 (C≡C). H NMR (CDCl3, 300 MHz): 8.06 (s,
1H), 7.81–7.78 (m, 3H), 7.56–7.47 (m, 3H), 7.31 (d, J = 8.7 Hz, 2H),
7.09–7.01 (m, 1H). 13C NMR (75 MHz): 132.9, 132.8, 131.9, 131.3,
128.1, 128.0, 127.8, 127.7, 127.3, 127.1, 126.7, 126.6, 123.3, 120.2,
93.4, 82.9. MS (ESI): m/z 305 (M + H+); Anal. Calcd for C16H10S: C,
82.01; H, 4.30; Found: C, 81.78; H, 4.43%.
1-chloro-4-(2-phenylethynyl)benzene (3ca): M.p. 81–82°C. IR (KBr,
cm-1): 2208 (C≡C). 1H NMR (CDCl3, 300 MHz): d 7.52–7.43 (m, 4H),
7.36–7.31 (m, 5H). 13C NMR (75 MHz): d 134.2, 132.8, 131.6, 128.6,
128.4, 128.3, 122.9. 121.8, 90.3, 88.2. MS (ESI) m/z 214 (M + H+).Anal.
Calcd for C14H9Cl: C, 79.06; H, 4.27. Found: C, 79.20; H, 4.12%.
1-(2-(4-chlorophenyl)ethynyl)-4-methylbenzene(3cb):M.p.149–150oC.
We thank the National Natural Science Foundation of China
(No. 20504023) for financial support.
1
IR (KBr, cm-1): 2215 (C≡C). H NMR (CDCl3, 300 MHz): d 7.44–
7.39 (m, 4H), 7.30 (d, J = 8.4 Hz, 2H), 7.14 (d, J = 8.0 Hz, 2H), 2.36
(s, 1H). 13C NMR (75 MHz): d 138.6, 134.0, 132.7, 131.4, 129.1, 128.6,
121.9, 119.8, 90.5, 87.6, 21.5. MS (ESI) m/z 228 (M + H+). Anal. Calcd
for C15H11Cl: C, 79.47; H, 4.89. Found: C, 79.67; H, 4.75%.
Received 1 April 2009; accepted 5 May 2009
Paper 09/0524 doi: 10.3184/030823409X465295
Published online: 10 August 2009
1-chloro-4-(2-(4-methoxyphenyl)ethynyl)benzene (3cc): M.p. 120–
1
121°C. IR (KBr, cm-1): 2220 (C≡C). H NMR (CDCl3, 300 MHz):
d 7.50–7.41 (m, 4H), 7.30 (d, J = 8.7 Hz, 2H), 6.87 (d, J = 8.7 Hz, 2H),
3.84 (s, 3H). 13C NMR (75 MHz): d 159.7, 133.8, 133.0, 132.6, 128.6,
122.1, 114.9, 114.0, 90.3, 86.9, 55.3. MS (ESI) m/z 244 (M + H+).
Anal. Calcd for C15H11ClO: C, 74.23; H, 4.57. Found: C, 74.38;
H, 4.43%.
2-(2-(4-chlorophenyl)ethynyl)thiophene (3ce): M.p. 92–94°C. IR
(KBr, cm-1): 2199 (C≡C). 1H NMR (CDCl3, 300 MHz): d 7.44–7.42
(m, 2H), 7.32–7.27 (m, 4H), 7.02–6.99 (m, 1H). 13C NMR (75 MHz):
d 134.4, 132.6, 132.1, 128.7, 127.5, 127.1, 121.4, 91.8, 83.6. MS
(ESI) m/z 220 (M + H+). Anal. Calcd for C12H7ClS: C, 65.90; H,
3.23. Found: C, 65.76; H, 3.35%.
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