Diazaphospholane as an efficient ligand for copper-catalyzed cross-coupling of thiols with aryl iodides

Article abstract of DOI:10.2174/157017811797249335

Copper-catalyzed cross-coupling of thiols with aryl iodides performed well using an air-stable diazaphospholane ligand in presence of NaOH in DMF at 110 °C and a variety of diaryl sulfides are synthesized in good yields.

Full text of DOI:10.2174/157017811797249335

Letters in Organic Chemistry, 2011, 8, 587-591
587
Diazaphospholane as an Efficient Ligand for Copper-Catalyzed Cross-
Coupling of Thiols with Aryl Iodides
Minghua Yang*, Ji Pei, Guobing Yan and Yunfa Zheng
Department of Chemistry, Lishui University, Lishui 323000, P. R. China
Received November 18, 2010: Revised April 23, 2011: Accepted May 16, 2011
Abstract: Copper-catalyzed cross-coupling of thiols with aryl iodides performed well using an air-stable diazaphospho-
lane ligand in presence of NaOH in DMF at 110 ºC and a variety of diaryl sulfides are synthesized in good yields.
Keywords: Arylation, copper, cross-coupling, diazaphospholane, thiols.
INTRODUCTION
then investigated in the copper-catalyzed coupling between
iodobenzene and benzenethiol. As shown in Table 1, only
trace amount of product was detected in the absence of
ligand (Table 1, entry 1). N, N`-dimethylethylenediamine
(L1) and L-proline (L3), these classical ligands for Ullmann
coupling were used in the reaction and gave low yields (Ta-
ble 1, entries 2 and 4). The common and simple ligands, di-
methylglyoxime (L2) and Ph3P (L5) were also introduced
into the reaction, but it seemed to be inefficient for the for-
mation of sulfides (Table 1, entries 4 and 6). We found that
the phosphine-containing ligand L4 was the most suitable
ligand for this transformation and gave 52% yield (Table 1,
entry 5) at 95 °C.
Aryl sulfides are important components for some phar-
maceuticals and polymeric materials [1, 2]. The coupling of
thiols with aryl halides using copper is recognized as an eco-
nomic method for synthesis of aryl sulfides. Over the past
decades, while ligand-free conditions were reported [3, 4],
some efficient ligands, such as amino acid [5-7], neocu-
proine [8-9], bis(7-azaindolyl)methane [10], benzotriazole
[11], ꢀ-Keto Ester[12], diols [13, 14], 1,2,3,4-tetrahydro-8-
hydroxy-quinoline [15], tris-(2-aminoethyl)amine [16] and
diamines [17], have been widely investigated in this reaction.
Indeed, significant improvement has been achieved by using
these ligands. Although the phosphine-containing ligands
were successfully applied in palladium-mediated coupling
reaction [18], these ligands have received less attention in
the copper-catalyzed coupling of thiols with aryl halides [19-
20]. The possible reasons are that most efficient phosphine-
containing ligands are not easily synthesized and are air-
sensitive [12]. Diazaphospholanes are a kind of air-stable,
easily prepared ligands and have been used in transition-
metal-catalyzed reactions such as allylic alkylation and hy-
droformylation [21-22]. Recently, we also found that this
kind of phosphine-containing ligands could be successfully
applied to the copper-catalyzed N–arylation of alkyl or het-
erocyclic amines [23]. Inspired by these results, we intended
to extend our campaign of carbon-heteroatom bond forma-
tion. Herein, we would like to report an efficient copper-
catalyzed coupling of aryl iodides with thiols using an air-
stable diazaphospholane for synthesizing a variety of aryl
sulfides.
Using L4 as the ligand, a range of combinations of copper
source, bases, and solvent were also examined (Table 1). The
bases had significant influence on the reaction. NaOH was
the most appropriate base and other bases, such as KOtBu,
NaOtBu, K2CO3, Cs2CO3 and Na2CO3 gave somewhat lower
yields (Table 1, entries 5 and 7-11). Both CuBr and CuI were
satisfactory, whereas CuBr was comparatively better than
CuI. Cu2O performed improperly for the coupling reaction
(Table 1, entry 13). Polar solvents, DMSO and DMF were
more beneficial to the coupling reaction than toluene or di-
oxane (Table 1, entries 10 and 14-16). DMF performed as
the prime solvent produces diphenyl sulfide in the best yield
(Table 1, entry 14). We found that reducing the amount of
catalyst loading from 10 mol% to 5 mol% obviously de-
creased the yield (Table 1, entry 17). Furthermore, when the
reaction temperature was increased from 95 °C to110 °C, the
yield increased to 85 % (Table 1, entry 18). Hence, the opti-
mum reaction conditions for the C-S cross-coupling em-
ployed 10 mol% of CuBr, 10 mol% of L4, 2.0 equiv of
NaOH in DMF at 110 °C.
RESULTS AND DISCUSSION
Racemic N, N`-phthaloyl-2, 5-(2-hydroxylphenyl)-phenyl-
3,4-diazaphospholane (L4) was easily synthesized through a
one-pot combination of the azine of salicyaldehyde, phtha-
loyl chloride and phenylphosphine, which was reported by
Landis and coworkers [22], and L4 and other ligands were
The substrate scope of this reaction was then examined
using a variety of aryl iodides and thiols, which was summa-
rized in Table 2. In general, this reaction provided moderate
to good yields for all of the substrates. Yields did not vary
significantly between the reaction of the aryl iodides and
thiols with varying electronic nature of the substituents on
the aryl iodides. For example, 4-methoxyiodobenzene, an
electron-rich aryl iodide, provided 84% yield (Table 2, entry
5), and 4-trifluoromethyliodobenzene, an electron-poor aryl
iodide, gave a comparable yield of 87% (Table 2, entry 3).
*Address correspondence to this author at the Department of Chemistry,
Lishui University, Xueyuan Road, Lishui city 323000, Zhejiang Province, P.
R. China; Tel: +86 578 2271087; Fax: +86 578 2271 308;
E-mail: mhyang@lsu.edu.cn
1570-1786/11 $58.00+.00
© 2011 Bentham Science Publishers

588 Letters in Organic Chemistry, 2011, Vol. 8, No. 8
Yang et al.
Table 1. S-Arylation of Thiols in Different Conditionsa
NOH
H3CHN
NHCH3
O
O
NOH
OH
Ph
OH
L1
N
N
L2
Ph3P
L5
P
COOH
N
H
L3
(Racemic form, L4)
Entry
Ligand
Base
[Cu]
Solvent
Yield (%)d
1
2
---
L1
L2
L3
L4
L5
L4
L4
L4
L4
L4
L4
L4
L4
L4
L4
L4
L4
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
KOtBu
NaOtBu
K2CO3
NaOH
Na2CO3
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
CuBr
CuBr
CuBr
CuBr
CuBr
CuBr
CuBr
CuBr
CuBr
CuBr
CuBr
CuI
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
12
22
16
40
52
36
35
35
43
64
31
60
27
72
47
35
51
85
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17b
18c
Cu2O
CuBr
CuBr
CuBr
CuBr
CuBr
Toluene
dioxane
DMF
DMF
aReaction conditions: PhI (1.0 mmol), benzenethiol (1.2 mmol), [Cu] (0.1 mmol), ligands (0.1 mmol), base (2.0 mmol), solvents (1.5 ml), 10 h, 95 °C.
b5 mol % of rac-L4 and CuBr were used.
cat 110 °C.
dIsolated yield.
The electronic nature of the substituents on the thiols play an
important role in controlling the reactivity, and the electron-
withdrawing group, such as fluoro and carboxyl group bear-
ing on the aromatic ring, gave much lower yield than that of
electron-donating group (e. g. Methoxyl) (Table 2, entries 9-
10 vs entry 11). When benzenethiol was replaced with
naphthyl thiol, the yield decreased slightly (Table 2, entries
4-5 vs entries 14-15). The coupling reaction between bro-
mobenzene and benzenethiol under optimum reaction condi-
tions was also tested and diphenyl sulfide was obtained in
less than 10% yield.
standard. Mass spectra were taken using GC-MS spectrome-
ter (Varian 431 GC-Varian 220 MS). All of ArI and ArSH
were purchased from Acros and used without further purifi-
cation. Ligand L4 was prepared according to the literature
[23]. Unless otherwise specified, reactions were performed
under a nitrogen atmosphere.
General Procedure for Cu-catalyzed S-arylation of Thiols
A mixture of aryl iodides (1.0 mmol), thiols (1.2 mmol),
base (2.0 mmol), CuBr (0.1 mmol), ligand (0.1 mmol) and
1.5 mL of solvent was heated at the indicated temperature
for the specified time and then allowed to cool to room tem-
perature. Ethyl acetate (3 ml) and water (3 ml) were then
added to the reaction mixture. The organic phase was sepa-
rated, and the aqueous phase was further extracted with ethyl
EXPERIMENTAL
NMR data were recorded on a Bruker AMX-300 spec-
trometer with chemical shifts referenced to SiMe4 as internal

Diazaphospholane as an Efficient Ligand
Letters in Organic Chemistry, 2011, Vol. 8, No. 8
589
Table 2. Copuling of Aryl Iodides with ArSH
10 mol% CuBr
10 mol% L4
I
ArSH
+
ArS
R
NaOH, DMF,110 ˚C
R
1
2
3
Aryl iodide
Thiol
Product
Entry
Yield (%)
I
SH
S
1
90
84
87
1a
2a
3a
F
I
SH
F
S
2
3
1b
2b
3b
F3C
I
SH
F3C
S
1c
2c
3c
O2N
O2N
SH
4
92
I
S
S
S
2d
1d
3d
H3CO
I
SH
H3CO
5
6
84
82
1e
2e
3e
H3C
I
SH
H3C
1f
2f
3f
O
O
SH
7
8
81
89
I
S
2g
1g
3g
S
CH(CH3)2
(H3C)2HC
SH
I
I
I
2h
1h
1i
3h
SH
S
9
67
67
HOOC
COOH
3i
2i
2j
F
F
10
SH
S
1j
3j
H3CO
SH
I
I
S
OCH3
11
12
13
95
85
87
1k
1l
3k
2k
Br
SH
S
Br
2l
3l
SH
I
S
1m
2m
3m

590 Letters in Organic Chemistry, 2011, Vol. 8, No. 8
Yang et al.
Yield (%)
80
(Table 2). Contd…..
Aryl iodide
O2N
Thiol
Product
Entry
O2N
SH
14
S
I
2n
3n
1n
SH
H3CO
I
15
16
78
65
H3CO
S
1o
2o
2p
3o
SH
I
I
I
S
1p
3p
aReaction conditions: ArI (1.0 mmol), thiols (1.2 mmol), CuBr (0.1 mmol), L4 (0.1 mmol), NaOH (2.0 mmol), DMF (1.5 ml), 24 h, 110 °C.
bIsolated yield.
acetate (4 ꢀ 5ml). The combined organic phase was washed
with brine, dried over MgSO4, and concentrated in vacuum.
The residue was separated with flash column chromatograph
on silica gel.
4-Tolyl phenyl sulfide 3f [3] (Table 2, entry 6)
1H NMR(300 MHz, CDCl3) ꢁ ppm: 7.35-7.46 (m, 6H,),
7.24-7.32 (m, 3H). 13C NMR (75 MHz, CDCl3) ꢁ ppm:
137.4, 137.0, 132.1, 131.2, 130.0, 129.7, 128.9, 126.3, 21.0.
The Procedure for Synthesis of 2-Phenylthiobenzoic Acid
3i (Table 2, entry 9)
4-Phenylsulfanylacetophenone 3g [3] (Table 2, entry 7)
1H NMR (300 MHz, CDCl3) ꢁ ppm: 7.82 (d, J = 8.4 Hz,
2H), 7.49-7.52 (m, 4H), 7.21 (d, J = 8.4 Hz, 2H), 2.54 (s,
3H). 13C NMR (75 MHz, CDCl3) ꢁ ppm: 196.8, 144.6, 134.2,
133.6, 131.9, 129.5, 128.7, 128.5, 127.2, 26.2.
Following the general procedure using benzenethiol (1.2
mmol) and 2-iodobenzoic acid (1.0 mmol) provided the cou-
pling product as a white solid after washing the crude mix-
ture with water and dichloromethane, further acidification
with 1M HCl and extraction of the aqueous layer with di-
chloromethane.
4-Isopropylphenyl phenyl sulfide 3h [24] (Table 2, entry 8)
1H NMR (300 MHz, CDCl3) ꢁ ppm: 7.31-7.38 (m, 5H),
7.21-7.28 (m, 4H), 2.91-2.99 (m, 1H), 1.29 (d，J = 6.9 Hz,
6H). 13C NMR (75 MHz, CDCl3) ꢁ ppm: 149.1, 137.6, 132.7,
132.5, 130.8, 129.8, 128.1, 127.2, 34.5, 24.6.
Diphenyl sulfide 3a [3] (Table 2, entry 1)
1H NMR (300 MHz, CDCl3) ꢁ ppm: 7.24-7.39 (m, 10H).
13C NMR (75 MHz, CDCl3) ꢁ ppm: 127.0, 129.2, 131.0,
135.7.
2-Phenylthiobenzoic acid 3i [26] (Table 2, entry 9)
1H NMR(300 MHz, CDCl3) ꢁ ppm: 13.2 (s, br, 1H), 7.94
(d, J = 7.5 Hz, 1H), 7.51-7.55 (m, 5H), 7.36 (d, J = 7.5 Hz,
1H), 7.23 (d, J = 7.5 Hz, 1H), 6.75 (d, J = 7.8 Hz, 1H). 13C
NMR(75 MHz, CDCl3) ꢁ ppm: 167.5, 141.7, 135.2, 132.5,
132.3, 131.0, 130.2, 129.4, 127.9, 127.1, 124.8.
4-Fluorophenyl phenyl sulfide 3b [24] (Table 2, entry 2)
1H NMR (300 MHz, CDCl3) ꢁ ppm: 7.37-7.42 (m, 2H),
7.23-7.29 (m, 5H), 7.01-7.07 (m, 2H). 13C NMR (75 MHz,
CDCl3) ꢁ ppm: 161.4, 137.3, 134.7, 130.9, 129.9, 127.4,
117.2, 116.9.
3-Fluorophenyl phenyl sulfide 3j [3] (Table 2, entry 10)
1H NMR (300 MHz, CDCl3) ꢁ ppm: 7.33-7.45 (m, 6H),
7.06 (d, J = 7.8 Hz, 1H), 6.90-6.96 (m, 2H). 13C NMR (75
MHz, CDCl3) ꢁ ppm: 165.3, 140.0, 134.4, 133.2, 131.0,
130.1, 128.7, 125.8, 116.9, 114.1
4-Trifluoromethylphenyl phenyl sulfide 3c [24] (Table 2,
entry 3)
1H NMR (300 MHz, CDCl3) ꢁ ppm: 7.53-7.55 (m, 1H),
7.33-7.46 (m, 8H). 13C NMR (75 MHz, CDCl3) ꢁ ppm:
139.1, 134.1, 133.3, 133.1, 130.2., 130.0, 128.7, 126.7,
123.7.
4-Bormophenyl phenyl sulfide 3l [3] (Table 2, entry 12)
1H NMR (300 MHz, CDCl3) ꢁ ppm: 7.17 (d, J = 8.4 Hz,
2H), 7.24-7.41 (m, 7H). 13C NMR (75 MHz, CDCl3) ꢁ ppm:
135.5, 134.8, 132.2, 132.0, 131.5, 129.3, 127.5, 120.8.
3-Nitrophenyl phenyl sulfide 3d [25] (Table 2, entry 4)
1H NMR (300 MHz, CDCl3) ꢁ ppm: 8.0 (m, 1H), 7.85(s,
1H), 7.57-7.59 (m, 2H), 7.47-7.42 (m, 5H). 13C NMR (75
MHz, CDCl3) ꢁ ppm: 148.5, 139.5, 134.8, 133.3, 131.7,
130.9, 130.3, 129.3, 122.5, 121.5.
2-Naphthyl phenyl sulfide 3m [24] (Table 2, entry 13)
1H NMR (300 MHz, CDCl3) ꢁ ppm: 7.75-7.87 (m, 4H),
7.30-7.51(m, 8H). 13C NMR (75 MHz, CDCl3) ꢁ ppm: 136.5,
134.5, 133.7, 133.0, 131.7, 130.6, 130.0, 129.6, 129.4, 128.4,
128.1, 127.8, 127.3, 126.9.
4-Methoxyphenyl phenyl sulfide 3e [3] (Table 2, entry 5)
1H NMR (300 MHz, CDCl3) ꢁ ppm: 7.44 (d，J = 8.7Hz,
2H), 7.20-7.26 (m, 5H), 6.92 (d，J = 8.7Hz, 2H), 3.83 (s,
3H). 13C NMR (75 MHz, CDCl3) ꢁ ppm: 160.6, 139.3, 136.0,
129.6, 128.9, 126.4, 125.0, 115.7, 56.0.
3-Nitrophenyl-2- naphthyl sulfide 3n (Table 2, entry 14)
1H NMR (300 MHz, DMSO) ꢁ ppm: 8.08 （s, 1H）,
7.85-7.99 (m, 5H), 7.41-7.58 (m, 5H). 13C NMR (75 MHz,

Diazaphospholane as an Efficient Ligand
Letters in Organic Chemistry, 2011, Vol. 8, No. 8
591
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CDCl3) ꢀ ppm: 148.5, 139.4, 134.9, 133.6, 132.7, 130.9,
129.9, 129.7, 129.0, 127.9, 127.4, 127.2, 122.6, 121.5. MS
(EI) (m/z, %) : 281 ([M+], 100), 234 (16), 115 (9).
[7]
4-Methoxyphenyl-2- naphthyl sulfide 3o [24] (Table 2, en-
try 15)
[8]
1H NMR (300 MHz, DMSO) ꢀ ppm: 7.63-7.74 (m, 3H),
7.56 (s, 1H), 7.33-7.37 (m, 4H), 7.14-7.17 (m, 1H), 6.89 (d
，J = 7.0 Hz, 2H), 3.67 (s, 3H). 13C NMR (75 MHz, CDCl3)
ꢀ ppm: 160.1, 135.6, 135.5, 133.7, 131.7, 129.2, 128.0,
127.4, 127.2, 126.7, 126.4, 126.3, 123.5, 115.8, 55.6.
[9]
[10]
[11]
[12]
[13]
[14]
[15]
4-Iodolphenyl-2- naphthyl sulfide 3p (Table 2, entry 16)
1H NMR (300 MHz, CDCl3) ꢀ ppm: 7.87（s,1H）, 7.79-
7.76 (m, 2H), 7.58 (d, J = 8.4 Hz 2H), 7.50-7.47 (m, 2H),
7.39(m, 2H), 7.05(d, J = 7.0Hz, 2H). 13C NMR (75 MHz,
CDCl3) ꢀ ppm: 138.1, 136.9, 135.4, 132.5, 131.3, 130.7,
130.4, 129.7, 127.8, 126.5, 126.3, 125.5, 125.3 91.8. MS (EI)
(m/z, %) : 362 ([M+], 100), 234 (9), 115 (7).
CONCLUSION
In conclusion, this work illustrates the use of an air-stable
diazaphospholane as a ligand for the copper-catalyzed cou-
pling of aryl iodides with thiols and a variety of diaryl sul-
fides are synthesized in good yields. Methoxyl, trifluoro-
methyl, nitro, methyl, fluoro, acetyl, carboxyl and isopropyl
groups were all tolerated in this reaction system, which will
broaden the scope of C–S bond forming reactions.
[16]
[17]
[18]
[19]
[20]
[21]
ACKNOWLEDGEMENT
We gratefully acknowledge the Science Foundation of
Zhejiang Province (Y407081) for financial support.
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