Synthesis of unsymmetrical sulfides using ethyl potassium xanthogenate and recyclable copper catalyst under ligand-free conditions

Article abstract of DOI:10.1021/jo200793k

The synthesis of unsymmetrical sulfides has been achieved in good to excellent yields with inexpensive ethyl potassium xanthogenate via cross-coupling reaction using recyclable CuO nanoparticles under ligand-free conditions.The copper oxide nanoparticles can be recovered and reused up to five cycles without loss of activity.

Full text of DOI:10.1021/jo200793k

NOTE
pubs.acs.org/joc
Synthesis of Unsymmetrical Sulfides Using Ethyl Potassium
Xanthogenate and Recyclable Copper Catalyst under
Ligand-Free Conditions
Vijay Kumar Akkilagunta and Rama Rao Kakulapati*
Organic Chemistry Division-I, Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad 500607, India
S Supporting Information
b
ABSTRACT: The synthesis of unsymmetrical sulfides has been achieved in
good to excellent yields with inexpensive ethyl potassium xanthogenate via
cross-coupling reaction using recyclable CuO nanoparticles under ligand-
free conditions.The copper oxide nanoparticles can be recovered and reused
up to five cycles without loss of activity.
he construction of biological and synthetically important
CꢀS bond through cross-coupling reactions using various
However, 5 mol % resulted in a slight decrease in the yield, and
hence, 7 mol % of the catalyst was used for further reactions. The
catalytic activity of bulk CuO as catalyst was significantly low as
compared to the CuO nps (19, Table 1). From this we infer
that the reaction might be taking place over the surface of the
nanoparticles, whereas the reaction did not take place in the absence
of the copper catalyst (18, Table 1). This has clearly proved that the
presence of a copper catalyst was crucial for the reaction.9
We further tested various aryl halides viz. bromo- and iodo-
benzenes with the optimized conditions. The yields of aryl sulfides
after two iterations were remarkably high with aryl iodides when
compared to aryl bromides (Table 2, entries 1, 2). Unfortunately,
the yields of the coupling between Ar-Br and Ar0-Br are dis-
couraging (Table 2, entry 3). Aryl iodides with different substit-
uents like nitro, methoxy, isopropyl, tert-butyl, chloro, and fluoro
were tested for their reactivities. The reaction of 4-nitroiodo-
benzene was faster as expected followed by chloro, fluoro, alkyl,
and methoxy substituents, which after the second iteration with
the respective aryl halides, gave good to excellent yields of the
coupled products (Table 2). Moreover, the double thiolation of
p-diiodobenzene required 2 equiv each of xanthogenate, KOH,
and iodobenzene to form the desired cross-coupled product in
78% yield (entry 6, Table 2).
We also succeeded in obtaining the heterothioethers in
moderate yields with 2-bromothiophene and 2-bromopyridine
in 73% and 66% yields, respectively (entries 14 and 15, Table 2).
To broaden the substrate scope, we investigated the synthesis of
various thioethers using alkyl halides in the second iteration.
Interestingly, alkyl halides such as cyclohexyl-, n-hexyl-, n-pentyl-,
n-decyl-, and 2-bromoethanol gave the desired products in
moderate to excellent yields. Nevertheless, the yields of the
products were moderate in the case of 2-bromonaphthalene with
both aryl and alkyl halides (Tables 2 and 3). To expand the utility
of this methodology, a reaction on a higher scale was performed
T
transition metals such as Pd,1 Cu,2 Fe,3 Co,4 In,5 Ni,6 etc. has been
well explored over the years owing to various developments
in the area of cross-coupling reactions. Most of these methods
require metal reagents in combination with different ligands for
achieving smooth conversions. The disadvantages, like metal accu-
mulations and organic waste generation associated with these
methods, make them less adoptable for the sustainable synthesis
of various sulfide molecules. In view of these drawbacks, the
development of efficient protocols using recyclable catalysts devoid
of ligands would address the problems associated with the metal
accumulation and toxic waste generation in the environment. This is
the main focus in the current organic research due to the growing
concern for sustainable chemistry. Cross-coupling reactions
using copper oxide nanoparticles (CuO nps) have the advantages
of recyclability and absence of external ligands that minimize the
organic waste generation as compared with the conventional
catalytic systems. So in continuation of our sustainable approach
using CuO nps for cross-coupling reactions,7 we report herein
the synthesis of unsymmetrical sulfides utilizing ethyl potassium
xanthogenate,8 CuO nps, and aryl halides under ligand-free conditions.
Initially, we studied the reaction of phenyl iodide with
potassium ethyl xanthogenate for the formation of diaryl sulfide
in DMSO at 85 °C. Phenyl iodide reacted completely within 15 h
as monitored by GC to form phenylxanthogenate ester in situ,
which, upon addition of KOH and 4-methyliodobenzene, af-
forded the CꢀS cross-coupled product (summarized in Table1).
The solvents like 1,4-dioxane, toluene, NMP, DMF, and acet-
onitrile, in combination with the bases such as Cs2CO3, Li2CO3,
K2CO3, Na2CO3, t-BuOK, and t-BuOLi, were found to be
inefficient in achieving a good conversion of the coupled product.
We observed 97% yield of the aryl sulfide formation with DMSO
and KOH as the solvent and base, respectively. The optimum
amount of CuO required was found to be 7 mol % to obtain the
maximum yield of the coupled product, whereas nearly the same
yield was obtained when 10 and 7 mol % of CuO was used.
Received: April 21, 2011
Published: July 06, 2011
r
2011 American Chemical Society
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|

The Journal of Organic Chemistry
NOTE
Table 1. Optimization of Solvents and Bases for CuO Nano Catalyzed Synthesis of Thioethersa
entry
copper
solvent
base
yield (%)
1
2
CuO nano
CuO nano
CuO nano
CuO nano
CuO nano
CuO nano
CuO nano
CuO nano
CuO nano
CuO nano
CuO nano
CuO nano
CuO nano
CuO nano
CuO nano
CuO nano
CuO nano
DMF
KOH
88
75
43
38
58
55
46
95b
97c
89d
32
24
29
25
14
67
dioxane
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
KOH
3
K2CO3
Li2CO3
t-BuOK
t-BuOLi
K3PO4
KOH
4
5
6
7
8
9
KOH
10
11
12
13
14
15
16
17
18
19
KOH
Cs2CO3
Cs2CO3
KOH
THF
CH3CN
Toluene
NMP
KOH
KOH
KOH
H2O
KOH
DMSO
KOH
<5
39
CuO
DMSO
KOH
a Reaction conditions: iodobenzene (1 mmol), CuO nanopowder (7 mol %), solvent (2 mL), base (3.0 equiv), p-MePhI (1.0 equiv), ethyl potassium
xanthogenate (1.0 equiv), 85 °C. b 5 mol % CuO nano. c 7 mol % CuO nano. d 10 mol % CuO nano.
Scheme 1. CuO Nano Catalyzed Synthesis of Thioethers on
5 mmol Scale
Scheme 2. Evidence for the Formation of the Aryl Xantho-
genate Ester
with 5 mmol of substrates. It is noteworthy that this reaction was
successful on an increased scale affording 93% yield of the
product (Scheme 1). Though a laboratory-scale procedure, this
indicates that it has a potential for further increased scale.
We suggest a possible mechanistic pathway based on the one
suggested by Zhang et al. in the arylation of heterocyclic CꢀH
bonds catalyzed by CuO nano.10 First, the aryl halide forms a
CꢀS bond with the xanthogenate followed by the hydrolysis of
the aryl xanthogenate ester to generate the aryl thiol salt. This
then undergoes a second cross-coupling reaction with the aryl
halide to form the final product (Figure 1). The formation of the
aryl xanthogenate ester during the reaction was confirmed by a
control experiment in which 4-methoxyiodobenzene was reacted
with potassium ethylxanthogenate in the presence of CuO nps
(Scheme 2). To isolate the intermediate, O-ethyl-S-4-methox-
yphenyl carbonodithioate, the reaction was arrested after 4.5 h,
and the product was isolated as pale yellow oil in 30% yield, which
was completely characterized by 1H and 13C NMR (Scheme 2).
In the case of alkyl halides, the control experiment in the
absence of copper for the second iteration was found to be base
catalyzed and noncatalytic with respect to the copper catalyst. To
find out whether the reaction was catalyzed by CuO nano
particles or leached copper species,11 we carefully analyzed the
reaction mixtures after each iteration (iterations 1 and 2) using
ICP-AES. It was found that around 0.8 and 1.2 ppm of copper
had leached into the solution after the first and second iterations,
respectively. Another control experiment was performed to
elucidate the extent to which the leached species can catalyze
the reaction. The catalyst was separated by centrifugation from
the reaction mixture after 6.5 h to get 50% conversion of the
iodobenzene with potassium ethyl xanthogenate. The filtered
reaction mixture was further continued to react after removal of
the catalyst, and the conversion was monitored by GC. There was
no progress in the conversion of iodobenzene even after 10 h.
Hence, from these experiments we conclude that the true catalyst
was the heterogeneous CuO nps and not the leached copper
species. In another experiment, the O-ethyl-S-4-methoxyphenyl
carbonodithioate was allowed to react with iodobenzene in the
absence of copper, with KOH as the base. The progress of the
reaction was monitored by GC. It was found that only the ester
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Table 2. CuO Nano Catalyzed Synthesis of Thioethers with Various Aryl Halidesa
a Reaction conditions: (i) iteration 1: CuO nanopowder (7 mol %), aryl halide (1) (1 mmol), ethylpotassium xanthogenate (1.0 equiv), DMSO (2 mL)
stirred for specified time at 85 °C; (ii) iteration 2: KOH (3.0 mmol), aryl halide (2) (1.0 mmol), 85 °C. b Ethyl potassium xanthogenate (2.0 mmol),
KOH (6.0 mmol), aryl halide (2) (2.0 mmol).
underwent hydrolysis generating the thiol, and no aryl sulfide
formation was detected in the reaction mixture. This further
confirmed that both the steps of the cross-coupling reaction, as
shown in Table 1, are catalyzed by copper.
Furthermore, we tested the recyclability of CuO nps to
ascertain the sustainability of this methodology. The aqueous
layer containing CuO nps was carefully centrifuged and washed
several times with water and acetone after workup. The nano-
particles were retrieved, oven-dried at 80 °C for 5 h, and used for
the next cycle. Likewise, the recovered CuO nps were recyclable
up to five cycles (Table 4).
The native and used CuO nanoparticles were analyzed by
powder XRD and TEM analysis. It was observed from the
TEM studies that the used CuO nanoparticles were intact in
size and shape even after five cycles as compared with the
native catalyst. The powder XRD spectra also confirmed the
intactness of the particles after five cycles (see the Supporting
Information).
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NOTE
Table 3. CuO Nano Catalyzed Synthesis of Thioethers with
Various Alkyl Halidesa
Table 4. Recycle of Copper Oxide Nanoparticlesa
entry
CuO recovered (%)
yield (%)
cycle 1
cycle 2
cycle 3
cycle 4
cycle 5
99
97
96
95
92
95
94
92
90
89
a Reaction conditions: iteration 1: CuO nanopowder (7 mol %),
iodobenzene (1 mmol), ethyl potassium xanthogenate (1.0 equiv),
DMSO (2 mL); iteration 2: KOH (3.0 equiv), iodobenzene (1.0 mmol),
85 °C.
of activity. The ligand-free and reusable copper combination
makes this a sustainable method for the synthesis of unsymme-
trical thioethers.
’ EXPERIMENTAL SECTION
General Information. Aryl halides, alkyl halides, CuO nanopow-
der (<50 nm), and dry solvents were purchased from commercial
sources. Column chromatography was carried out using silica gel
(60ꢀ120 mesh size). Visualization was accomplished with UV lamp,
I2 stain. 1H and 13C NMR spectra were recorded at 300 and 75 MHz,
respectively, in CDCl3 using TMS as the internal standard. Chemical
shifts were reported in parts per million (ppm) downfield from TMS.
Typical Procedure for Phenyl p-Tolylsulfane Synthesis
Using Ethyl Potassium Xanthogenate. A mixture of iodobenzene
(204 mg, 1 mmol), CuO nanopowder (5.5 mg, 7 mol %), and ethyl
potassium xanthogenate (160.30 mg, 1 mmol) was stirred in DMSO
(2 mL) in a 25 mL round-bottom flask equipped with a reflux condenser
at 85 °C under nitrogen atmosphere. After complete conversion of the
iodobenzene as monitored by GCꢀMS, the reaction mixture was
allowed to cool to room temperature, 4-iodotoluene (218.1 mg, 1 mmol)
and KOH (168 mg, 3 mmol) were added, and the mixture was heated at
85 °C for 20 h. The reaction mixture was allowed to cool to room
temperature, water (5 mL) was added, and the product was extracted
with ethyl acetate (2 ꢁ 5 mL). The combined organic extracts were dried
with anhydrous Na2SO4, and the solvent and the volatiles were
completely removed under vacuum to give the crude product, which
was purified by column chromatography on silica gel (petroleum
a Reaction conditions: iteration 1: CuO nanopowder (7 mol %), aryl
halide (1) (1 mmol), ethyl potassium xanthogenate (1.0 equiv), DMSO
(2 mL) stirred for specified time at 85 °C, iteration 2: KOH (3.0 equiv),
alkyl halide (2) (1.0 mmol), 50 °C.
In conclusion, we have developed an efficient synthesis of
unsymmetrical thioethers using copper oxide nanoparticles without
the use of any external ligands. The copper oxide nanoparticles
can be easily recovered and reused up to five cycles without loss
Figure 1. Possible mechanistic pathway for the synthesis of sulfides with xanthogenate.
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NOTE
ether/ethyl acetate) to afford the corresponding coupling product in
97% yield. Phenyl (p-tolyl) sulfane (3a):4 colorless oil; 1H NMR (300
MHz, CDCl3, TMS) δ = 7.28 (d, J = 8.0 Hz, 2H), 7.25ꢀ7.14 (m, 5H),
7.10 (d, J = 8.0 Hz, 2H), 2.32 (s, 3H); 13C NMR (75 MHz, CDCl3,
TMS) δ = 137.5, 137.0, 132.2, 131.2, 130.0, 129.7, 129.0, 126.3, 21.1
Typical Procedure for Pentyl Phenylsulfane Synthesis
Using Ethyl Potassium Xanthogenate. A mixture of iodobenzene
(204 mg, 1 mmol), CuO nanopowder (5.5 mg, 7 mol %), and ethyl
potassium xanthogenate (160.30 mg, 1 mmol) was stirred in DMSO
(2 mL) in a 25 mL round-bottom flask equipped with a reflux condenser
at 85 °C under nitrogen atmosphere. After complete conversion of the
iodobenzene as monitored by GCꢀMS, the reaction mixture was
allowed to cool to room temperature, 1-bromopentane (151 mg, 1 mmol)
and KOH (168 mg, 3 mmol) were added, and the mixture was heated at
50 °C for 2 h. The reaction mixture was allowed to cool to room
temperature, water (5 mL) was added, and the product was extracted
with ethyl acetate (2 ꢁ 5 mL). The combined organic extracts were dried
with anhydrous Na2SO4, and the solvent and the volatiles were completely
removed under vacuum to give the crude product, which was purified by
column chromatography on silica gel (petroleum ether/ethyl acetate) to
afford the corresponding coupling product in 93% yield. Pentyl phe-
nylsulfane (3n):5a colorless oil; 1H NMR (300 MHz, CDCl3, TMS) δ =
7.27ꢀ7.17 (m, 4H), 7.14ꢀ7.05 (m, 1H), 2.86 (t, 2H, J = 7.5 Hz), 1.63
(m, 2H), 1.45ꢀ1.25 (m, 4H), 0.89 (t, J = 7.5 Hz, 3H); 13C NMR (75
MHz, CDCl3, TMS) δ = 136.9, 128.6, 125.5, 33.4, 30.9, 28.7, 22.1, 13.8
Experimental Procedure for Recycling of CuO Nanoparti-
cles. The aqueous layer containing CuO nanoparticles was carefully
centrifuged at 10000 rpm for 60 min and washed several times with
water and acetone after workup of the reaction mixture. The retrieved
nanoparticles were oven-dried at 80 °C for 5 h and used for the next cycle.
(4-Isopropylphenyl)phenylsulfane (3b):5a colorless oil; 1H
NMR (300 MHz, CDCl3, TMS) δ = 7.44ꢀ 7.11 (m, 9H), 3.03ꢀ2.76
(m, 1H), 1.28 (d, J = 7.0 Hz, 6H); 13C NMR (75 MHz, CDCl3, TMS)
δ = 148.3, 136.8, 131.9, 131.7, 130.0, 129.0, 128.1, 127.3, 127.1, 126.4,
33.7, 23.8.
(Naphthalen-2-yl)phenylsulfane (3j):4 white solid; mp 49 °C;
1H NMR (300 MHz, CDCl3, TMS) δ = 7.96ꢀ7.62 (m, 4H), 7.58ꢀ7.05
(m, 8H); 13C NMR (75 MHz, CDCl3, TMS) δ = 135.7, 133.7, 132.9,
132.2, 130.8, 129.8, 129.1, 128.8, 128.6, 127.6, 127.3, 126.9, 126.5, 126.1.
(4-Chlorophenyl)naphthalen-1-ylsulfane (3k):5a colorless
1
oil; H NMR (300 MHz, CDCl3, TMS) δ = 8.31 (dd, J = 3.0 Hz,
1H), 7.87ꢀ7.84 (m, 2H), 7.68ꢀ7.66 (m, 1H), 7.49 (dd, J = 3.0, 3.7 Hz,
2H), 7.42 (t, J = 8.5 Hz, 1H), 7.14 (d, J = 9.0 Hz, 2H), 7.04 (d, J = 9.0 Hz,
2H); 13C NMR (75 MHz, CDCl3, TMS) δ = 135.7, 134.2, 133.5, 133.0,
131.8, 130.3, 129.7, 129.6, 129.1, 128.6, 127.1, 126.5, 125.8, 125.4.
2-(Phenylthio)thiophene (3l):3c colorless oil; H NMR (300
1
MHz, CDCl3, TMS) δ = 7.05 (t, J = 7.2 Hz, 1H), 7.05ꢀ7.19 (m, 3H),
7.20ꢀ7.26 (m, 3H), 7.43 (d, J = 8.0 Hz, 1H); 13C NMR (75 MHz,
CDCl3, TMS) δ = 124.3, 125.9, 127.0, 127.9, 128.9, 131.2, 135.9, 138.6.
2-(Phenylthio)pyridine (3m):3c colorless oil; 1H NMR (300
MHz, CDCl3, TMS) δ = 6.93 (d, 1H), 6.60ꢀ6.99 (m, 1H), 7.39ꢀ7.45
(m, 4H), 7.56ꢀ7.60 (m, 2H), 8.41 (d, J = 7.2 Hz, 1H); 13C NMR (75
MHz, CDCl3, TMS) δ = 119.9, 121.3, 129.1, 129.6 (2C), 131.1, 134.9
(2C), 136.7, 149.6, 161.5.
Cyclohexylphenylsulfane (3o):1e colorless oil; H NMR (300
1
MHz, CDCl3, TMS) δ = 7.38 (d, J = 8.0 Hz, 2H), 7.30ꢀ7.17 (m, 3H),
3.14ꢀ3.05 (m, 1H), 2.01ꢀ1.92 (m, 2H), 1.81ꢀ1.74 (m, 2H),
1.65ꢀ1.57 (m, 1H), 1.44ꢀ1.20 (m, 5H); 13C NMR (75 MHz, CDCl3,
TMS) δ = 135.1, 131.8, 128.7, 126.5, 46.5, 33.3, 26.0, 25.7.
n-Decylphenylsulfane (3p):5b colorless oil; 1H NMR (300 MHz,
CDCl3, TMS) δ = 7.31ꢀ 7.04 (m, 5H), 2.87 (t, J = 7.0, 2H), 1.70 (m,
2H), 1.44ꢀ1.12 (m, 14H), 0.88 (t, J = 7.0, 3H); 13C NMR (75 MHz,
CDCl3, TMS) δ = 137.4, 129.4, 125.9, 33.6, 31.9, 29.5, 29.3, 29.2, 28.8,
22.7, 14.1
n-Pentyl-p-tolylsulfane (3q):5b colorless oil; 1H NMR (300
MHz, CDCl3, TMS) δ = 7.17 (d, J = 8.5 Hz, 2H), 7.02 (d, J = 8.5 Hz,
2H), 2.82 (t, J = 7.5 Hz, 2H), 2.31 (s, 3H), 1.60 (m, 2H), 1.43ꢀ1.25 (m,
4H), 0.89 (t, J = 7.0 Hz, 3H); 13C NMR (75 MHz, CDCl3, TMS) δ =
135.7, 133.1, 129.7, 129.5, 34.3, 30.9, 28.9, 22.2, 20.9, 13.9
n-Hexyl-p-tolylsulfane (3r):5b colorless oil; 1H NMR (300 MHz,
CDCl3, TMS) δ = 7.15 (d, J = 7.5 Hz, 2H), 6.99 (d, J = 7.5 Hz, 2H), 2.80
(t, J = 7.0 Hz, 2H), 2.29 (s, 3H), 1.64ꢀ1.51 (m, 2H), 1.45ꢀ1.16 (m,
6H), 0.86 (t, J = 7.0 Hz, 3H); 13C NMR (75 MHz, CDCl3, TMS) δ =
135.8, 133.1, 131.0, 129.7, 129.6, 34.4, 31.4, 29.2, 28.0, 22.6, 20.98, 14.0.
n-Decyl-p-tolylsulfane (3s):5a colorless oil; 1H NMR (300 MHz,
CDCl3, TMS) δ = 7.17 (d, J = 8.0 Hz, 2H), 7.01 (d, J = 8.0 Hz, 2H), 2.82
(t, J = 7.5 Hz, 2H), 2.31 (s, 3H), 1.59 (m, 2H), 1.42ꢀ1.17 (m, 14H),
0.88 (t, J = 7.0 Hz, 3H); 13C NMR (75 MHz, CDCl3, TMS) δ = 135.7,
133.1, 129.7, 129.5, 34.3, 31.8, 29.5, 29.3, 29.2, 29.1, 28.8, 22.6,
20.9, 14.1.
(4-Chlorophenyl)phenylsulfane (3c):2e colorless oil; 1H NMR
(300 MHz, CDCl3, TMS) δ = 7.40ꢀ7.22 (m, 7H), 7.16 (d, J = 8.5 Hz,
2H); 13C NMR (75 MHz, CDCl3, TMS) δ = 135.4, 134.7, 132.1, 132.0,
131.4, 129.3, 127.5.
1, 4-Bis(phenylthio)benzene (3d):12 white solid; mp 73ꢀ74 °C;
1H NMR (300 MHz, CDCl3, TMS) δ = 7.73 (s, 6H), 7.50ꢀ7.43 (m, 2H),
7.32ꢀ7.23 (m, 6H); 13C NMR (75 MHz, CDCl3, TMS) δ = 133.3, 133.2,
130.5, 130.4, 129.4, 127.6.
(4-tert-Butylphenyl)phenylsulfane (3e):5a colorless oil; 1H
NMR (300 MHz, CDCl3, TMS) δ = 7.35ꢀ7.08 (m, 9H), 1.31 (s,
9H); 13C NMR (75 MHz, CDCl3, TMS) δ = 150.5, 136.7, 131.4, 130.4,
130.2, 129.0, 126.7, 126.2, 35.0, 31.2.
4
1
Cyclohexyl-p-tolylsulfane (3t): colorless oil; H NMR (300
MHz, CDCl3, TMS) δ = 7.23 (d, J = 8.0 Hz, 2H), 7.02 (d, J = 8.0 Hz,
2H), 3.01ꢀ2.85 (m, 1H), 2.32 (s, 3H), 1.98ꢀ1.51 (m, 5H), 1.42ꢀ1.20
(m, 5H); 13C NMR (75 MHz, CDCl3, TMS) δ = 136.7, 132.7, 131.1,
129.4, 47.0, 33.3, 26.0, 25.7, 21.0
(4-Nitrophenyl)phenylsulfane (3f):2d yellow solid; mp 52ꢀ55 °C;
1H NMR (300 MHz, CDCl3, TMS) δ = 8.05 (d, J = 9.0 Hz, 2H), 7.54
(m, 2H), 7.46 (m, 3H), 7.16 (d, J = 9.0 Hz, 2H); 13C NMR (75 MHz,
CDCl3, TMS) δ = 148.4, 145.2, 134.6, 130.3, 129.9, 129.5, 126.6,
123.9.
Hexylnaphthalen-1-ylsulfane (3u):5a colorless oil; H NMR
1
(4-Methoxyphenyl)phenylsulfane (3g):4 colorlessoil;1H NMR
(300 MHz, CDCl3, TMS) δ = 7.42 (d, J = 8.0 Hz, 2H), 7.23ꢀ7.19 (m,
2H), 7.16ꢀ7.12(m, 3H), 6.82 (d, J =8.0 Hz, 2H), 3.78 (s, 3H); 13CNMR
(75 MHz, CDCl3, TMS) δ = 159.7, 138.5, 135.3, 128.8, 128.1, 125.7,
124.2, 114.9, 55.3.
(300 MHz, CDCl3, TMS) δ = 8.34 (d, J = 8.5 Hz, 1H), 7.79 (d, J = 7.5
Hz, 1H), 7.67 (d, J = 7.5 Hz, 1H), 7.48 (q, J = 7.2 Hz, 3H), 7.35 (t, J = 7.5
Hz, 1H), 2.93 (t, J = 7.5 Hz, 2H), 1.65 (m, 2H), 1.49ꢀ1.20 (m, 6H), 0.88
(t, J = 7.0 Hz, 3H).13C NMR (75 MHz, CDCl3, TMS) δ = 134.2, 133.8,
132.8, 128.4, 127.2, 126.7, 126.19, 126.1, 125.5, 124.9, 34.1, 31.3, 29.1,
28.5, 22.5, 14.0.
Diphenylsulfane (3h):4 colorless oil; 1H NMR (300 MHz, CDCl3,
TMS) δ = 7.34ꢀ7.14 (m, 10H); 13C NMR (75 MHz, CDCl3, TMS) δ =
135.7, 131.0, 129.1, 127.0.
2-(Phenylthio)ethanol (3v): pale yellow oil; 1H NMR (300 MHz,
CDCl3, TMS) δ = 7.35ꢀ7.33 (m, 2H), 7.27ꢀ7.22 (m, 2H), 7.18ꢀ7.14
(m, 1H), 3.68 (m, 2H), 3.05 (t, J = 6.1 Hz, 2H), 2.38 (m, 1H); 13C NMR
(75 MHz, CDCl3, TMS) δ = 134.8, 129.7, 128.9, 126.3, 60.2, 36.7. Anal.
Calcd for C8H10S: C, 62.30; H, 6.54; S, 20.79. Found: C, 62.00; H, 6.51;
S, 20.21.
4
1
(4-Fluorophenyl)phenylsulfane (3i): colorless oil; H NMR
(300 MHz, CDCl3, TMS) δ = 7.36ꢀ7.30 (m, 2H), 7.26ꢀ7.13 (m, 5H),
6.99 (t, J = 8.3 Hz, 2H); 13C NMR (75 MHz, CDCl3, TMS) δ = 163.9,
160.6, 136.6, 134.0, 133.9, 130.1, 129.8, 129.1, 126.7, 116.5, 116.2.
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The Journal of Organic Chemistry
NOTE
(Naphthalene-2-yl)pentylsulfane (3w):5a colorless oil; 1H
NMR (300 MHz, CDCl3, TMS) δ = 7.73ꢀ7.66 (m, 4H), 7.42ꢀ7.33
(m, 3H), 2.97 (t, J = 7.5 Hz, 2H), 1.68 (m, 2H), 1.48 ꢀ 1.24 (m, 4H),
0.90 (t, J = 7.5 Hz, 3H); 13C NMR (75 MHz, CDCl3, TMS) δ = 134.2,
133.8, 132.8, 128.5, 127.3, 126.7, 126.2, 126.1, 125.5, 124.9, 34.1, 31.0,
28.8, 22.2, 13.9
(7) (a) Reddy, V. P.; Vijay, K. A.; Rao, K. R. J. Org. Chem. 2010,
75, 8720. (b) Reddy, V. P.; Vijay, K. A.; Swapna, K.; Rao, K. R. Org. Lett.
2009, 11, 951. (c) Reddy, V. P.; Vijay, K. A.; Rao, K. R. Tetrahedron Lett.
2010, 51, 3181.
(8) Prasad, D. J. C.; Sekar, G. Org. Lett. 2011, 13, 1008.
(9) For transition-metal-free cross-coupling reactions, see: (a) Cano,
R.; Ramon, D. J.; Yus, M. J. Org. Chem. 2011, 76, 654. (b) Yuan, Y.;
Thome, I.; Kim, S. W.; Chen, D.; Beyer, A.; Bonnamour, J.; Zuidema, E.;
Chang, S.; Bolm, C. Adv. Synth. Catal. 2010, 17, 2892.
(10) Zhang, W.; Zeng, Q.; Zhang, X.; Tian, Y.; Yue, Y.; Guo, Y.;
Wang, Z. J. Org. Chem. 2011, 76, 4741.
(11) (a) Pachon, L. D.; Rothenberg, G. Appl. Organomet. Chem.
2008, 22, 288. (b) Gaikwad, A. V.; Holuigue, A.; Thathagar, M. B.; ten
Elshof, J. E.; Rothenberg, G. Chem.—Eur. J. 2007, 13, 6908. (c)
Thathagar, M. B.; Beckers, J.; Rothenberg, G. Adv. Synth. Catal. 2003,
345, 979.
O-Ethyl S-4-methoxyphenyl carbonodithioate (3x): pale
1
yellow oil; H NMR (300 MHz, CDCl3, TMS) δ = 7.48 (d, J = 8.8
Hz, 2H), 6.86 (d, J = 8.8 Hz, 2H), 3.81 (s, 3H), 2.76 (q, J = 7.8, 2H), 1.32
(t, J = 7.3 Hz, 3H); 13C NMR (75 MHz, CDCl3, TMS) δ = 159.4, 133.9,
131.6, 114.5, 55.4, 32.5, 29.7, 14.1. Anal. Calcd for C10H12S2: C, 52.60;
H, 5.30; S, 28.09. Found: C, 52.45; H, 5.12; S, 27.89.
’ ASSOCIATED CONTENT
S
(12) Bunnett, J. F.; Creary, X. J. Org. Chem. 1974, 39, 3611.
Supporting Information. General experimental proce-
b
dures, catalyst charaterization (TEM images, powder XRD of
native and used CuO nano), and H, 13C NMR for all com-
1
pounds. This material is available free of charge via the Internet at
http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Fax: +91-40-27160512. E-mail: kakulapatirama@gmail.com.
’ ACKNOWLEDGMENT
V.K.A. is grateful to the University Grants Commision (UGC),
New Delhi, for the research fellowship.
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