Copper-catalyzed direct thiolation of azoles with aliphatic thiols

Article abstract of DOI:10.1039/c1ob05395g

Cu(ii)-catalyzed direct thiolation of azoles with thiols is described via intermolecular C-S bond formation/C-H functionalization under oxidative conditions. Both aryl thiols and aliphatic thiols are used as coupling partners, and furnished the thiolation

Full text of DOI:10.1039/c1ob05395g

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PAPER
Copper-catalyzed direct thiolation of azoles with aliphatic thiols†
An-Xi Zhou, Xue-Yuan Liu,* Ke Yang, Shu-Chun Zhao and Yong-Min Liang
Received 14th March 2011, Accepted 21st April 2011
DOI: 10.1039/c1ob05395g
Cu(II)-catalyzed direct thiolation of azoles with thiols is described via intermolecular C–S bond
formation/C–H functionalization under oxidative conditions. Both aryl thiols and aliphatic thiols are
used as coupling partners, and furnished the thiolation products in moderate to good yields. The
reaction is compatible with a wide range of heterocycles including oxazole, thiazole, imidazole and
oxadiazole.
thiolation of a benzoxazole C–H bond with diaryl disulfides and
aryl thiols.9
Introduction
The direct arylation,10 alkenylation11 and amination12 of hetero-
cycles through the transition-metal-catalyzed C–H functionaliza-
tion has been developed considerably. However, only one example
of the formation of a C–S bond through the analogous reaction
has been reported,9 and the application of aliphatic thiols in
the reaction of direct C–H functionalization/intermolecular C–S
bond formation is still unexplored. These drawbacks have limited
this reaction which prepares sulfides with biological activity or
sulfides that lead to biologically active compounds. Thus, further
development for direct C–H thiolation is strongly desired. Herein,
we report an efficient copper-catalyzed direct thiolation of azoles
with aliphatic thiols.
Transition-metal-catalyzed C–S bond formation has been a sub-
ject of intense study due to the importance of aryl sulfides,
aliphatic-heteroaromatic sulfides and their derivatives in numerous
biological and pharmaceutically active compounds.1 In the past
decade, the transition-metal-catalyzed cross-coupling reactions of
ArX (X = Cl, Br, I, OTf and B(OH)2) with sulfur nucleophiles, such
as, aryl thiols, aliphatic thiols and diaryl disulfides, are powerful
tools for the formation of C–S bonds.2
In contrast, with the increasing requirements for environmen-
tally benign and atom economic processes, the transition-metal-
catalyzed C–H functionalization has received substantial attention
in recent years, as a potentially more efficient and complementary
process to the conventional cross-coupling methodology. How-
ever, in this aforementioned class of reactions, much effort has been
paid on C–C and C–hetero bonds. The formation of a C–S bond via
transition-metal-catalyzed C–H activation was not realized until
Yu and co-workers first reported the thiolation of 2-phenylpyridine
with PhSH and MeSSMe using Cu(OAc)2 as a catalyst under
oxygen atmosphere.3 Recently, Dong and co-workers described
the Pd-catalyzed direct sulfonylation of a 2-phenylpyridine C–
H bond with ArSO2Cl.4 Very recently, Qing described a Cu(II)-
mediated reaction of an aryl C–H bond with DMSO for ortho-
substituted methylthiolation.5 Meanwhile, Cheng reported CuI-
catalyzed thiolation of the di- or trimethoxyl- benzene arene C–
H bond with ArSSAr.6 Besides the aforementioned aromatic C–S
bond formation, the related counterparts on heterocycles were also
revealed. Doi and Batey independently illustrated Pd-catalyzed
reactions to produce 2-substituted benzothiazoles through C–H
functionalization/intramolecular C–S bond formation.7 Subse-
quently, Li and co-workers disclosed iron-catalyzed sulfenylation
of an indole C–H bond with diaryl disulfides, with a catalytic
amount of iodine supplied to promote the reaction.8 Additionally,
Fukuzawa and co-workers demonstrated a copper-catalyzed direct
Results and discussion
Our initial efforts focused on the direct thiolation of benzoxazole
(1a) (0.4 mmol) with 1-dodecanethiol (2a) (0.6 mmol) by using a
stoichiometric amount of Cu(OAc)2·H2O (2.2 equiv.) in DMSO
under air atmosphere; the desired product was obtained in 27%
isolated yield in 8 h (Table 1, entry 1). Encouraged by this
preliminary result, we further investigated the reaction parameters
and found that toluene was a better reaction medium than other
solvents such as DMSO, DMF, xylene and dioxane (Table 1,
entries 2–5). However, the desired cross-coupling was not observed
when the amount of Cu(OAc)2·H2O was reduced to 20 mol%
(Table 1, entry 6). We hypothesized that stoichiometric amounts
of copper were needed because it was consumed as a base and an
oxidant. With use of 20 mol% of Cu(OAc)2·H2O in the presence
of 2.0 equiv. Cs2CO3 or K2CO3 (Table 1, entries 7–8), the reaction
under O2 resulted in trace yield of 3a. Thus, further reactions
with catalytic amounts of Cu(OAc)2·H2O were conducted in the
presence of metal salts as a base and an oxidant including all
kinds of copper and silver salts, and these experiments showed
that reactions conducted with CuO as the additive formed the
cross-coupling product 3a in excellent yield (Table 1, entry 9).
When O2 was employed (1 atm) instead of air under the optimized
conditions, the yield of 3a dropped to 50% (Table 1, entry 10). A
State Key Laboratory of Applied Organic Chemistry, Lanzhou University,
Lanzhou 730000, People’s Republic of China. E-mail: liuxuey@lzu.edu.cn
† Electronic supplementary information (ESI) available: 1H NMR and 13
NMR spectra for all new compounds. See DOI: 10.1039/c1ob05395g
C
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Table 1 Optimization of the Reaction Conditionsa
3q and 3r in 63% and 69% yield, respectively (Table 3, entries 3
and 4). However, when 2-methylpropane-2-thiol (2f) was reacted
with benzoxazole (1a), the thiolation product 3s was isolated only
in 4% yield even with a prolonged reaction time of 24 h (Table 3,
entry 5). These results indicated that the steric hindrance factors of
the thiols play a key role in controlling the reactivity. We were also
interested in extending the direct thiolation of azoles to aryl thiols.
Benzoxazole, benzothiazole and 1-methylimidazole all smoothly
reacted with benzenethiol (2k) to afford the desired products in
low to moderate yields (Table 3, entries 11–13).
A mechanism analogous to those proposed for similar copper-
catalyzed processes involving thiol copper species might be
applicable to this thiolation procedure.6,9 To investigate the
reaction mechanism, the thiolations of benzoxazole with dodecyl
disulfide and bis(dodecylthio)copper ((C12H25S)2Cu) were studied,
respectively. When dodecyl disulfide was used as the reaction
partner, the product 3a was obtained in 46% yield under the
optimized conditions for 24 h (Scheme 1, eq 1). On the other
hand, the reaction of benzoxazole and (C12H25S)2Cu under the
same conditions for 8 h produced 3a in 81% yield (Scheme 1, eq 2).
Moreover, in the absence of CuO, the reaction yield was decreased
to 57%, while in the absence of both CuO and Cu(OAc)2·H2O, the
yield was further decreased to 25% (Scheme 1, eq 3). These results
indicated the importance of the formation of (C12H25S)2Cu as a
key intermediate, which might be obtained more quickly from the
reaction of the copper salt with a thiol than from the corresponding
disulfide under these reaction conditions. Therefore, a plausible
mechanism is proposed. The key intermediate (RS)2Cu would be
firstly formed in the presence of a thiol and the copper salt. It reacts
with benzoxazole (1a) to produce the corresponding ArCuSPh
intermediate, which can then undergo reductive elimination to
afford the product 3a. Finally, the Cu(II) catalyst is regenerated by
the oxidant.
Entry
Catalyst
Additive
Solvent
Yieldb (%)
1
2
3
4
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
CuO
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
—
Cs2CO3
K2CO3
CuO
CuO
Cu(OH)2CO3
Cu(OH)2
Ag2CO3
Ag2O
AgOAc
AgNO3
AgI
CuO
CuO
DMSO
DMF
xylene
27
38
35
37
48
0
trace
trace
86
50
73
38
53
36
trace
0
dioxane
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
5
6
7c
8c
9
10c
11
12
13
14
15
16
17
18
19d
0
17
52
Cu(OAc)2·H2O
a 1a (0.4 mmol), dodecanethiol 2a (0.6 mmol), Cu(II) (20 mol%), additive
(2.0 equiv.), dry solvent (2 mL), under air, 120 ◦C, 8 h. b Isolated yields.
c Under O2 atmosphere. d Cu(OAc)2·H2O (10 mol%).
comparable reaction efficiency was presented by Cu(OH)2CO3,
while Cu(OH)2, Ag2CO3 and Ag2O showed lower reactivity
(Table 1, entries 11–14). Other silver species, such as AgOAc,
AgNO3 and AgI were ineffective for this reaction (Table 1, entries
15–17). Notably, with the use of CuO instead of Cu(OAc)2·H2O
as the catalyst, the desired product was isolated in only 17% yield
under the same reaction conditions (Table 1, entry 18). Along with
reducing the amount of catalyst by 10 mol%, the yield decreased
to 52% (Table 1, entry 19).
Under the optimized conditions, the substrate scope towards
this thiolation reaction was further investigated. A wide array
of heterocycle compounds 1 were tested in the reaction with 1-
dodecanethiol (2a), and the results are listed in Table 2. Benzoxa-
zoles bearing substituents with diverse electronic properties, such
as electron donation (methyl, methoxy groups) and slight electron
deficiency (chloro derivative), all showed the better reactivity
and furnished the products in moderate to good yields (Table 2,
entries 2–4). However, a low yield was obtained in the case of 5-
nitrobenzoxazole (Table 2, entry 5), which was deactivated by the
strongly electron withdrawing nitro group. Various azoles, such
as oxazoles, thiazoles and imidazoles, all smoothly reacted with
2a to afford the desired products in good yields (Table 2, entries
6–13). Moreover, 2-phenyl-1,3,4-oxadiazole is a good coupling
partner, and the desired corresponding product 3n was obtained
in moderate yield (Table 2, entry 14).
The Cu-catalyzed thiolation of azoles with various thiols
was also investigated. Primary aliphatic thiols, whether short,
medium or long chain, were engaged in the system, the desired
corresponding products were obtained in moderate to good yields
(Table 3, entries 1, 2, 6–10). Moreover, secondary aliphatic thiols,
such as 2-propanethiol (2d) and cyclohexylmercaptan (2e), were
used in this reaction, which produced the corresponding product
Scheme 1 Preliminary mechanism study.
Conclusions
In conclusion, we have disclosed an efficient C–H function-
alization/intermolecular C–S bond formation process. Various
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Table 2 Reactions of 2a with various heterocyclesa
Entry
Heterocycle
1
Product
3
Yieldb (%)
1
2
3
4
5
6
1a (R = H)
3a (R = H)
86
84
63
67
11
63
1b (R = 5-Me)
1c (R = 5-OMe)
1d (R = 6-Cl)
1e (R = 5-NO2)
1f
3b (R = 5-Me)
3c (R = 5-OMe)
3d (R = 6-Cl)
3e (R = 5-NO2)
3f
7
8
1g (R = H)
1h(R = 6-Me)
3g (R = H)
3h (R = 6-Me)
82
84
9
10
1i (R1, R2 = H)
1j (R1, R2 = Me)
3i (R1, R2 = H)
3j (R1, R2 = Me)
83
89
11
12
1k
1l
3k
3l
70
69
13
14
1m
1n
3m
3n
73
50
a 1 (0.4 mmol), dodecanethiol 2 (0.6 mmol), Cu(OAc)2 · H2O (20 mol %), CuO (2.0 equiv), toluene (2 mL), under air, 120 ◦C, 8h. b Isolated yields.
thioethers could be efficiently obtained from this method.
Aliphatic thiols as reaction partners were used for the first time in
the direct thiolationof azoles. This approach is simple, general, and
practical which complemented the classic methods for the rapid
construction of C–S bonds.
were uncorrected. All new compounds were further characterized
by HRMS (high resolution mass spectra); copies of their 1H
NMR and 13C NMR spectra are provided. Unless otherwise
noted, materials obtained from commercial suppliers were used
without further purification. Toluene was dried and distilled from
sodium/benzophenone.
Experimental section
General procedure for the preparation of 3
General remarks
Under air atmosphere, a reaction vessel was charged with hetero-
cycle 1 (0.4 mmol), RSH 2 (0.6 mmol), Cu(OAc)2·H2O (16 mg, 20
mol%), CuO (64 mg, 0.8 mmol), and PhMe (2 mL). The mixture
was stirred at 120 ◦C and monitored by TLC. After the completion
of the reaction, the residue was purified directly by short flash
column chromatography on silica gel with hexane/ethyl acetate as
an eluent to give the desired corresponding product.
Column chromatography was carried out on silica gel. Unless
1
noted H NMR spectra were recorded at 400 MHz in CDCl3,
13C NMR spectra were recorded at 100 MHz in CDCl3 using
TMS as internal standard. IR spectra were recorded on an FT-
IR spectrometer and only major peaks are reported in cm-1.
Melting points were determined on a microscopic apparatus and
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Table 3 Reactions of heterocycles with various thiolsa
2-(Dodecylthio)benzo[d]oxazole (3a). Silica gel column purifi-
cation wit◦h hexane/ethyl acetate (80/1, v/v); white solid, mp:
23.0–24.2 C. 1H NMR (400 MHz, CDCl3) d 0.88 (t, J = 6.8 Hz,
3H), 1.25–1.31 (m, 16H), 1.43–1.50 (m, 2H), 1.78–1.86 (m, 2H),
3.30 (t, J = 7.2 Hz, 2H), 7.20–7.28 (m, 2H), 7.42 (d, J = 7.6 Hz, 1H),
7.59 (d, J = 7.6 Hz, 1H); 13C NMR (100 MHz, CDCl3) d 165.2,
151.7, 142.0, 124.1, 123.7, 118.3, 109.7, 32.2, 31.9, 29.6, 29.5, 29.4,
29.3, 29.2, 29.0, 28.6, 22.7, 14.1; IR (thin film, cm-1) 2921, 2849,
1503, 1468, 1130, 744; HRMS (ESI) m/z: calcd for C19H29NOS
[M + H]+: 320.2043, found: 320.2047.
Entry
1
1
Thiol 2
Product
Yieldb (%)
80
1a
2-(Dodecylthio)-5-methylbenzo[d]oxazole (3b). Silica gel col-
2
1a
78
umn purification with hexane/ethyl acetate (80/1, v/v); white
◦
1
solid, mp: 29.2–31.0 C. H NMR (400 MHz, CDCl3) d 0.88 (t,
J = 6.8 Hz, 3H), 1.26–1.31 (m, 16H), 1.43–1.50 (m, 2H), 1.77–1.85
(m, 2H), 2.43 (s, 3H), 3.29 (t, J = 7.2 Hz, 2H), 7.02 (d, J = 8.0 Hz,
2H), 7.28 (d, J = 8.0 Hz, 2H), 7.38 (s, 1H); 13C NMR (100 MHz,
CDCl3) d 165.1, 150.0, 142.2, 133.9, 124.6, 118.4, 109.1, 32.2,
31.9, 29.6, 29.5, 29.4, 29.3, 29.2, 29.0, 28.6, 22.7, 21.4, 14.1; IR
(thin film, cm-1) 2919, 2850, 1637, 1497, 1152, 805; HRMS (ESI)
m/z: calcd for C20H31NOS [M + H]+: 334.2199, found: 334.2191.
3
1a
1a
63
69
4c
5d
6
1a
1j
4
2-(Dodecylthio)-5-methoxybenzo[d]oxazole (3c). Silica gel col-
umn purification with hexane/ethyl acetate (80/1, v/v); white
◦
1
solid, mp: 24.8–26.0 C. H NMR (400 MHz, CDCl3) d 0.88 (t,
J = 6.8 Hz, 3H), 1.26–1.31 (m, 16H), 1.43–1.50 (m, 2H), 1.78–
1.85 (m, 2H), 3.29 (t, J = 7.2 Hz, 2H), 3.83 (s, 3H), 6.81 (dd, J =
8.8, 2.4 Hz, 1H), 7.11 (d, J = 2.4 Hz, 1H), 7.29 (d, J = 9.2 Hz,
1H); 13C NMR (100 MHz, CDCl3) d 165.8, 157.1, 146.4, 142.8,
111.6, 109.8, 102.0, 55.9, 32.3, 31.9, 29.6, 29.5, 29.4, 29.3, 29.2,
29.0, 28.6, 22.7, 14.1; IR (thin film, cm-1) 2916, 1636, 1476, 1142,
826; HRMS (ESI) m/z: calcd for C20H31NO2S [M + H]+: 350.2148,
found: 350.2143.
CH3(CH2)3SH 2g
82
7
1j
1j
1j
CH3(CH2)5SH 2h
CH3(CH2)7SH 2i
CH3(CH2)17SH 2j
81
84
68
77
33
8
6-Chloro-2-(dodecylthio)benzo[d]oxazole (3d). Silica gel col-
umn purification with hexane/ethyl acetate (80/1, v/v); white
solid, mp: 41.2–42.8 ◦C. 1H NMR (400 MHz, CDCl3) d 0.88 (t, J =
6.8 Hz, 3H), 1.26–1.30 (m, 16H), 1.45–1.50 (m, 2H), 1.78–1.85 (m,
2H), 3.29 (t, J = 7.2 Hz, 2H), 7.24 (dd, J = 8.4, 1.6 Hz, 1H), 7.42
(d, J = 1.6 Hz, 1H), 7.47 (d, J = 8.4 Hz, 1H); 13C NMR (100 MHz,
CDCl3) d 166.1, 151.9, 140.8, 129.3, 124.7, 118.6, 110.4, 32.4,
31.9, 29.7, 29.6, 29.5, 29.4, 29.3, 29.2, 29.0, 28.6, 22.7, 14.1; IR
(thin film, cm-1) 2915, 2850, 1504, 1467, 1214, 1140, 817; HRMS
(ESI) m/z: calcd for C19H28ClNOS [M + H]+: 354.1653, found:
354.1660.
9
10
11e
1m 2h
1a
2-(Dodecylthio)-5-nitrobenzo[d]oxazole (3e). Silica gel column
purification with hexane/ethyl acetate (80/1, v/v); mp: 58.0–
59.8 ◦C. 1H NMR (400 MHz, CDCl3) d 0.88 (t, J = 6.8 Hz, 3H),
1.26–1.35 (m, 16H), 1.45–1.52 (m, 2H), 1.82–1.89 (m, 2H), 3.34
(t, J = 7.2 Hz, 2H), 7.52 (d, J = 9.2 Hz, 1H), 8.22 (dd, J = 8.8,
1.6 Hz, 1H), 8.46 (d, J = 2.0 Hz, 1H); 13C NMR (100 MHz, CDCl3)
d 169.4, 155.3, 145.2, 142.5, 119.9, 114.4, 109.7, 32.6, 31.9, 29.6,
29.5, 29.4, 29.3, 29.1, 29.0, 28.6, 22.7, 14.1; IR (thin film, cm-1)
2915, 2851, 2360, 1639, 1527, 1494, 1342, 1108, 819, 736; HRMS
(ESI) m/z: calcd for C19H28ClNOS [M + H]+: 365.1893, found:
365.1896.
12e
13e
1g
1n
2k
2k
41
55
a 1 (0.4 mmol), thiol 2 (0.6 mmol), Cu(OAc)2·H2O (20 mol%), CuO (2.0
equiv.), toluene (2 mL), under air, 120 ◦C, 8 h. b Isolated yields. c 2e (0.72
mmol), Cu(OAc)2·H2O (40 mol%) were used. d 24 h. e 2k (0.72 mmol), 10 h.
2-(Dodecylthio)-5-phenyloxazole (3f). Silica gel column purifi-
cation wit◦h hexane/ethyl acetate (80/1, v/v); white solid, mp:
37.8–39.0 C. 1H NMR (400 MHz, CDCl3) d 0.88 (t, J = 6.8 Hz,
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3H), 1.25–1.31 (m, 16H), 1.41–1.48 (m, 2H), 1.75–1.82 (m, 2H),
3.20 (t, J = 7.2 Hz, 2H), 7.26–7.31 (m, 2H), 7.37–7.40 (m, 2H),
7.56–7.59 (m, 2H); 13C NMR (100 MHz, CDCl3) d 160.1, 152.6,
128.8, 128.1, 127.8, 123.7, 123.0, 32.6, 31.9, 29.6, 29.5, 29.4, 29.3,
29.1, 28.6, 22.7, 14.1; IR (thin film, cm-1) 2920, 2849, 1633, 1476,
1165, 1121, 759, 689; HRMS (ESI) m/z: calcd for C21H31NOS
[M + H]+: 346.2199, found: 346.2190.
1-Benzyl-2-(dodecylthio)-1H-benzo[d]imidazole (3l). Silica gel
column purification with hexane/ethyl acetate (4/1, v/v); white
◦
1
solid, mp: 47.6–49.2 C. H NMR (400 MHz, CDCl3) d 0.88 (t,
J = 6.8 Hz, 3H), 1.25–1.30 (m, 16H), 1.40–1.45 (m, 2H), 1.73–1.80
(m, 2H), 3.39 (t, J = 7.2 Hz, 2H), 5.27 (s, 2H), 7.10–7.21 (m, 5H),
7.21–7.31 (m, 3H), 7.70 (d, J = 8.0 Hz, 1H); 13C NMR (100 MHz,
CDCl3) d 152.5, 143.7, 136.2, 135.7, 128.8, 127.8, 126.8, 121.8,
118.2, 109.0, 47.4, 32.8, 31.9, 29.6, 29.5, 29.4, 29.3, 29.2, 29.1, 28.7,
22.6, 14.1; IR (thin film, cm-1) 2924, 1642, 1440, 731; HRMS (ESI)
m/z: calcd for C26H36N2S [M + H]+: 409.2672, found: 409.2670.
2-(Dodecylthio)benzo[d]thiazole (3g). Silica gel column purifi-
cation with hexane/ethyl acetate (80/1, v/v); colorless liquid. 1H
NMR (400 MHz, CDCl3) d 0.88 (t, J = 6.8 Hz, 3H), 1.26–1.30 (m,
16H), 1.43–1.50 (m, 2H), 1.77–1.84 (m, 2H), 3.33 (t, J = 7.2 Hz,
2H), 7.25–7.28 (m, 1H), 7.37–7.41 (m, 1H), 7.73 (d, J = 8.0 Hz,
1H), 7.86 (d, J = 8.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) d
167.3, 153.4, 135.1, 125.9, 124.0, 121.4, 120.8, 33.6, 31.9, 29.6,
29.5, 29.4, 29.3, 29.2, 29.1, 28.7, 22.7, 14.1; IR (thin film, cm-1)
2924, 2852, 2360, 1461, 1428, 1239, 996, 755; HRMS (ESI) m/z:
calcd for C19H29NS2 [M + H]+: 336.1814, found: 336.1809.
2-(Dodecylthio)-1-methyl-1H-imidazole (3m). Silica gel col-
umn purification with hexane/ethyl acetate (4/1, v/v); colorless
1
liquid. H NMR (400 MHz, CDCl3) d 0.88 (t, J = 6.8 Hz, 3H),
1.25–1.30 (m, 16H), 1.36–1.41 (m, 2H), 1.61–1.68 (m, 2H), 3.05
(t, J = 7.2 Hz, 2H), 3.61 (s, 3H), 6.91 (s, 1H), 7.05 (s, 1H), 7.38
(s, 1H); 13C NMR (100 MHz, CDCl3) d 142.1, 129.1, 121.9, 34.3,
33.1, 31.8, 29.7, 29.6, 29.5, 29.4, 29.3, 29.1, 28.6, 22.6, 14.0; IR
(thin film, cm-1) 2924, 2853, 1461, 1279, 1124, 1079, 913, 723;
HRMS (ESI) m/z: calcd for C16H30N2S [M + H]+: 283.2202, found:
283.2198.
2-(Dodecylthio)-6-methylbenzo[d]thiazole (3h). Silica gel col-
umn purification with hexane/ethyl acetate (80/1, v/v); colorless
1
liquid. H NMR (400 MHz, CDCl3) d 0.88 (t, J = 6.8 Hz, 3H),
1.26–1.31 (m, 16H), 1.42–1.49 (m, 2H), 1.76–1.84 (m, 2H), 2.44 (s,
3H), 3.31 (t, J = 7.2 Hz, 2H), 7.20 (dd, J = 8.4, 1.2 Hz, 1H), 7.52 (s,
1H), 7.73 (d, J = 8.4 Hz, 1H); 13C NMR (100 MHz, CDCl3) d 166.0,
151.5, 135.3, 134.1, 127.4, 120.9, 120.7, 33.6, 31.9, 29.6, 29.5, 29.4,
29.3, 29.2, 29.1, 28.7, 22.7, 21.4, 14.1; IR (thin film, cm-1) 2920,
1641, 1446, 994, 813, 728; HRMS (ESI) m/z: calcd for C20H31NS2
[M + H]+: 350.1971, found: 350.1980.
2-(Dodecylthio)-5-phenyl-1,3,4-oxadiazole (3n). Silica gel col-
umn purification◦with hexane/ethyl acetate (80/1, v/v); mp: white
1
solid, 32.4–34.0 C. H NMR (400 MHz, CDCl3) d 0.88 (t, J =
6.8 Hz, 3H), 1.26–1.31 (m, 16H), 1.43–1.50 (m, 2H), 1.80–1.87 (m,
2H), 3.29 (t, J = 7.2 Hz, 2H), 7.46–7.51 (m, 3H), 7.99–8.01 (m,
2H); 13C NMR (100 MHz, CDCl3) d 165.5, 164.5, 131.5, 128.9,
126.6, 123.7, 32.6, 31.9, 29.6, 29.5, 29.4, 29.3, 29.2, 29.0, 28.5, 22.6,
14.1; IR (thin film, cm-1) 2921, 2846, 1637, 1468, 1382, 1186, 1064;
HRMS (ESI) m/z: calcd for C20H30N2OS [M + H]+: 347.2152,
found: 347.2147.
2-(Dodecylthio)thiazole (3i). Silica gel column purification
with hexane/ethyl acetate (80/1, v/v); colorless liquid. 1H NMR
(400 MHz, CDCl3) d 0.88 (t, J = 6.8 Hz, 3H), 1.26–1.30 (m, 16H),
1.40–1.47 (m, 2H), 1.71–1.79 (m, 2H), 3.20 (t, J = 7.2 Hz, 2H),
7.19 (d, J = 3.6 Hz, 1H), 7.65 (d, J = 3.6 Hz, 1H); 13C NMR
(100 MHz, CDCl3) d 165.4, 142.7, 118.5, 34.6, 31.9, 29.6, 29.5,
29.4, 29.3, 29.2, 29.1, 28.7, 22.6, 14.1; IR (thin film, cm-1) 2924,
2853, 2360, 1462, 1388, 1301, 1020, 706; HRMS (ESI) m/z: calcd
for C15H27NS2 [M + H]+: 286.1658, found: 286.1656.
2-(Ethylthio)benzo[d]oxazol (3o). Silica gel column purifica-
1
tion with hexane/ethyl acetate (80/1, v/v); colorless liquid. H
NMR (400 MHz, CDCl3) d 1.50 (t, J = 7.2 Hz, 3H), 3.32 (q, J =
14.8 Hz, 2H), 7.20–7.29 (m, 2H), 7.42–7.44 (m, 1H), 7.59–7.61 (m,
1H); 13C NMR (100 MHz, CDCl3) d 165.0, 151.7, 142.0, 124.2,
123.7, 118.3, 109.8, 26.6, 14.7; IR (thin film, cm-1) 2930, 2868,
1640, 1451, 1238, 1130, 1096, 924, 743; HRMS (ESI) m/z: calcd
for C9H9NOS [M + H]+: 180.0478, found: 180.0482.
2-(Dodecylthio)-4,5-dimethylthiazole (3j). Silica gel column
purification with hexane/ethyl acetate (80/1, v/v); colorless
1
liquid. H NMR (400 MHz, CDCl3) d 0.88 (t, J = 6.8 Hz, 3H),
2-(Propylthio)benzo[d]oxazole (3p). Silica gel column purifi-
cation with hexane/ethyl acetate (80/1, v/v); colorless liquid. 1H
NMR (400 MHz, CDCl3) d 1.08 (t, J = 7.2 Hz, 3H), 1.86 (m,
2H), 3.29 (t, J = 7.2 Hz, 2H), 7.20–7.29 (m, 2H), 7.41–7.43 (m,
1H), 7.59–7.61 (m, 1H); 13C NMR (100 MHz, CDCl3) d 165.2,
151.7, 141.9, 124.1, 123.7, 118.3, 109.7, 34.1, 22.7, 13.2; IR (thin
film, cm-1) 2965, 2873, 1640, 1500, 1452, 1238, 1214, 1130, 1095,
805, 742; HRMS (ESI) m/z: calcd for C10H11NOS [M + H]+:
194.0634, found: 194.0639.
1.26–1.32 (m, 16H), 1.38–1.43 (m, 2H), 1.68–1.75 (m, 2H), 2.28 (s,
3H), 2.29 (s, 3H), 3.08 (t, J = 7.2 Hz, 2H); 13C NMR (100 MHz,
CDCl3) d 159.4, 148.4, 126.4, 34.9, 31.9, 29.6, 29.5, 29.4, 29.3,
29.0, 28.6, 22.6, 14.6, 14.1, 11.2; IR (thin film, cm-1) 2924, 2853,
1642, 1560, 1460, 1420, 1297, 1110, 1020, 723; HRMS (ESI) m/z:
calcd for C17H31NS2 [M + H]+: 314.1971, found: 314.1975.
2-(Dodecylthio)-1-methyl-1H-benzo[d]imidazole (3k). Silica
gel column purification with hexane/ethyl acetate (4/1, v/v);
◦
1
white solid, mp: 32.0–33.6 C. H NMR (400 MHz, CDCl3) d
0.88 (t, J = 6.8 Hz, 3H), 1.25–1.31 (m, 16H), 1.43–1.50 (m, 2H),
1.75–1.82 (m, 2H), 3.38 (t, J = 7.2 Hz, 2H), 3.63 (s, 3H), 7.18–7.20
(m, 3H), 7.65–7.68 (m, 1H); 13C NMR (100 MHz, CDCl3) d
152.5, 143.5, 136.7, 121.6, 118.1, 108.2, 32.5, 31.8, 29.8, 29.6,
29.5, 29.4, 29.3, 29.2, 29.1, 28.7, 22.6, 14.0; IR (thin film, cm-1)
2922, 2851, 1462, 1441, 1362, 1275, 1230, 911, 731; HRMS (ESI)
m/z: calcd for C20H32N2S [M + H]+: 333.2359, found: 333.2362.
2-(Isopropylthio)benzo[d]oxazole (3q). Silica gel column pu-
rification with hexane/ethyl acetate (80/1, v/v); colorless liquid.
1H NMR (400 MHz, CDCl3) d 1.53 (d, J = 6.8 Hz, 6H), 4.04 (m,
1H), 7.21–7.29 (m, 2H), 7.43 (d, J = 7.6 Hz, 1H), 7.60–7.62 (m,
1H); 13C NMR (100 MHz, CDCl3) d 164.7, 151.5, 142.0, 124.1,
123.8, 118.4, 109.8, 38.3, 23.3; IR (thin film, cm-1) 2968, 2360,
1648, 1500, 1453, 1237, 1128, 1094, 743; HRMS (ESI) m/z: calcd
for C10H11NOS [M + H]+: 194.0634, found: 194.0638.
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2-(Cyclohexylthio)benzo[d]oxazole (3r). Silica gel column pu-
rification with hexane/ethyl acetate (80/1, v/v); colorless liquid.
1H NMR (400 MHz, CDCl3) d 1.35–1.39 (m, 1H), 1.44–1.66 (m,
5H), 1.78–1.83 (m, 2H), 2.19–2.23 (m, 2H), 3.86–3.93 (m, 1H),
7.20–7.29 (m, 2H), 7.41–7.43 (m, 1H), 7.60 (d, J = 7.2 Hz, 1H);
13C NMR (100 MHz, CDCl3) d 164.7, 151.6, 142.0, 124.1, 123.7,
118.3, 109.8, 46.0, 33.3, 25.7, 25.5; IR (thin film, cm-1) 3056, 2931,
2854, 1498, 1451, 1238, 1128, 1094, 999, 807, 743; HRMS (ESI)
m/z: calcd for C13H15NOS [M + H]+: 234.0947, found: 234.0950.
2H), 3.61 (s, 3H), 6.91 (s, 1H), 7.05 (s, 1H); 13C NMR (100 MHz,
CDCl3) d 142.0, 129.1, 121.9, 34.3, 33.1, 31.2, 29.6, 28.2, 22.4,
13.9; IR (thin film, cm-1) 3106, 2927, 2856, 1459, 1414, 1377, 1279,
1124, 914, 728, 685; HRMS (ESI) m/z: calcd for C23H43NS2 [M +
H]+: 199.1263, found: 199.1269.
2-(Phenylthio)benzo[d]oxazole (3y). Silica gel column purifi-
1
cation with hexane/ethyl acetate (4/1, v/v); colorless liquid. H
NMR (400 MHz, CDCl3) d 7.21–7.29 (m, 2H), 7.39–7.41 (m,
1H), 7.43–7.47 (m, 3H), 7.59–7.61 (m, 1H), 7.69–7.71 (m, 2H); 13
C
2-(tert-Butylthio)benzo[d]oxazole (3s). Silica gel column pu-
rification with hexane/ethyl acetate (80/1, v/v); colorless liquid.
1H NMR (400 MHz, CDCl3) d 1.65 (s, 9H), 7.26–7.30 (m, 2H),
7.46–7.48 (m, 1H), 7.64–7.67 (m, 1H); 13C NMR (100 MHz,
CDCl3) d 163.3, 151.3, 142.0, 124.3, 124.2, 119.0, 109.9, 49.7,
30.9; IR (thin film, cm-1) 2964, 1500, 1452, 1238, 1120, 1089, 806,
743; HRMS (ESI) m/z: calcd for C11H13NOS [M + H]+: 208.0791,
found: 208.0789.
NMR (100 MHz, CDCl3) d 163.2, 151.9, 142.0, 134.4, 129.8, 129.6,
127.2, 124.3, 119.1, 110.0; IR (thin film, cm-1) 3060, 2925, 1799,
1500, 1450, 1237, 1127, 1093, 1024, 925, 804, 743; HRMS (ESI)
m/z: calcd for C23H43NS2 [M + H]+: 228.0478, found: 228.0481.
2-(Phenylthio)benzo[d]thiazole (3z). Silica gel column purifi-
cation with hexane/ethyl acetate (80/1, v/v); colorless liquid. 1H
NMR (400 MHz, CDCl3) d 7.28 (t, J = 7.2 Hz, 1H), 7.40–7.55
(m, 4H), 7.66 (d, J = 8.0 Hz, 1H), 7.76 (d, J = 6.8 Hz, 2H), 7.90
(d, J = 8.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) d 169.6, 153.9,
135.3, 130.4, 129.9, 126.1, 124.3, 121.9, 120.7; IR (thin film, cm-1)
3059, 2930, 1580, 1458, 1425, 1309, 1237, 1080, 1004, 753, 690;
HRMS (ESI) m/z: calcd for C20H31NS2 [M + H]+: 244.0249, found:
244.0252.
2-(Butylthio)-4,5-dimethylthiazole (3t). Silica gel column pu-
rification with hexane/ethyl acetate (80/1, v/v); colorless liquid.
1H NMR (400 MHz, CDCl3) d 0.93 (t, J = 7.2 Hz, 3H), 1.41–1.50
(m, 2H), 1.67–1.74 (m, 2H), 2.28 (s, 3H), 2.30 (s, 3H), 3.09 (t, J =
7.2 Hz, 2H); 13C NMR (100 MHz, CDCl3) d 159.3, 148.4, 126.4,
34.6, 31.3, 21.8, 14.6, 13.5, 11.2; IR (thin film, cm-1) 2958, 2867,
1560, 1419, 1375, 1297, 1111, 1019; HRMS (ESI) m/z: calcd for
C9H15NS2 [M + H]+: 202.0719, found: 202.0724.
1-Methyl-2-(phenylthio)-1H-imidazole (3aa). Silica gel col-
umn purification with hexane/ethyl acetate (4/1, v/v); colorless
1
liquid. H NMR (400 MHz, CDCl3) d 3.61 (s, 3H), 7.06 (d, J =
1.2 Hz, 1H), 7.11–7.17 (m, 4H), 7.22–7.29 (m, 2H); 13C NMR
(100 MHz, CDCl3) d 137.8, 134.8, 130.0, 129.1, 127.8, 126.4, 123.7,
33.7; IR (thin film, cm-1) 3056, 2946, 1582, 1456, 1411, 1280, 1122,
1081, 1024, 915, 743, 693; HRMS (ESI) m/z: calcd for C20H31NS2
[M + H]+: 191.0637, found: 191.0640.
2-(Hexylthio)-4,5-dimethylthiazole (3u). Silica gel column pu-
rification with hexane/ethyl acetate (80/1, v/v); colorless liquid.
1H NMR (400 MHz, CDCl3) d 0.88 (t, J = 6.8 Hz, 3H), 1.27–1.33
(m, 4H), 1.39–1.46 (m, 2H), 1.68–1.75 (m, 2H), 2.28 (s, 3H), 2.29
(s, 3H), 3.09 (t, J = 7.2 Hz, 2H); 13C NMR (100 MHz, CDCl3) d
159.3, 148.3, 126.4, 34.9, 31.2, 29.2, 28.3, 22.4, 14.6, 13.9, 11.2; IR
(thin film, cm-1) 2925, 2856, 1639, 1419, 1375, 1296, 1111, 1020,
726; HRMS (ESI) m/z: calcd for C11H19NS2 [M + H]+: 230.1032,
found: 230.1038.
Note added after first publication
This article replaces the version published on 7th June 2011, which
contained errors in Table 3.
4,5-Dimethyl-2-(octylthio)thiazole (3v). Silica gel column pu-
rification with hexane/ethyl acetate (80/1, v/v); colorless liquid.
1H NMR (400 MHz, CDCl3) d 0.88 (t, J = 6.8 Hz, 3H), 1.27–
1.33 (m, 8H), 1.38–1.43 (m, 2H), 2.28 (s, 3H), 2.29 (s, 3H), 3.08
(t, J = 7.2 Hz, 2H); 13C NMR (100 MHz, CDCl3) d 159.3, 148.3,
126.4, 34.9, 31.7, 29.2, 29.0, 28.6, 22.6, 14.6, 14.0, 11.2; IR (thin
film, cm-1) 2924, 2854, 1560, 1461, 1420, 1374, 1296, 1111, 1019,
730; HRMS (ESI) m/z: calcd for C13H23NS2 [M + H]+: 258.1345,
found: 258.1343.
Acknowledgements
We thank the National Natural Science Foundation of China (No.
21072081), and the Fundamental Research Funds for the Central
Universities (lzujbky-2009-81) for financial support.
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purificatio◦n with hexane/ethyl acetate (80/1, v/v); white solid, mp:
36.0–38.0 C. 1H NMR (400 MHz, CDCl3) d 0.88 (t, J = 6.8 Hz,
3H), 1.25 (brs, 28H), 1.38–1.43 (m, 2H), 1.67–1.75 (m, 2H), 2.28
(s, 3H), 2.29 (s, 3H), 3.08 (t, J = 7.2 Hz, 2H); 13C NMR (100 MHz,
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purification with hexane/ethyl acetate (4/1, v/v); colorless liquid.
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(m, 4H), 1.37–1.44 (m, 2H), 1.61–1.69 (m, 2H), 3.05 (t, J = 7.2 Hz,
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