Copper-catalyzed oxidative C-H, N-H coupling of azoles and thiophenes

Article abstract of DOI:10.1016/j.tet.2012.03.001

CH, NH coupling of azole and thiophene derivatives takes place in the presence of a catalytic amount of Cu(OAc)₂ and an additive. The reaction of azoles smoothly occurs with several amines and amides catalyzed by 20 mol % of Cu(OAc)₂-2PPh₃ and 4 equiv of NaOAc under O₂ or in the presence of Ag₂CO₃ under N ₂. The coupling reaction leads to a facile synthesis of a N-substituted analogue of 2,5-diarylthiazole, which shows photoluminescent properties with extended π-conjugation. Spectroscopic characteristics of the obtained thiazole derivatives are discussed by measurements of UV-vis absorption and photoluminescent spectra. Under the reaction conditions using Ag ₂CO₃ as an additive and Cu(OAc)₂-2PPh ₃ as a catalyst, thiophene derivatives also react with 2-pyrrolidone to undergo CH, NH amidation.

Full text of DOI:10.1016/j.tet.2012.03.001

Tetrahedron 68 (2012) 3585e3590
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Copper-catalyzed oxidative C‒H, N‒H coupling of azoles and thiophenes
*
Shinobu Mitsuda, Taiki Fujiwara, Katsuyoshi Kimigafukuro, Daiki Monguchi, Atsunori Mori
Department of Chemical Science and Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
C‒H, N‒H coupling of azole and thiophene derivatives takes place in the presence of a catalytic amount of
Cu(OAc)2 and an additive. The reaction of azoles smoothly occurs with several amines and amides cat-
alyzed by 20 mol % of Cu(OAc)2e2PPh3 and 4 equiv of NaOAc under O2 or in the presence of Ag2CO3
under N2. The coupling reaction leads to a facile synthesis of a N-substituted analogue of 2,5-
Received 27 January 2012
Received in revised form 28 February 2012
Accepted 1 March 2012
Available online 8 March 2012
diarylthiazole, which shows photoluminescent properties with extended
p-conjugation. Spectroscopic
characteristics of the obtained thiazole derivatives are discussed by measurements of UVevis absorption
and photoluminescent spectra. Under the reaction conditions using Ag2CO3 as an additive and
Cu(OAc)2e2PPh3 as a catalyst, thiophene derivatives also react with 2-pyrrolidone to undergo C‒H, N‒H
amidation.
Keywords:
Azoles
Copper catalyst
C‒H, N‒H coupling
Thiophene
Ó 2012 Elsevier Ltd. All rights reserved.
Silver(I) carbonate
1. Introduction
Although it is a method of choice to undergo coupling of het-
eroaromatic halides with amines, which is well-known as Buch-
Transition-metal-catalyzed CeH functionalization reactions are
of great interest in organic synthesis because the reaction shows
advantage in atom efficiency compared to related cross-coupling
with organometallic compounds. A wide range of CeH coupling
reaction has been shown to proceed in the presence of a metal
catalyst.1 Among those, the reaction of heteroaromatic compounds
with organic halides is particularly important since a number of
organic molecules bearing such heteroaromatic moieties are found
in biologically important compounds as pharmaceutical products
and agrochemicals2 as well as advanced organic materials such as
electronic and optical devices.3 CeH functionalization of hetero-
aromatic compounds has thus been extensively studied and various
reactions have been developed so far. We have also been engaged in
the CeH coupling reaction of thiophene and thiazoles to reveal that
several reactions with combination of catalyst system and additives
are effective to form the carbonecarbon bond.4
By contrast to a wide range of examples forming the carbon-
ecarbon bond with the reaction of heteroaromatics and aryl ha-
lides, the coupling reaction at the CeH bond with amines or amides
leading to CeN bond formation has less been studied.5 However, it
is also important in organic synthesis to form the carbonenitrogen
bond since a variety of nitrogen-substituted heteroaromatic com-
pounds are also found in a wide range of biologically active organic
molecules.6
waldeHartwig amination,7 it is intriguing to perform the reaction
at the CeH bond of a heteroaromatic compound with amine, which
is recognized as a class of CeH, NeH coupling. However, such
a reaction has rarely been studied so far except several limited
examples of the intramolecular case.5c,8 Herein, we report that
CeH, NeH coupling of azoles that are five-membered hetero-
aromatic compounds takes place in the presence of a copper cat-
alyst under oxidative conditions.9,10 The related coupling with
thiophene derivatives under similar conditions is also described.
2. Results and discussion
CeH, NeH coupling of terminal alkynes and amides are shown
to proceed by Stahl to form the corresponding alkynyl amides.5a,11
The reaction occurs with a copper(II) catalyst in the presence of
a metal carbonate or acetate as a base under an oxygen atmosphere.
Accordingly, we started to find a suitable reaction conditions to
undergo the amination reactions at the 2-position of azoles using
related conditions to those for terminal alkynes. The reaction of
benzothiazole (1) with N-methylaniline (2a) was carried out in the
presence of 20 mol % of a copper salt under an oxygen atmosphere
at 140 ꢀC (Eq. 1). Table 1 summarizes the results of the reaction of 1
and 2a with several catalysts and additives. The reaction with
a stoichiometric amount of copper(II) acetate afforded the corre-
sponding aminated product 3a in 49% yield. The reaction was found
to proceed in 51% yield when the reaction was performed with
20 mol % of the catalyst. NaHCO3 and NaF were also found to be
* Corresponding author. Tel./fax: þ81 78 803 6181; e-mail address: amori@kobe-
u.ac.jp (A. Mori).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.03.001

3586
S. Mitsuda et al. / Tetrahedron 68 (2012) 3585e3590
Table 1
Cu(OAc)2- 2PPh3
(20 mol%)
R1
R2
R1
R2
N
N
CeH, NeH coupling of benzothiazole 1 and N-methylaniline 2aa
+
H
H
N
N
S
S
O2, NaOAc, xylene,
140 °C, 20 h
1
2
3
1
2
1
n
2
2b
2c
: R =R =Ph; : R = C3H7, R =SO2(C6H3)-4-Me;
2d: R1,R2=-(CH2)3CO-; 2e: R1,R2=-(CH2)5-;
2i: R1,R2=-(CH2)2O(CH2)2-
Entry Catalyst (mol %) Ligand
Additive (equiv) Yield of 3ae
O
N
1
2
3
4
5
6
7
7
Cu(OAc)2 (100)
Cu(OAc)2 (20)
Cu(OAc)2 (20)
Cu(OAc)2 (20)
Cu(OAc)2 (20)
Cu(OAc)2 (20)
Cu(OAc)2 (10)
Cu(OAc)2 (20)
Cu(OAc)2 (20)
Cu(OAc)2 (20)
CuCl2 (20)
None
Na2CO3 (4)
Na2CO3 (4)
NaHCO3 (4)
NaF (4)
49
51
51
52
33
82 (75)
64
0
0
0
23
0
0
N
N
N
PPh3 (40)
PPh3 (40)
PPh3 (40)
PPh3 (40)
PPh3 (40)
PPh3 (40)
PPh3 (40)
PPh3 (40)
PPh3 (40)
PPh3 (40)
PPh3 (40)
PPh3 (40)
TMEDA (20)
NPh2
N
S
S
S
3d
Ts
3b
, 47%
, 32%
3c, 65%
Et3N (4)
NaOAc (4)
NaOAc (4)
NaOH (4)
NaOtBu (4)
Cs2CO3 (4)
NaOAc (4)
NaOAc (4)
NaOAc (4)
NaOAc (4)
N
N
S
N
N
O
S
8
9
3e, 0%
3i, 0%
Scheme 1. CeH, NeH Coupling of 1 with several amines and amides.
10
11
12
13
14
15
16c
17d
CuI (20)
Pd(OAc)2 (20)
Cu(OAc)2 (20)
Cu(OAc)2 (20)
Cu(OAc)2 (20)
Cu(OAc)2 (20)
Cu(OAc)2 (20)
52
68
42
46
0
XANTPHOSb (20) NaOAc (4)
DPPE (20)
PPh3 (40)
PPh3 (40)
NaOAc (4)
NaOAc (4)
NaOAc (4)
Table 2
CeH, NeH coupling of azoles with a secondary aminea
Entry
AryleH
Amine
Product
Yield (%)b
71
a
The reaction was carried out with 0.2 mmol of 1 and 0.8 mmol of 2a at 140 ꢀC for
20 h.
N
b
c
Me
Ph
N
XANTPHOS: 4,5-Bis(diphenylphosphino)-9,9-dimethylxanthene.
The reaction under air.
N
1
4
H
HNMePh
2a
O
O
4
d
e
The reaction under N2 atmosphere.
5a
The yield based on 1H NMR. In parenthesis, isolated yield was shown.
effective additives. Although an organic base Et3N was also an
available additive, the yield was slightly decreased compared with
the above inorganic bases. The highest yield was obtained when
sodium acetate was employed as an additive. Stronger bases such as
sodium hydroxide and sodium t-butoxide were not effective to
afford the desired CeH, NeH coupling product. The reaction with
other copper salt CuCl2 was found to be less effective and other
catalyst copper(I) iodide or palladium(II) acetate did not undergo
the reaction. Among several ligands examined in place of PPh3,
XANTPHOS and DPPE also promoted the reaction. It seems to be
essential to perform the reaction under an oxygen atmosphere,
otherwise the reaction under air resulted in giving 3 in a lower yield
(46%) and the reaction did not take place under nitrogen.
The reaction was examined with other nitrogen compounds
such as secondary amines, sulfonamide and carbamides. As sum-
marized in Scheme 1, the reaction of benzothiazole 1 proceeded to
afford the corresponding CeH, NeH coupling products. Di-
phenylamine (2b) also reacted with 1 in a slightly lower yield. The
reaction with N-propyl-tosylamide (2c) also proceeded to afford
the corresponding coupling product in 65% yield and a cyclic car-
bamide 2-pyrrolidinone (2d) reacted with 1 in a lower yield (32%),
whereas no reaction took place with aliphatic amines piperidine
(2e) and morpholine (2i) probably due to the high reaction tem-
perature under oxygen atmosphere, which may prefer oxidation of
amine to the desired CeH, NeH coupling.
Table 2 summarizes the reaction of several azoles with a sec-
ondary amine. The reaction of benzoxazole (4) was found to pro-
ceed with N-methylaniline (2a) smoothly to afford the coupling
product 5a in 71% yield. In addition, 4 reacted also with di-
phenylamine 2b, piperidine 2e, and diethylamine 2f. The corre-
sponding CeH, NeH coupling products 5b, 5e and 5f were obtained
in 66%, 72% and 47% yields, respectively. Benzoimidazole 6 also
underwent the reaction of 2a in 51% yield. Although the reaction of
unsubstituted thiazole 8 with 2a did not afford the amination
product, 4,5-dimethylthiazole (9) reacted with 2a in 73% yield. By
contrast to the limited substrate scope in the reaction of benzo-
thiazole (1), benzoxazole (4) allowed to react with a broad range of
2
4
HNPh2
2b
66
5b
N
H
N
3
4
4
4
72
47
N
O
2e
5e
Et2NH
2f
5f
N
N
Me
Ph
H
N
5
6
6
2a
2a
51
0
N
Me
N
Me
6
7a
8
ee
8
Me
Me
Me
Me
N
N
Me
7
9
2a
73
H
N
Ph
S
10a
S
9
a
The reaction was carried out with 0.2 mmol of AryleH and 0.8 mmol of amine at
140 ꢀC for 20 h.
b
Isolated yield.
amines. Although it has not been clear for the understanding of the
reaction mechanism, the reaction of 4 may proceed in a different
manner.10g
We consider that the mechanism of the CeH, NeH coupling of
azoles proceed in a similar manner to the case of the amination
reaction of a terminal alkyne shown by Stahl5a as shown in
Scheme 2. The CeH bond of azole at the 2-position and the NeH
bond of amine (amide) react with a copper catalyst to form the
intermediate A. Reductive coupling forming CeN bond leads to the

S. Mitsuda et al. / Tetrahedron 68 (2012) 3585e3590
3587
coupling product accompanied by a reduced copper species, which
is oxidized to copper(II) by oxygen. Thus, we considered that a basic
oxidant may serve both as a base and the oxidizing agent. The re-
lated effect was previously revealed in the palladium-catalyzed
homocoupling of thiophenes with a silver salt.4b Accordingly, the
CeH, NeH coupling reaction was examined with several silver salts
as an additive.
not afford the coupling products under similar conditions. The re-
action of secondary amines also took place in a comparable yield to
the case with NaOAc under O2. On the other hand, the reaction with
sulfonamide 2c proceeded less efficiently probably due to the
poisoning of silver by the interaction with the sulfonamide group. It
should be pointed out that unsubstituted thiazole 8 reacted with 3d
in 72% yield. The result markedly contrasts to that with NaOAc/O2
(0% yield). The CeH, NeH coupling with 8 and 4-methylthiazole
(11) also proceeded with several amines and amides to afford the
corresponding products 10 and 13 in a reasonable yield. The im-
proved substrate scope in the reaction of 1 with variety of amines
and amides compared with our initial conditions would be the
lower reaction temperature and inferior solubility of Ag2CO3 in
a less polar organic solvent. In addition, superior basicity of silver to
NaOAc may improve the efficiency in the reaction with amides 3d,
3g and 3h.
Azole
H
H
N
2 Base
H2O
II
Cu X2
O2
2 BaseH+X-
Azole
N
Azole
N
II
Cu
A
Cu(OAc)2- 2PPh3
R1
R2
R1
R2
N
N
(20 mol%)
Scheme 2. Plausible mechanism of CH, NH Coupling of Azole with a copper catalyst.
+
H
H
N
N
S
S
Ag2CO3, toluene,
100 °C, 20 h
1
2
3
Table 3 summarizes the CeH, NeH coupling reaction of ben-
zothiazole (1) and 2-pyrrolidinone (2d) with several additives. The
reaction was carried out with 2 equiv of 1 to 2d in the presence of
20 mol % Cu(OAc)2e2PPh3 in xylene at 100 ꢀC. When the reaction
was performed under similar conditions shown in Scheme 1, the
lower temperature further decreased the yield to 7%. Among sev-
eral silver salts examined, the use of silver(I) carbonate efficiently
promoted the reaction to afford the corresponding CeH, NeH
coupling product 3d in 75% yield. Although it has recently been
shown that CeH, NeH coupling of oxazole derivatives takes place,
there is still few example for the reaction of thiazoles.12 The re-
action with silver(I) nitrate also afforded 3d in 24% yield, however,
other silver species resulted in much lower yields. Although the
reaction with toluene as a solvent was found to be the optimum
choice,1,4-dioxane also effected the reaction to give 3d in 60% yield.
Other solvents such as acetonitrile, DMF, and 1,2-dichloroethane
resulted in slightly lower yields, whereas the reaction in DMSO
was ineffective. The role of silver would be a kind of base to facil-
itate activation of CeH and/or NeH bond as well as an oxidizing
agent to regenerate the copper(II) species from the reduced copper.
O
O
N
O
N
N
S
N
S
N
N
S
3g
, 50%
3h, 50%
3d, 75%
N
N
N
O
N
N
S
NPh2
S
S
3i, 30%
3b, 81%
3j
, 61%
N
S
N
N
N
S
Ts
, 20%
3c
10j
, 66%
O
N
O
N
O
N
S
N
S
N
S
N
10d, 72%
13d, 78%
10h 42%
,
Scheme 3. CeH, NeH coupling of thiazole derivatives with several amines and amides
with Ag2CO3 as an additive.
Table 3
CeH, NeH coupling of benzothiazole 1 with 2d with a silver salt as an additivea
The CeH, NeH coupling of thiazole was applied to the synthesis
of N-substituted analogue of 2,5-diarylthiazole, which was shown
to exhibit photoluminescent properties by the donor-acceptor-type
substituent effect.4a,4g It is intriguing to study electroeoptical
properties of thiazole derivatives if the donor substituent at the 2-
position of thiazole is replaced with diarylamino group, which can
be introduced by the CeH, NeH coupling.
Synthesis of the N-substituted analogue of 2,5-diarylthiazole 15
was performed as outlined in Scheme 4. The reaction of 2-aminated
thiazole 10j was treated with an aryl iodide bearing a electron-
withdrawing substituent in the presence of PdCl2(PPh3)2 and
AgNO3/KF to afford the corresponding coupling product 15aj, 15bj
(Method A).13 Alternatively, 17 was prepared by the reaction of 5-
arylthiazole, which was obtained by palladium-catalyzed CeH
arylation of masked thiazole and following removal of the masking
group, with several secondary amines.14
Entry
Additive
Solvent
Yield of 3d (%)
1
2
3
4
5
6
7
8
NaOAc (O2)
AgNO3
AgOAc
AgF
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
1,4-dioxane
DMSO
CH3CN
DMF
1,2-dichloroethane
Toluene
7
24
Trace
3
Ag2O
7
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
75
60
Trace
38
42
20
0
9
10
11b
12c
a
Unless otherwise specified, the reaction was carried out with 0.2 mmol of 3d
and 0.4 mmol of 1 at 100 ꢀC for 15 h under N2. The yield was estimated by 1H NMR.
b
The reaction at 80 ꢀC.
The reaction without copper catalyst.
c
Table 4 summarizes UVevis absorption and photoluminescent
properties of thus obtained N-substituted analogue of 2,5-
diarylthiazole 15 along with 2,5-diarylthiazole 18 and 5-
arylthiazole 17. Remarkable shifts of both absorption and emis-
sion maxima to longer wavelength were observed by the in-
troduction of amino groups into the 2-position of thiazole
comparing with that of 17. These values were similar to the case of
With the optimized reaction conditions in hand, we then ex-
amined the reaction of several thiazole derivatives with amines and
amides. As shown in Scheme 3, the reaction of benzothiazole (1)
with six and seven-membered cyclic amides with less steric con-
gestion than acyclic ones afforded the corresponding CeH, NeH
coupling products, while primary and acyclic secondary amides did

3588
S. Mitsuda et al. / Tetrahedron 68 (2012) 3585e3590
Method A
N
N
Aryl
14
I
+
H
S
10j
KF 1.25 eq
AgNO3 1.25 eq
PdCl2(PPh3)2
N
N
Aryl
S
DMSO, 100 °C, 7 h
15
:
Aryl
CO2Et
CN
15bj
15aj
, 56%
, 74%
Fig. 1. Photoluminescence of N-substituted analogue of 2,5-diarylthiazole by the ir-
radiation of 366 nm UV light to 1 mM solution of chloroform: 15aj (left); 15aa (centre);
15ab (right).
Method B
EtO2C
KF 2.0 eq
AgNO3 1.25 eq
OH
Ph
Ph
N
I
H
+
Pd cat. 0.05 eq
100 °C, 5 h, 96%
S
in a mixed solvent system of chlorobenzene and 1,4-dioxane, 62% of
the corresponding CeH, NeH coupling product was obtained
(Scheme 5).15 Several thiophene derivatives were found to react
with 3d as summarized in Scheme 5. Thiophene derivatives bearing
an alkyl substituent at the 4- and 5-positions reacted smoothly to
afford the corresponding coupling products. Thiophene bearing an
ester functionality was found to be tolerable for the reaction con-
ditions. In addition, halothiophenes such as bromo and chlor-
othiophenes also tolerated to afford the corresponding CeH, NeH
coupling products bearing a halogen atom.16,17
14a
16
N
S
Cs2CO3 1.2 eq
H
EtO2C
xylene, reflux
59 h, 99%
17
H
NR2
Cu(OAc)2 0.2 eq
PPh3 0.4 eq
N
S
NR2
EtO2C
Ag2CO3 1.2 eq
xylene, 140 °C
15
NR2
:
CH3
N
N
15aa
, 68%
15ab
, 55%
Scheme 4. CeH, NeH coupling of thiazole derivatives with several amines and
amides.
Table 4
UVevis absorption and photoluminescent properties of thiazole derivativesa
Compound
Substituents 5-position,
2-position
lmax, nm
absorption
lmax, nm
emission
Fb
15aj
15ab
15aa
15bj
17
4-C6H4COOEt, carbazole
4-C6H4COOEt, NPh2
4-C6H4COOEt, NMePh
4-C6H4CN, carbazole
4-C6H4COOEt, H
355
361
366
369
292
347
415
447
434
451
348
424
0.71
0.51
0.26
0.64
0.17
0.24
18
4-C6H4COOEt, 4-C6H4OMe
a
Measurements of the spectra were carried out as
a chloroform solution
(2.5ꢁ10ꢂ6 M).
Scheme 5. CeH, NeH coupling of thiophene derivatives with 3d.
b
The quantum yield
F
was estimated based on 7-diethylamino-4-
¼0.99).
methylcoumarin as 0.01 mM solution of ethyl acetate (
F
3. Conclusion
the donor-acceptor-type 2,5-diarylthiazole 18. However, it was
found that much stronger photoluminescence was observed in the
N-substituted analogue particularly in diarylaminated ones 15aj
and 15ab, whereas 15aa derived from N-methylaniline indicated
a smaller quantum yield. Worthy of note is the strongest photo-
In conclusion, we have shown that azoles and thiophenes reacts
with several organic molecules bearing a NeH bond at the 2-
position of azoles or the CeH bond adjacent to the sulfur atom of
thiophene. Since a number of aminated derivatives of five-
membered heteroaromatic compounds are found in biologically
active molecules and advanced organic materials, the method
would be a potentially effective tool for the introduction of nitrogen
functionality to such heteroaromatic compounds.
luminescence in 15aj bearing carbazole group showing the
F value
of 0.71. Photoluminescent behaviours of thiazole derivatives by the
irradiation of long-wave UV light (366 nm) was shown in Fig. 1.
It was also found that the reaction conditions of CeH, NeH
coupling of azoles with silver(I) carbonate was applicable to the
reaction of thiophene derivatives. Although several examples of the
amination reaction at an electron-deficient CeH bond like azoles
has been shown to proceed,9,10 it is unrevealed, to the best of our
knowledge, that the related reaction at the CeH bond of an
electron-enriched carbon atom takes place. When the reaction of
benzothiophene (19a) and 2-pyrollidinone (3d) was carried out
with silver(I) carbonate and a catalytic amount of Cu(OAc)2e2PPh3
4. Experimental section
4.1. General
1H NMR (500 or 300 MHz) and 13C NMR (125 or 75 MHz) spectra
were measured on a Brucker Avance 500 spectrometer or Varian
Gemini 300. Unless noted, CDCl3 was used as a solvent. The

S. Mitsuda et al. / Tetrahedron 68 (2012) 3585e3590
3589
chemical shifts were expressed in parts per million with CHCl3
(7.26 ppm for 1H) or CDCl3 (77.0 ppm for 13C) as internal standards.
IR spectra were recorded on Bruker Alpha with an ATR attachment
(Ge). High resolution mass spectra (HRMS) were measured by JEOL
JMS-T100LP AccuTOF LC-Plus (ESI) with a JEOL MS-5414DART at-
tachment at Kobe University or JEOL JMS-700 MStation (EI) at the
Graduate School of Material Science, Nara Institute of Science and
Technology. For thin layer chromatography (TLC) analyses
throughout this work, Merck precoated TLC plates (silica gel 60
F254) were used. UVevis spectra were measured by ALS SEC-2000
UV/VIS spectrometer with SEC-2000 DH as a light source. Photo-
luminescent spectra were measured with HITACHI F-7000.
HRMS (EIþ) Calcd for C24H18N2O2S [M]þ: 398.1089; found: m/z
398.1086.
4.1.7. 2-(Carbazole-9-yl)-5-(4-cyanophenyl)thiazole
188.2e188.7 ꢀC; 1H NMR (300 MHz)
7.41 (m, 2H), 7.55 (m, 2H),
7.73 (m, 4H), 8.02 (s, 1H), 8.10 (d, J¼7.6 Hz, 2H), 8.35 (d, J¼8.3 Hz,
2H); 13C NMR (75 MHz)
111.3, 112.9, 118.5, 120.2, 122.8, 125.1,
(15bj). Mp
d
d
126.4, 127.0, 127.9, 132.8, 132.9, 137.0, 139.0, 159.1; IR (ATR) 2227,
1496, 1465, 1450, 1338, 1214, 1160, 824, 751, 720 cmꢂ1; HRMS
(DART-ESIþ) Calcd for C22H13N3S [MþH]þ: 352.0908; found: m/z
352.0900.
4.1.8. 2-Diphenylamino-5-(4-ethoxycarbonylphenyl)thiazole
4.1.1. N-Benzothiazole-2-yl-N-methlyaniline (3a).18
copper(II) acetate (7.3 mg, 0.04 mmol), triphenylphosphine (21 mg,
0.08 mmol), benzothiazole (1, 22 L, 0.2 mmol), N-methylaniline 2a
(0.088 mL, 0.8 mmol) and NaOAc (66 mg, 0.8 mmol) in 1.0 mL of
xylene was stirred at 140 ꢀC for 20 h under O2. After cooling to room
temperature, the mixture was passed through a Celite pad, which
was washed with chloroform repeatedly. The filtrate was washed
with water three times. The organic layer was concentrated under
reduced pressure to leave a crude oil, which was purified by column
chromatography on silica gel to afford 39 mg of 3a as a colourless oil
(75%).
A
solution of
(15ab). Mp 141.3e142.0 ꢀC; 1H NMR (300 MHz)
d
1.39(t, J¼7.1, 3H),
4.37 (q, J¼7.1 Hz, 2H), 7.28 (m, 2H), 7.41 (m,10H), 7.61 (s,1H), 7.97(d,
m
J¼8.4, 2H); 13C NMR (75 MHz)
d 14.3, 61.0, 125.0, 126.1, 126.7, 128.5,
128.9, 129.9, 130.2, 135.7, 136.1, 144.6, 166.1, 169.3; IR (ATR) 2968,
2926, 1703, 1490, 1472, 1447, 1279, 1185, 1105, 695 cmꢂ1; HRMS
(DART-ESIþ) Calcd for C24H20N2O2S [MþH]þ: 401.1324; found: m/z
401.1303.
4.1.9. 2-(N-Methyl-N-phenylamino)-5-(4-ethoxycarbonylphenyl)thi-
azole (15aa). Mp 71.2e72.0 ꢀC; 1H NMR (300 MHz)
d 1.38 (t,
J¼7.1 Hz, 3H), 3.59 (s, 3H), 4.36 (q, J¼7.1 Hz, 2H), 7.40 (m, 7H), 7.58
(s, 1H), 7.96 (d, J¼7.7 Hz, 2H); 13C NMR (75 MHz)
d 14.3, 40.3, 60.9,
4.1.2. N-Benzothiazole-2-yl-
d
-valerolactam(3g). Mp 128.6e129.1 ꢀC;
124.7, 125.2, 126.2, 127.1, 128.3, 130.0, 130.1, 136.3, 136.6, 145.9,
166.2, 170.2; IR (ATR) 2982, 2929, 1710, 1519, 1290, 1272, 1189, 1107,
771, 761, 697 cmꢂ1; HRMS (DART-ESIþ) Calcd for C19H18N2O2S
[MþH]þ: 339.1167; found: m/z 339.1165.
1H NMR (500 MHz)
d
1.87e1.95 (m, 4H), 1.98e2.05 (m, 2H), 4.26 (t,
J¼6.1 Hz, 2H), 7.29 (dd, J¼7.6 Hz, 1H), 7.42 (dd, J¼7.6, 1H), 7.80 (d,
J¼7.9 Hz, 1H), 7.82 (d, J¼8.1 Hz,1H); 13C NMR (125 MHz)
d 20.0, 22.6,
33.0, 48.5, 121.0, 121.2, 123.8, 125.8, 133.3, 148.0, 159.2, 170.3; IR
(ATR) 2946, 2910, 2881, 1655, 1502, 1442, 1399, 1253, 1174, 956, 759,
724 cmꢂ1; HRMS (EIþ) Calcd for C12H12N2OS [M]þ 232.0670; found:
m/z 232.0670.
4.2. General procedure for the oxidative copper-catalyzed
amination of heteroaromatic compounds
A solution of Cu(OAc)2 (18.2 mg, 0.1 mmol), PPh3 (52.4 mg,
0.2 mmol), benzothiophene (134.2 mg, 1.0 mmol), 2-pyrrolidinone
(38 mL, 0.5 mmol) and Ag2CO3 (165.4 mg, 0.6 mmol) in 5 mL of
4.1.3. N-Benzothiazole-2-yl-
1.75e1.95 (m, 6H), 2.80e2.89 (m, 2H), 4.58 (t, J¼4.4 Hz, 2H), 7.39
(dd, J¼7.7, 1.1 Hz, 1H), 7.41 (dd, J¼7.8, 1.1 Hz, 1H), 7.76e7.83 (m, 2H);
13C NMR (125 MHz)
23.4, 28.0, 29.3, 37.8, 47.7, 121.0, 121.1, 123.6,
125.8, 133.5, 147.8, 159.7, 175.4; IR (ATR) 839, 964, 1156, 1189, 1217,
1247, 1267, 1397, 1441, 1459, 1497, 1671 cmꢂ1; HRMS (EIþ) Calcd for
C13H14N2OS [M]þ: 246.0827; found: m/z 246.0826.
3
-caprolactam (3h). 1H NMR (500 MHz)
d
C6H5Cl/dioxane (4:1) were stirred at 140 ꢀC for 20 h under O2. After
cooling to room temperature, the mixture was passed through
a Celite pad, which was washed with chloroform or dichloro-
methane repeatedly. The filtrate was concentrated under reduced
pressure to leave a crude oil, which was purified by column chro-
matography on silica gel to afford 66.7 mg of 20ad as a pale yellow
solid (62%).
d
4.1.4. N-Benzothiazole-2-yl-carbazole (3j). Mp 128.4e129.2 ꢀC; 1H
NMR (500 MHz)
d 7.25e7.30 (m, 4H), 7.39e7.45 (m, 4H), 7.75 (d,
J¼8.1 Hz, 1H), 7.93e7.97 (m, 3H), 8.37 (d, J¼8.5 Hz, 2H); 13C NMR
4.2.1. N-Benzothiophene-2-yl-2-pyrrolidinone (20ad). Mp 191.2e
(125 MHz)
d
113.2,120.1,121.1,122.2,122.7,124.5,125.2,126.5,127.0,
192.1 ꢀC;1H NMR (300 MHz)
d 2.18e2.33 (m, 2H), 2.66 (t,
132.0,139.2,150.2,157.7; IR (ATR) 1596,1510,1442,1335,1274,1210,
954 cmꢂ1; HRMS (EIþ) Calcd for C19H12N2S [M]þ: 300.0712; found:
m/z 300.0721.
J¼7.7 Hz, 2H), 3.94 (t, J¼7.3 Hz, 2H), 6.67 (s, 1H), 7.25 (dd, J¼7.3,
1.2 Hz, 1H), 7.32 (dd, J¼7.3, 1.2 Hz, 1H), 7.63 (d, J¼7.5 Hz, 1H), 7.76
(d, J¼7.5 Hz, 1H); 13C NMR (75 MHz)
d 17.7, 31.3, 48.7, 106.0, 121.9,
122.1, 123.1, 124.4, 135.5, 136.9, 140.3, 172.7; IR (ATR) 3055, 2973,
2939, 2898, 1687, 1536, 1442, 1400, 1270, 806, 750 cmꢂ1; HRMS
(DART-ESIþ) Calcd for C12H11NOS [MþH]þ: 218.0640; found: m/z
218.06401.
4.1.5. N-Thiazole-2-yl-
-caprolactam (10h). Mp 88.4e89.4 ꢀC; 1H
3
NMR (500 MHz) d 1.75e1.95 (m, 6H), 2.80e2.89 (m, 2H), 4.40e4.53
(m, 2H), 6.97 (d, J¼3.6, Hz, 1H), 7.46 (dd, J¼3.6 Hz, 1H) 13C NMR
(75 MHz)
d 23.2, 27.6, 29.3, 37.4, 47.5, 114.7, 136.3, 159.9, 174.3; IR
(ATR) 2927, 2867, 1653, 1499, 1442, 1265, 1220, 1171, 732, 624 cmꢂ1
;
4.2.2. N-(4-Hexylthiophene-2-yl)-2-pyrrolidinone (20cd). Mp 74.1e
HRMS (DART-ESIþ) Calcd for C9H12N2OS [MþH]þ: 197.0749; found:
m/z 197.0749.
75.0 ꢀC; 1H NMR (300 MHz)
d
0.87 (t, J¼6.6 Hz, 3H), 1.22e1.38 (m,
6H), 1.51e1.66 (m, 2H), 2.13e2.28 (m, 2H), 2.53 (t, J¼7.6 Hz, 2H),
2.60(t, J¼8.0 Hz, 2H), 3.85(t, J¼7.0 Hz, 2H), 6.37 (d, J¼1.7 Hz, 1H),
4.1.6. 2-(Carbazole-9-yl)-5-(4-ethoxycarbonylphenyl)thiazole
6.48e6.53 (m, 1H); 13C NMR (75 MHz)
d14.1, 17.8, 22.6, 28.9, 30.2,
(15aj). Mp 124.1e124.9 ꢀC; 1H NMR (500 MHz)
d
1.43 (t, J¼6.9,
30.7, 31.2, 31.6, 48.7, 11.1, 112.4, 139.9, 140.1, 171.9; IR (ATR) 2954,
2925, 2851, 1683, 1554, 1494, 1294, 801, 730 cmꢂ1; HRMS (DART-
ESIþ) Calcd for C14H21NOS [MþH]þ: 252.1422; found: m/z 252.1423.
3H), 4.11 (q, J¼7.7 Hz, 2H), 7.41 (dd, J¼7.4 Hz, 2H), 7.55 (dd, J¼7.8,
1.1 Hz, 2H), 7.69 (d, J¼8.4 Hz, 2H), 8.03 (s, 1H), 8.11 (m, 4H), 8.34
(d, J¼8.2 Hz, 2H); 13C NMR (125 MHz)
d14.2, 60.9, 112.8, 119.9,
122.3, 124.8, 125.5, 126.7, 129.5, 130.2, 132.5, 135.2, 136.0, 138.8,
158.3, 165.8; IR (ATR) 3061, 2974, 2928, 2909, 1703, 1606, 1495,
4.2.3. N-(5-Ethoxycarbonylthiophene-2-yl)-2-pyrrolidinone
(20dd). Mp 117.9e118.5 ꢀC; 1H NMR (300 MHz)
3H), 2.18e2.33 (m, 2H), 2.64 (t, J¼8.0 Hz, 2H), 3. 89 (t, J¼7.3 Hz, 2H),
d
1.35 (t, J¼7.1 Hz,
1466, 1452, 1334, 1276, 1213, 1190, 1108, 846, 767, 743, 712 cmꢂ1
;

3590
S. Mitsuda et al. / Tetrahedron 68 (2012) 3585e3590
6. (a) Kubicek, S.; O’Sullivan, R. J.; August, E. M.; Hickey, E. R.; Zhan, Q.; Teodoro,
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4.30 (q, J¼7.1 Hz, 2H), 6.76 (d, J¼4.1 Hz, 1H), 7.62 (d, J¼4.1 Hz, 1H)
13C NMR (75 MHz)
14.3, 17.7, 30.9, 48.2, 60.8, 110.9, 124.8, 131.2,
145.9, 162.8, 172.5; IR (ATR) 2969, 2925, 1696, 1686, 1454, 1269,
1238, 1093, 811, 751 cmꢂ1; HRMS (DART-ESIþ) Calcd for C11H13NO3S
[MþH]þ: 240.0694; found: m/z 240.0695.
d
4.2.4. N-(5-Chloro-4-hexylthiophene-2-yl)-2-pyrrolidinone
(20fd). Mp 99.7e100.4 ꢀC; 1H NMR (300 MHz)
d
0.87 (t, J¼6.3 Hz,
3H), 1.21e1.38 (m, 6H), 1.46e1.62 (m, 2H), 2.14e2.32 (m, 2H), 2.50
(t, J¼7.6 Hz, 2H), 2.59 (t, J¼8.0 Hz, 2H), 3.80 (t, J¼7.0 Hz, 2H), 6.13 (s,
1H); 13C NMR (75 MHz)
d 14.0, 17.7, 22.5, 27.9, 28.8, 29.5, 30.8, 31.5,
47.7, 110.1, 117.3, 135.4, 136.2, 171.9; IR (ATR) 2953, 2924, 2858, 1678,
1565, 1499, 1411, 1295, 1035, 797, 723, 699 cmꢂ1; HRMS (DART-
ESIþ) Calcd for C14H20ClNOS [MþH]þ: 286.1032; found: m/z.
286.1031.
Other coupling products 3a,18 3b,19 3c,9 3d,10a 5a,9 5b,9 5e,20
5f,21 7a,18 10a,9 3i,22 10d,23 13d24 10j,25 17,14 18,26 20bd,23 20ed27
and 20gd28 are known in the literature.
Acknowledgements
This work was partially supported by KAKENHI (Priority Areas,
"Advanced Molecular Transformation of Carbon Resources") by
MEXT (gs1), Japan and A-STEP (Adaptable and Seamless Technology
transfer Program through target-driven R&D) by Japan Science and
Technology Agency (gs2). The authors thank Nara Institute of
Science and Technology, Kyoto-Advanced Nanotechnology Net-
work, supported by MEXT, Japan for measurements of high reso-
lution mass spectra.
9. Preliminary communication: Monguchi, D.; Fujiwara, T.; Furukawa, H.; Mori, A.
Org. Lett. 2009, 11, 1607.
10. After we have reported the preliminary communication (Ref. 9), the related
works on CN-bond-forming reactions have been published: (a) Wang, Q.;
Schreiber, S. L. Org. Lett. 2009, 11, 5178; (b) Kawano, T.; Hirano, K.; Satoh, T.;
Miura, M. J. Am. Chem. Soc. 2010, 132, 6900; (c) Matsuda, N.; Hirano, K.; Satoh,
T.; Miura, M. Org. Lett. 2011, 13, 2860; (d) Miyasaka, M.; Hirano, K.; Satoh, T.;
Kowalczyk, R.; Bolm, C.; Miura, M. Org. Lett. 2011, 13, 359; (e) Hirano, K.; Satoh,
T.; Miura, M. Org. Lett. 2011, 13, 2395; (f) Kim, J. Y.; Cho, S. H.; Joseph, J.; Chang,
S. Angew. Chem., Int. Ed. 2010, 49, 9899; (g) Joseph, J.; Kim, J. Y.; Chang, S. Chem.
dEur. J. 2011, 17, 8294; (h) Li, Y.; Xie, Y.; Zhang, R.; Jin, K.; Wang, X.; Duan, C. J.
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Lett. 2011, 13, 522; (j) Lamani, M.; Prabhu, K. R. J. Org. Chem. 2011, 76, 7938; (k)
Froehr, T.; Sindlinger, C. P.; Kloeckner, U.; Finkbeiner, P.; Nachtsheim, B. J. Org.
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12. During the course of our studies Chang reported the related coupling with
oxazole derivatives, however, no reaction was found to occur with thiazole
derivatives under similar conditions. See: Cho, S. H.; Kim, J. Y.; Lee, S. Y.; Chang,
S. Angew. Chem., Int. Ed. 2009, 48, 9127.
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16. Vasseur, A.; Muzart, J.; Bras, J. L. Chem.dEur. J. 2011, 17, 12556.
17. Although attempted reactions of thiophene derivatives with several secondary
amines in place of amides have been examined, it is not successful so far. In
addition, CH, NH coupling of thiophenes with amines and amides with NaOAc/
O2 did not proceed at all.
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