Copper/N,N,N',N'-tetramethylethylenediamine-catalyzed synthesis of N-substituted benzoheterocycles via C-S cross-coupling at ambient temperature in water

Article abstract of DOI:10.1002/adsc.201400043

Copper/N,N,N',N'-tetramethylethylenediamine (Cu/TMEDA)-catalyzed ambient temperature tandem reactions of isothiocyanates with 2-iodophenols or 2-iodoanilines in water without the protection of an inert atmosphere are described, which provide a simple, rapid, environmental method for the synthesis of a variety of 2-iminobenzo-1, 3- oxathioles and 2-aminobenzothiazoles in good yields. More important, the present reaction process needs only low amounts of copper catalyst (<1mol%) and can yield the products on a gram scale.

Full text of DOI:10.1002/adsc.201400043

FULL PAPERS
DOI: 10.1002/adsc.201400043
Copper/N,N,N’,N’-Tetramethylethylenediamine-Catalyzed
À
Synthesis of N-Substituted Benzoheterocycles via C S Cross-
Coupling at Ambient Temperature in Water
Na Zhao,a Liang Liu,a Fei Wang,a Jia Li,a and Wu Zhanga,*
a
Key Laboratory of Functional Molecular Solids, Ministry of Education, Anhui Laboratory of Molecule-Based Materials,
College of Chemistry and Materials Science, Anhui Normal University, Wuhu 241000, Peopleꢀs Republic of China
E-mail: zhangwu@mail.ahnu.edu.cn
Received: January 12, 2014; Revised: April 4, 2014; Published online: July 17, 2014
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201400043.
Abstract: Copper/N,N,N’,N’-tetramethylethylenedi- portant, the present reaction process needs only low
ACHTUNGTRENNUNGamine (Cu/TMEDA)-catalyzed ambient temperature amounts of copper catalyst (<1 mol%) and can yield
tandem reactions of isothiocyanates with 2-iodophe- the products on a gram scale.
nols or 2-iodoanilines in water without the protection
of an inert atmosphere are described, which provide Keywords: ambient temperature reaction; copper/
a simple, rapid, environmental method for the syn- N,N,N’,N’-tetramethylethylenediamine
thesis of a variety of 2-iminobenzo-1, 3- oxathioles TMEDA); C S cross-coupling; N-substituted benzo-
and 2-aminobenzothiazoles in good yields. More im- heterocycles; water
(Cu/
À
Introduction
high temperature and N2 protection were necessary.[9a]
We have developed a transition metal-free synthesis
Nitrogen-substituted benzoheterocycles especially 2- of 2-aminobenzothiazoles from 2-iodoanilines and iso-
iminobenzo-1,3-oxathioles and 2-aminobenzothiazoles thiocyanates using Phen as catalyst in water.[9b] Cai
are ubiquitous scaffolds found in many heterocyclic et al. also reported a copper-catalyzed approach to
derivatives. Most of them have been extensively stud- synthesize 2-imino-1,3-oxathioles in ionic liquids.[9c]
ied for their biological activity and medicinal value Despite these interesting works, developing an envi-
(Figure 1, A–D).[1–5] For example, compound A have ronmentally friendly process to synthesize N-substi-
been used as an agro-chemical pesticide,[2] the 2-imi- tuted benzoheterocycles at ambient temperature in
nobenzo-1,3-oxathiole derivative B has antifungal ac- water is still meaningful.
tivity,[3] while compound C has exhibited antioxidant
activity,[4] and compound D (R116010) is generally
used as a kind of inhibitor on retinoid metabolism.[5]
Hence, efficient strategies for constructing N-substi-
tuted benzoheterocycles have attracted a great deal of
attention.[6] Among them, the most common synthesis
À
method is intramolecular C S cross-coupling, and
copper was often utilized as the catalyst due to its low
cost and high activity.[7] For example, Bao et al. have
À
reported Cu-catalyzed intramolecular C S cross-cou-
pling for the preparation of 2-imino-1,3-oxathioles
and 2-aminobenzothiazoles in good yields.[8] However,
there still exist several problems, such as use of organ-
ic solvent, high temperature, long reaction time, large
amount of catalyst, and so on.
Recently, Dingꢀs group has realized the synthesis of
2-imino-1,3-oxathioles in water with 37% yield in the
Figure 1. Several nitrogen-substituted benzoheterocycle de-
rivatives which show biological activities and medicinal
presence of an inexpensive base, and in this reaction, value.
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Na Zhao et al.
Table 1. Optimization of the reaction conditions for the
preparation of 3a.[a]
Through a literature search we found that copper/
TMEDA catalyst has been widely used in organic syn-
thesis. In 1962, Hay utilized CuCl/TMEDA as catalyst
to synthesize diynes successfully.[10] Since then, the
catalyst was applied in the oxidative coupling reac-
tions of alkynes,[11] naphthol,[12] and some other cou-
pling reactions.[13] Domꢂnguez and co-workers utilized
copper salts to synthesize benzofuran and benzoxa-
zoles in the presence of TMEDA in water.[14] In 2011,
Lee et al. have synthesized various benzimidazoles
and 2H-indazoles with copper/TMEDA as catalyst.[15]
Herein, we envisioned a copper/TMEDA-catalyzed
synthesis of 2-iminobenzo-1,3-oxathioles and 2-amino-
benzothiazoles at ambient temperature in water.
Entry Catalyst
Base
Ligand
3a [%][b]
1
2
3
4
5
6
7
8
FeCl2·4H2O
FeCl3·6H2O
ZnCl2
CoCl2·6H2O
NiCl2·6H2O
CuSO4·5H2O
Cu (OAc)2·H2O
CuCl2·2H2O
NaHCO3 TMEDA trace
NaHCO3 TMEDA 57
NaHCO3 TMEDA trace
NaHCO3 TMEDA 34
NaHCO3 TMEDA 35
NaHCO3 TMEDA 93
NaHCO3 TMEDA 93
NaHCO3 TMEDA 93
9
Cu (NO3)2·3H2O NaHCO3 TMEDA 93
Cu (NO3)2·3H2O NaHCO3 TMEDA 81
10[c]
11
12
13[d]
14
15
16
17
18
19
20
21
22
23[e]
Results and Discussion
–
NaHCO3 TMEDA 42
NaHCO3
NaHCO3 TMEDA 82
Cu
Cu
Cu
Cu
Cu
Cu
Cu
Cu
Cu
Cu
Cu
Cu
G
AHCTUNGTRENNUNG
–
0
Initially, 2-iodophenol and phenyl isothiocyanate were
chosen as the model substrates for the synthesis of 2-
iminobenzo-1,3-oxathioles at ambient temperature in
water. The effects of catalyst, ligand, base and reac-
tion time were researched and the results are sum-
marized in Table 1. To explore the effect of catalyst
and ligand, several transition metal salts, such as iron,
zinc, cobalt, nickel and copper combined with
TMEDA were chosen as catalysts (Table 1, entries 1–
9). To our great delight, pleasing results were ob-
tained when copper salts/TMEDA were used as cata-
lyst, and the anion has negligible influence on the re-
action (Table 1, entries 6–9). Further study showed
A
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
NaHCO3 phen
NaHCO3 EDA
NaHCO3 DMEDA
NaHCO3 l-Pro
0
0
0
0
A
AHCTUNGTRENNUNG
Na2CO3
KOH
NaOH
K2CO3
TMEDA 87
TMEDA 90
TMEDA 84
TMEDA 88
U
AHCTUNGTRENNUNG
A
DABCO TMEDA 93
NaHCO3 TMEDA 80
AHCTUNGTRENNUNG
[a]
Reaction conditions: 1a (0.25 mmol), 2a (0.3 mmol), base
(1.0 equiv.), ligand (10 mol%), catalyst (0.8 mol%), H2O
(1 mL), stirred under air, ambient temperature, 4 h.
Isolated yield.
CuACHTNUGRTNEUNG(NO3)2·3H2O (1 ppm).
TMEDA (5 mol%).
2 h.
that 0.8 mol% CuACTHNUTRGNEUNG(NO3)2·3H2O could efficiently cata-
lyze the coupling reactions, and an 81% yield of prod-
uct was obtained with just a trace of catalyst [1 ppm
[b]
[c]
[d]
[e]
CuACHTUNGTRENNUNG(NO3)2·3H2O] (Table 1, entries 9 and 10). Blank
experiments without metal have been done (Table 1,
entry 11). The result showed that the target product
could be obtained with 42% yield in the presence of
10 mol% TMEDA alone.
action time was shortened to 2 h, the yield decreased
No product was obtained in the absence of to 80% (Table 1, entry 23). Therefore, the optimized
À
TMEDA (Table 1, entry 12). Changing the amount of reaction conditions for this C S bond cross-coupling
ligand from 10 to 5 mol% resulted in a decrease of are
Cu
R
(0.8 mol%),
TMEDA
yields (Table 1, entry 13). Then, 1,10-phenanthroline (10 mol%), NaHCO3 (1.0 equiv.), H2O (1 mL) and
(phen) was examined, because it was reported as an the reaction mixtures were stirred at ambient temper-
efficient ligand for this transformation at 808C. How- ature for 4 h without the protection of an inert atmos-
ever, the reaction was retarded at ambient tempera- phere.
ture, which is in accordance with the literature.[9a]
With the optimal conditions in hand, the scope and
(Table 1, entry 14). Subsequently, several other li- functional group compatibility of this method were in-
gands such as EDA, DMEDA and l-proline were also vestigated to prepare various 2-iminobenzo-1,3-oxa-
tested (Table 1, entries 15–17), the results showed that thioles and 2-aminobenzothiazoles. It is noteworthy
À
the addition of TMEDA is crucial to the C S cross- that the reaction could tolerate several functional
coupling reaction at ambient temperature. The reac- groups such as trifluoromethyl, cyano, chloro and
tion conditions were further optimized through chang- alkoxy (Table 2 and Table 3).
ing different bases (Table 1, entries 18–22), the result
It was found that excellent yields were afforded for
shows that both NaHCO3 and DABCO led to good substituted phenyl isothiocyanates with both electron-
yield. Taking the “green chemistry” concept into con- donating and electron-withdrawing substituents at
sideration, we choose NaHCO3 as base. When the re- a para or meso position (Table 2, entries 1–5). When
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Copper/N,N,N’,N’-Tetramethylethylenediamine-Catalyzed Synthesis
Table 2. Synthesis of 2-iminobenzo-1,3-oxathioles.[a] Table 3. Synthesis of 2-aminobenzothiazoles.[a]
R3
R2
Product
Yield [%][b]
Entry
R1/X
R2
Product
Yield [%][b]
Entry
1
2
3
4
5
6
7
8
H/I
H/I
H/I
H/I
H/I
H/I
H/I
H/I
4-CF3C6H4
4-ClC6H4
4-EtOC6H4
4-MeC6H4
3-ClC6H4
2-MeC6H4
2,6-Me2C6H3
C6H5CH2
n-dodecyl
cyclohexyl
C6H5
4-MeC6H4
4-ClC6H4
C6H5
4-MeC6H4
4-ClC6H4
C6H5
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3a
3a
99
95
94
91
1
2
3
4
5
6
7
8
H
H
H
H
H
H
H
H
H
H
H
4-Me
4-Me
4-Me
4-Cl
4-Cl
4-Cl
4-NO2
H
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
5o
5p
5q
–
99
99
99
99
91
89
4-CF3C6H4
4-CNC6H4
4-ClC6H4
4-EtOC6H4
4-MeC6H4
3-ClC6H4
2-MeC6H4
C6H5CH2
n-dodecyl
cyclohexyl
C6H5
4-MeC6H4
4-ClC6H4
C6H5
4-MeC6H4
4-ClC6H4
C6H5
97
52 (81)[c]
trace (64)[c]
93
61 (97)[c]
50 (91)[c]
24 (55)[c]
9
61 (99)[c]
9
H/I
H/I
15 (54)[c]
10
11
12
13
14
15
16
17
18
trace (87)[c]
10
11
12
13
14
15
16
17
18
trace (56)[c]
4-Me/I
4-Me/I
4-Me/I
4-Cl/I
4-Cl/I
4-Cl/I
H/Br
H/Cl
95
93
99
91
89
94
–
93
91
97
41
33
62
nr
C6H5
–
[a]
[a]
Reaction conditions: 1 (0.25 mmol), 2 (0.3 mmol), base
(1.0 equiv.), ligand (10 mol%), Cu(NO3)2·3H2O
Reaction conditions: 4 (0.25 mmol), 2 (0.3 mmol), base
(1.0 equiv.), ligand (10 mol%), Cu(NO3)2·3H2O
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
(0.8 mol%), H2O (1 mL), stirred under air, ambient tem-
perature, 4 h.
Isolated yield.
(0.8 mol%), H2O (1 mL), stirred under air, ambient tem-
perature, 2 h.
Isolated yield.
[b]
[c]
[b]
[c]
Yields at 808C are given in parentheses.
Yields at 808C are given in parentheses.
the ortho position of the phenyl ring was occupied phenyl isothiocyanate were used under the optimized
with a methyl group, the reaction yield was decreased conditions.
to 52% (Table 2, entry 6). This result showed that the
Having successfully developed the copper/
steric hindrance had an adverse effect on the reaction, TMEDA-catalyzed one-pot synthesis of 2-iminoben-
no product was detected when 2,6-dimethylphenyl zo-1,3-oxathioles, we attempted to further apply this
isothiocyanate was employed as substrate (Table 2, method
entry 7), and 64% of the product was obtained at (Table 3). To our surprise, various 2-aminobenzothia-
808C. zoles were obtained within 2 h at ambient tempera-
to
synthesize
2-aminobenzothiazoles
The alkyl isothiocyanates participated in the de- ture in water. As with 2-iodophenols, there was no
sired products, albeit in low yields. However, the significant substituent effects of the phenyl isothiocya-
yields could be improved by raising the temperature nates (Table 3, entries 2–7). Besides, sterically hin-
to 808C (Table 2, entries 8–10). Several typical 2-iodo- dered 2-methylphenyl isothiocyanate and benzyl iso-
phenol derivatives were then probed, and the results thiocyanates were tolerated in this reaction (Table 3,
are showed in Table 2 (entries 11–16). Fortunately, entries 8 and 9). However, n-dodecyl and cyclohexyl
both electron-poor and electron-rich 2-iodophenols isothiocyanates only gave traces of the corresponding
gave the corresponding products in excellent yields. products at ambient temperature, and moderate to
Unfortunately, the desired compounds were not ob- good yield coulds be obtained at 808C (Table 3, en-
tained upon using o-bromophenol and o-chlorophe- tries 10 and 11). The electronic effects of 2-iodoani-
nol, respectively, at ambient temperature in water lines played a significant role. In general, the reactivi-
(Table 2, entries 17 and 18).
ty of 2-iodoanilines with electron-withdrawing sub-
With the consideration that 2-iminobenzo-1,3-oxa- stituents was obviously lower than those with elec-
thioles are mainly applied in pharmaceutical inter- tron-donating substitutes (Table 3, entries 12–17). Fur-
mediates, gram-scale syntheses were tried. To our sat- thermore, the reaction was hardly inhibited in the
isfaction, a 91% yield was obtained when 10.96 g presence of a nitro group (Table 3, entry 18). It is
(50 mmol) of 2-iodophenol and 7.2 mL (60 mmol) of worth mentioning that most of the crude products
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Na Zhao et al.
with ethyl acetate or dimethyl sulfoxide (3ꢃ10 mL), the or-
ganic layer was washed with water (2ꢃ10 mL), then dried
over anhydrous Na2SO4 and evaporated under vacuum.
Most of the crude products were recrystallized to afford the
pure corresponding products 5a–5q.
were recrystallized to afford the pure corresponding
2-aminobenzothiazoles.
Conclusions
To sum up, a facile and efficient copper/TMEDA-cat-
alyzed method has been developed for one-pot con-
struction of nitrogen-substituted O,S or N,S benzohe-
terocycles in yields up to 99%. The low amount of
catalyst makes this procedure attractive to the
chemistry community. One point worthy of special at-
tention is that the reactions were carried out at ambi-
ent temperature in water and this new method has
potential value for industrial applications.
Acknowledgements
Financial supports from the National Natural Science Foun-
dation of China (20972002, 21272006) are gratefully appreci-
ated.
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Typical Experimental Procedure for Copper/
TMEDA-Catalyzed Tandem Reactions of 2-
Iodophenols with Isothiocyanates
A mixture of 2-iodophenols 1 (0.25 mmol), isothiocyanate 2
(0.30 mmol, 1.2 equiv.), NaHCO3 (0.25 mmol, 1 equiv.),
TMEDA (10 mol%), CuACHTUNTRGNEUNG(NO3)2·3H2O (0.8 mol%) and H2O
(1 mL) was stirred 4 h in air at ambient temperature. Then
the reaction was stopped and the mixture was extracted
with ethyl acetate (3ꢃ10 mL), the organic layer was washed
with water (2ꢃ10 mL), then dried over anhydrous Na2SO4
and evaporated under vacuum. The crude product was puri-
fied by column chromatography on silica gel using petrole-
um ether/ethyl acetate as an eluent to give the correspond-
ing products 3a–3q.
Typical Experimental Procedure for Copper/
TMEDA-Catalyzed Tandem Reactions of 2-
Iodoanilines with Isothiocyanates
A mixture of 2-iodoanilines 4 (0.25 mmol), isothiocyanates 2
(0.30 mmol, 1.2 equiv.), NaHCO3 (0.25 mmol, 1 equiv.),
TMEDA (10 mol%), CuACHTUNTRGNEUNG(NO3)2·3H2O (0.8 mol%) and H2O
(1 mL) was stirred 2 h in air at ambient temperature. Then
the reaction was stopped and the mixture was extracted
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