An efficient tandem elimination-cyclization-desulfitative arylation of 2-(gem-dibromovinyl)phenols(thiophenols) with sodium arylsulfinates

Article abstract of DOI:10.1039/c2ob27232f

An efficient tandem elimination-cyclization-desulfitative arylation of 2-(gem-dibromovinyl)phenols(thiophenols) with sodium arylsulfinates has been developed. In the presence of TBAF-PdCl₂-Cu(OAc)₂-NEt ₃, the reactions gen

Full text of DOI:10.1039/c2ob27232f

Organic &
Biomolecular
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An efficient tandem elimination–cyclization–
desulfitative arylation of 2-(gem-dibromovinyl)phenols-
thiophenols) with sodium arylsulfinates†
Cite this: Org. Biomol. Chem., 2013, 11,
420
(
Received 4th September 2012,
Accepted 19th November 2012
a
a
a
a
a,b
Wei Chen, Pinhua Li, Tao Miao, Ling-Guo Meng* and Lei Wang*
DOI: 10.1039/c2ob27232f
www.rsc.org/obc
An efficient tandem elimination–cyclization–desulfitative aryla- and have been less used as an aryl source via desulfitative
8
tion of 2-(gem-dibromovinyl)phenols(thiophenols) with sodium reactions. Most recently, there are several reports on the
arylsulfinates has been developed. In the presence of TBAF–PdCl
Cu(OAc) –NEt , the reactions generated 2-arylbenzofurans(thio- equivalents of organometallics in the presence of Pd-catalyst,
phenes) with good yields in one-pot under ligand-free conditions. with olefins, nitriles, aldehydes, CuCN, and desulfitative
2
–
tandem desulfitative reactions of sodium arylsulfinates, as
2
3
9
10
11
12
1
3
C–H arylation with a variety of heterocyclic compounds. It
should be noted that Sato and Okoshi reported a Pd-catalyzed
desulfitative biaryl synthesis using sodium sulfinates with
aromatic bromides under harsh conditions (at 150 °C) in the
presence of an essential P-ligand 1,2-bis(diphenylphosphino)-
Heterocyclic compounds are widely found in nature, such as
in biological systems, pharmaceuticals, materials, agriculture
and photography. Benzofurans and benzothiophenes are not
1
only important as building blocks, but also as the structural
2
skeleton of natural products and potential drugs. Because of
14
ethane in 1992. However, little progress has been made in
this field since then.
their importance, the development of practical synthetic
methods for the synthesis of them is highly desirable. Among
the reported synthetic methods, the palladium-catalyzed cross-
gem-Dihaloolefins, as one of the important and valuable
synthetic intermediates because of their higher reactivity and
coupling–cyclization reaction from alkynes and o-halophenols
15
easy preparation, have attracted much attention in recent
3
(
thiophenols) is one of the most efficient protocols. Although
16
years. Especially, 2-(gem-dibromovinyl)phenols, 2-(gem-dibromo-
it offers functional group tolerance and good yields of the pro-
ducts, the scope of o-halophenols(thiophenols) is limited.
Recently, the syntheses of benzofurans via Pd-catalyzed reac-
tion of phenols with propiolates, and Fe-catalyzed reaction of
vinyl)thiophenols and 2-(gem-dibromovinyl)anilines were used
17
for the synthesis of heterocycles, including indoles, ben-
18
17d,18b
zothiophenes, and benzofurans
on the basis of tran-
sition-metal-catalyzed tandem C–N/C–C coupling with
4
phenols with β-ketoesters were developed, respectively.
17a,18a
17c
17d
organoborons,
alkenes,
and alkynes.
During the
Arenesulfonyl chlorides, as aryl sources for C–C bond for-
investigation of the mechanistic pathway of Pd-catalyzed C–N/
mation via tandem desulfitative C–C coupling reactions have
Suzuki reaction, Lautens suggested 2-bromoindole as an
5
been explored by Kasahara, Miura, Vogel, and Dong et al.
17i
intermediate,
and 2-bromobenzofurans(thiophenes) and
After then, Wang developed a desulfitative Heck-type reaction
of arylsulfinic acids with alkenes, and the desulfitative
2
-bromoindoles from 2-(gem-dibromovinyl)phenols(thiophe-
18b
19
nols) and 2-(gem-dibromovinyl)anilines via Cu- and Pd-cata-
lyzed intramolecular reactions were obtained. It is essential to
expand the application of 2-bromobenzofused heterocycles
from gem-dibromoolefins and their further transformations.
As part of our ongoing efforts on the organic reactions
6
addition of arylsulfinic acids to nitriles. Compared with
moisture-sensitive arylsulfonyl chlorides and arylsulfinic acids,
sodium arylsulfinates are more stable, and may serve as the
aryl source via the expulsion of SO for C–C bond formation,
2
7
although they are generally used as sulfonylation reagents
20
of gem-dihaloolefins, herein, we report a novel tandem
elimination–cyclization–desulfitative arylation reaction of 2-(gem-
a
dibromovinyl)phenols(thiophenols) with sodium arylsulfinates
Department of Chemistry, Huaibei Normal University, Huaibei, Anhui 235000,
2 2 3
in the presence of TBAF–PdCl –Cu(OAc) –NEt . The reactions
afforded 2-arylbenzofurans(thiophenes) with good yields in
one-pot at 110 °C under mild conditions (Scheme 1).
P. R. China. E-mail: leiwang@chnu.edu.cn; Fax: +86-561-309-0518;
Tel: +86-561-380-2069
b
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, Shanghai 200032, P. R. China
The initial investigation was focused on the optimization of
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c2ob27232f
reaction conditions for
a
model reaction of 2-(gem-
1
4
20 | Org. Biomol. Chem., 2013, 11, 420–424
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a
Table 2 Effect of base and solvent on the model reaction
b
Entry
Base
KF
Solvent
3a [%]
1
2
3
4
5
6
7
8
9
DMF
DMF
DMF
DMF
DMF
DMF
DMF
NMP
THF
17
30
36
41
52
54
72
55
44
41
35
Trace
K
2
CO
Cs CO
DBU
3
2
3
DABCO
N(n-Bu)
3
Scheme 1
NEt
NEt
NEt
NEt
NEt
NEt
3
3
3
3
3
3
10
DMSO
Toluene
a
Table 1 Effect of Pd source and oxidant on the model reaction
11
12
3
CH CN
a
Reaction conditions: 1a (0.50 mmol), TBAF (1.0 mmol) in solvent
(
(
1
3.0 mL) at room temperature for 4 h, then 2a (1.0 mmol), PdCl
2
0.050 mmol), Cu(OAc)
2
(1.0 mmol), base (1.0 mmol) at 110 °C for
b
2 h. Isolated yields.
b
Entry
Pd catal.
Oxidant
3a [%]
1
2
3
4
5
6
7
8
9
PdCl
PdCl
Pd(OAc)
Pd(PPh
Pd(PPh
Pd(dba)
2
Cu(OAc)
—
2
72
10
61
55
49
45
38
42
35
32
27
Trace
Trace
On the other hand, the base is also essential in the reac-
tion. A variety of bases were examined and the results indi-
cated that NEt was the most effective one among the
examined bases (Table 2, entry 7). Other bases, N(n-Bu)3,
DABCO (1,4-diazabicyclo[2.2.2]octane), DBU (1,8-diazabicyclo-
2
2
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
2
2
2
2
2
3
)
)
2
Cl
2
3
3
4
2
PdCl
PdCl
PdCl
PdCl
PdCl
PdCl
PdCl
2
2
2
2
2
2
2
(CH
3
CN)
2
PhI(OAc)
2
2 3 2 3
[5.4.0]undec-7-ene), Cs CO K CO and KF were inferior and
K
2
S
2
O
8
S
10
11
12
13
(NH
Ag
DDQ
TBHP
)
4 2
2
O
8
generated 3a in 17–54% yields (Table 2, entries 1–6). The
solvent plays an important role in the model reaction. Among
the solvents examined, DMF (N,N-dimethylformamide) was the
most suitable media (Table 2, entry 7). NMP (N-methyl-2-pyrro-
lidone), THF (tetrahydrofuran), DMSO (dimethyl sulfoxide)
and toluene were less effective solvents, and 35–55% yields of
3a were obtained (Table 2, entries 8–11). When the model reac-
2
O
a
Reaction conditions: 1a (0.50 mmol), TBAF (1.0 mmol) in DMF
(
(
3.0 mL) at room temperature for 4 h, then 2a (1.0 mmol), Pd catal.
0.050 mmol), oxidant (1.0 mmol), NEt (1.0 mmol) in DMF at 110 °C
3
b
for 12 h. Isolated yields.
tion was performed in CH
3
CN, no product was detected and
the starting materials were recovered (Table 2, entry 12). The
dibromovinyl)phenol (1a) with sodium benzenesulfinate (2a). reaction temperature and time also effected the reaction. The
tetra-(n-Butyl)ammonium fluoride (TBAF), palladium and model reaction was accomplished in the presence of TBAF–
oxidant are essential in the reaction. As listed in Table 1, PdCl
exhibited the highest reactivity in the model reaction among
the palladium catalysts tested in the presence of TBAF and Cu dibromovinyl)thiophenols was examined in the elimination–
OAc) in DMF (Table 1, entry 1). In the absence of Cu(OAc)
cyclization–desulfitative arylation with sodium benzenesulfi-
2
2 2 3
PdCl –Cu(OAc) –NEt at 110 °C in 12 h.
The scope of the 2-(gem-dibromovinyl)phenols and 2-(gem-
(
2
2
,
the desired product 3a was isolated only in 10% yield (Table 1, nate (2a) under the optimized reaction conditions. As can be
entry 2). Other palladium catalysts, Pd(OAc) , Pd(PPh ) Cl , Pd seen from Table 3, the tandem reactions of 2a with 2-(gem-
2
3 2
2
3 4 2 2 3 2
(PPh ) , Pd(dba) and PdCl (CH CN) were subsequently dibromovinyl)phenols (1a-j) generated the corresponding pro-
inferior (Table 1, entries 3–7). Next, a number of oxidants were ducts (3a-j) in good yields. Electron-donating and electron-
examined in the presence of TBAF–PdCl –NEt3 in DMF, and withdrawing groups on the benzene rings of 2-(gem-dibromo-
2
Cu-(OAc)
OAc) , K
efficiency, and only 27–42% yields of 3a were obtained C H , and a weak electron-withdrawing group, such as Cl, on
2
was found to be the most effective. The use of PhI- vinyl)phenols were tolerated. 2-(gem-Dibromovinyl)phenols
(
2
2
S
2
O
8
, (NH and Ag O showed relatively lower with an electron-donating group, such as CH , CH O, and t-
4
)
2
S
2
O
8
2
3
3
4
9
(Table 1, entries 8–11). However, DDQ (2,3-dichloro-5,6- the para-positions of phenols, gave superior yields of the pro-
dicyano-1,4-benzoquinone) and TBHP (tert-butyl hydroperox- ducts (3b-e) to that of 3a and 3g, without a substituted group
ide) were inactive (Table 1, entries 12 and 13).
and with a strong electron-withdrawing group (NO ) on the
2
benzene rings. It is obvious that 2-(gem-dibromovinyl)phenols
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a
Table 3 The scope of 2-(gem-dibromovinyl)phenols(thiophenols) in the
Table 4 The scope of sodium arylsulfinates in the tandem reaction
a
reaction
a
Reaction conditions: 1a (0.50 mmol), TBAF (1.0 mmol) in DMF
(
(
3.0 mL) at room temperature for 4 h, then 2 (1.0 mmol), PdCl
2
0.05 mmol), Cu(OAc)
2
(1.0 mmol), NEt
3
(1.0 mmol) in DMF at 110 °C
b
for 12 h. Isolated yields.
a
Reaction conditions: 1 (0.50 mmol), TBAF (1.0 mmol) in DMF
(
3.0 mL) at room temperature for 4 h, then 2a (1.0 mmol), PdCl
0.05 mmol), Cu(OAc) (1.0 mmol), NEt (1.0 mmol) in DMF at 110 °C
2
(
2
3
b
for 12 h. Isolated yields.
with CH
product yield than that on the para-position of phenol
3f vs. 3c).
Meanwhile, a slight ortho-position effect of phenol was
3
O on the meta-position of phenol gave an inferior
(
observed in the reaction (3c and 3f vs. 3h). 2-(gem-Dibromo-
vinyl)(2,4-dichloro)phenol (1i) and 2-(gem-dibromovinyl)(2,4-
dimethyl)phenol (1j) underwent the reaction well and afforded
the corresponding products 3i and 3j in 81% and 62% yields,
respectively. Under the present reaction conditions, 1-(gem-
dibromovinyl)-2-naphthalenol also underwent the tandem
reaction to generate 3k in 63% yield.
Scheme 2 Possible reaction mechanism.
Although the exact mechanism of this reaction is not clear,
It should be noted that 2-(gem-dibromovinyl)thiophenols a possible pathway is proposed in Scheme 2. The reaction
1l and 1m) also reacted with 2a under the present reaction might be through an elimination of 2-(gem-dibromovinyl)-
(
conditions to afford the corresponding products 2-arylbenzo- phenol and then intramolecular nucleophilic addition
thiophenes 3l and 3m in 65% and 71% yields, respectively.
(cyclization) affording 2-bromobenzofuran, and Pd-catalyzed
On the other hand, the desulfitative arylation reaction desulfitative arylation of sodium arylsulfinate with 2-bromo-
between 2-(gem-dibromovinyl)phenol (1a) with various sodium benzofuran to generate the desired product. Firstly, an elimi-
substituted arylsulfinates was investigated and the results were nation of HBr from 2-(gem-dibromovinyl)phenol (1a) was
summarized in Table 4. Sodium arylsulfinates, with different promoted by TBAF to give an intermediate C, followed by an
3 4 9 3
functional groups, including CH , Cl, Br, tert-C H , CH O, intramolecular nucleophilic addition of C assisted by fluoride
NO , F, and CN groups on the para- or meta-position of anion to afford 2-bromobenzofuran. On the other hand,
2
benzene rings, reacted with 1a smoothly to generate the sodium arylsulfinate (2) reacted with Pd(II) through a ligand
desired products (4a–h) in 60–74% yields. It is obvious that an exchange to form a Pd(II)-sulfinate intermediate A, which sub-
ortho-position effect was observed in the reaction and 53% sequently underwent desulfitation to form an aryl–Pd(II)–X
yield of the product (4i) was isolated.
species B and release SO . The formed B reacted with D, which
2
was generated from an oxidative addition of the obtained
4
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(
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2
the reduction of PdCl in DMF–NEt at 110 °C for 6 h, followed
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(
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(
2
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furans(thiophenes) has been developed. In the presence of
TBAF–PdCl –Cu(OAc) –NEt , the reactions of 2-(gem-dibromo-
vinyl)phenols(thiophenols) with sodium arylsulfinates pro-
ceeded well to afford the desired products with good yields in
one-pot under ligand-free conditions. An extended investi-
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