A highly efficient tandem reaction of 2-(gem-dibromovinyl) phenols(thiophenols) with organosilanes to 2-arylbenzofurans (thiophenes)

Article abstract of DOI:10.1002/adsc.201100875

2-Arylbenzofurans(thiophenes) were prepared through an efficient tandem elimination-intramolecular addition-Hiyama cross-coupling reaction. In the presence of tetra-(n-butyl)ammonium fluoride (TBAF), palladium(II) acetate [Pd(OAc)₂] and triphenylphosphine (PPh₃), the reaction of 2-(gem-dibromovinyl)phenols(thiophenols) with phenyl(trialkoxy)silanes proceeded smoothly and generated the corresponding products with good yields in one-pot. It should be noted that TBAF plays an important role in the tandem reaction. Copyright

Full text of DOI:10.1002/adsc.201100875

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DOI: 10.1002/adsc.201100875
A Highly Efficient Tandem Reaction of 2-(gem-Dibromovinyl)-
phenols(thiophenols) with Organosilanes to 2-Arylbenzofurans
(thiophenes)
Jie Liu,a,b Wei Chen,a Yong Ji,c and Lei Wanga,*
a
Department of Chemistry, Huaibei Normal University, Huaibei, Anhui 235000, Peopleꢀs Republic of China
Fax : (+86)-561-309-0518, phone: (+86)-561-380-2069; e-mail: leiwang@chnu.edu.cn
College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, Jiangsu 215123,
b
Peopleꢀs Republic of China
Department of Chemistry, Anhui Agricultural University, Hefei, Anhui 230036, Peopleꢀs Republic of China
c
Received: November 7, 2011; Revised: January 29, 2012; Published online: && &&, 0000
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201100875.
Abstract: 2-Arylbenzofurans(thiophenes) were pre- corresponding products with good yields in one-pot.
pared through an efficient tandem elimination–intra- It should be noted that TBAF plays an important
molecular addition–Hiyama cross-coupling reaction. role in the tandem reaction.
In the presence of tetra-(n-butyl)ammonium fluoride
(TBAF), palladium(II) acetate [Pd
(OAc)2] and tri- Keywords:
2-arylbenzofurans;
2-arylbenzothio-
phenylphosphine (PPh3), the reaction of 2-(gem-di- phenes; 2-(gem-dibromovinyl)phenols; 2-(gem-dibro-
bromovinyl)phenols(thiophenols) with phenyl(trialk- movinyl)thiophenols; organosilanes; tandem reac-
ACHTUNGTRENNUNGoxy)silanes proceeded smoothly and generated the tions
Introduction
general, the Hiyama reaction is catalyzed by palladi-
um and promoted by fluoride anion, which is needed
Benzofurans(thiophenes) are versatile building blocks for activation of the stable silicon-carbon bond.[5d]
and an important structural skeleton of natural prod-
Over the past decade, gem-dihaloolefins have re-
ucts, optoelectronic materials and potential drug mol- ceived much attention owing to their higher reactivity
ecules.[1,2] Because of their extensive applications, the and easy accessibility from aldehydes.[7] Especially, 2-
development of practical synthetic methods is more (gem-dibromovinyl)phenols, -thiophenols and -ani-
and more essential. Among the syntheses of benzofur- lines, were widely used for the synthesis of various
ans(thiophenes), the palladium-catalyzed tandem heterocycles, including indoles,[8] benzothiophenes,[9]
cross-coupling/cyclization starting from alkynes and o- and benzofurans[8d,9b] through a transition metal-cata-
halophenols(thiophenol) is the most efficient and lyzed tandem Ullman-type reaction (or amination)–
modern protocol.[3] Although it offers increased func- Suzuki (or Heck, or Sonogashira) cross-coupling with
tional group tolerance and improved yields of the de- organoboron reagents,[8a,9a] alkenes,[8c] or alkynes.[8d]
sired compounds, the scope of o-halophenols(thiophe- Most recently, Lautens et al. first isolated 2-bromo-
nol) is limited. Recently, a palladium-catalyzed syn- benzofurans(thiophenes) and 2-bromoindoles from 2-
thesis of benzofurans from simple phenols with pro- (gem-dibromovinyl)phenols(thiophenols)[9b] and 2-
piolates, and an iron- catalyzed synthesis of benzofur- (gem-dibromovinyl)anilines[10] through Cu- and Pd-
ans through reaction of simple phenols with b-keto catalyzed intramolecular cross-coupling reactions, re-
esters were developed, respectively.[4]
spectively.
The Hiyama reaction of aryl halides with organosi-
It is highly desirable to expand the application
lanes has been recognized as one of the powerful scope of gem-dibromoolefins and provide a practical
tools for carbon-carbon bond formation.[5] Organosi- straightforward route to 2-bromobenzofused hetero-
lanes, due to their low cost and toxicity, easy availabil- cycles, as significant synthetic intermediates, which
ity, and high stability,[5c] were used as the an alterna- subsequently were used as electrophiles for carbon-
tive coupling partner to organoborons in Suzuki cou- carbon bond formation via transition metal-catalyzed
pling, and organostannanes in Stille reactions.[6] In cross-coupling reactions. In continuation of our efforts
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Scheme 1.
Table 1. Optimization of the reaction conditions for the
on the organic transformations of gem-dihaloole-
fins,[11] here we report a novel tandem reaction of 2-
(gem-dibromovinyl)phenols(thiophenols) with phe-
nyl(trialkoxy)silanes in the presence of tetra-(n-but-
model reaction.[a]
ACHTUNGTRENNUNGyl)ammonium fluoride (TBAF) and PdACHTUNGTREN(NUNG OAc)2/PPh3.
The reaction proceeded smoothly under the present
reaction conditions through an elimination/intramo-
lecular addition/Hiyama cross-coupling tandem reac-
tion process and generated the corresponding 2-aryl-
benzofurans(thiophenes) with good yields in one-pot
(Scheme 1). It is important to note that TBAF plays
an important role in the tandem elimination, intramo-
lecular addition and Hiyama coupling reaction.
Entry Pd catal./ligand
(mol%)
Solvent/
3a
AHCTUNGTRENNUNG
temp. [8C] [%][b]
1
Pd
U
NMP/80
DMF/80
dioxane/80 31
THF/80
DMSO/80
76; 0[c]
46
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16[d]
17[e]
18[f]
19[g]
Pd(OAc)2 (5)/PPh3 (10)
Pd(OAc)2 (5)/PPh3 (10)
Pd(OAc)2 (5)/PPh3 (10)
Pd(OAc)2 (5)/PPh3 (10)
Pd(OAc)2 (5)/PPh3 (10)
Pd(TFA)2 (5)/PPh3 (10)
PdCl2 (5)/PPh3 (10)
Pd(PPh3)4 (5)
Pd(PPh3)2Cl2 (5)
PdCl2A(CH3CN)2 (5)
Pd(OAc)2 (5)/dppf (10)
Pd(OAc)2 (5)/PCy3 (10)
Pd(OAc)2 (5)/P
Pd(OAc)2 (5)
Pd(OAc)2 (5)/PPh3 (10)
Pd(OAc)2 (5)/PPh3 (10)
Pd(OAc)2 (5)/PPh3 (10)
Pd(OAc)2 (5)/PPh3 (10)
ACHTUNGTRENNUNG
A
N
N
R
N
15
11
toluene/80 trace
NMP/80
NMP/80
NMP/80
NMP/80
NMP/80
NMP/80
NMP/80
55
41
47
34
61
50
45
36
trace
55
76
56
63
Results and Discussion
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
The initial investigation was focused on the optimiza-
tion of reaction conditions for the model reaction of
2-(gem-dibromovinyl)phenol (1a) and phenyltrime-
thoxysilane (2a). Tetra-(n-butyl)ammonium fluoride
(TBAF), palladium catalyst, as well as a suitable P
ligand are essential for the model reaction. As listed
in Table 1, the solvent plays an important role in the
model reaction. Among the solvents tested, N-
methyl-2-pyrrolidone (NMP) was the most suitable
reaction media. N,N-Dimethylformamide (DMF), di-
oxane, tetrahydrofuran (THF), and dimethyl sulfoxide
(DMSO) were subsequently found to be inferior.
However, only a trace amount of the desired product
3a was detected when the model reaction was carried
out in toluene (Table 1, entries 1–6). For screening the
effect of the palladium salt and its complex on the re-
action, the model reaction could be performed in the
presence of a catalytic amount (5 mol%) of palladium
salt/P ligand or palladium complex, such as
CTHUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
N
N
E
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
NMP/80
NMP/80
NMP/80
NMP/60
NMP/100
[a]
Reaction conditions: 1a (0.5 mmol), 2a (1.0 mmol), Pd
catal. (5.0 mol%), ligand (10 mol%) if necessary,
P
TBAF (3 equiv.) in solvent (2.0 mL), sealed tube, 808C,
air, 12 h.
Isolated yields.
In the absence of TBAF.
TBAF (2 equiv.).
TBAF (4 equiv.).
[b]
[c]
[d]
[e]
[f]
At 608C for 18 h.
At 1008C for 12 h.
[g]
Pd
Pd
N
Pd
E
PdCl2/PPh3,
(OAc)2/
G
N
ACHTUNGTRENNUNG
dppf, Pd
N
N
ACHTUNGTRENNUNG
at 808C for 12 h and 3a was isolated in 34–76% yields not completed with less than 3 equiv. of TBAF. But,
(Table 1, entries 1 and 7–14). To our delight, a 76% no increased yield of 3a was found with more than
yield of 3a was obtained, representing the best result, 3 equiv. of TBAF (Table 1, entries 16 and 17). It
when PdACHTUNGTRENNUNG(OAc)2/PPh3 and TBAF (3 equiv.) were used should be noted that an inferior yield of 3a was ob-
in the model reaction (entry 1). It is obvious that pal- tained when the reaction temperature is below 808C
ladium, as well as the P ligand are essential in the re- on prolonging reaction time, and the reaction was
action (Table 1, entries 1 and 15). With respect to the completed in 12 h at 808C (Table 1, entries 18 and
amount of TBAF in the reaction, 3 equiv. of TBAF 19).
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A Highly Efficient Tandem Reaction of 2-(gem-Dibromovinyl)phenols(thiophenols) with Organosilanes
Scheme 2. The scope of 2-(gem-dibromovinyl)phenols(thiophenols) in the tandem reaction. Reaction conditions:
1 (0.50 mmol), 2a (1.0 mmol), Pd
tube, 808C, air, 12 h.
ACHTUGNRTEN(NUGN OAc)2 (0.025 mmol), PPh3 (0.050 mmol), TBAF (1.50 mmol) in NMP (2.0 mL), sealed
Under the optimized reaction conditions, the scope group, such as Cl, on the para-position of phenols,
of substituted 2-(gem-dibromovinyl)phenols and 2- gave superior yields of the products (3b–e) over that
(gem-dibromovinyl)thiophenols with phenyl(trime- of 3a or 3f, without any substituted group, or a strong
thoxy)silane (2a) in the tandem elimination/addition/ electron-withdrawing group, such as NO2 on the phe-
cross-coupling reaction was investigated. As can be nols. It should be noted that 2-(gem-dibromovinyl)-
seen from Scheme 2, the tandem reactions of phenyl- phenol with a strong electron-donating functionality,
ACHTUNGTRENNUNG(trimethoxy)silane with substituted 2-(gem-dibromovi- such as MeO on the meta-position of phenol gave an
nyl)phenols (Scheme 2, 1a–o) produced the corre- inferior yield of the product (3g). Meanwhile, an
sponding products (3a–o) in moderate to good yields. ortho-position effect is not obvious for Me, MeO, and
A variety of 2-(gem-dibromovinyl)phenols bearing Ph groups on the ortho-position of the phenols in the
substituents on the benzene ring were examined. The reaction (3h–j vs. 3a). However, a slight ortho-effect
results in Scheme 2 indicated that a variety of func- has been observed for relatively larger bulky groups,
tional groups, including electron-donating and elec- such as EtO and t-Bu groups (3k and 3l). Disubstitut-
tron-withdrawing ones were tolerated. 2-(gem-Dibro- ed 2-(gem-dibromovinyl)phenols, such as 1m and 1n,
movinyl)phenols with an electron-donating group, also underwent good conversions and afforded the
such as Me, MeO, t-Bu, and a weak electron-donating corresponding products 3m and 3n in 79 and 67%
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Scheme 3. The reactions of phenyl(triethoxy)silane. Reaction conditions:
1 (0.50 mmol), 2b (1.0 mmol), PdACHTUNGTRENNUNG(OAc)2
(0.025 mmol), PPh3 (0.050 mmol), TBAF (1.50 mmol) in NMP (2.0 mL), sealed tube, 808C, air, 12 h.
Scheme 4. The tandem reaction of 1r with 2a. Reaction conditions: 1r (0.50 mmol), 2a (0.5 or 1.0 mmol), Pd
(0.025 mmol), PPh3 (0.050 mmol), TBAF (1.50 mmol) in NMP (2.0 mL), sealed tube, 808C, air, 12 or 24 h.
ACHTUNGTRENNUNG(OAc)2
yields, respectively. Under the recommended reaction benzofuran. Initially, an elimination of HBr from 2-
conditions, 1-(gem-dibromovinyl)-2-naphthalenol also (gem-dibromovinyl)phenol (1a) to intermediate I
underwent the tandem reaction to generate the corre- takes place in the presence of TBAF,[12] followed by
sponding product 3o in 81% yield. The present reac- an intramolecular nucleophilic addition of an oxygen
tion conditions were also suitable for the synthesis of atom of I to afford a cyclization product, 2-bromoben-
2-arylbenzothiophenes (3p and 3q) from the corre- zofuran, assisted by fluoride anion. The obtained 2-
sponding 2-(gem-dibromovinyl)thiophenols (1p and bromobenzofuran then underwent an intermolecular
1q) and phenyl(trimethoxy)silane (2a).
cross-coupling with phenyl(trimethoxy)silane (2a) in
In order to expand to the scope of organosilanes, the presence of classical Hiyama reaction conditions
the tandem reactions of phenyl(triethoxy)silane (2b) (Pd as catalyst and TBAF as assistant) to afford the
with 1a and 1e were carried out under the present re- final product (3a) through a general oxidative addi-
action conditions, and the anticipated products, 3a tion–transmetallation–reductive elimination process.
and 3e were isolated in 74 and 83% yields, respective-
ly (Scheme 3).
To verify the formation of 2-bromobenzofuran, the
reaction of 1a was carried out in the presence of
When the reaction of 4-bromo-2-(gem-dibromovi- TBAF, and 2-bromobenzofuran was isolated in 92%
nyl)phenol (1r) and phenyl(trimethoxy)silane (2a) in yield. The obtained 2-bromobenzofuran was then re-
a 1:1 molar ratio was performed at 708C for 12 h, the acted with 2a under the present reaction conditions
corresponding product 3r was obtained in 65% yield. [TBAF/PdACTHNUGRTNEUNG(OAc)2/PPh3] to give 3a in 85% yield
On the other hand, when the reaction of 1r and 2a in [Scheme 5, Eq. (1)]. We also investigated the reaction
a 1:2 molar ratio was carried out at 808C for 24 h, of 1-bromo-2-phenylacetylene with 2a under the pres-
a di-Hiyama cross-coupling product, 2,5-diphenylben- ent reaction conditions. However, no Hiyama cross-
zofuran 3s, was isolated in 56% yield (Scheme 4).
coupling product was detected, and a homo-coupling
We also tried the reaction of 2-(gem-dibromovin- product of the terminal alkyne bromide was obtained
ACHTUNGTRENNUNG
ing 2-phenylindole product was obtained.
carried out in the presence of TBAF·0.23H2O, ob-
Our proposed mechanism for the tandem reaction tained from commercially available TBAF hydrate by
is shown in Scheme 5. The reaction occurs involving D2O exchange, 2-bromobenzofuran and 2-bromo-3-d-
an elimination of hydrogen bromide from 2-(gem-di- benzofuran were obtained in 95% isolated yield with
bromovinyl)phenol, and subsequently intramolecular a ratio of 21:79 [Scheme 5, Eq. (3)]. This also sup-
addition, affording 2-bromobenzofuran; and an inter- ports the assumption that the reaction proceeds
molecular Hiyama cross-coupling of 2-bromobenzo- through a (2-hydroxyphenyl)ethynyl bromide inter-
furan with phenyl(trimethoxy)silane, affording 2-aryl- mediate I (see Supporting Information for details).
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A Highly Efficient Tandem Reaction of 2-(gem-Dibromovinyl)phenols(thiophenols) with Organosilanes
Scheme 5. Proposed reaction mechanism and Eq. (1) to Eq. (3).
All the gem-dibromovinyl substrates were synthesized ac-
Conclusions
cording to the reported procedures.[9b,13]
In conclusion, a novel and highly efficient synthetic
method for the preparation of 2-arylbenzofurans and
2-arylbenzothiophenes has been developed. In the
presence of tetra-(n-butyl)ammonium fluoride
Typical Procedure for the Tandem Reaction
A sealable reaction tube equipped with a magnetic stirrer
bar was charged with gem-dibromovinyl substrate
(0.50 mmol), phenyl(trimethoxy)silane (1.0 mmol), TBAF
(TBAF) and PdACHTUNGTRENNUNG(OAc)2/PPh3, 2-(gem-dibromovinyl)-
phenols(thiophenols) reacted with phenyl(trialkoxy)-
silanes smoothly to generate the corresponding prod-
ucts in good yields through a tandem elimination–in-
tramolecular addition–Hiyama cross-coupling reaction
in one-pot. It is important to note that TBAF plays
an important role in the tandem elimination, intramo-
lecular addition and Hiyama coupling reactions.
(1.5 mmol), PdACTHNUTRGNE(UNG OAc)2 (0.025 mmol), PPh3 (0.05 mmol) and
NMP (2.0 mL). The rubber septum was then replaced by
a Teflon-coated screw cap, and the reaction vessel placed in
an oil bath at 808C. After stirring the mixture at this tem-
perature for 12 h, it was cooled to room temperature and di-
luted with ethyl acetate, washed with water and brine, dried
over Mg2SO4. After the solvent was removed under reduced
pressure, the residue was purified by column chromatogra-
phy on silica gel (eluent: petroleum ether) to afford the cor-
responding product.
Experimental Section
Characterization Data for all Products
2-Phenylbenzofuran (3a): White solid, mp 119–1208C (lit.[14]
General Remarks
All the tandem reactions of 2-(gem-dibromovinyl)phenols
(thiophenols) with organosilanes were carried out under an
1
air atmosphere. H NMR, 13C NMR spectra were measured
on a Bruker Avance NMR spectrometer (400 MHz or
100 MHz, respectively) with CDCl3 as solvent and recorded
in ppm relative to internal tetramethylsilane standard. The
peak patterns are indicated as follows: s, singlet; d, doublet;
t, triplet; m, multiplet; q, quartet. The coupling constants, J,
are reported in Hertz (Hz). High resolution mass spectros-
copy data of the product were collected on a Waters Micro-
mass GCT instrument.
1
121.6–122.28C). H NMR (400 MHz, CDCl3): d=7.92 (d, J=
8.0 Hz, 2H), 7.63 (d, J=8.0 Hz, 1H), 7.58 (d, J=8.0 Hz,
1H), 7.51–7.47 (m, 2H), 7.42–7.38 (m, 1H), 7.36–7.27 (m,
2H), 7.06 (s, 1H); 13C NMR (100 MHz, CDCl3): d=155.9,
154.9, 130.5, 129.2, 128.8, 128.5, 124.9, 124.2, 122.9, 120.9,
111.1, 101.3.
5-Methyl-2-phenylbenzofuran (3b): White solid, mp 128–
1298C (lit.[15] 128–1308C). H NMR (400 MHz, CDCl3): d=
1
General chemicals and solvents were purchased from
commercial suppliers and used without further purification.
7.90 (d, J=8.0 Hz, 2H), 7.51–7.45 (m, 3H), 7.41–7.37 (m,
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7-Methyl-2-phenylbenzofuran (3h): Colorless oil.[15]
2H), 7.15 (d, J=8.4 Hz, 1H), 6.98 (s, 1H), 2.50 (s, 3H);
13C NMR (100 MHz, CDCl3): d=156.0, 153.3, 132.3, 130.6,
129.3, 128.7, 128.4, 125.5, 124.8, 120.7, 110.6, 101.1, 21.3.
5-Methoxy-2-phenylbenzofuran (3c): White solid, mp 131–
1H NMR (400 MHz, CDCl3): d=7.94–7.91 (m, 2H), 7.50–
7.44 (m, 3H), 7.41–7.37 (m, 1H), 7.20–7.16 (m, 1H), 7.14–
7.11 (m, 1H), 7.05 (s, 1H), 2.64 (s, 3H); 13C NMR
(100 MHz, CDCl3): d=155.5, 153.9, 130.7, 128.7, 128.7,
128.4, 125.2, 124.9, 122.9, 121.4, 118.3, 101.6, 15.0.
1
1328C (lit.[16] 131.4–131.98C). H NMR (400 MHz, CDCl3):
2,7-Diphenylbenzofuran (3i): White solid, mp 104–1058C.
d=7.88 (d, J=7.2 Hz, 2H), 7.49–7.44 (m, 3H), 7.40–7.36 (m,
1H), 7.07 (d, J=2.4 Hz, 1H), 7.00 (s, 1H), 6.93 (dd, J=8.8,
2.4 Hz, 1H), 3.88 (s, 3H); 13C NMR (100 MHz, CDCl3): d=
156.7, 156.1, 149.9, 130.5, 129.7, 128.7, 128.4, 124.8, 113.0,
111.5, 103.3, 101.4, 55.8.
5-(tert-Butyl)-2-phenylbenzofuran (3d): White solid, mp
1H NMR (400 MHz, CDCl3): d=8.03 (d, J=7.2 Hz, 2H),
7.93 (d, J=7.2 Hz, 2H), 7.63–7.60 (m, 3H), 7.54–7.48 (m,
4H), 7.42–7.36 (m, 2H), 7.13 (s, 1H); 13C NMR (100 MHz,
CDCl3): d=156.0, 152.0, 136.6, 130.4, 130.0, 128.7, 128.6,
128.6, 128.5, 127.6, 125.3, 124.9, 123.8, 123.5, 120.1, 101.4;
HR-MS (EI): m/z=270.1044, calcd. for C20H14O ([M]+):
270.1045.
1
104–1058C (lit.[17] 103–1058C). H NMR (400 MHz, CDCl3):
d=7.92 (d, J=8.0 Hz, 2H), 7.65–7.64 (m, 1H), 7.52–7.47 (m,
3H), 7.43–7.37 (m, 2H), 7.04 (s, 1H), 1.46 (s, 9H); 13C NMR
(100 MHz, CDCl3): d=156.0, 153.2, 146.0, 130.7, 128.9,
128.7, 128.3, 124.8, 122.2, 117.1, 110.4, 101.5, 34.7, 31.8.
5-Chloro-2-phenylbenzofuran (3e): White solid, mp 156–
7-Methoxy-2-phenylbenzofuran (3j): White solid, mp 78–
808C (lit.[16] 79–808C). H NMR (400 MHz, CDCl3): d=7.93
1
1
1578C (lit.[18] 155–1578C). H NMR (400 MHz, CDCl3): d=
(d, J=7.2 Hz, 2H), 7.49–7.45 (m, 2H), 7.40–7.36 (m, 1H),
7.24–7.17 (m, 2H), 7.04 (s, 1H), 6.84 (dd, J=7.6, 1.6 Hz,
1H), 4.08 (s, 3H); 13C NMR (100 MHz, CDCl3): d=156.0,
145.3, 144.1, 130.9, 130.3, 128.6, 128.5, 125.0, 123.5, 113.3,
106.7, 101.6, 56.1.
7.86 (d, J=7.2 Hz, 2H), 7.55 (d, J=2.0 Hz, 1H), 7.49–7.38
(m, 4H), 7.25 (dd, J=8.8, 2.0 Hz, 1H), 6.95 (s, 1H);
13C NMR (100 MHz, CDCl3): d=157.4, 153.2, 130.5, 129.9,
128.9, 128.8, 128.5, 125.0, 124.3, 120.4, 112.1, 100.8.
7-Ethoxy-2-phenylbenzofuran
(3k):
Colorless
oil.
5-Nitro-2-phenylbenzofuran (3f): Yellow solid, mp 151–
1
1528C (lit.[19] 152–1538C). H NMR (400 MHz, CDCl3): d=
1H NMR (400 MHz, CDCl3): d=7.93 (d, J=7.6 Hz, 2H),
7.49–7.46 (m, 2H), 7.40–7.36 (m, 1H), 7.22–7.15 (m, 2H),
7.04 (s, 1H), 6.85–6.83 (m, 1H), 4.35 (q, J=7.0 Hz, 2H),
1.58 (t, J=7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3): d=
155.9, 144.5, 144.4, 131.0, 130.4, 128.6, 128.4, 125.0, 123.5,
113.2, 108.2, 101.6, 64.7, 15.0; HR-MS (EI): m/z=238.1000,
calcd. for C16H14O2 ([M]+): 238.0994.
8.51 (d, J=2.4 Hz, 1H), 8.22 (dd, J=9.2, 2.4 Hz, 1H), 7.90–
7.88 (m, 2H), 7.60 (d, J=9.2 Hz, 1H), 7.52–7.49 (m, 2H),
7.46–7.44 (m, 1H), 7.14 (s, 1H); 13C NMR (100 MHz,
CDCl3): d=159.3, 157.6, 129.7, 129.6, 129.2, 129.0, 125.3,
120.1, 117.2, 111.4, 101.6.
6-Methoxy-2-phenylbenzofuran (3g): White solid,[20] mp
7-(tert-Butyl)-2-phenylbenzofuran (3l): Colorless oil.
77–788C. 1H NMR (400 MHz, CDCl3): d=7.86–7.83 (m,
2H), 7.47–7.44 (m, 3H), 7.37–7.33 (m, 1H), 7.11–7.10 (m,
1H), 6.97 (s, 1H), 6.91 (dd, J=8.4, 2.0 Hz, 1H), 3.90 (s,
3H); 13C NMR (100 MHz, CDCl3): d=158.1, 155.9, 155.1,
130.7, 128.7, 128.0, 124.4, 122.6, 120.9, 111.9, 101.1, 95.9,
55.7.
1H NMR (400 MHz, CDCl3): d=7.91 (d, J=7.6 Hz, 2H),
7.51–7.47 (m, 3H), 7.40–7.36 (m, 1H), 7.23–7.17 (m, 2H),
7.04 (s, 1H), 1.61 (s, 9H); 13C NMR (100 MHz, CDCl3): d=
6
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A Highly Efficient Tandem Reaction of 2-(gem-Dibromovinyl)phenols(thiophenols) with Organosilanes
155.0, 153.0, 134.7, 130.7, 129.7, 128.8, 128.4, 124.8, 122.9,
121.0, 118.9, 101.2, 34.4, 30.0; HR-MS (EI): m/z=250.1357,
calcd. for C18H18O ([M]+): 250.1358.
133.8, 129.0, 128.6, 128.5, 126.6, 124.9, 124.5, 120.7, 117.6;
HR-MS (EI): m/z=244.0110, calcd. for C14H9ClS ([M]+):
244.0113.
5,7-Dimethyl-2-phenylbenzofuran (3m): White solid, mp
5-Bromo-2-phenylbenzofuran (3r): White solid, mp 156–
1578C (lit.[18] 1578C). H NMR (400 MHz, CDCl3): d=7.86
1
1
60–628C (lit.[21] 60–628C). H NMR (400 MHz, CDCl3): d=
(d, J=7.2 Hz, 2H), 7.71 (s, 1H), 7.49–7.45 (m, 2H), 7.42–
7.37 (m, 3H), 6.96 (s, 1H); 13C NMR (100 MHz, CDCl3):
d=157.2, 153.6, 131.2, 129.9, 129.0, 128.8, 127.1, 125.1, 123.5,
116.0, 112.6, 100.6.
7.91 (d, J=7.2 Hz, 2H), 7.51–7.47 (m, 2H), 7.40–7.36 (m,
1H), 7.23 (s, 1H), 6.97–6.96 (m, 2H), 2.60 (s, 3H), 2.46 (s,
3H); 13C NMR (100 MHz, CDCl3): d=155.6, 152.4, 132.3,
130.8, 128.8, 128.7, 128.2, 126.6, 124.8, 120.8, 118.1, 101.3,
21.2, 15.0.
2,5-Diphenylbenzofuran (3s): White solid, mp 166–1678C
6,7-Dimethyl-2-phenylbenzofuran (3n): White solid, mp
1
(lit.[18] 166–1678C). H NMR (400 MHz, CDCl3): d=7.91 (d,
J=7.6 Hz, 2H), 7.80–7.78 (m, 1H), 7.67–7.65 (m, 2H), 7.61–
7.59 (m, 1H), 7.55–7.52 (m, 1H), 7.50–7.46 (m, 4H), 7.41–
7.35 (m, 2H), 7.09 (s, 1H); 13C NMR (100 MHz, CDCl3):
d=156.6, 154.5, 141.7, 136.7, 130.4, 129.8, 128.8, 128.7, 128.6,
127.4, 126.9, 125.0, 124.0, 119.4, 111.2, 101.5.
77–788C. 1H NMR (400 MHz, CDCl3): d=7.92–7.90 (m,
2H), 7.50–7.46 (m, 2H), 7.39–7.33 (m, 2H), 7.08 (d, J=
7.6 Hz, 1H), 7.00 (s, 1H), 2.55 (s, 3H), 2.44 (s, 3H);
13C NMR (100 MHz, CDCl3): d=155.0, 154.4, 132.7, 130.9,
128.7, 128.1, 126.5, 125.0, 124.7, 119.7, 117.4, 101.6, 19.2,
11.7. HR-MS (EI): m/z=222.1050, calcd. for C16H14O
([M]+): 222.1045.
2-PhenylnaphthoACHTUNGTRENNUNG
[2,1-b]furan (3o): White solid,[22] mp
Acknowledgements
This work was financially supported by the National Science
Foundation of China (Nos. 21172092 and 20102039).
1
1428C. H NMR (400 MHz, CDCl3): d=8.21 (d, J=7.2 Hz,
1H), 7.98–7.94 (m, 3H), 7.76–7.70 (m, 2H), 7.64–7.60 (m,
1H), 7.51–7.48 (m, 4H), 7.40–7.36 (m, 1H); 13C NMR
(100 MHz, CDCl3): d=155.4, 152.4, 130.7, 130. 4, 128.8,
128.8, 128.3, 127.6, 126.3, 125.2, 124.7, 124.6, 124.6, 123.4,
112.3, 100.4.
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A Highly Efficient Tandem Reaction of 2-(gem-
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2-Arylbenzofurans(thiophenes)
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Jie Liu, Wei Chen, Yong Ji, Lei Wang*
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