Selectivity of Br/Li exchange and deprotonation of 4,4′-dibromo-3, 3′-bithiophene for synthesis of symmetrical and unsymmetrical dithienoheteroaromatic rings

Article abstract of DOI:10.1021/jo302635y

The novel selective synthesis of symmetrical and unsymmetrical dithienoheteroaromatic rings (DTHAs) has been developed via intramolecular cyclization of 4,4′-dibromo-3,3′-bithiophene (3). Four reaction conditions including n-BuLi/Et₂O, n-BuLi/T

Full text of DOI:10.1021/jo302635y

Note
pubs.acs.org/joc
Selectivity of Br/Li Exchange and Deprotonation of 4,4′-Dibromo-
3,3′-bithiophene for Synthesis of Symmetrical and Unsymmetrical
Dithienoheteroaromatic Rings
Hui Han, Wenling Zhao, Jinsheng Song, Chunli Li, and Hua Wang*
Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004, China
S
* Supporting Information
ABSTRACT: The novel selective synthesis of symmetrical and unsymmetrical dithienoheteroaromatic rings (DTHAs) has been
developed via intramolecular cyclization of 4,4′-dibromo-3,3′-bithiophene (3). Four reaction conditions including n-BuLi/Et2O,
n-BuLi/THF, s-BuLi/Et2O, and t-BuLi/Et2O were employed to react with 3 for selective formation of two types of dicarbanions,
which generate the symmetrical and unsymmetrical DTHAs after quenching with three electrophilic reagents (4a−c). The
possible mechanism of formation of DTHAs was proposed. In addition, two unsymmetrical DTHAs were confirmed by X-ray
single-crystal analyses.
ue to versatile applications in organic field effect
yield has been greatly improved, there are still four steps in that
route. Iyoda et al.13 showed the efficient synthesis of 2c in
which 3 was dilithiated with n-BuLi at −100 °C and then
treated with 4c in tetrahydrofuran (THF) with a yield of 89%.
Nevertheless, those reports on improving the yields were
mainly focused on the symmetrical DTHAs, and it is rare to
find efficient methods for unsymmetrical DTHAs synthesis.
Recently, our group reported the first example in preparation of
an unsymmetrical DTHA, dithieno[2,3-b:4′,3′-d]silole (bs-
DTS).14 The efficient and novel method for the preparation
of bs-DTSs in high yields occurred by intramolecular silole
formation in which 4,4′-dibromo-2,2′,5,5′-tetrakis(trimethyl-
silyl)[3,3′]bithienyl was employed to react with t-BuLi and then
quenched with water without addition of dichlorodimethylsi-
lane or any other silicon source. The unsymmetrical DTHAs
are novel building blocks in organic synthesis and important to
be applied to organic electric materials because of their low
LUMO energy level.15
In this work, the novel selectivity of the Br/Li exchange
(including mono and double Br/Li exchanges) and deproto-
nation of 3 were observed when 3 was treated with 2 equiv of
n-BuLi in Et2O. By using this kind of selectivity, both
symmetrical DTHAs (ss-DTT, ss-CDT and ss-DTS) and
unsymmetrical DTHAs (bs-DTT, bs-CDT and bs-DTS,
Scheme 1) have been developed via intramolecular cyclization
of 3 using three electrophilic reagents. In addition, it is
fascinating to find that the kinds of BuLi and the solvent
1−3
Dtransistors (OFETs),
organic light-emitting diodes
(OLEDs),4−6 and dye-sensitized solar cells (DSSCs),7−9
a
variety of symmetric DTHA compounds, such as dithienothio-
phenes (DTTs), cyclopentadithiophenones (CDTs), and
dithienosiloles (DTSs) derivatives have attracted considerable
attention in recent years. Wong and Wu et al.9b reported two
new sensitizers for DSSCs that adopted coplanar 4,4-
diphenyldithieno[3,2-b:2′,3′-d]silole as the central linkage,
and the best power conversion efficiency of those dyes achieved
7.6%. In our previous work, the synthesis of 2,5-
distyryldithieno[2,3-b:3′,2′-d]thiophene and its high field-effect
mobility of 2.2 cm2 V−1 s−1 were studied.1d Most of these fused
aromatic compounds have shown excellent properties in the
organic electronic field, but there are only a few works
regarding to the preparation of DTHAs and their derivatives,
which will limit their applications in organic electronics. Further
development on efficient synthesis of DTHAs is desirable for
the realization of their diverse applications in materials science.
Some symmetric DTHA compounds have been synthesized
and reported with several steps and low yields,10−12 and in the
literature they generally include two key steps: formation of
dibromodithienyl intermediates (dibromodithienyl dimethylsi-
lane, dibromodithienyl ketone, and dibromodithienyl sulfide)
and intramolecular cyclization. Most of the methods are not
efficient for the following reasons: hard to obtain intermediates,
expensive reagent for ring closure, harsh reaction conditions,
multiple steps, and low total yield. Our previous work improved
the synthesis of ss-DTT in a total yield of 55−63% through
introduction of trimethylsilyl (TMS) groups as protecting and
solubilizing groups to 3,4-dibromothiophene.10b Although the
Received: December 3, 2012
© XXXX American Chemical Society
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Note
Scheme 1. Molecular Structures of DTHAs
Scheme 2. Synthesis of 1 and 2 under Different Reaction
Conditions
systems will greatly influence this kind of selectivity and further
determine the final components of the products.
Compound 3 was synthesized by the homocoupling of 3,4-
dibromothiophene.16 In this paper, the Br/Li exchange reaction
of 3 was first carried out with n-BuLi (2.2 equiv) in ethyl ether
at −78 °C for 2 h, followed by addition of an electrophilic
reagent, bis(phenylsulfonyl)sulfide (4a), and after workup, it
was interesting to find out that both unsymmetrical 1a and
symmetrical 2a were obtained in one pot with isolated yields of
57.3% and 11.3%, respectively. To compare the influence of
reaction temperature, parallel experiments were set up from
−78 to −45 and −20 °C, and the yield of 1a decreased and the
yield of 2a increased accordingly, but the total yield decreased
(entries 1−3, Table 1). In the meantime, the polymerization
the case of t-BuLi/Et2O, 70.8%, 57.6%, and 59.0% yields for 2a,
2b, and 2c were obtained, respectively.
It is interesting to note that the kinds of BuLi and the solvent
systems will greatly influence this type of selectivity and further
decide the final components of the products. It is known that n-
BuLi exists as a hexameric aggregate in hydrocarbons,17
a
tetrameric aggregate in diethyl ether,18 and a temperature-
dependent equilibrium of dimeric and tetrameric aggregates in
THF.18b,19 The reactivity of n-BuLi depends on its aggregation
types. The tetrameric aggregate of n-BuLi in ethyl ether means
weaker reactivity with the novel selectivity of both Br/Li
exchange and deprotonation took place at the same time in our
case, which generated both 1 and 2. However, n-BuLi in THF
gives lower oligomers assigned as a mixture of tetramer and
dimer, which means higher reactivity with the selectivity of only
double Br/Li exchanges of 3. As a result, only 2 could be
generated in this case. From the reactions in our work, we can
conclude that the aggregation state of n-BuLi in ethyl ether or
THF really plays a role to control the reaction selectivity.
From the experimental results above, it is obvious that the
selectivity of Br/Li exchange and deprotonation of 3 depends
on the reaction conditions. When n-BuLi and ethyl ether were
utilized in the reaction, both Br/Li exchange and deprotonation
reactions took place at the same time. During this process, two
possible dicarbanions, 5 and 6 (Scheme 3), were generated
after n-BuLi was added at −78 °C in Et2O. Intermediate 5 was
formed by both Br/Li exchange and deprotonation, and 6 was
generated via double Br/Li exchanges of 3. From the ratio (∼
5:1) of the final yields of 1 and 2, we can conclude that 5 was
the favorite intermediate. When THF was utilized instead of
ethyl ether, 2 was obtained in good yields and only a trace of 1c
was observed. This result implies that dianionic intermediate 6
should be the favorite intermediate. From the experimental
results, we can conclude that the reactivity of the α-H and β-Br
on the thiophene ring was greatly influenced by the solvent
system utilized in the reaction and result in the reaction
selectivity difference between deprotonation and Br/Li
exchange due to the reactivity difference between the
aggregative types of n-BuLi in ethyl ether and THF. On the
basis of this idea, it is easy to understand the temperature effect
in Table 1. High temperature decreases the aggregation of n-
BuLi in Et2O, which increases its reactivity and the ratio of 2 in
the products.
Table 1. Formation of 1a and 2a through Cyclization at
Different Temperatures
entry n-BuLi (equiv) reaction temp (°C)/time (h) 1a (%) 2a (%)
1
2
3
2.2
2.2
2.2
−78/2
−45/2
−20/2
57.3
36.9
28.4
11.3
15.7
26.1
was increased and confirmed by 1H NMR. Finally, 2.2 equiv of
n-BuLi at −78 °C in ethyl ether were chosen as the optimal
reaction conditions for preparation of unsymmetrical DTHAs.
Under these optimal reaction conditions, 1b and 1c were
efficiently obtained in 56.0% and 58.6% yields, respectively,
when dimethylcarbamic chloride (4b) and dichlorodimethylsi-
lane (4c) were employed (Scheme 2). In the meantime, the
symmetrical DTHAs, 2b, and 2c were also obtained in low
yields of 9.6% and 9.0%, respectively.
In order to better understand such novel selectivity, the
influence of BuLi types and solvent effects were taken into
account. As shown in Scheme 2, when ethyl ether was replaced
by THF, 2 was generated in moderate yields (43.0%, 35.9%,
and 48.2% yields for 2a, 2b, and 2c, respectively), and only a
trace 1c was observed by GCMS. On the other hand, if s-BuLi
or t-BuLi was used instead of n-BuLi in ethyl ether, no 1 was
observed, and only 2 was formed in good yields (Scheme 2).
For example, in the case of s-BuLi/Et2O, 45.2%, 56.2%, and
59.7% yields for 2a, 2b, and 2c were obtained, respectively; in
B
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Note
Scheme 3. Possible Mechanism for the Formation of 1 and 2
In order to further understand the mechanism of the
reaction, another reaction of 3 with 1 equiv of n-BuLi in ethyl
ether was employed. After quenching with CH3OH, 4-bromo-
3,3′-bithiophene (55.1%), 4,4′-dibromo-3,3′-bithiophene
(24.3%), and 3,3′-bithiophene (5.2%) were observed by
GCMS (see the Supporting Information). The possible
mechanism was proposed in Scheme 4. The carbanions 7 and
Scheme 4. Reaction of 3 with 1 equiv of n-BuLi in Et2O
Figure 1. Molecular structures and conformations (top view) for 1a
(a) and 1b (b). Carbon, bromine, oxygen, and sulfur atoms are
depicted with thermal ellipsoids set at the 30% probability level, and all
hydrogen atoms are omitted for clarity.
dihedral angle between the two side thiophenes is 2.6°, and the
torsion angles are 3.8° (C2−C3−C6−C7) and 4.9° (Br1−C2−
C7−H7A). In crystal packing of 1a, the S···S and Br···Br
interactions can be clearly observed. The distances of S2···S2
and Br1···Br1 are 3.482 and 3.620 Å, respectively. Compound
1b belongs to triclinic space group P-1 with four molecules in
one unit cell. In the crystal packing of 1b, each of two
molecules stack orthogonally together and the dihedral angle of
the two molecules is 85.6°. Each molecule is approximately
coplanar with torisions of −1.3° (C4−C3−C5−C8) and −5.2°
(C11−C12−C16−C17). The S···O, C···H, and Br···Br
interactions are clearly observed in crystal packing. The
distances of S1···O1, S4···O2, H18···C1, and Br2···Br1 are
3.193, 3.140, 2.886, and 3.690 Å, respectively.
In summary, we have established a novel and efficient way to
selectively synthesize unsymmetrical DTHAs (1a, 1b, and 1c)
and symmetrical DTHAs (2a, 2b, and 2c) via intramolecular
cyclization. The product distribution depends on the selectivity
of deprotonation and/or Br/Li exchange occurred on 3 due to
the reaction conditions including the kinds of BuLi and the
solvent systems. The aggregation state of BuLi in different
solvent system plays a role to control the reaction selectivity.
The presence of n-BuLi/Et2O gives an efficient yield of
unsymmetrical DTHAs due to the selectivity of the
deprotonation and Br/Li exchange reactions. When the
reaction conditions change to n-BuLi/THF, s-BuLi/Et2O, or
t-BuLi/Et2O, only symmetrical DTHAs could be obtained
efficiently. Both symmetrical and unsymmetrical DTHAs are
important to materials science; however, the synthetic method
in making unsymmetrical DTHAs gives a simple and efficient
manner that may show a wide application in both synthetic
chemistry and organic electronics.
8 were the main intermediates, which were generated from
protonation and Br/Li exchange of 3, respectively, and the Br/
Li exchange was the favorite path. When another 1 equiv of n-
BuLi was employed in our work, the second carbanion should
be formed on the neighboring thiophene, which means that Br/
Li exchange should occur on 7 and deprotonation occur on 8.
Both of the changes formed dicarbanion 5, which generated 1
as major product after quenching with 4. There was some
byproduct 2 as a minor product observed due to dicarbanion 6
from the double Br/Li exchange (Schemes 3 and 4).
Compared with the case of n-BuLi, t-BuLi exists as a dimeric
aggregate in Et2O20 and primarily as a solvated monomer in
THF,19b so t-BuLi normally shows much higher reactivity
priority than n-BuLi in the selection of Br/Li exchange.21,22 In
general, s-BuLi shows a moderate reactivity between n-BuLi and
t-BuLi. From the experimental data, the case of s-BuLi showed
behavior similar to that of t-BuLi under the reaction conditions.
In the case of s-BuLi and t-BuLi, instead of protonation, only
double Br/Li exchanges occurred on 3 and only 2 was
generated in good yields in ethyl ether (Scheme 2).
In all, because of the selectivity of the deprotonation and Br/
Li exchange in the reaction, we have found an efficient and
general way to obtain the symmetrical and unsymmetrical
DTHAs in which new bonds (C−S, C−C, and C−Si) could be
formed efficiently.
The molecular structures of 1a and 1b were confirmed by
single-crystal X-ray analysis (Figure 1). Compound 1a belongs
to monoclinic space group P2(1)/c, with four molecules in one
unit cell. From the single-crystal structure of 1a, it is obvious
that all of the thiophene rings are approximately coplanar. The
C
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143.9, 141.0, 132.2, 130.0, 114.7, 107.4, −1.8; IR (KBr) 3100.4 (CH)
cm−1; HRMS (FTMS ESI) m/z [M + H]+ calcd for [C10H10SiS2Br]
300.9177, found 300.9171. 2c: mp 102−104 °C (lit.13 mp 104.2−
EXPERIMENTAL SECTION
■
Synthesis of 3-Bromodithieno[2,3-b:3′,4′-d]thiophene (1a)
and Dithieno[3,4-b:3′,4′-d]thiophene (2a). To a solution of 3
(211.8 mg, 0.65 mmol) in dry ethyl ether (20 mL) was added n-BuLi
(2.38 M, 0.60 mL, 1.43 mmol, 2.2 equiv) dropwise at −78 °C. After 2
h at −78 °C, 4a (207.4 mg, 0.66 mmol, 1.01 equiv) was added under
argon. The reaction mixture was kept at −78 °C for 1 h and −55 °C
for 2 h and then warmed slowly to ambient temperature overnight.
After being quenched with H2O (20 mL), the reaction mixture was
extracted with CHCl3 (3 × 20 mL), and the organic phase was washed
with H2O (40 mL), saturated NaCl solution (40 mL), and H2O (40
mL) and dried over anhydrous MgSO4. After the solvent was removed
in vacuo, the residue was purified by column chromatography on silica
gel (300−400 mesh) with petroleum ether (60−90 °C) as eluent to
yield 1a (103.1 mg, 57.3%) as a white solid and 2a (14.5 mg, 11.3%) as
a white solid. From the other two reactions on the 489.0 mg and 513.3
mg scales of 3, 203.7 mg (49.0%) and 222.8 mg (51.2%) of 1a and
24.7 mg (8.3%) and 34.3 mg (11.1%) of 2a were obtained,
1
105.0 °C); H NMR (400 MHz,CDCl3) δ 7.43 (d, J = 2.0 Hz, 2 H),
7.32 (d, J = 2.4 Hz, 2 H), 0.45 (s, 6 H); 13C NMR (100 MHz, CDCl3)
δ 146.7, 146.4, 129.9, 114.5, −1.5 (this analysis is in agreement with
the literature data13); IR (KBr) 3083.7 (CH) cm−1.
Synthesis of Dithieno[3,4-b:3′,4′-d]thiophene (2a). Method A
(n-BuLi in THF). The procedure was same as that for the preparation of
2a in ethyl ether. The only difference was that the reaction solvent was
changed to THF. From the reaction on a 115.3 mg (0.36 mmol) scale
of 3, 10 mL of dry THF was employed. A 30.0 mg (43.0%) portion of
2a was obtained by column chromatography on silica gel (200−300
mesh) with petroleum ether (60−90 °C) as eluent.
Method B (s-BuLi in Ethyl Ether). The procedure was same as that
for the preparation of 2a in ethyl ether. The only difference was that n-
BuLi was used instead of s-BuLi. From the reaction on a 201.4 mg
(0.65 mmol) scale of 3, 57.7 mg (45.2%) of 2a was obtained by
column chromatography on silica gel (200−300 mesh) with petroleum
ether (60−90 °C) as eluent.
Method C (t-BuLi in Ethyl Ether). The procedure was same as that
for the preparation of 2a in ethyl ether. The only difference was that
4.0 equiv of t-BuLi was used instead of 2.0 equiv of n-BuLi. From the
reaction on a 1.9654 g (6.04 mmol) scale of 3, 842.5 mg (70.8%) of 2a
was obtained by column chromatography on silica gel (200−300
mesh) with petroleum ether (60−90 °C) as eluent. From the other
reaction on a 2.2620 g scale of 3, 836.2 mg (61.0%) of 2a was
obtained.
Synthesis of 7H-Cyclopenta[1,2-c:3,4-c′]dithiophen-7-one
(2b). Method A (n-BuLi in THF). The procedure was the same as
that for the preparation of 2b in ethyl ether. The only difference was
that the reaction solvent was changed to THF. From the reaction on a
111.4 mg (0.34 mmol) scale of 3 with 10 mL dry THF, 23.7 mg
(35.9%) of 2b was obtained by column chromatography on silica gel
(200−300 mesh) with petroleum ether (60−90 °C)/chloroform = 1:1
(v/v) as eluent.
Method B (s-BuLi in Ethyl Ether). The procedure was the same as
that for the preparation of 2b in ethyl ether. The only difference was
that s-BuLi was used instead of n-BuLi. From the reaction on a 213.0
mg (0.66 mmol) scale of 3, 71.3 mg (56.2%) of 2b was obtained by
column chromatography on silica gel (200−300 mesh) with petroleum
ether (60−90 °C)/chloroform (1:1, v/v) as eluent.
Method B (t-BuLi in Ethyl Ether). The procedure was same as that
for the preparation of 2b in ethyl ether. The only difference is that 4.0
equiv of t-BuLi was used instead of 2.0 equiv of n-BuLi. From the
reaction on the 350.8 mg (1.08 mmol) scale of 3, 119.6 mg (57.6%) of
2b was obtained by column chromatography on silica gel (200−300
mesh) with petroleum ether (60−90 °C): chloroform (1:1, v/v) as
eluent. From the other two reactions on the 480.2 mg and 509.0 mg
scales of 3, 168.0 mg (59.0%) and 170.0 mg (56.3%) of 2b were
obtained respectively.
Synthesis of 7,7-Dimethyl-7H-silolo[2,3-c:4,5-c′]dithiophene
(2c). Method A (n-BuLi in THF). The procedure was same as that for
the preparation of 2c in ethyl ether. The only difference was that the
reaction solvent was changed to THF. From the reaction on the 262.8
mg (0.81 mmol) scale of 3, and using 20 mL of dry THF, 86.8 mg
(48.2%) of 2c was obtained by column chromatography on silica gel
(200−300 mesh) with petroleum ether (60−90 °C) as eluent and then
precipitation twice by CHCl3−CH3OH (1:5, v/v).
1
respectively. 1a: mp 89−91 °C; H NMR (400 MHz,CDCl3) δ 7.74
(d, J = 2.8 Hz, 1 H), 7.26 (d, J = 2.8 Hz, 1 H), 7.19 (s, 1 H); 13C NMR
(100 MHz, CDCl3) δ 142.7, 141.5, 137.7, 133.3, 123.2, 111.9, 111.3,
104.1; IR (KBr) 3109.1 (CH) cm−1; HRMS (TOF MS EI+) m/z calcd
for [C8H3S3Br] 273.8580, found 273.8583 [C8H3S379Br] and 275.8564
10a
[C8H3S381Br]. 2a: mp 71−72 °C (lit. mp 87−87.5 °C); H NMR
1
(400 MHz, CDCl3) δ 7.48 (d, J = 2.4, 2 H), 7.04 (d, J = 2.8, 2 H); 13
C
NMR (100 MHz, CDCl3): δ 142.9, 136.1, 114.0, 111.6 (this analysis is
in agreement with the literature data10b); IR (KBr) 3091.7 (CH) cm−1.
Parallel experiments were set up following procedures similar to
those described above. When the reaction temperature was set at −45
°C, 1a (47.2 mg, 36.9%) and 2a (14.3 mg, 15.7%) were obtained from
3 (150.6 mg, 0.46 mmol). When the reaction temperature was set at
−20 °C, 1a (40.1 mg, 28.4%) and 2a (26.3 mg, 26.1%) were obtained
from 3 (166.4 mg, 0.51 mmol).
Synthesis of 3-Bromo-7H-cyclopenta[1,2-b:3,4-c′]-
dithiophen-7-one (1b) and 7H-Cyclopenta[1,2-c:3,4-c′]-
dithiophen-7-one (2b). To a solution of 3 (350.5 mg, 1.08
mmol) in dry ethyl ether (50 mL) was added n-BuLi (1.59 M, 1.50
mL, 2.38 mmol, 2.2 equiv) dropwise at −78 °C. After the solution was
kept at −78 °C for 2 h, 4b (0.10 mL, 1.09 mmol, 1.0 equiv) was added
dropwise under argon. The reaction mixture was warmed up slowly to
ambient temperature overnight. The workup the same as that for
preparation of 1a and 1b. The crude product was purified by column
chromatography on silica gel (200−300 mesh) with petroleum ether
(60−90 °C)/chloroform (1:1, v/v) as eluent to yield 1b (164.1 mg,
56.0%) as a yellow solid and 2b (20.0 mg, 9.6%) as a yellow solid. 1b:
mp 140−142 °C; 1H NMR (400 MHz,CDCl3) δ 7.62 (d, J = 1.6 Hz, 1
H), 7.55 (s, 1 H), 7.12 (d, J = 2.0 Hz, 1 H); 13C NMR (100 MHz,
CDCl3) δ 177.6, 152.9, 144.1, 143.6, 138.5, 135.1, 127.6, 115.1, 105.2;
IR (KBr) 3076.3 (CH), 1697.3 (CO) cm−1; HRMS (TOF MS EI+)
m/z [M + H]+ calcd for [C9H3BrOS2] 269.8803, found 269.8809. 2b:
mp 165−167 °C (lit.11 mp 172−173 °C); 1H NMR (400 MHz,
CDCl3) δ 7.76 (d, J = 2.0 Hz, 2 H), 7.09 (d, J = 2.0 Hz, 2 H); 13C
NMR (100 MHz, CDCl3) δ 179.2, 148.3, 140.9, 127.0, 115.4; IR
(KBr) 3083.1 (CH) cm−1, 1704.3 (CO) cm−1.
Synthesis of 3-Bromo-7,7-dimethyl-7H-silolo[2,3-b:4,5-c′]-
dithiophene (1c) and 7,7-Dimethyl-7H-silolo[2,3-c:4,5-c′]-
dithiophene (2c). To a solution of 3 (105.0 mg, 0.32 mmol) in
dry ethyl ether (10 mL) was added n-BuLi (2.59 M, 0.26 mL, 0.68
mmol, 2.1 equiv) dropwise at −78 °C. After the solution was kept at
−78 °C for 2 h, 4c (0.04 mL, 0.33 mmol, 1.0 equiv) was added
dropwise. The reaction mixture was warmed slowly to ambient
temperature overnight. The workup was same as that for preparation
of 1a and 2a. The crude product was purified by column
chromatography on silica gel (300−400 mesh) with petroleum ether
(60−90 °C) as eluent to yield 1c (57.2 mg, 58.6%) as a white solid
and 2c (6.5 mg, 9.0%) as a colorless solid. From the other reaction on
the 108.0 mg scale of 3, 54.1 mg (53.9%) of 1c and 6.7 mg (9.0%) of
2c were obtained respectively. 1c: mp 45−47 °C; 1H NMR (400 MHz,
CDCl3) δ 7.80 (d, J = 2.4 Hz, 1 H), 7.52 (s, 1 H), 7.41 (d, J = 2.4 Hz,
1 H), 0.47 (s, 6 H); 13C NMR (100 MHz, CDCl3) δ 149.0, 145.6,
Method B (s-BuLi in Ethyl Ether). The procedure was same as that
for the preparation of 2c in ethyl ether. The only difference was that s-
BuLi was used instead of n-BuLi. From the reaction on the 397.8 mg
(1.23 mmol) scale of 3, 163.4 mg (59.7%) of 2c was obtained by
column chromatography on silica gel (200−300 mesh) with petroleum
ether (60−90 °C) as eluent.
Method B (t-BuLi in Ethyl Ether). The procedure was was same as
that for the preparation of 2c in ethyl ether. The only difference was
that 4.0 equiv of t-BuLi was used instead of 2.0 equiv of n-BuLi. From
the reaction on a 204.2 mg (0.63 mmol) scale of 3, 82.6 mg (59.0%) of
2c was obtained by column chromatography on silica gel (200−300
D
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The Journal of Organic Chemistry
Note
mesh) with petroleum ether (60−90 °C) as eluent. From the other
reaction on a 212.4 mg scale of 3, 82.2 mg (56.4%) of 2c was obtained.
Kim, J.; Ko, J.; Kang, Y. J. Mater. Chem. 2010, 20, 2391. (d) Hong, Y.-
R.; Wong, H.-K.; Moh, L. C. H.; Tan, H.-S.; Chen, Z.-K. Chem.
́
Commun. 2011, 47, 4920. (e) Chu, T.-Y.; Lu, J.; Beaupre, S.; Zhang,
Y.; Pouliot, J.-R.; Wakim, S.; Zhou, J.; Leclerc, M.; Li, Z.; Ding, J.; Tao,
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44.
ASSOCIATED CONTENT
* Supporting Information
Characterization of all compounds and crystallographic files of
1a and 1b (CIF). This material is available free of charge via the
Internet at http://pubs.acs.org.
■
S
(10) (a) De Jong, F.; Janssen, M. J. J. Org. Chem. 1971, 36, 1645.
(b) Xu, L.; Wang, Z.; Xu, K.; Shi, J.; Wang, H. Lett. Org. Chem. 2009,
6, 474.
AUTHOR INFORMATION
Corresponding Author
*Tel: (0086)-378-3897112.Fax: 3881358. E-mail: hwang@
henu.edu.cn.
Notes
(11) (a) Jordens, P.; Rawson, G.; Wynberg, H. J. Chem. Soc. C 1970,
273. (b) Iyoda, M.; Miura, M.; Sasaki, S.; Kabir, S. M. H.; Kuwatani,
Y.; Yoshida, M. Tetrahedron Lett. 1997, 38, 4581.
(12) (a) Zhao, C.; Xu, L.; Shi, J.; Li, C.; Wang, Z.; Wang, H. Int. J.
Org. Chem. 2011, 1, 162. (b) Zhao, C.; Shi, J.; Li, C.; Wang, H. Lett.
Org. Chem. 2011, 21, 728.
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The authors declare no competing financial interest.
(13) Ohmae, T.; Nishinaga, T.; Wu, M.; Iyoda, M. J. Am. Chem. Soc.
2010, 132, 1066.
(14) Zhao, J.; Qiu, D.; Shi, J.; Wang, H. J. Org. Chem. 2012, 77, 2929.
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(16) Rajca, A.; Wang, H.; Pink, M.; Rajca, S. Angew. Chem., Int. Ed.
2000, 39, 4481.
ACKNOWLEDGMENTS
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This research was supported by the National Natural Science
Foundation of China (21270255, U1204212, 20972041),
Program for Innovation Scientists and Technicians Troop
Construction Projects of Henan Province (104100510011),
Program for Changjiang Scholars and Innovative Research
Team in University (PCS IRT1126), and Program for
SBGJ090506.
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