Clean and direct synthesis of α,α′-bithiophenes and bipyrroles by metal-free oxidative coupling using recyclable hypervalent iodine(III) reagents

Article abstract of DOI:10.1248/cpb.57.710

The facile and clean oxidative biaryl coupling reaction of thiophenes and pyrroles has been achieved using the recyclable hypervalent iodine(III) reagents having adamantane or methane structures. These iodine(III) reagents could be recovered from the reaction mixtures by a simple solid-liquid separation, i.e., filtration.

Full text of DOI:10.1248/cpb.57.710

7
10
Chem. Pharm. Bull. 57(7) 710—713 (2009)
Vol. 57, No. 7
Clean and Direct Synthesis of a,aꢀ-Bithiophenes and Bipyrroles by Metal-
Free Oxidative Coupling Using Recyclable Hypervalent Iodine(III)
Reagents
a,b
b
b
b
,a
Toshifumi DOHI, Koji MORIMOTO, Chieko OGAWA, Hiromichi FUJIOKA, and Yasuyuki KITA*
a
College of Pharmaceutical Sciences, Ritsumeikan University; 1–1–1 Nojihigashi, Kusatsu, Shiga 525–8577, Japan: and
Graduate School of Pharmaceutical Sciences, Osaka University; 1–6 Yamada-oka, Suita, Osaka 565–0871, Japan.
b
Received February 10, 2009; accepted April 10, 2009; published online April 14, 2009
The facile and clean oxidative biaryl coupling reaction of thiophenes and pyrroles has been achieved using
the recyclable hypervalent iodine(III) reagents having adamantane or methane structures. These iodine(III)
reagents could be recovered from the reaction mixtures by a simple solid–liquid separation, i.e., filtration.
Key words oxidative coupling; hypervalent iodine(III) reagent; recycling; heteroaromatic compound; biaryl
Biaryl compounds serve as key structures of bioactive nat- degradation of their backbones after repeated use, which are
ural products and chiral ligands for asymmetric reactions and derived from the well-defined tetrahedral structures. We thus
as precursors of various organic materials due to their unique initially attempted the biaryl coupling reaction of 3-hexylthi-
1
—3)
physical properties.
attractive as synthetic targets in modern organic chemistry.
A large number of the straightforward methods that involve with the several Lewis acids, such as BF ·Et O, TMSOTf,
These beneficial features make them ophene 5a using the recyclable reagent 1a based on the stan-
4,5)
dard reaction conditions at ꢀ78 °C in CH Cl in combination
2
2
3
2
9,10)
the oxidative coupling processes of unfunctionalized aro- and TMSBr,
matic compounds have been reported using oxidizing agents phene 6a was only obtained in low yields and large amounts
to produce these important biaryl compounds. Over the past of the starting 5a remained unchanged. We assumed that
decade, we originally developed a new oxidative biaryl cou- these results should be attributed to the low solubility of the
pling method using the hypervalent iodine(III) reagents, such reagent 1a in CH Cl at ꢀ78 °C, and therefore, decided to
as phenyliodine bis(trifluoroacetate) (PIFA), and have ex- examine the reactions at room temperature. Although the re-
tended the method to work in alkylarenes, and even in actions of 5a using the reagent 1a in ordinary solvents, such
heteroaromatic compounds, i.e., thiophenes and pyrroles.
but unexpectedly, the product a,aꢁ-bithio-
6)
2
2
7)
8)
9)
10)
as CH Cl , CH CN and MeOH, were similarly not produc-
2 2 3
Our new biaryl coupling methods using the low toxic, safe tive, the dimer 6a was formed exclusively as a single regioi-
and easy handling trivalent organoiodine oxidants have sig- somer in 69% yield when the reaction was carried out in a
nificant synthetic merits that avoid not only the pre-function- highly polar, but low nucleophilic 1,1,1,3,3,3-hexafluoroiso-
alization of aromatic compounds to the corresponding acti- propanol (HFIP, (CF ) CHOH) solvent in the presence of
3
2
vated halide or metal forms, but also the use of toxic heavy- TMSBr (Chart 1). One of the important roles of the HFIP
metal agent or metal catalyst.
The use of recyclable hypervalent iodine reagents, such as
polymer-supported reagents, in the reactions should be a fur-
ther promising and ecological approach for enhancing the
practicability of the methods and for reducing the iodoarene
wastes, as a result of the easy removal of the reagents from
11)
the reaction mixtures and their reuse. During the course of
this study, poly[bis(trifluoroacetoxy)iodo]styrene (PBTIS)
has been already applied to the oxidative biaryl coupling re-
12)
actions of phenyl ethers and alkylarenes. However, we
noted that the utilization of the polymer-supported reagent is
not successful for the coupling reactions of heteroaromatic
compounds, thiophenes and pyrroles, due to its low reactivity
and insolubility in most organic solvent systems. Further-
more, PBTIS is sometimes degraded after repeated use.
We have succeeded in the practical oxidative coupling re-
actions of thiophenes and pyrroles using the non-polymer-
supported recyclable iodine(III) reagents 1 (Fig. 1) that can
directly provide useful classes of heteroaromatic biaryls.
Fig. 1. Recyclable Hypervalent Iodine(III) Reagents Having Tetrahedral
Cores
(1)
13)
Our recyclable hypervalent iodine(III) reagents 1 and
with an adamantane or methane core have several advan-
14)
3
tages over the conventional polymer-supported reagents in
The molar ratio of thiophene 5a, 1a, b or 3b, TMSBr is 1 : 0.5ꢂ1/4 : 1. The percent-
reactivity and recyclability; they typically show higher reac- ages indicate the isolated yields of 6a after purification.
tivities compared to the polymer-supported reagents and no
Chart 1
∗
To whom correspondence should be addressed. e-mail: kita@ph.ritsumei.ac.jp
© 2009 Pharmaceutical Society of Japan

July 2009
711
solvent selected in the reactions is considered to be the en- Table 1. Oxidative Biaryl Coupling Reaction of 3-Substituted Thiophenes
Using 1b (Eq. 2)
hancement of the reactivity of the reagent 1a to generate re-
active aromatic cation intermediates of thiophene 5a.
15,16)
The use of trifluoroethanol (TFE) instead of HFIP or other
Lewis acids such as BF ·Et O and TMSOTf in HFIP resulted
(2)
3
2
in no production of the desired coupling product, because
17)
formation of the diaryliodonium salts occurred. We also
evaluated the reactivities of the related reagents 1b and 3b in
the coupling reaction. The reagent 1b could work more effec-
tively, giving the product 6a in higher yield than the reagent
Substrate 5
Total yield
(%)
a)
Entry
Product
b)
R
1
a and an alternative reagent having a methane core 3b. In
contrast, the polymer-supported reagent, PBTIS, was still in-
effective under the given conditions due to its low solubility
in the HFIP solvent.
The oxidants 1a, b or 3b could be easily separated from
the reaction mixtures as the corresponding reduced forms,
i.e., the tetraiodide 2 (from 1a and 1b) or 4 (from 3b), by a
simple solid–liquid separation. The procedure to recover the
tetraiodides was started with the removal of the solvent under
1
2
3
4
5
6
7
8
Hex
Me
Butyl
Octyl
i-Butyl (5e)
c-Hex (5f)
(5a)
(5b)
(5c)
(5d)
6a : 7aꢃꢄ99 : 1
6b : 7bꢃ93 : 7
6c : 7cꢃ98 : 2
6d : 7dꢃꢄ99 : 1
6e : 7eꢃ98 : 2
6f : 7fꢃꢄ99 : 1
6g : 7gꢃꢄ99 : 1
6h : 7hꢃꢄ99 : 1
75
64
62
54
71
54
50
67
(CH ) Br (5g)
OMe
2
6
(5h)
a) The molar ratio of thiophenes 5, 1b, TMSBr is 1 : 0.5ꢂ1/4 : 1. In each case, 10—
reduced pressure by a rotary evaporator. MeOH was then 20% of the starting materials 5 were recovered. b) Isolated yield after purification.
added to the resulting oily residues to precipitate the tetraio-
dide 2 or 4. As the tetraiodides are hardly soluble in MeOH,
they were simultaneously precipitated as a white powder by
adding MeOH and were collected by filtration to recover the
tetraiodide 2 or 4. A series of recycle processes was finally
completed by reoxidation of the recovered tetraiodide 2 or 4
to the initial reagents 1a, b or 3b using m-chloroperbenzoic
acid (mCPBA). In this way, the reagents could be reproduced
with almost the same purity and have been repeatedly used
11)
without any loss of activities. Indeed, the reuse of the
reagent 1b in the same reaction gave a comparable result
(3 h, 70% yield of coupling product 6a), and the tetraiodide 2
was also recovered in over 95% yield.
The molar ratio of pyrroles 8, 1b, TMSBr is 1 : 0.5ꢂ1/4 : 1. The percentages indicate
the isolated yields of 9—11 after purification.
With the reagent 1b (0.5ꢂ1/4 eq, 50 mol% of iodine(III)
atom relative to the substrates 5), the reactions of the thio-
phenes 5 smoothly proceeded under the homogeneous condi-
Chart 2
tions in the HFIP solvent in the presence of TMSBr (Table tive N–H pyrroles, but the acid-sensitive N–H pyrrole 8a
). This facile and clean method could mainly give the head gave a number of insoluble identified byproducts in acidic
1
to tail (H-T) linked dimers 6 from various 3-substituted thio- HFIP. Therefore, we screened other non-acidic solvents, and
phenes 5 under mild conditions. Typically, the high reactivity CH Cl gave a better result for N–H pyrrole 8a (Chart 2).
2
2
of 1b allowed no requirement for excess amounts of the The reaction of 3-alkylpyrrole 8b was, unfortunately, not as
reagent in the reactions. In each case, the recovery of the selective as thiophenes 5, but the two regioisomers 9b and
reagent 1b was over 95% by the above mentioned recycling 10b could be separated by column chromatography tech-
19)
procedure, and thus the crude products 6 could be obtained niques. The N-substituted pyrrole 8c, on the other hand, re-
from the MeOH filtrates and purified by short column chro- acted at the both a- and b-positions to give the a,bꢁ-bipyr-
20)
matography on silica gel. Similar to the substrate 5a, the 3- role 11c rather than the a,aꢁ-bipyrrole albeit in low yield.
substituted thiophenes 5b—d having the shorter or longer
In summary, we have established the first facile and clean
alkyl substituents gave the desired products 6b—d in compa- method for the oxidative biaryl coupling reaction of het-
rable yields with a high degree of regioselectivities (entries eroaromatic compounds using recyclable hypervalent iodine
2
—4). The bulkier substituents did not affect the yield of the reagents. The present protocol is quite simple, and cleanly
products 6e and 6f (entries 5, 6). In our metal-free method, gave the useful H-T dimers 6 and 9, the oligomers or poly-
the bromo group in the substrate 5g was tolerable during the mers of which have recently gained considerable attention as
reaction (entry 7). The thiophene 5h having the alkoxy group unique electroactive organic materials having excellent de-
21,22)
was subjected to the reaction to give the corresponding cou- gree of co-planarity of the heteroaromatic rings.
pling dimer 6h in an excellent yield without any reoptimiza-
tion of the reaction conditions (entry 8). The synthesis of Experimental
1
13
electron-rich alkoxy substituted bithiophenes is known to be
especially challenging in other oxidation strategies due to
their low oxidation potentials for facilitating additional in
General The H- and C-NMR spectra were recorded by a JEOL JMN-
3
00 spectrometer operating at 300 MHz in CDCl at 25 °C with tetramethyl-
3
silane as the internal standard. The data are reported as follows: chemical
shift in ppm (d), integration, multiplicity (sꢃsinglet, dꢃdoublet, tꢃtriplet,
qꢃquartet, brꢃbroad singlet, mꢃmultiplet), and coupling constant (Hz).
18)
situ undesired oligomerizations of the formed dimers.
We next tried to extend the coupling method to more reac- The infrared spectra (IR) were obtained using a Hitachi 270-50 spectrome-

7
12
Vol. 57, No. 7
24)
1
ter; absorptions are reported in reciprocal centimeters with the following rel-
3,4ꢁ-Bis(2-methylpropyl)-2,2ꢁ-bithiophene (6e) : Slightly yellow oil; H-
ative intensities: s (strong), m (medium), or w (weak). The mass spectra NMR (CDCl ) d: 0.90—0.94 (12H, m), 1.83—1.96 (2H, m), 2.46 (2H, d,
3
were obtained using a Shimadzu GCMS-QP 5000 instrument with ionization
Jꢃ7.2 Hz), 2.61 (2H, d, Jꢃ7.2 Hz), 6.85 (1H, d, Jꢃ1.2 Hz), 6.89 (1H, d,
voltages of 70 eV. The high resolution mass spectra and elemental analysis Jꢃ5.1 Hz), 6.90 (1H, d, Jꢃ1.2 Hz), 7.13 (1H, d, Jꢃ5.1 Hz) ppm. HR-FAB-
ꢅ
were performed by the Elemental Analysis Section of Osaka University. The MS m/z: 278.1152 [M] (Calcd for C H S : 278.1163).
1
6
22 2
1
column chromatography and TLC were carried out on Merck Silica gel 60
3,4ꢁ-Dicyclohexyl-2,2ꢁ-bithiophene (6f): Slightly yellow oil; H-NMR
(
230—400 mesh) and Merck Silica gel F254 plates (0.25 mm), respectively. (CDCl ) d: 1.26—1.56 (12H, m), 1.72—1.87 (6H, m), 1.99—2.02 (2H, m),
3
The spots and bands were detected by UV irradiation (254, 365 nm).
2.57—2.59 (1H, m), 2.96—3.01 (1H, m), 6.91 (1H, s), 6.97—7.03 (2H, m),
1
3
All commercially available reagents and solvents were used as received 7.15 (1H, d, Jꢃ5.4 Hz) ppm. C-NMR (75 MHz, CDCl ) d: 26.1 (ꢂ2),
3
without further purification.
26.6, 26.7, 34.1, 34.4, 38.2, 39.6, 118.5, 123.8, 126.4, 127.3, 130.1, 135.5,
ꢀ
1
Preparation of 1b To
a
stirred solution of 1,3,5,7-tetrakis(4-
144.8, 149.3 ppm. IR (KBr) cm : 2923 s, 2851 s, 1728 w, 1448 s, 1263 m,
iodophenyl)adamantane 2 (1.42 g, 1.5 mmol) in CH Cl2 (150 ml)–AcOH 1124 w, 943 w, 833 m, 731 m, 708 w, 650 m. HR-FAB-MS m/z: 330.1470
2
ꢅ
(
3
150 ml) was added m-chloroperbenzoic acid (mCPBA) (ca. 69% purity, [M] (Calcd for C H S : 330.1476).
20 26 2
1
.12 g, 18 mmol) at room temperature. The mixture was stirred for 12 h
3,4ꢁ-Bis(6-bromohexyl)-2,2ꢁ-bithiophene (6g): Slightly yellow oil; H-
under the same reaction conditions until the cloudy solution became clear.
NMR (CDCl ) d: 1.30—1.51 (8H, m), 1.59—1.71 (4H, m), 1.80—1.92 (4H,
3
The resultant mixture was filtered, and CH Cl was removed using a rotary m), 2.61 (2H, t, Jꢃ7.5 Hz), 2.75 (2H, t, Jꢃ7.5 Hz), 3.40 (4H, q, Jꢃ7.5 Hz),
2
2
1
3
evaporator. Hexane was added to the residue to precipitate 1,3,5,7-tetrakis[4- 6.89—6.92 (3H, m), 7.20 (1H, d, Jꢃ5.1 Hz) ppm. C-NMR (75 MHz,
diacetoxyiodo)phenyl]adamantane. After filtration, the crude product was CDCl ) d: 27.9, 28.4, 28.5, 28.9, 30.1, 30.2, 30.3, 30.4, 32.7, 33.9 (ꢂ2),
(
3
obtained in nearly quantitative yield.
120.0, 123.6, 127.3, 129.8, 131.0, 135.8, 139.0, 143.2 ppm. HR-FAB-MS
ꢅ
1,3,5,7-Tetrakis[4-(diacetoxyiodo)phenyl]adamantane (1.01 g, 0.71 mmol) m/z: 489.9988 [M] (Calcd for C H Br S : 489.9999).
20 28 2 2
25)
1
was dissolved in CH CN (15 ml), then p-toluenesulfonic acid monohydrate
3,4ꢁ-Dimethoxy-2,2ꢁ-bithiophene (6h) : Slightly yellow oil; H-NMR
3
(
1.64 g, 5.6 mmol) was added to the solution at room temperature. The mix-
(CDCl ) d: 3.81 (3H, s), 3.94 (3H, s), 6.12 (1H, d, Jꢃ1.2 Hz), 6.85 (1H, d,
3
13
ture was stirred for an additional 3 h. The resulting precipitate was filtered Jꢃ5.4 Hz), 6.89 (1H, d, Jꢃ1.2 Hz), 7.06 (1H, d, Jꢃ5.4 Hz) ppm. C-NMR
and washed several times with CH CN and hexane, then dried in vacuo to (75 MHz, CDCl ) d: 57.2, 58.8, 95.0, 114.7, 115.1, 116.8, 121.7, 133.9,
give 1b (1.05 g, 94%) as a slightly yellow solid.
3
3
153.7, 157.9 ppm.
13)
1
,3,5,7-Tetrakis[4-{hydroxy(tosyloxy)iodo}phenyl]adamantane
(1b)
:
Bipyrrole compounds 9—11 were obtained by a procedure similar to that
1
Slightly yellow crystals. mp (decomp.) 183—190 °C. H-NMR (CDCl3/ described for the thiophenes 5. CH Cl was used as solvent instead of HFIP.
2
2
26)
CF CO Hꢃ10/1) d: 2.26 (12H, s), 2.38 (12H, s), 7.26 (8H, d, Jꢃ8.1 Hz),
2,2ꢁ-Bipyrrole (9a) : White solid; mp: 187—189 °C; Rfꢃ0.32 (hexane/
EtOAcꢃ4/1); H-NMR (CDCl ) d: 6.05—6.19 (4H, m), 6.70—6.72 (2H,
m), 8.23 (2H, bs) ppm. C-NMR (75 MHz, CDCl ) d: 103.5, 109.4, 117.6,
3
2
1
7
.65 (8H, d, Jꢃ8.4 Hz), 7.70 (8H, d, Jꢃ8.9 Hz), 8.25 (8H, d, Jꢃ8.9 Hz).
C-NMR (75 MHz, CDCl /CF CO Hꢃ10/1) d: 21.4, 39.9, 45.8, 121.1,
3
13
13
3
3
2
3
ꢀ
1
1
26.3, 129.0, 129.8, 135.1, 135.9, 144.5, 154.2. Anal. Calcd for 125.9 ppm. IR (KBr) cm : 3366 m, 3123 w, 3103 w, 1574 w, 1518 w, 1454
C H I O S ·4H O: C, 42.09; H, 3.87; I, 28.69, S, 7.25. Found: C, 42.03; w, 1425 w, 1404 w, 1261 w, 1097 m, 1032 m, 912 s, 891 w, 775 m, 743 s,
62
60
4
16
4
2
H, 3.64; I, 28.32, S, 7.25.
658 w. Anal. Calcd for C H N : C, 72.70; H, 6.10; S, 21.20. Found: C,
8 8 2
Typical Procedure for Direct Oxidative Biaryl Coupling Reaction 72.41; H, 6.22; S, 20.92.
1
Using 1b To a stirred solution of 3-hexylthiophene 5a (101 mg, 0.6 mmol)
in (CF ) CHOH (6 ml) was added 1b (127.8 mg, 0.3ꢂ1/4 mmol) and then
3,4ꢁ-Dioctyl-2,2ꢁ-bipyrrole (9b): Slightly brown oil; H-NMR (CDCl ) d:
3
0.86—0.89 (6H, m), 1.23—1.28 (20H, m), 1.55—1.60 (4H, m), 2.48 (2H, t,
Jꢃ7.8 Hz), 2.56 (2H, t, Jꢃ7.8 Hz), 6.02—6.04 (1H, m), 6.12 (1H, t,
Jꢃ2.7 Hz), 6.54–6.57 (1H, m), 6.68 (1H, t, Jꢃ2.7 Hz), 7.88 (1H, bs), 7.93
3
2
TMSBr (0.08 ml, 0.6 mmol) at room temperature when the color of the solu-
tion immediately changed to brown. After stirring for 3 h, CH Cl , saturated
2
2
1
3
NaHCO aq. and solid Na S O ·5H O were successively added to the reac- (1H, bs) ppm. C-NMR (75 MHz, CDCl ) d: 14.1, 22.7, 26.5, 27.0, 29.3,
3
2
2
3
2
3
tion mixture with stirring. The organic layer was then separated and evapo- 29.5, 29.6, 29.7, 29.9, 31.1, 31.2, 31.9 (ꢂ2), 106.0, 109.8, 114.6, 116.6,
ꢀ
1
rated to dryness. MeOH (10 ml) was added to the reaction mixture, and it
was filtered to give the tetraiodide 2 (confirmed by H-NMR analysis and 2359 m, 2340 m, 2307 m, 1421 m, 1261 w, 1155 s, 895 m, 748 w, 704 w.
120.4, 121.7, 125.4, 125.6 ppm. IR (KBr) cm : 3053 m, 2986 m, 2928 s,
1
ꢅ
TLC), which was washed several times with small portions of MeOH for pu- HR-FAB-MS m/z: 356.3191 [M] (Calcd for C H N : 356.3197).
2
4
40
2
1
rification. The filtrate was evaporated and subjected to column chromatogra-
3,3ꢁ-Dioctyl-2,2ꢁ-bipyrrole (10b): Slightly yellow oil; H-NMR (CDCl3)
d: 0.84—0.89 (6H, m), 1.23—1.27 (20H, m), 1.43—1.56 (4H, m), 2.42 (4H,
t, Jꢃ7.8 Hz), 6.16 (2H, t, Jꢃ2.7 Hz), 6.77 (2H, t, Jꢃ2.7 Hz), 7.90 (2H, bs)
ppm. C-NMR (75 MHz, CDCl ) d: 13.9, 22.5, 26.1, 29.1, 29.3, 29.4, 31.2,
3
ꢀ1
phy (SiO , hexane) to give 3,4ꢁ-dihexyl-2,2ꢁ-bithiophene 6a (75 mg, 75%) as
2
a slightly yellow oil. The regiochemistry of the product 6a was determined
1
3
by comparing it to the authentic sample.
23)
1
3
,4ꢁ-Dihexyl-2,2ꢁ-bithiophene (6a)
: Slightly yellow oil; H-NMR 31.7, 108.9, 116.9, 120.5, 122.8 ppm. IR (KBr) cm : 3942 s, 3053 m, 2986
(
2
(
2
1
CDCl ) d: 0.84—0.92 (6H, m), 1.20—1.35 (12H, m), 1.52—1.70 (4H, m), m, 2959 m, 2928 m, 2855 m, 2685 s, 2359 s, 2305 m, 1421 m, 1377 s, 1261
3
ꢅ
.63 (2H, t, Jꢃ8.4 Hz), 2.74 (2H, t, Jꢃ8.4 Hz), 6.89—6.92 (2H, m), 7.03 w, 1157 s, 895 m, 748 w, 706 w. HR-FAB-MS m/z: 356.3191 [M] (Calcd
1
3
1H, s), 7.12 (1H, d, Jꢃ5.5 Hz) ppm. C-NMR (75 MHz, CDCl ) d: 14.1, for C H N : 356.3186).
3
24 40
2
1
2.6, 29.0, 29.1, 29.2, 29.7, 30.4, 30.5, 30.7, 31.6, 31.7, 119.9, 123.4, 127.3,
29.9, 130.9, 135.8, 139.3, 143.5 ppm. HR-FAB-MS: m/z 334.1784 [M]
1,1ꢁ-Diphenyl-2,3ꢁ-bipyrrole (11c): Slightly yellow oil; H-NMR (CDCl )
3
ꢅ
d: 6.07 (1H, dd, Jꢃ3.3, 1.7 Hz), 6.31—6.40 (2H, m), 6.63—6.66 (1H, m),
(Calcd for C H S : 334.1789).
6.83—6.86 (1H, m), 6.90—6.94 (1H, m), 7.16—7.28 (4H, m), 7.31—7.40
20
30 2
1
13
3
,4ꢁ-Dimethyl-2,2ꢁ-bithiophene (6b): Slightly yellow oil; H-NMR (6H, m) ppm. C-NMR (75 MHz, CDCl ) d: 107.9, 108.7, 110.5, 116.2,
3
(
CDCl ) d: 2.28 (3H, s), 2.38 (3H, s), 6.86—6.87 (2H, m), 6.94 (1H, s), 7.11 118.4, 118.8, 119.8, 122.8, 125.3, 126.5, 126.9, 128.7, 129.0, 129.4, 140.2,
3
13
ꢀ1
(1H, d, Jꢃ5.1 Hz) ppm. C-NMR (75 MHz, CDCl ) d: 15.3, 15.7, 120.4, 140.7 ppm. IR (KBr) cm : 3058 w, 1599 w, 1504 m, 1462 w, 1352 w, 1319
3
1
23.0, 127.8, 131.3, 133.7, 136.3, 138.0, 141.3 ppm.
,4ꢁ-Dibutyl-2,2ꢁ-bithiophene (6c): Slightly yellow oil; H-NMR (CDCl ) 285.1394 [MꢅH] (Calcd for C H N : 285.1392).
w, 1184 w, 1074 w, 1036 w, 912 s, 743 s, 694 w, 650 w. HR-FAB-MS m/z:
1
ꢅ
3
3
20 17
2
d: 0.83—0.96 (6H, m), 1.29—1.42 (4H, m), 1.58—1.67 (4H, m), 2.61 (2H,
t, Jꢃ7.5 Hz), 2.75 (2H, t, Jꢃ7.5 Hz), 6.87—6.96 (3H, m), 7.13 (1H, d,
Acknowledgements This work was supported by a Grant-in-Aid for
13
Jꢃ5.1 Hz) ppm. C-NMR (75 MHz, CDCl ) d: 13.9, 22.4, 22.6, 28.9, 30.2 Scientific Research (A) and Young Scientists (B) and for Scientific Research
3
(
ꢂ2), 32.6, 32.9, 119.9, 123.4, 127.3, 129.9, 130.9, 134.1, 139.3, 143.5 ppm. on Priority Areas “Advanced Molecular Transformations of Carbon Re-
ꢀ1
IR (KBr) cm : 3051 w, 2930 s, 2858 s, 1732 w, 1456 m, 1377 m, 1263 s, sources” from the Ministry of Education, Culture, Sports, Science and Tech-
1
088 w, 831 m, 748 s, 652 m. Anal. Calcd for C H S : C, 69.01; H, 7.96; nology-Japan. T. D. also acknowledges support from the Industrial Technol-
16 22 2
S, 23.03. Found: C, 69.01; H, 7.93; S, 22.74.
ogy Research Grant Program from the New Energy and Industrial Technol-
1
3
,4ꢁ-Dioctyl-2,2ꢁ-bithiophene (6d): Slightly yellow oil; H-NMR (CDCl ) ogy Development Organization (NEDO) of Japan.
3
d: 0.86—0.88 (6H, m), 1.20—1.30 (20H, m), 1.56—1.63 (4H, m), 2.52 (2H,
t, Jꢃ7.5 Hz), 2.74 (2H, t, Jꢃ7.5 Hz), 6.80—6.86 (3H, m), 7.05 (1H, d, References and Notes
1
3
Jꢃ5.1 Hz) ppm. C-NMR (75 MHz, CDCl ) d: 14.1, 15.3, 22.7, 29.1, 29.3,
1) Bringmann G., Walter R., Weirich R., Angew. Chem. Int. Ed., Engl.,
3
2
9.4 (ꢂ3), 29.6, 30.4, 30.5, 30.7, 31.9, 119.9, 123.4, 127.3, 129.9, 131.0,
ꢀ
29, 977—991 (1990).
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1
1
35.8, 139.4, 143.5 ppm. IR (KBr) cm : 2923 s, 2853 s, 1464 m, 1377 w,
1
200 w, 1086 w, 831 m, 721 m, 652 w. Anal. Calcd for C H S : C, 73.78;
2
4
38 2
H, 9.80; S, 16.41. Found: C, 73.83; H, 9.82; S, 16.13.
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6
19) The coupling reaction of other 3-substituted pyrroles 8 proceeded in
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