Iron-catalyzed cross-coupling reaction of aryl Grignard reagents with bis(2-bromovinyl)benzenes

Article abstract of DOI:10.2174/157017809789869519

Fe(acac)₃ has been used as the catalyst in cross-coupling reactions of aryl Grignard reagents with 1, 4-bis(2-bromovinyl)benzenes affording bis(2-arylvinyl)benzenes. Effects of alkoxy substituents on both reactants and of the temperature on the

Full text of DOI:10.2174/157017809789869519

Letters in Organic Chemistry, 2009, 6, 573-578
573
Iron-Catalyzed Cross-Coupling Reaction of Aryl Grignard Reagents with
bis(2-bromovinyl)benzenes
Alessandra Operamollaa, Omar Hassan Omarb, Francesco Babudria,b, Michele Vitullia,
Gianluca M. Farinola*,a
aDipartimento di Chimica - Università degli Studi di Bari -via Orabona,4 I-70126 - Bari, Italy
bCNR ICCOM - Dipartimento di Chimica- Università degli Studi di Bari - Via Orabona, 4 I-70126 - Bari, Italy
Received February 02, 2009: Revised August 07, 2009 Accepted August 25, 2009
Abstract: Fe(acac)3 has been used as the catalyst in cross-coupling reactions of aryl Grignard reagents with 1,4-bis(2-
bromovinyl)benzenes affording bis(2-arylvinyl)benzenes. Effects of alkoxy substituents on both reactants and of the
temperature on the reaction outcome are investigated.
Keywords: Iron catalyst, Fe(acac)3, cross-coupling, Grignard reagents, bis(2-arylvinyl)benzenes, PPV oligomers.
INTRODUCTION
Stilbene-like derivatives and bis(2-arylvinyl)benzenes,
represent the most simple terms of the oligo(p-
arylenevinylene) series and are studied as model systems of
their polymeric counterparts [9]. Indeed, the interest toward
arylenevinylene compounds for photonic and electronic
applications stimulates the continuous research for
convenient synthetic routes leading to polymeric or
oligomeric compounds with this structure [10].
Transition metal-catalyzed cross-coupling reactions are
widely used in organic synthesis as valuable methodologies
for C-C bond formation [1]. Along with the most commonly
employed Pd and Ni catalysts some Fe salts or complexes
can promote efficiently cross-coupling reactions of
organomagnesium reagents with various electrophiles [2].
The use of Fe catalysis offers several advantages, since Fe
compounds are cheap and benign alternatives to other toxic
or expensive transition metal catalysts, like nickel or
palladium complexes. Furthermore, iron compounds can be
handled more easily as they are usually air-stable and non
hygroscopic and their catalytic activity is often effective at
room temperature or below [2a, 2b]. In spite of these
advantages, and even though iron-catalyzed cross-coupling
reactions [3] were disclosed before the corresponding Ni- or
Pd-catalyzed processes [4], their chemistry remained largely
unexplored for a long time. Only recently the study of the
mechanism, scope and limitations of such reactions has
again attracted the attention of several groups and interest in
them is rapidly increasing [2, 5].
In connection with our continuous interest in the
synthesis and characterization of conjugated materials for
photonics and electronics [11] we developed organometallic
synthetic protocols for functionalized phenylenevinylene
oligomers based on coupling reactions of vinylsilanes [12] or
vinylstannanes [13]. We have also reported a general
polymerization protocol based on Pd-catalyzed cross-
coupling reaction of aromatic bis-organomagnesium reagents
with arylhalides [14].
In this framework, we became interested in the extension
of the Fe-catalyzed vinylation of aryl Grignard reagents [8b]
to bis(bromovinyl)benzenes as a further step towards the
application of this reaction to the synthesis of larger
arylenevinylenes. Thus, we report herein our investigation
on cross-coupling reactions of aryl Grignard reagents 1a-c
and (E,E)-1,4-bis (2-bromovinyl)benzenes 2a-b using
tris(acetylacetonate) iron(III) complex as catalyst. The
methodology proposed is summarized in the Scheme 1.
The most accepted mechanistic hypothesis [3, 6] for this
cross-coupling reaction assumes that a catalytically active
reduced iron species, whose nature is still debated, is
generated in situ by the organometallic compound. A recent
study has pointed out that a different mechanism can operate
in the presence of additives such as TMEDA [5o].
Among the various synthetic applications of this versatile
reaction, highly stereo-specific vinylation of Grignard
reagents [6a] with vinyl halides [3, 7] was found to be
effectively promoted by iron 1,3-diketonate, and the reaction
was also applied to the synthesis of several stilbene
derivatives [8].
RESULTS AND DISCUSSION
The halides 2a [15] and 2b appear useful starting
materials for the synthesis of oligo-p-phenylenevinylenes. In
particular it is worth investigating the reactivity of the
dihalide 2b functionalized with two long alkoxy chains
because these substituents are commonly introduced in more
extended phenylenevinylene derivatives to confer solubility
in common organic solvents.
*Address correspondence to this author at the Dipartimento di Chimica -
Università degli Studi di Bari -via Orabona,4 I-70126 - Bari, Italy; Tel: 0039
080 5442076; Fax: 0039 080 5442924; E-mail: farinola@chimica.uniba.it
The alkoxy-substituted bis-(2-bromovinyl)benzene (2b)
was prepared starting from the 2,5-bis(octyloxybenzene)-
1570-1786/09 $55.00+.00
© 2009 Bentham Science Publishers Ltd.

574 Letters in Organic Chemistry, 2009, Vol. 6, No. 7
Operamolla et al.
OR
OR
OR
Fe(acac)3
THF
Br
Ar
ArMgX
+
Br
Ar
OR
3a-f
R = H
2a
1a-c
C8H17 2b
S
Ar- =
1a;
1b;
MgBr
MgBr
H3CO
1c.
MgBr
Scheme 1. Iron catalyzed cross-coupling reaction leading to (E,E)-bis(2-arylvinyl)benzenes.
OC8H17
OC8H17
Br
CBr4
PPh3
CHO
Br
Br
Br
CH2Cl2
-10°C
OHC
OC8H17
OC8H17
4
5
65%
OC8H17
Br
(EtO)2POH
Et3N
90°C
Br
OC8H17
2b
87%
Scheme 2. Synthesis of 2b.
1,4-dicarbaldehyde (4) [16] as reported in Scheme 2. The
synthetic sequence consists of two steps: a Wittig-type
reaction of the aromatic dialdehyde 4 with CBr4 affords the
tetrabromo-substituted precursor 5 which is then reacted
with diethylphosphite in triethylamine yielding stereo-
selectively the dihalide 2b.
to THF, on the reactivity of aryl magnesium compounds with
(2-bromovinyl)arenes in the presence of iron-1,3-diketonate.
On the contrary, in our study DME appears to reduce the
efficiency of the cross-coupling reaction.
Table 1. Reaction of 1a with 2aa
Fe(acac)3
-20°C to r.t.
As reported in the literature [8b], the iron-1,3-diketonate-
catalyzed vinylation of aryl Grignard reagents at low
temperatures (-20°C) and in dimethoxyethane as solvent
affords stereoselectively stilbene derivatives.
1a + 2a
3a
We extended this protocol to the reaction between the
dihalide 2a and phenylmagnesium bromide (1a). In our
experiment a fair excess of the organometallic reagent (about
10% in moles exceeding the stoichiometric amount) was
employed to carry out the reduction of the catalyst precursor
to its active oxidation state. The reaction was tested with
different amounts of the catalyst with respect to 2a. The
results are summarized in Table 1.
Entry
Solvent
Amount of Catalyst
Yieldb
1
2
3
DME
DME
THF
1%
5%
5%
37%
55%
83%
aAll the reactions were performed under a nitrogen atmosphere. The reactions were
monitored via GC-MS analysis. bOverall isolated yields.
In the first experiment, carried out in dimethoxyethane
solvent, 1% molar amount of catalyst with respect to the
dihalide was used and the cross-coupling product, (E,E)-1,4-
bis(2-phenylethenyl)benzene (3a) was isolated in 37% yield
(Table 1, Entry 1). Increasing the amount of catalyst to 5%
resulted in an improved yield (entry 2) and changing the
solvent from dimethoxyethane to tetrahydrofuran caused a
remarkable yield increase to 83% in two hours reaction time.
Our results on the effect of the solvent differ from those
previously published by Molander et al. [8b] who reported a
positive effect of the coordinating solvent DME, compared
To address the scope and possible limitations of the
methodology under investigation, we extended the reaction
to other aryl and heteroaryl Grignard reagents and to a
different divinylbenzene. In particular the introduction of
alkoxy groups was considered on both the reaction partners,
in view of the wide use of these substituents as solubilizing
moieties in phenylenevinilene oligomers and polymers. A
series of experiments were carried out reacting halides 2a
and 2b with phenylmagnesium bromide 1a, 4-methoxyph-

Iron-Catalyzed Synthesis of Bis(2-arylvinyl)benzenes
Letters in Organic Chemistry, 2009, Vol. 6, No. 7
575
Table 2. Reactions of aryl Grignard Reagents 1a, b, c with 2a and 2ba
Entry
ArMgBr
Halide
Yield %b
Product
1
1a
(83) 85c
3a
OCH3
2a
2
3
1b
1c
(27) 65d
H3CO
3b
(36) 45e
S
S
3c
C8H17
C8H17
C8H17
O
O
O
4
5
6
1a
1b
1c
(27) 55f
(26) 71g
(29) 40h
3d
OC8H17
OC8H17
OC8H17
OCH3
2b
H3CO
3e
S
S
3f
aAll the reactions were performed under a nitrogen atmosphere. The reactions were monitored through TLC or GC-MS analysis. bOverall isolated yields. In parentheses: yields
e
g
h
obtained at -20°C reaction temperature. cLit.: 72% [10m]. dLit. 70% (E,E)-isomer; after chemical isomerization [10j]. Lit. 68% [17]. fLit. 56% [12]. Lit. 66% [12] Lit. 68% after
chemical isomerization [18].
enylmagnesium bromide (1b) and 2-thienylmagnesium
bromide (1c), in the same conditions as entry 3 in Table 1.
of the desired product. Therefore, the protocol developed
appears a versatile synthetic method for distyrilbenzene
derivatives that compares well with other protocols based on
the Wittig reaction [10j, 10m, 17, 18], or on coupling
processes of vinylsilanes [12], with the advantage of easy
experimental procedure. Comparison with the yields
reported in the literature are provided in footnotes of the
Table 2. As a further advantage, our procedure does not
require the use of Fe coordinating agents and slow addition
of the organomagnesium reagent which are necessary in
other recently reported iron-catalyzed stilbene synthesis
[5b,n]. Studies are in progress in our laboratories to extend
the protocol to polymerization reactions, and the results will
be reported in due course.
When the reactions were carried out at -20°C low yields
were obtained (reported in parentheses in Table 2) except in
the case of the unsubstituted product 3a. These data suggest
that the presence of alkoxy groups on the aryl Grignard
reagents (entries 1, 4) and on the aromatic ring of the
divinylbenzene derivatives (entry 4) negatively affects the
reaction outcome under these experimental conditions.
The use of the Grignard reagent of 2-bromothiophene 1c
(entries 2, 5) also resulted in low reaction yields. The
unsatisfactory results obtained prompted us to repeat the
experiments summarized in the Table 2 and Table 1 raising
the temperature from -20°C to 25°C.
Increasing the reaction temperature resulted in an
improvement of the yields even in the presence of the alkoxy
group. The yields of the reactions carried out at 25°C range
from acceptable to very good, with the only exception of the
reaction of 1c and 2b (entry 6) that gave moderate formation
CONCLUSIONS
In conclusion, Fe(acac)3 has been reported to be effective
catalyst in stereoselective cross-coupling reaction of aryl
Grignard reagents with (E,E)-bis(2-bromovinyl)arenes. The

576 Letters in Organic Chemistry, 2009, Vol. 6, No. 7
Operamolla et al.
protocol offers the benefit of low cost of the catalyst and of
the organometallic reagent used. The possibility to carry out
the reactions at room temperature represents a further
advantage. The reaction proceeds smoothly, in the presence
of a fair excess of arylmagnesium compound, and affords
(E,E)-1,4-bis(2-phenylethenyl)benzenes in good yields.
dichloromethane 95:5 as the eluent. A white solid was
isolated in a 65% yield. m.p. 72-74°C (hexane) H-NMR
1
(400 MHz, CDCl3) ꢀ0.87 (t, J=6.8, 6H), 1.21-1.37 (m, 16H),
1.42 (quintet, J=6.8 Hz, 4H), 1.76 (quintet, J=6.9 Hz, 4H),
3.91 (t, J=6.5 Hz, 4H), 7.30 (s, 2H), 7.59 (s, 2H) ppm; 13C-
NMR (100 MHz, CDCl3) ꢀ 149.6, 132.2, 125.3, 112.5, 89.6,
69.4, 31.7, 29.3, 29.2, 29.1, 26.0, 22.6, 14.1 ppm; IR (KBr) ꢁ
2952, 2933, 2905, 2867, 2848, 1490, 1468, 1418, 1385,
1163, 865 cm-1; GC-MS 706 (M+8, 12%), 704 (M+6, 34%),
702 (M+4, 62%), 700 (M+2, 37%), 698 (M, 10%), 594 (9%),
592 (27%), 590 (42%), 588 (27%), 586 (8%), 482 (16%),
480 (55%), 478 (81%), 476 (61%), 474 (17%), 320 (45%),
318 (100%), 316 (51%), 158 (99%) m/z. Anal Calcd for
C26H38Br4O2: C, 44.47; H, 5.45; Found: C, 44.42; H, 5.31.
EXPERIMENTAL SECTION
General Remarks
All reactions were carried out under
a nitrogen
atmosphere in oven-dried glassware, with dry solvents unless
otherwise stated. All the solvents were distilled immediately
prior to use. Tetrahydrofuran and dimethoxyethane were
distilled from benzophenone ketyl. Dichloromethane was
distilled from phosphorus pentoxide. Reagents were
purchased at the highest commercial quality and used
without further purification, except triethylamine, that was
distilled from KOH and then stored over molecular sieves.
(E,E)-1,4-bis(2-bromoethenyl)-2,5-bisoctyloxybenzene 2b
A 100 ml three-necked round bottom flask equipped with
a stirrer and a water condenser was charged under nitrogen
with
1,4-bis-(2,2-dibromoethenyl)-2,5-bis-n-octyloxyben-
zene (6.135 g, 8.74 mmol), diethylphosphite ( 7.86 ml, 61.2
mmol) and triethylamine (13 ml). The mixture was heated to
80°C. After 4 hours, GC analysis showed the disappearance
of 1,4-bis-(2,2-dibromovinyl)-2,5-bisoctyloxybenzene. The
reaction mixture was then cooled to room temperature,
neutralized with a solution of HCl 5% and extracted with
dichloromethane (3 x 80 ml). The organic phase was
collected, washed with a saturated solution of NaCl (3 x 80
ml), dried over Na2SO4, filtered and concentrated under
reduced pressure. The crude product was purified through
silica gel chromatography eluting with a mixture of
petroleum ether: dichloromethane 9:1. A white solid was
(E,E)-1,4-bis(2-bromovinyl)benzene
(2a)
and
2,5-
bisoctyloxybenzene-1,4-dicarbaldehyde (4) were synthesized
as reported elsewhere [15, 16]. The Grignard reagents 1a-c
were prepared in dry tetrahydrofuran from the corresponding
commercially available aryl bromides by standard methods,
in concentrations between 0.7-1.0 M. Preparative column
chromatography was carried out by using 0.04-0.063 mm
silica gel. All the compounds were characterized by 1H-
NMR, 13C-NMR, IR spectroscopy, elemental analysis and
GC-MS analysis. GC analyses were performed on a gas
chromatograph equipped with a SE-30 (methyl silicone, 30
m x 0.25 mm id) capillary column and a FID detector. GC-
MS analyses were performed on a gas chromatograph
equipped with a SE-30 (methyl silicone, 30 m x 0.25 mm id)
1
isolated in a 87% yield. m.p. 99-101°C (hexane). H-NMR
(400 MHz, CDCl3) ꢀ 0.90 (t, J=6.8 Hz, 6H), 1.24-1.50 (m,
20H), 1.80 (quintet, J=7.0 Hz, 4H), 3.93 (t, J=6.6 Hz, 4H),
6.74 (bs, 2H), 6.96 (d, J=14.4 Hz, 2H), 7.24 (d, J=14.4 Hz,
2H) ppm; 13C-NMR (100 MHz, CDCl3) ꢀ 150.2, 132.8,
125.2, 111.7, 108.4, 69.2, 31.8, 29.4, 29.3, 29.2, 26.1, 22.7,
14.1 ppm; IR (KBr) ꢁ 3071, 2919, 2850, 1473, 1416, 1393,
1212, 1043, 936, 702 cm-1; GC-MS 546 (M+4, 35%), 544
(M+2, 67%), 542 (M, 28%), 434 (31%), 432 (48%), 430
(38%), 322 (52%) 320 (100%), 318 (44%), 241 (40%), 239
(45%), 159 (37%) m/z. Anal Calcd for C26H40Br2O2: C,
57.36; H, 7.41; Found: C, 57.24; H, 7.33.
1
capillary column and ion trap selective mass detector. H-
NMR and 13C-NMR spectra were recorded at 400 MHz and
100 MHz, or at 500 MHz (1H-NMR) and 125 MHz (13C-
NMR), using the residual proton peak of CDCl3 at 7.26 ppm
1
as reference for H spectra and the signals of CDCl3 at 77
ppm for 13C spectra. Melting points (uncorrected) were
obtained on a capillary melting point apparatus.
1,4-Bis(2,2-dibromoethenyl)-2,5-bisoctyloxybenzene 5
A 250 ml three-necked round bottom flask equipped with
a stirrer, a low temperature thermometer and a 50 ml
dropping funnel, was charged under nitrogen with 2,5-
bisoctyloxybenzene-1,4-dicarbaldehyde (6.20g, 15.9 mmol)
and triphenylphosphine (17.5g, 66.7 mmol). The mixture
was dissolved in 70 ml of dry dichloromethane. The reaction
mixture was cooled to -10°C with vigorous stirring and a
solution of carbon tetrabromide (11.58 g, 34.9 mmol) in 30
ml of dry dichloromethane was added dropwise over 90
minutes. After a total time of 3 hours GC analysis showed
the disappearance of the aldehyde. The reaction mixture was
then allowed to reach room temperature and quenched with a
saturated aqueous solution of Na2CO3. The mixture was
extracted with dichloromethane (3 x 120 mL). The organic
phase was collected, washed with a saturated solution of
NaCl (3 x 100 ml) and dried over anhydrous Na2SO4, filtered
and concentrated under reduced pressure. The crude product
was purified by preparative column chromatography over
General procedure for the cross-coupling of 2a and 2b at -
20°C
A 25 ml three-necked round bottom flask equipped with
a stirrer, a 10 ml dropping funnel and a low temperature
thermometer was charged under nitrogen with (E,E)-1,4-
bis(2-bromoethenyl)benzene (0.213g, 0.745 mmol) or (E,E)-
1,4-bis(2-bromoethenyl)-2,5-bis-octyloxy-benzene (0.150g,
0.290 mmol). Iron(III) tris-acetylacetonate (0.013g, 0.037
mmol or 0.005g, 0.014 mmol) was then added. The mixture
was dissolved in 10 ml of dry tetrahydrofurane and cooled to
-20°C with vigorous stirring.
A
solution of the
arylmagnesium bromide (2.2 eq. with respect to the halide),
preventively diluted with 6 ml of dry THF was added
dropwise over 10 minutes to the reaction mixture. Then the
reaction was slowly allowed to reach room temperature.
After a total time from 2 to 12 hours GC-MS analysis or
TLC analysis showed the completion of the reaction. The
reaction mixture was then quenched with a 5% aqueous
silica gel, using
a
mixture of petroleum ether:

Iron-Catalyzed Synthesis of Bis(2-arylvinyl)benzenes
Letters in Organic Chemistry, 2009, Vol. 6, No. 7
577
solution of HCl. The mixture was extracted with
dichloromethane (3 x 80 mL). The organic phase was
collected and washed thrice with a saturated solution of
NaCl, dried over anhydrous Na2SO4, filtered and
concentrated under reduced pressure. The crude product was
purified by preparative column chromatography over silica
gel.
(125 MHz, CDCl3) ꢀ 151.1, 137.9, 128.6, 127.3, 126.8,
126.5, 123.5, 110.6, 69.5, 31.8, 29.5, 29.4, 29.3, 26.3, 22.6,
14.1 ppm; IR (KBr) ꢁ 1592, 1182, 1057, 962, 759 cm-1. Anal
Calcd for C38H50O2: C, 84.71; H, 9.35; Found: C, 84.53; H,
9.25.
(E,E)-1,4-bis(octyloxy)-2,5-bis[2-(4-methoxyphenyl)-
ethenyl]benzene 3e
General Procedure for the Cross-Coupling of 2a and 2b at
r.t.
Purified by silica gel chromatography eluting with
petroleum ether: dichloromethane 8:2. Yellow solid m.p.
112-113°C (methanol); Lit. [12] 112-113°C.. H-NMR (500
1
The procedure was the same as above, with exception of
the reaction temperature.
MHz, CDCl3) ꢀ 0.86 (t, J=6.8 Hz, 6H), 1.22-1.61 (m, 20H),
1.84 (quintet, J=6.4 Hz, 4H), 3.82 (s, 6H), 4.02 (t, J=6.5 Hz,
4H), 6.88 (d like, J=8.7 Hz, 4H), 7.06 (d, J=16.4 Hz, 2H),
7.08 (bs, 2H), 7.32 (d, J=16.4 Hz, 2H), 7.45 (d like, J=8.7
Hz, 4H) ppm; 13C-NMR (125 MHz, CDCl3) ꢀ 159.1, 150.9,
130.8, 128.1, 127.8, 126.6, 121.4, 114.1, 110.5, 69.6, 55.2,
31.8, 29.5, 29.4, 29.3, 26.3, 22.7, 14.1 ppm; IR (KBr) ꢁ
1604, 1511, 1424, 1259, 1176, 1032, 821, 805 cm-1. Anal
Calcd for C40H54O4: C, 80.22; H, 9.09; Found: C, 79.99; H,
8.83.
(E,E)-1,4-bis(2-phenylethenyl)benzene 3a
Purified by silica gel chromatography eluting with
petroleum ether: dichloromethane 8:2. Yellow-green solid
1
m.p. 252-253°C (chloroform); Lit. [10m]: 257°C. H-NMR
(400 MHz, CDCl3) ꢀ 6.76 (d, J=14.0 Hz, 2H), 7.00-7.15 (m,
4H), 7.26 (d, 14 Hz, 2H), 7.34 (t like, J=7.3 Hz, 2H), 7.40-
7.53 (m, 8H) ppm; 13C-NMR (100 MHz, CDCl3) ꢀ 137.3,
136.7, 128.7, 128.6, 128.2, 127.6, 126.8, 126.5 ppm; IR
(KBr) ꢁ 3023 (w), 1447 (w), 968, 815, 746, 690 cm-1; GC-
MS 283 (M+1, 24%), 282 (M, 100%), 203 (17%), 178 (35%)
m/z. Anal Calcd for C22H18: C, 93.57; H, 6.43, Found: C,
93.51; H, 6.39.
(E,E)-1,4-bis(octyloxy)-2,5-bis[2-(thiophen-2-yl)-
ethenyl]benzene 3f
Purified by silica gel chromatography eluting with
petroleum ether: dichloromethane 75:25. Pale green solid
m.p. 99-101°C (methanol); Lit. [18] 72-76°C. 1H-NMR (500
MHz, CDCl3) ꢀ 0.88 (t, J=6.9 Hz, 6H), 1.22-1.33 (m, 20H),
1.86 (quintet, J=6.5 Hz, 4H), 4.03 (t, J=6.5 Hz, 4H), 7.00
(dd, J1=5.0 Hz, J2=3.5 Hz, 2H), 7.03 (bs, 2H), 7.06 (d, J=3.5
Hz, 2H), 7.18 (d, J=5.0 Hz, 2H), 7.24 (d, J=16.1 Hz, 2H),
7.30 (d, J=16.1 Hz, 2H) ppm; 13C-NMR 100 MHz, CDCl3) ꢀ
150.9, 143.8, 127.5, 126.3, 125.6, 124.1, 123.3, 122.0, 110.6,
69.4, 31.8, 29.6, 29.4, 29.3, 26.2, 22.6, 14.1, 1.0 ppm; IR
(KBr) ꢁ 2960, 2923, 2851, 1457, 1261, 1084, 1023, 811cm-1.
Anal Calcd for C36H46O2S2: C, 74.13; H, 8.42; S, 11.64;
Found: C, 74.03; H, 8.35; S, 11.53.
(E,E)-1,4-bis[2-(4-methoxyphenyl)-ethenyl]benzene 3b
Purified by silica gel chromatography eluting with
petroleum ether: dichloromethane 75:25. Yellow-green solid
1
m.p. 306-308°C (chloroform); Lit. [10j] 302-304°C. H-
NMR (400 MHz, CDCl3) ꢀ 4.14 (s, 6H), 7.07 (d, J=13.9 Hz,
2H), 7.20 (d like, J=8.7 Hz, 4H), 7.39 (d, J=13.9 Hz, 2H),
7.57 (d like, J=8.4 Hz, 4H), 7.70-7.79 (m, 4H) ppm; 13C-
NMR (100 MHz, CDCl3) ꢀ 159.3, 136.8, 127.7, 126.5,
126.3, 125.8, 114.1, 106.1, 55.3 ppm; IR (KBr) ꢁ 3066 (w),
2960 (w), 1931 (w), 2836 (w), 1597, 1513, 1254, 1175,
1029, 935, 832 cm-1. Anal Calcd for C24H22O2: C, 84.18; H,
6.48, Found: C, 84.03; H, 6.37.
(E,E)-1,4-bis[2-(thiophen-2-yl)-ethenyl]benzene 3c
ACKNOWLEDGEMENTS
Purified by silica gel chromatography eluting with
petroleum ether: dichloromethane 75:25. Yellow-green solid
m.p. 249-251°C (chloroform); Lit. [17]: 269°C. H-NMR
This work was financially supported by Ministero
dell’Istruzione, dell’Università e della Ricerca (MIUR),
“Progetto PRIN 2007 PBWN44” and by Università degli
Studi di Bari.
1
(400 MHz, CDCl3) ꢀ 6.92 (d, J=16.1 Hz, 2H), 7.00 (dd,
J1=5.0 Hz, J2= 3.6 Hz, 2H), 7.08 (d, J=3.5 Hz, 2H), 7.20 (d,
J=5.0 Hz, 2H), 7.25 (d, J=16.1 Hz, 2H), 7.44 (bs, 4H) ppm;
13C-NMR (100 MHz, CDCl3) ꢀ 142.9, 136.2, 127.8, 127.6,
126.6, 126.1, 124.4, 121.6 ppm; IR (KBr) ꢁ 2919 (w), 2848
(w), 954, 828, 655 cm-1; GC-MS 295 (M+1, 22%), 294
(100%), 209 (10%), 184 (19%) m/z. Anal Calcd for
C18H14S2: C, 73.43; H, 4.79; S, 21.78 Found: C, 73.32; H,
4.77; S, 21.71.
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1
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