Photobehaviour of 2- and 3-heteroaryl substituted o-divinylbenzenes; formation of fused 2,3- and 3,2-heteroareno-benzobicyclo[3.2.1]octadienes and 3-heteroaryl benzobicyclo[2.1.1]hexenes

Article abstract of DOI:10.1016/j.tet.2008.02.062

New β-3-thienyl (8) and β-3-furyl derivatives of o-divinylbenzene (9) have been synthesised and their photochemical behaviour compared with 2-thienyl (7) and 2-furyl derivatives (2). Whereas the β-(2-heteroaryl) substituted o-divinylbenzenes (7 or 2) give only bicyclo[3.2.1]octadiene structure (14 or 1) by 1,6-ring closure of the biradical intermediate, β-(3-heteroaryl) substituted o-divinylbenzenes (8 or 9) give bicyclo[3.2.1]octadiene structure (23 or 24) and bicyclo[2.1.1]hexene structure (25 or 26) by 1,6- and 1,4-ring closure, respectively. This photochemical approach provides a simple method to 2,3- and 3,2-fused thiophene and furan polycyclic compounds.

Full text of DOI:10.1016/j.tet.2008.02.062

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 3928e3934
www.elsevier.com/locate/tet
Photobehaviour of 2- and 3-heteroaryl substituted o-divinylbenzenes;
formation of fused 2,3- and 3,2-heteroareno-benzobicyclo[3.2.1]octadienes
and 3-heteroaryl benzobicyclo[2.1.1]hexenes
a
Dragana Vidakovic , Irena Skoric , Margareta Horvat , Zeljko Marinic ,
a
a
b
ˇ
ˇ
´
´
´
a,
ˇ
Marija Sindler-Kulyk
*
a
´
Department of Organic Chemistry, Faculty of Chemical Engineering and Technology, University of Zagreb, Marulicev trg 19, 10000 Zagreb, Croatia
b
´
NMR Center, Rudjer Bosˇkovic Institute, Bijenicka cesta 54, 10000 Zagreb, Croatia
ꢀ
Received 12 November 2007; received in revised form 1 February 2008; accepted 21 February 2008
Available online 26 February 2008
Dedicated to Professor Douglas C. Neckers on the occasion of his 70th birthday
Abstract
New b-3-thienyl (8) and b-3-furyl derivatives of o-divinylbenzene (9) have been synthesised and their photochemical behaviour compared
with 2-thienyl (7) and 2-furyl derivatives (2). Whereas the b-(2-heteroaryl) substituted o-divinylbenzenes (7 or 2) give only bicyclo[3.2.1]octa-
diene structure (14 or 1) by 1,6-ring closure of the biradical intermediate, b-(3-heteroaryl) substituted o-divinylbenzenes (8 or 9) give
bicyclo[3.2.1]octadiene structure (23 or 24) and bicyclo[2.1.1]hexene structure (25 or 26) by 1,6- and 1,4-ring closure, respectively. This
photochemical approach provides a simple method to 2,3- and 3,2-fused thiophene and furan polycyclic compounds.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Oxygen heterocycles; Sulfur heterocycles; Furan; Thiophene; Photochemistry; Photocycloaddition; Synthesis
1. Introduction
only alkoxycarbonyl substituted pyrrole derivatives21 gave
pyrrolo-fused benzobicyclo[3.2.1]octadiene structure (4). In
the case of 2-(o-vinylstyryl)furans with the substituent in po-
sition 3 of the furan ring (5) formation of the bicyclo[2.1.1]-
hexene structure (6) was observed,9 presumably due to the
steric reasons.
There is an increasing interest in the bicyclo[3.2.1]octane
structures since they represent the basic framework of numer-
ous important biologically active natural compounds or their
metabolites. Their skeleton has also proved to be useful reac-
tive intermediate in various stereoselective transformations
making these derivatives powerful building blocks in organic
synthesis.1 In one of our previous papers2 on the photochemi-
stry of styryl substituted furan derivatives2e12 we demon-
strated for the first time the photochemical approach to
furano-fused bicyclo[3.2.1]octadiene structure (1) by simple
irradiation of 2-(o-vinylstyryl)furan (2) (Fig. 1). On the other
hand, their nitrogen analogues, pyrrole derivatives (3),13e20
gave completely different photoproducts. It was found that
In continuation of our interest for the effect of heteroatoms,
as well as their position in the heteroaromatic ring on the
R
R
X
1: X=O
4: X=NCOOR
2: R=2-furyl
3: R=2-pyrrolyl
5: R=2-(3-X)furyl
7: R=2-thienyl
8: R=3-thienyl
9: R=3-furyl
6: R=2-(3-X)furyl
11: R=phenyl
10: R=phenyl
* Corresponding author. Tel.: þ385 1 4597242; fax: þ385 1 4597250.
ˇ
E-mail address: marija.sindler@fkit.hr (M. Sindler-Kulyk).
Figure 1.
0040-4020/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.02.062

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D. Vidakovic et al. / Tetrahedron 64 (2008) 3928e3934
3929
formation of heteropolycyclic compounds, we present here for
the first time the photochemical behaviour of thiophene deriva-
tives (7, 8) and furan derivative (9). We anticipated that intro-
duction of sulfur as heteroatom, by replacing the furan moiety
with the thiophenes, may have influence on the excited state
properties of this new hexatriene system and as a consequence
the formation of diverse photoproducts. Based solely on the
aromaticity of heterocycles,22,23 the thiophene being more
aromatic than furan, it might be expected that thiophene deriva-
tive 7 resembles the photochemical behaviour of its parent
benzene derivative 10, which upon irradiation closes to bicy-
clo[2.1.1]hexene 11.24e28
S
S
S
trans-7
.
.
.
.
12
1,4- closure
1,6- closure
S
H
S
cis-7
2. Results and discussion
S
13
15
(not isolated)
Starting compounds, 2-[2-(2-ethenylphenyl)ethenyl]thio-
phene (7),3 3-[2-(2-ethenylphenyl)ethenyl]thiophene (8) and
3-[2-(2-ethenylphenyl)ethenyl]furan (9) were synthesised in
a good to very good yields (50e85%) by the Wittig reaction
of b,b-o-xylyl(ditriphenylphosphonium) dibromide and the
corresponding aldehydes (Scheme 1) according to the general
procedure described for the b-heteroaryl-o-divinylbenzenes.3
They were obtained as mixtures of trans- (60e70%) and cis-
isomer (30e40%) that were separated by column chromatog-
raphy and characterised spectroscopically.
S
shift
1,3-H
S
16 (<1%)
17 (<1%)
14 (45 %)
Scheme 2.
properties of the corresponding phenyl analogous 10, o-vinyl-
stilbene,24,25 where the main product was the phenyl-benzo-
bicyclo[2.1.1]hexene 11.
Formation of byproducts 16 and 17 can occur from the
cis-configuration of 7 by two different mechanisms: the intra-
molecular photoinduced [4þ2] cycloaddition followed by
elimination of H2S produces phenanthrene (16)29 while photo-
chemical electrocyclization process leads to vinylnaphthothio-
phene 17. The presence of phenanthrene (16) was confirmed
1. R-CHO
CH2PPh3Br
CH2PPh3Br
R
2. CH2O
NaOEt
EtOH
7: R=2-thienyl (76%)
8: R=3-thienyl (73%)
9: R=3-furyl (53%)
Scheme 1.
1
1
by comparison of its H NMR spectrum with the H NMR
spectrum of authentic sample. The structure of new 6-vinyl-
naphtho[2,1-b]thiophene (17), formed in too small quantities
to be analysed completely, was confirmed by its independent
synthesis. The vinylnaphthothiophene derivative 17 was pre-
pared by photochemical ring closure of 18 to 19 followed by
a sequence of reactions according to Scheme 3.
The irradiation experiments were performed under anaero-
bic conditions and in petroleum ether as a solvent. On irradi-
ation of 2-thienyl substituted o-divinylbenzene 7 (Scheme 2)
the thieno-fused benzobicyclo[3.2.1]octadiene 14 was isolated
as the main product in 45% yield. In addition, minor quantities
of phenanthrene (16) and vinylnaphthothiophene (17) were
found in the first fractions during the column chromatography
and the high-molecular-weight products remained on the
column.
S
S
hν
The photoproducts are easily identified by their NMR spec-
tra, using one- and two-dimensional NMR techniques, and
their comparison with the spectra of photoproducts, previously
obtained on irradiation of 2-[2-(2-ethenylphenyl)ethenyl]furan
(2).2 The proposed mechanism for the formation of the main
product, bicyclo[3.2.1]octadiene derivative 14, as in the case
of furan derivative 2,2 involves intramolecular cycloaddition
via biradical intermediate 12 followed by preferred 1,6-ring
closure to 13 and subsequent 1,3-H shift. The 2-thienyl-bicy-
clo[2.1.1]hexene derivative 15, which could be formed by
1,4-ring closure of 12, was not detected. The 1,4-ring closure
was also not observed on irradiation of 2-[2-(2-ethenylphenyl)-
ethenyl]furan (2)2,4,8,9 contrary to the photochemical
CH3
CH3
cis-18
hν
trans-18
O2/I
S
S
1. NBS
2. Ph3P
3. CH2O
NaOEt
EtOH
CH3
17
19
Scheme 3.

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D. Vidakovic et al. / Tetrahedron 64 (2008) 3928e3934
3930
E
F
Irradiation of 3-[2-(2-ethenylphenyl)ethenyl]thiophene (8)
3f
O
A
until the full conversion and under the same conditions as
2-thienyl derivative 7, gave, after chromatographic separation
on silica gel, not only the expected bicyclo[3.2.1]octadiene de-
rivative 23, as in case of 2-furyl 1 and 2-thienyl derivative 7,
but also the bicyclo[2.1.1]hexene derivative 25. Formation of
both bicyclic systems is explained via the same intermediate,
biradical 20, followed by possible 1,6- and 1,4-ring closure,
respectively (Scheme 4). Further investigation of the hitherto
unknown 3-furyl analogue, 3-[2-(2-ethenylphenyl)ethenyl]-
furan (9), afforded very similar results: bicyclo[3.2.1]octa-
diene derivative 24 and bicyclo[2.1.1]hexene derivative 26
were isolated, besides oxidation and high-molecular-weight
products.
F
2f
C
D
A
B
D
B
1
E
C
PPM4.0
3.6
3.2
2.8
2.4
2.0
E
F
A
C
D
3t
S
2t
B
F
A
14
B
D
E
C
X
PPM4.0
3.6
3.2
2.8
2.4
2.0
E
F
trans-8: X = S
trans-9: X = O
A
S
2t
3t
C
B
23
X
X
D
F
X
A
B
D
C
E
20
1,4- closure
1,6- closure
PPM 4.0
3.6
3.2
E
2.8
2.4
2.0
X
H
X
cis-8: X = S
cis-9: X = O
F
A
C
O
2f
3f
F
B
21: X = S
22: X = O
D
A
25: X = S (5 %)
26: X = O (9 %)
24
B
D
E
C
shift
1,3-H
X
PPM4.0
3.6
3.2
2.8
2.4
2.0
23: X = S (25 %)
24: X = O (27 %)
Figure 2. 1H NMR spectra (600 MHz, in CDCl3) of the aliphatic region of
three new bicyclo[3.2.1]octadiene structures (14, 23, 24) compared with the
known structure 1.2
Scheme 4.
The structures of new photoproducts have been elucidated
1
from their spectral data, H NMR being the most informative.
The aliphatic region of polycyclic compounds 1, 14, 23 and 24
1
and 26 have also well recognisable H NMR spectra showing
the symmetric benzobicyclo[2.1.1]hexene structure (Fig. 3).
The isolated yields on bicyclic structures in case of irradi-
ation of 3-styryl substituted thiophenes or 3-styryl substituted
furans were in the same range. The difference in photochemi-
cal behaviour between thiophene and furan derivatives is in the
rate of conversion. Thus, for the same conversion the irra-
diation time of thiophene derivatives is considerably longer
than irradiation time of furan derivatives. To get more insight
into this process the reaction course of all four compounds, the
2-thienyl derivative 7 and 3-thienyl derivative 8 as well as the
2-furyl 2 and 3-furyl 9, was followed by examination of NMR
spectra of the reaction mixtures obtained in the time intervals
on parallel irradiation of the sample solutions. After 30 min of
1
is presented in Figure 2. The well recognisable pattern of H
NMR spectra of all photoproducts in the region between 2
and 4 ppm, undoubtedly indicates the same bicyclo[3.2.1]octa-
diene structure. Regardless of heteroatom, sulfur or oxygen, or
its position in the ring the pattern of six aliphatic protons does
not change substantially. They resonate in a narrow region:
protons A appear at d 3.81e4.03, protons B at d 3.50e
3.61 ppm, protons E at d 2.42e2.50 ppm and protons F at
d 2.04e2.19 ppm. In somewhat wider region resonate the pro-
tons C (2.97e3.29 ppm) and protons D (2.40e2.78 ppm),
which are because of vicinity of heteroatom, in structures 1
and 14, shifted to the lower field in relation to the same pro-
tons in structures 24 and 23. The polycyclic compounds 25
1
irradiation the H NMR spectrum of 2-thienyl derivative 7,

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D. Vidakovic et al. / Tetrahedron 64 (2008) 3928e3934
3931
5t
S
R
R
R
X
4t
X
X
A
B
2t
B
C
D
B
25
A
C
D
2 A
2 C
2 B
PPM
3.6
3.4
3.2
3.0
2.8
2.6
2.4
1,6-ring closure
5f
4f
O
A
bicyclo[3.2.1]octadiene
B
2f
C
B
Figure 4.
B
26
D
D
C
A
X
X
PPM
3.6
3.4
3.2
3.0
2.8
2.6
2.4
Figure 3. 1H NMR spectra (in CDCl3) of the aliphatic region of two bicy-
clo[2.1.1]hexenes (25, 26).
3 A
3 B
using internal standard, showed only the presence of starting
material, cis-7 (72%) and trans-7 (14%), while the photomix-
ture of 2-furyl derivative 2 contained cis-2 (22%), trans-2
(10%) and already 23% of bicyclic [3.2.1] structure 1. The
3-styryl thiophene 8 and 3-styryl furan derivative 9 mixtures
did not differ significantly. After 30 min of irradiation the pho-
tomixture of 3-thienyl derivative 8 contained cis-8 (63%),
trans-8 (8%), bicyclic [3.2.1] structure 23 (3%) and bicyclic
[2.1.1] structure 25 (3%) while the 3-furyl derivative 9 con-
tained cis-9 (35%), trans-9 (10%), bicyclic [3.2.1] structure
24 (3%) and bicyclic [2.1.1] structure 26 (1%). After 1 h of
irradiation the 2-furyl derivative 2 was fully consumed while
2-thienyl 7 (74%), 3-thienyl 8 (46%) and 3-furyl 9 (37%)
were still present in the reaction mixture, respectively. It
should be mentioned that in all experiments besides transe
cis isomerisation, intramolecular cycloaddition reactions and
formation of bicyclic structures, decomposition and formation
of high-molecular-weight products are competitive processes.
bicyclo[2.1.1]hexene
bicyclo[3.2.1]octadiene
Figure 5.
In the case of 3-furan substitution9 (Fig. 6) only the 1,4-ring
closure took place due to the streric hinderance of the methyl
group. We assume that even if the 1,6-ring closure is operat-
ing, via the more stable biradical 2(3x)B in comparison to
2(3x)A, the formed bicyclic structure opens back to the start-
ing compound. Moreover, the 1,3-H shift, which normally
follows and stabilises the whole system by irreversible aroma-
tisation, is not in this case possible. Contrary to 2-heteroaryl
unsubstituted derivatives (2, 7) the 3-heteroaryl unsubstituted
derivatives (8, 9) give upon irradiation the biradical 3Ae3B,
which closes to both bicyclic systems via 1,4- and 1,6-ring
closure (Fig. 5). The probability for 1,4- and 1,6-ring closure
is in this case roughly equal, as the 3B is less stable due to
1
the vicinity of heteroatom. According to H NMR data, from
experiments after short time of irradiation, the yield of both
types of bicyclic structures is in the same range (2e3%).
The isolated yields on bicyclic [2.1.1] structures (25, 26) are
relatively low, compared to major bicyclic [3.2.1] structures
(23, 24). The reason could be due to thermal instability of
bicyclic [2.1.1] structures, which after prolonged irradiation
3. Conclusion
o-Vinyl furo- and thienostilbenes (2, 7e9) show compara-
ble photochemical behaviour. Based on the experimental
data we propose the formation of bicyclo[3.2.1]octadiene
structures (1, 14, 23, 24) as well as bicyclo[2.1.1]hexene struc-
tures (25, 26) via the same type of resonance stabilised birad-
icals, 2Ae2C or 3Ae3B (Figs. 4 and 5).
X
X
X
Irradiation of 2-furyl and 2-thienyl derivatives afforded
only bicyclo[3.2.1]octadiene structures 1 and 14, respectively,
due to the sterically and electronically most favourable 1,6-
ring closure, via 2B. This is in accord with the results obtained
on irradiation of 5- and 3-substituted 2-styrylfurans.4,9 In the
case of 5-furan substitution (R¼Ph)4 with electronically
most favourable 2C (Fig. 4), which could undergo sterically
unfavourable 1,8-ring closure, only traces of intramolecular
bicyclic [3.2.1] structure have been found, besides high-mo-
lecular-weight products as a result of competitive processes.
CH3
CH3
CH3
2(3x)A
2(3x)C
2(3x)B
1,4-ring closure
bicyclo[2.1.1]hexene
Figure 6.

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D. Vidakovic et al. / Tetrahedron 64 (2008) 3928e3934
3932
time undergo cycloreversion into the starting compounds. The
starting compound can be excited again giving cycloadduct
products.
We find that this photochemical approach provides a simple
method to 2,3- and 3,2-fused thiophene and furan polycyclic
compounds, which can be the scaffolds for diverse
transformations.
removal of the solvent, the residue was worked up with water
and benzene. The benzene extracts were dried (anhydrous
MgSO4) and concentrated. The crude reaction mixture was pu-
rified and the isomers of products 7e9 were separated by re-
peated column chromatography on silica gel using petroleum
ether as the eluent. The first fractions yielded cis-isomer and
the last fractions trans-isomer. The 2-[2-(2-ethenylphenyl)-
ethenyl]thiophene (7) is described.3 The data of the new com-
pounds 8 and 9 are given below.
4. Experimental
4.1. General
4.2.1. 3-[2-(2-Ethenylphenyl)ethenyl]thiophene (8)
1
Yield 73.0%; according to H NMR spectra a mixture of
1
The H and 13C NMR spectra were recorded on a Bruker
39% cis-8 and 61% trans-8.
AV-600 Spectrometer at 300 and 600 MHz. All NMR spectra
were measured in CDCl3 using tetramethylsilane as reference.
The assignment of the signals is based on 2D-CH correlation
and 2D-HH-COSY and NOESY experiments. UV spectra
were measured on a Varian Cary 50 UV/VIS Spectrophotom-
eter. IR spectra were recorded on FTIR-ATR Vertex 70 Bruker.
Mass spectra were obtained on a Varian Saturn 2200 equipped
with FactorFour Capillary Column VF-5ms. Irradiations were
performed in a quartz or Pyrex vessel in petroleum ether solu-
tions in a Rayonet reactor equipped with RPR 3000 and
cis-8: Rf 0.44 (petroleum ether); colourless oil; UV (EtOH)
1
lmax (log 3) 250 (3.96); H NMR (CDCl3, 300 MHz) d 7.56
(d, J¼7.9 Hz, 1H, H-ar), 7.14e7.30 (m, 3H, H-ar), 7.00 (dd,
J¼5.0, 3.0 Hz, 1H), 6.95 (d, J¼3.0 Hz, 1H), 6.90 (dd, J¼
17.5, 11.0 Hz, 1H, eCH]CH2), 6.66 (d, J¼5.0, 1H),
6.65 (d, J¼12.0 Hz, 1H, eCH]CHe), 6.59 (d, J¼
12.0 Hz, 1H, eCH]CHe), 5.67 (dd, J¼17.5, 1.0 Hz,
1H, eCH]CH2), 5.21 (dd, J¼11.0, 1.0 Hz, 1H, eCH]CH2);
13C NMR (CDCl3, 75 MHz) d 137.8 (s), 136.4 (s), 135.6 (s),
134.5 (d), 129.1 (d), 127.5 (d), 127.4 (d), 127.3 (d), 127.1 (d),
125.0 (d), 125.0 (d), 124.3 (d), 124.0 (d), 114.8 (t); IR 3009,
1691, 1414, 991, 771 cmꢀ1; MS m/z (%) 212 (Mþ, 100).
trans-8: Rf 0.42 (petroleum ether); colourless oil; UV (EtOH)
lmax (log 3) 299 (4.41), 250 (4.26); 1H NMR (CDCl3, 300 MHz)
d 7.20e7.56 (m, 8H), 7.08 (dd, J¼17.4; 11.0 Hz, 1H, eCH]
CH2), 6.98 (d, J¼16.1 Hz, 1H, eCH]CHe), 5.64 (dd,
J¼17.4, 1.3 Hz, 1H, eCH]CH2), 5.36 (dd, J¼11.0, 1.3 Hz,
1H, eCH]CH2); 13C NMR (CDCl3, 75 MHz) d 140.3 (s),
136.3 (s), 135.6 (s), 135.0 (d), 127.9 (d), 127.5 (d), 126.6 (d),
126.4 (d), 126.2 (d), 126.0 (d), 125.2 (d), 125.0 (d), 122.5 (d),
116.5 (t); IR 3055, 1626, 1474, 959, 768 cmꢀ1; MS m/z (%)
212 (Mþ, 100). Anal. Calcd for C14H12S: C, 79.20; H, 5.70.
Found: C, 79.49; H, 5.60.
˚
3500 A lamps. All irradiation experiments were carried out
in deaerated solutions by bubbling a stream of argon prior to
irradiation. Melting points were obtained using an Original
Kofler Mikroheitztisch apparatus (Reichert, Wien) and are
uncorrected. Elemental analyses were carried out on
PerkineElmer, Series II, CHNS Analyzer 2400. Silica gel
(Merck 0.063e0.2 mm) was used for chromatographic purifi-
cations. Thin layer chromatography (TLC) was performed on
Merck precoated silica gel 60 F254 plates. Solvents were
purified by distillation.
Thiophene-2-carbaldehyde, thiophene-3-carbaldehyde and
furan-3-carbaldehyde were obtained from a commercial
source; b,b-o-xylyl(ditriphenylphosphonium) dibromide was
prepared from o-xylyldibromide and triphenylphosphine in
dimethylformamide.3
4.2.2. 3-[2-(2-Ethenylphenyl)ethenyl]furan (9)
1
Yield 53.0%; according to H NMR spectra a mixture of
4.2. Preparation of 7e9
28% cis-9 and 72% trans-9.
cis-9: Rf 0.44 (petroleum ether); colourless oil; UV (EtOH)
1
lmax (log 3) 243 (4.15); H NMR (CDCl3, 600 MHz) d 7.58
Starting compounds 7e9 were prepared by Wittig reaction
from o-xylylenebis(triphenylphosphonium bromide) and the
corresponding aldehydes, thiophene-2-carbaldehyde, thio-
phene-3-carbaldehyde and furan-3-carbaldehyde, respectively,
as described in the literature3 for 2-[2-(2-ethenylphenyl)ethenyl]-
thiophene. To a stirred solution of the triphenylphosphonium
salt (0.001 mol) and the corresponding aldehyde (0.011 mol)
in absolute ethanol (200 mL), a solution of sodium ethoxide
(0.253 g, 0.011 mol in 15 mL of absolute ethanol) was added
dropwise. Stirring was continued under a stream of nitrogen
for 1 h at rt. Under the stream of dry nitrogen, gaseous form-
aldehyde (obtained by decomposition of paraformaldehyde
taken in excess, 1.5 g) was introduced and the next quantity
of sodium ethoxide (0.253 g, 0.011 mol in 15 mL of absolute
ethanol) was added dropwise. The reaction was completed
within 3e4 h (usually was left to stand overnight). After
(d, J¼7.8 Hz, 1H, H-ar), 7.28 (m, 1H, H-ar), 7.20e7.26 (m,
3H, 2H-ar, H-2f), 7.15 (d, J¼1.4 Hz, 1H, H-5f), 6.90 (dd,
J¼17.6, 11.0 Hz, 1H, eCH]CH2), 6.58 (d, J¼11.8 Hz, 1H,
eCH]CHe), 6.48 (d, J¼11.8 Hz, 1H, eCH]CHe), 5.87
(d, J¼1.4 Hz, 1H, H-4f), 5.68 (dd, J¼17.6, 1.1 Hz, 1H, eCH]
CH2), 5.22 (dd, J¼3.2; 1.1 Hz, 1H, eCH]CH2); 13C NMR
(CDCl3, 150 MHz) d 142.0 (d, C2f//C5f), 141.6 (d, C2f//C5f),
136.3 (s), 135.5 (s), 134.4 (d), 129.0 (d), 127.4 (d), 127.1 (d),
127.1 (d), 124.7 (d), 122.0 (s), 121.0 (d), 114.6 (t), 109.6 (d,
C4f); IR 2914, 2839, 1634, 1470, 1277, 1016, 752 cmꢀ1; MS
m/z (EI) 196 (Mþ, 100%), 167 (15), 117 (5).
trans-9: Rf 0.42 (petroleum ether); colourless oil; UV
(EtOH) lmax (log 3) 289 (4.30), 247 (4.25), 226 (4.18, sh);
1H NMR (CDCl3, 600 MHz) d 7.52 (d, J¼0.6 Hz, 1H, H-2f),
7.49 (dd, J¼7.5; 1.4 Hz, 1H, H-ar), 7.46 (dd, J¼7.5; 1.4 Hz,

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D. Vidakovic et al. / Tetrahedron 64 (2008) 3928e3934
3933
1H, H-ar), 7.41 (m, 1H, H-5f), 7.22e7.28 (m, 2H, H-ar), 7.09
(d, J¼16.0 Hz, 1H, eCH]CHe), 7.07 (dd, J¼17.4; 10.9 Hz,
1H, eCH]CH2), 6.83 (d, J¼16.0 Hz, 1H, eCH]CHe), 6.66
(dd, J¼16.0; 0.6 Hz, 1H, H-4f), 5.64 (dd, J¼17.4; 1.3 Hz,
1H, eCH]CH2), 5.35 (dd, J¼10.9; 1.3 Hz, 1H, eCH]
CH2); 13C NMR (CDCl3, 150 MHz) d 143.2 (d, C2f//C5f),
140.5 (d, C2f//C5f), 135.7 (s), 135.1 (s), 134.5 (d), 127.4 (d),
126.9 (d), 126.1 (d), 125.6 (d), 125.6 (d), 124.3 (s), 120.3
(d), 115.9 (t), 106.9 (d, C4f); IR 2945, 2837, 1680, 1470,
964, 748 cþmꢀ1; MS m/z (EI)þ196 (Mþ, 100%), 167 (10);
HRMS: Mcalcd. 196.088266; Mexp. 196.090431.
mp 90 ꢂC; UV (EtOH) lmax (log 3) 270 (3.00), 267 (3.07),
1
255 (3.40), 228 (3.90); H NMR (CDCl3, 600 MHz) d 7.30
(d, J¼7.1 Hz, 1H, H-ar), 7.11 (d, 1H, J¼7.1 Hz, H-ar), 7.08
(t, 1H, J¼7.1 Hz, H-ar), 7.04 (t, J¼7.1 Hz, 1H, H-ar), 6.97
(d, J2t,3t¼5.0 Hz, 1H, H-2 t), 6.82 (d, J2t,3t¼5.0 Hz, 1H, H-3 t),
3.98 (d, JA,E¼4.3 Hz, 1H, H-A), 3.58 (t, J¼4.5 Hz, 1H, H-B),
3.29 (dd, JB,C¼4.5 Hz, JC,D¼16.5 Hz, 1H, H-C), 2.78 (d,
JC,D¼16.5 Hz, 1H, H-D), 2.47e2.54 (m, 1H, H-E), 2.14 (d,
JE,F¼10.3 Hz, 1H, H-F); 13C NMR (CDCl3, 75 MHz)
d 151.4 (s), 144.9 (s), 141.8 (s), 131.6 (s), 126.4 (d), 126.3
(d), 125.0 (d, C3t), 123.6 (d), 122.2 (d, C2t), 120.8 (d), 42.4
(d, CA), 42.2 (t, CE,F), 40.6 (d, CB), 31.6 (t, CC,D); IR
2941, 1468, 1136, 748 cmꢀ1; MS m/z 212 (100%). Anal.
Calcd for C14H12S: C, 79.20; H, 5.70. Found: C, 79.24; H,
5.88.
4.3. Irradiation experiments of 7e9
A mixture of cis- and trans-isomers of 7e9 in petroleum
ether (7: 7.1ꢁ10ꢀ3 M; 8: 2.4ꢁ10ꢀ3 M; 9: 5.1ꢁ10ꢀ3 M) was
purged with argon for 30 min and irradiated at 350 nm (7)
and 300 nm (8, 9) in a Rayonet reactor (16 lamps) in a quartz
4.3.2. Irradiation of 3-[2-(2-ethenylphenyl)ethenyl]-
thiophene (8)
In the first fractions exo-5-(3-thienyl)benzobicyclo[2.1.1]-
hex-2-ene (25, 11 mg, 5%) was isolated followed by 2,3-[2,3-
b-thieno]-6,7-benzobicyclo[3.2.1]octa-2,6-diene (23, 55 mg,
25%). High-molecular-weight products (70%) remained on
the column.
1
vessel. The reaction course was followed by GCeMS and H
NMR measurements. After irradiation of 7e9 (7: 92 h; 8:
64 h; 9: 17 h) the solvent was removed in vacuo and the oily
residue chromatographed on a silica gel column using petro-
leum ether as the eluent.
4.3.2.1. exo-5-(3-Thienyl)benzobicyclo[2.1.1]hex-2-ene (exo-
25). Rf 0.39 (petroleum ether); colourless crystals; mp
64 ꢂC; UV (EtOH) lmax (log 3) 275 (3.35), 268 (3.34),
263 (3.34), 240 (3.91); 1H NMR (CDCl3, 600 MHz)
d 7.32 (dd, J2t,5t¼2.9 Hz, J4t,5t¼4.9 Hz, 1H, H-5t), 7.22e
4.3.1. Irradiation of 2-[2-(2-ethenylphenyl)ethenyl]-
thiophene (7)
Traces of phenanthrene (16, <1%) and 6-vinylnaphtho-
[2,1-b]thiophene (17, <1%) were found in the enriched first
chromatographic fractions followed by 2,3-[3,2-b-thieno]-6,7-
benzobicyclo[3.2.1]octa-2,6-diene (14, 661 mg, 45%). High-
molecular-weight products (56%) remained on the column.
7.27 (m, 2H, H-ar), 7.19 (ddd, J2t,4t¼1.1; J2t,5t¼2.9; J2t,A
1.1 Hz, 1H, H-2t), 7.08 (dd, J2t,4t¼1.1 Hz, J4t,5t
¼
¼
4.9 Hz, 1H, H-4t), 7.00 (d, J¼8.0 Hz, 2H, H-ar), 3.83 (dd,
J2t,A¼1.1 Hz, JA,D¼7.4 Hz, 1H, H-A), 3.36 (d, JB,C¼2.5 Hz,
2H, H-B), 3.23 (dt, JB,C¼2.5 Hz, JC,D¼6.4 Hz, 1H, H-C),
2.41 (dd, JA,D¼7.4; JC,D¼6.4 Hz, 1H, H-D); 13C NMR
(CDCl3, 150 MHz) d 152.7 (2s), 141.8 (s), 128.2 (d, C3t),
125.3 (d, C2t), 124.2 (2d), 121.3 (d, C5t), 118.7 (2d), 74.2
(d, CA), 60.5 (t, CC,D), 49.3 (d, CB); IR 2891, 2854,
1435, 1080, 835, 750 cmꢀ1; MS m/z (ES) 212 (100%).
Anal. Calcd for C14H12S: C, 79.20; H, 5.70. Found: C,
79.55; H, 5.67.
4.3.1.1. 6-Vinylnaphtho[2,1-b]thiophene (17). The compound
is identical with the authentic sample 17, independently
prepared by a sequence of reactions: a benzene solution of
2-(o-methylstyryl)thiophene (18)30 was irradiated in the pres-
ence of iodine and obtained 6-methylnaphtho[2,1-b]thiophene
(19)31 subjected to bromination with NBS, treatment with
triphenylphosphine, followed by Wittig reaction with formal-
dehyde (Scheme 3) in overall yield of 11%.
Compound 17: Rf 0.46 (petroleum ether); colourless crystals;
mp 100 ꢂC; UV (EtOH) lmax (log 3) 308 (4.07), 246 (4.48), 235
(4.44); H NMR (CDCl3, 300 MHz) d 8.31 (d, J¼8.1 Hz, 1H,
4.3.2.2. 2,3-[2,3-b-Thieno]-6,7-benzobicyclo[3.2.1]octa-2,6-
diene (23). Rf 0.33 (petroleum ether); colourless crystals; mp
50e52 ꢂC; UV (EtOH) lmax (log 3) 269 (3.32), 262 (3.53),
1
H-ar), 8.05 (d, J¼9.1 Hz, 1H), 8.00 (dd, J¼5.4, 0.5 Hz, 1H),
7.93 (dd, J¼9.1, 0.5 Hz, 1H), 7.67 (d, J¼8.1 Hz, 1H, H-ar),
7.60 (d, J¼5.4 Hz, 1H), 7.59 (t, J¼8.1 Hz, 1H, H-ar), 7.54
(dd, J¼17.3, 10.9 Hz, 1H, eCH]CH2), 5.82 (dd, J¼17.3,
1.5 Hz, 1H, eCH]CH2), 5.52 (dd, J¼10.9, 1.5 Hz, 1H, eCH]
CH2); 13C NMR (CDCl3, 75 MHz) d 136.7 (s), 135.9 (s), 135.8
(s), 134.5 (d), 129.0 (s), 128.0 (s), 125.7 (d), 125.4 (d), 123.0 (d),
122.8 (d), 121.8 (d), 120.3 (d), 120.2 (d), 116.9 (t); MS m/z 210
(100%). Anal. Calcd for C14H10S: C, 79.96; H, 4.79. Found: C,
79.84; H, 4.94.
1
254 (3.71), 243 (3.74); H NMR (CDCl3, 600 MHz) d 7.30
(d, J¼7.1 Hz, 1H, H-ar), 7.02e7.16 (m, 3H, H-ar), 6.90 (d,
J2t,3t¼5.0 Hz, 1H), 6.63 (d, J2t,3t¼5.0 Hz, 1H), 4.03 (d,
JA,E¼4.4 Hz, 1H, H-A), 3.54 (t, J¼4.7 Hz, 1H, H-B), 3.15
(dd, JB,C¼4.7 Hz, JC,D¼16.3 Hz, 1H, H-C), 2.65 (d,
JC,D¼16.3 Hz, 1H, H-D), 2.54e2.59 (m, 1H, H-E), 2.19 (d,
JE,F¼10.3 Hz, 1H, H-F); 13C NMR (CDCl3, 150 MHz)
d 150.0 (s), 144.8 (s), 139.6 (s), 129.8 (s), 127.8 (d), 126.0
(d), 125.9 (d), 123.1 (d), 120.4 (d), 120.2 (d), 42.0 (t), 41.0
(d), 39.5 (d), 31.6 (t); IR 2926, 2827, 1468, 1294, 696 cmꢀ1
;
MS m/z 212 (100%). Anal. Calcd for C14H12S: C, 79.20; H,
5.70. Found: C, 79.52; H, 5.64.
4.3.1.2. 2,3-[3,2-b-Thieno]-6,7-benzobicyclo[3.2.1]octa-2,6-
diene (14). Rf 0.33 (petroleum ether); colourless crystals;

´
D. Vidakovic et al. / Tetrahedron 64 (2008) 3928e3934
3934
ˇ
3. Sindler-Kulyk, M.; Stiplosek, Z.; Vojnovic, D.; Metelko, B.; Marinic, Z.
ˇ
´
ˇ
Heterocycles 1991, 32, 2357e2363.
´
4.3.3. Irradiation of 3-[2-(2-ethenylphenyl)ethenyl]furan (9)
Inthefirstfractionsexo-5-(3-furyl)benzobicyclo[2.1.1]hex-2-
ene (26, 45 mg, 9%) was isolated followed by 2,3-[2,3-b-furo]-
6,7-benzobicyclo[3.2.1]octa-2,6-diene (24, 135 mg, 27%).
High-molecular-weightproducts (64%)remainedonthe column.
ˇ
4. Sindler-Kulyk, M.; Kragol, G.; Piantanida, I.; Tomsic, S.; Vujkovic Cvijin,
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´
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I.; Marinic, Z.; Metelko, B. Croat. Chem. Acta 1996, 69, 1593e1602.
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5. Vujkovic Cvijin, I.; Marinic, Z.; Sindler-Kulyk, M. Spectrosc. Lett. 1998,
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31, 989e1000.
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6. Sindler-Kulyk, M.; Skoric, I.; Tomsic, S.; Marinic, Z.; Mrvos-Sermek, D.
ˇ
ˇ
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´
ˇ ´
ˇ
Heterocycles 1999, 51, 1355e1369.
4.3.3.1. exo-5-(3-Furyl)benzobicyclo[2.1.1]hex-2-ene (exo-
26). Rf 0.39 (petroleum ether); colourless oil; UV (EtOH)
lmax (log 3) 267 (2.99), 261 (2.92), 255 (2.87); 1H NMR
(CDCl3, 600 MHz) d 7.42e7.45 (m, 2H, H-2f, H-5f),
7.26e7.23 (m, 2H, H-ar), 6.98e7.01 (m, 2H, H-ar), 6.40e
6.41 (m, 1H, H-4f), 3.65 (dd, J2f,A¼1.3 Hz, JA,D¼7.3 Hz,
1H, H-A), 3.30 (dd, JB,C¼2.3 Hz, JC,D¼6.2 Hz, 1H, H-C),
3.24 (d, JB,C¼2.3 Hz, 2H, H-B), 2.39 (dd, JA,D¼7.3 Hz,
JC,D¼6.2 Hz, 1H, H-D); 13C NMR (CDCl3, 150 MHz)
d 152.2 (s), 142.2 (d), 139.4 (d), 124.1 (s), 123.6 (d), 118.2
(d), 110.6 (d), 69.3 (d, CA), 59.7 (t, CC,D), 48.4 (d, CB); IR
2922, 2850, 1454, 1030, 750 cmꢀ1; MS m/z (EI) 196
(100%). Anal. Calcd for C14H12O: C, 85.68; H, 6.16. Found:
C, 85.73; H, 6.06.
ˇ
7. Skoric, I.; Marinic, Z.; Sindler-Kulyk, M. Heterocycles 2000, 53,
ˇ
ˇ
´
55e68.
´
ˇ
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8. Skoric, I.; Basaric, N.; Marinic, Z.; Sindler-Kulyk, M. Heterocycles 2001,
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55, 1889e1896.
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9. Skoric, I.; Hutinec, A.; Marinic, Z.; Sindler-Kulyk, M. ARKIVOC 2003,
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ˇ
´
87e97.
ˇ
ˇ
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ˇ
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10. Skoric, I.; Marinic, Z.; Sindler-Kulyk, M. Croat. Chem. Acta 2004, 77,
161e166.
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11. Skoric, I.; Basaric, N.; Marinic, Z.; Visnjevac, A.; Kojic-Prodic, B.;
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´
´
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Sindler-Kulyk, M. Chem.dEur. J. 2005, 11, 534e551.
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12. Skoric, I.; Flegar, I.; Marinic, Z.; Sindler-Kulyk, M. Tetrahedron 2006,
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62, 7396e7407.
´
ˇ
13. Sindler-Kulyk, M.; Tomsic, S.; Marinic, Z.; Metelko, B. Recl. Trav. Chim.
ˇ
´
ˇ ´
Pays-Bas 1995, 114, 476e479.
ˇ
´
ˇ
14. Basaric, N.; Tomsic, S.; Marinic, Z.; Sindler-Kulyk, M. Tetrahedron 2000,
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56, 1587e1593.
ˇ ´
ˇ
´
ˇ
15. Basaric, N.; Marinic, Z.; Sindler-Kulyk, M. Tetrahedron Lett. 2001, 42,
´
4.3.3.2. 2,3-[2,3-b-Furo]-6,7-benzobicyclo[3.2.1]octa-2,6-di-
ene (24). Rf 0.33 (petroleum ether); colourless crystals; mp
64e65 ꢂC; UV (EtOH) lmax (log 3) 274 (3.13), 267 (3.18),
3641e3643.
16. Rademacher, P.; Basaric, N.; Kowski, K.; Sindler-Kulyk, M. Eur. J. Org.
Chem. 2002, 551e556.
ˇ
´
ˇ
17. Basaric, N.; Marinic, Z.; Visnjevac, A.; Kojic-Prodic, B.; Griesbeck,
´
´
ˇ
´
´
1
260 (3.20), 248 (3.65); H NMR (CDCl3, 600 MHz) d 7.00e
ˇ
A. G.; Sindler-Kulyk, M. Photochem. Photobiol. Sci. 2002, 1, 1017e1023.
7.32 (m, 5H, H-ar, H-2f), 6.03 (d, J2f,3f¼2.0 Hz, 1H, H-3f),
3.92 (d, JA,E¼4.6 Hz, 1H, H-A), 3.50 (dt, JB,C¼4.7 Hz,
JB,D¼1.8 Hz, JB,E¼5.1 Hz, 1H, H-B), 2.97 (dd, JB,C¼4.7 Hz,
ˇ
ˇ
´
´
18. Basaric, N.; Marinic, Z.; Sindler-Kulyk, M. Tetrahedron Lett. 2003, 44,
7337e7340.
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19. Basaric, N.; Ivekovic, D.; Zimmermann, B.; Marinic, Z.; Kowski, K.;
´
´
´
ˇ
Rademacher, P.; Sindler-Kulyk, M. J. Photochem. Photobiol., A 2003,
154, 123e130.
JC,D¼15.8 Hz, 1H, H-C), 2.51 (dt, JA,E¼4.6 Hz, JB,E
¼
5.1 Hz, JE,F¼10.3 Hz, 1H, H-E), 2.40 (dd, JC,D¼15.8;
JB,D¼1.8 Hz, 1H, H-D), 2.16 (d, JE,F¼10.3 Hz, 1H, H-F); 13C
NMR (CDCl3, 150 MHz) d 154.8 (s), 149.7 (s), 145.3 (s), 139.7
(d), 126.3 (d), 126.1 (d), 123.6 (d), 120.6 (d), 111.0 (d), 110.3
(s), 42.5 (t), 40.5 (d), 40.4 (d), 28.6 (t); IR 2916, 2841, 1634,
1472, 1279, 1024, 754 cmꢀ1; MS m/z (EI) 196 (100%). Anal.
Calcd for C14H12O: C, 85.68; H, 6.16. Found: C, 85.59; H, 6.07.
ˇ
´
ˇ
20. Basaric, N.; Marinic, Z.; Sindler-Kulyk, M. J. Org. Chem. 2006, 71,
´
9382e9392.
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´
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21. Basaric, N.; Marinic, Z.; Sindler-Kulyk, M. J. Org. Chem. 2003, 68,
7524e7527.
22. Eicher, Th.; Hauptmann, S. The Chemistry of Heterocycles; Thieme:
Stuttgart, New York, NY, 1995; pp 52e218.
23. Katritzky, A. R.;Karelson, M.;Malhotra,N. Heterocycles1991, 32, 127e161.
24. Sindler-Kulyk, M.; Laarhoven, W. H. J. Am. Chem. Soc. 1976, 98,
1052e1053.
ˇ
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25. Sindler-Kulyk, M.; Laarhoven, W. H. J. Am. Chem. Soc. 1978, 100,
3819e3830.
Acknowledgements
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26. Sindler-Kulyk, M.; Laarhoven, W. H. Recl. Trav. Chim. Pays-Bas 1979,
98, 187e191.
This work was supported by grants from the Ministry of
Science, Education and Sports of the Republic of Croatia
(grant nos. 125-0982933-2926, 098-0982929-2917).
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27. Sindler-Kulyk, M.; Laarhoven, W. H. Recl. Trav. Chim. Pays-Bas 1979,
98, 452e459.
28. Laarhoven, W. H.; CuppenTh, J. H. M. J. Photochem. 1986, 32, 105e118.
29. Compound 16 was formed on irradiation of furan analogue followed by
elimination of water. See Ref. 4.
References and notes
30. Carruthers, W.; Stewart, H. N. M. J. Chem. Soc. 1965, 6221e6227.
31. Tominaga, Y.; Tedjamulia, M. L.; Castle, R. N. J. Heterocycl. Chem.
1983, 20, 487e490.
1. Filippini, M.-H.; Rodriguez, J. Chem. Rev. 1999, 99, 27e76.
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2. Sindler-Kulyk, M.; Spoljaric, L.; Marinic, Z. Heterocycles 1989, 29, 679e682.