Synthesis and phototransformations of novel styryl-substituted furo-benzobicyclo[3.2.1]octadiene derivatives

Article abstract of DOI:10.1016/j.tet.2010.09.093

Novel cis- and trans-(o-H/Me/vinyl) substituted styryl furo-benzobicyclo[3. 2.1]octadiene derivatives (7a,b, 8) were prepared and transformed to the novel naphthofuran derivatives of benzobicyclo[3.2.1]octadiene (6a,b) and novel phenanthrene-benzobicyclo[

Full text of DOI:10.1016/j.tet.2010.09.093

Tetrahedron 66 (2010) 9405e9414
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Tetrahedron
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Synthesis and phototransformations of novel styryl-substituted furo-benzobicyclo
[3.2.1]octadiene derivatives
a
,
ꢀa
ꢁa
ꢁb
ꢀ
ꢀ
ꢀ
*
Ilijana Kikas , Irena Skoric , Zeljko Marinic , Marija Sindler-Kulyk
a
ꢁ
Department of Organic Chemistry, Faculty of Chemical Engineering and Technology, University of Zagreb, Marulicev trg 19, 10 000 Zagreb, Croatia
b
ꢀ
ꢁ
ꢀ
NMR Center, Rudjer Boskovic Institute, Bijenicka cesta 54, 10 000 Zagreb, Croatia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 July 2010
Received in revised form 9 September 2010
Accepted 28 September 2010
Available online 8 October 2010
Novel cis- and trans-(o-H/Me/vinyl) substituted styryl furo-benzobicyclo[3.2.1]octadiene derivatives
(7a,b, 8) were prepared and transformed to the novel naphthofuran derivatives of benzobicyclo[3.2.1]
octadiene (6a,b) and novel phenanthrene-benzobicyclo[3.2.1]octadiene derivative (11) by photochemical
electrocyclic ring closure in the presence of iodine and by intramolecular photoinduced [4þ2] cyclo-
addition, respectively. These novel annelated bicyclo[3.2.1]octadiene derivatives (6a,b, 11) are especially
interesting for their rigid methano-bridged junction of two aromatic units at defined geometrical ar-
rangement and thereby as potentials for molecular clips.
Keywords:
Electrocyclization
Furan
Ó 2010 Elsevier Ltd. All rights reserved.
Intramolecular cycloaddition
Photochemistry
Synthesis
1. Introduction
With further annelation, naphthofuran derivative 5 gave no
intramolecularcycloadditionproduct6 (Scheme 2). The only products
Photochemical reactions are very important key steps in many
syntheses of complex polycyclic compounds1 and might in some
cases shorten a total synthesis going from rather simple substrates.
Thus, the o-vinyl substituted hetero-stilbene derivatives are con-
venient substrates for one-step photochemical ring closure to fused
heteroaromatic benzobicyclo[3.2.1]octadienes.2e11 The photoreac-
tions of furo-stilbenes have been particularly thoroughly inves-
tigated.2e10 Thus, irradiation of furan (1) and its annelated
derivative, benzofuran (2), resulted in intramolecular cycloaddition
and efficient formation of benzobicyclo[3.2.1]octadiene structures
3 and 4, respectively, as the main photoproducts (Scheme 1).
observed were traces of dimeric cyclobutanederivatives, although the
irradiation has been performed under the same conditions, in diluted
Scheme 1.
* Corresponding author. Tel.: þ385 1 4597242; fax: þ385 1 4597250; e-mail
ꢀ
Scheme 2.
address: marija.sindler@fkit.hr (M. Sindler-Kulyk).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.09.093

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I. Kikas et al. / Tetrahedron 66 (2010) 9405e9414
9406
solution.7 The intermolecularphotocycloadditionwasconfirmedwith
the experiments performed in concentrated solutions.12,13
2. Results and discussion
Continuing our interest on the synthesis of rigid methano-
bridged aromatics/heteroaromatics we turned our attention in this
work to one other synthetic strategy: to synthesize the properly
substituted novel styryl derivatives 7 and 8 (Scheme 2) from already
available benzo-furo bicyclic structure 3 and submit them to addi-
tional photochemical transformations. Based on previous experi-
ences with styryl furans2e10 and known photochemical
Benzobicyclo[3.2.1]octadiene derivative 3 was obtained in one
photochemical step according to the described method10 from the
previously prepared
b-furyl substituted o-divinylbenzene 1. It is
transformed via formyl derivative 10 followed by Wittig reaction
with corresponding triphenylphosphonium salts to styryl de-
rivatives 7a,b and 8, respectively (Scheme 3), the novel starting
substrates for the further photochemical transformations.
The compounds 7a,b and 8 were synthesized in very good yields
(66e96%). All the new compounds 7a,b and 8 were obtained as
mixtures of cis-(12e20%) and trans-isomers (80e88%) that were
separated by column chromatography and completely analysed and
identified spectroscopically. The ratio of the isomers was de-
termined from the NMR spectra. All the three cis-isomers show
absorption maxima at 305e333 nm, while trans-isomers show
bathochromic shift to the maxima at 331e338 nm. Irradiation ex-
periments were performed with their cisetrans mixtures.
reactions14e21 we visualized the synthesis of 6 by a 6
p
electro-
cyclization reaction of 7 and double bicyclic structure like 9 from the
o-vinyl derivative 8 by intramolecular cycloaddition reaction. Both
annelated bicyclo[3.2.1]octadiene derivatives, 6 and 9, are especially
interesting for their rigid methano-bridged junction of two aromatic
units at defined geometrical arrangement (Figs.1 and 2) and thereby
have potential for the construction of molecular clips.22
On irradiation of a 10ꢀ3 M benzene solution of cis- and trans-7a, in
the presence of iodine at 300 nm, naphthofuran derivative of benzo-
bicyclo[3.2.1]octadiene 6a in 53% of isolated yield was obtained
(Scheme 3). On irradiation of methyl derivative 7b a mixture of two
naphthofuran derivatives 6a and 6b, in 49% of isolated yield was
found.Accordingto1HNMRspectrumof thephotomixturetheratioof
the methyl derivative 6b and demethylated 6a was 3:1. The formation
of both naphthofuran derivatives, 6a and 6b, can be explained by
electrocyclization process from different conformations of cis con-
figuration (cis-7b) followed by an aromatization step with concomi-
tant loss of hydrogen and methane,19e22 respectively. The o-vinyl
derivative 8, irradiated under the anaerobic conditions at 300 nm,
produced a large amount of tarry material and therefore the irradia-
tions were performed at 350 nm. Contrary to our expectation, the ir-
radiation of vinyl derivative 8 resulted in fused phenanthrene bicyclic
derivative 11 in 33% isolated yield, besides high-molecular-weight
products. A double bicyclic structure, such as 9 was not isolated. In the
1H NMR spectrum of some enriched chromatographic fractions traces
of the easily recognisable bicyclo[3.2.1]octadiene pattern has been
seen but in to small quantities to be completely identified.
Fig. 1. Space filling model of the expected annelated photoproduct 6a.
The photoproducts, 6a, 6b and 11 were isolated by column and
thin-layer chromatographyand characterized spectroscopically. The
structure of these photoproducts was obvious from the presence of
the characteristic aromatic protons of the naphthofuran and phen-
anthrene moieties. As it is seen in the 1H NMR spectrum (Fig. 3b) two
doublets for naphthofuran moiety of 6a appeared between 7.9 and
Fig. 2. Space filling model of the expected double bicyclic photoproduct 9 (one of two
possible diastereoisomers).
Scheme 3.

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I. Kikas et al. / Tetrahedron 66 (2010) 9405e9414
9407
8.7 ppm with characteristic aromatic coupling constants. The pho-
toproduct 11 has in the region 8.2e8.7 ppm (Fig. 3c) singlet and
doublet of H1 and H2, respectively, characteristic signals for inner
phenanthrene protons. In the aliphatic region (Fig. 4b and c) the well
resolved and recognisable six-proton-patterns of 6a and 11, re-
spectively, between 2.0 and 4.8 ppm unmistakably pointed to the
bicyclo[3.2.1]octadiene structure in both compounds as shown for
comparison with the known bicyclic structure 3 (Fig. 4a). Moreover,
proton A in 6a (Fig. 4b) as expected is shifted to lower field in
comparisonwith the proton A in 3 (Fig. 4a) and 11 (Fig. 4c) due to the
anisotropic effect of the properly oriented naphthalene moiety.
Additionally, MS spectrawereveryinformative. Molecularions m/z
296 (6a) and m/z 310 (6b), two mass units lower than starting com-
pounds 7a and 7b, respectively, indicated that an electrocyclization
process and loss of hydrogen molecule occurred. The byproduct in the
reaction of 7b had also molecular ion m/z 296 but as a consequence of
electrocyclization process and loss of methane molecule. Molecular
ion m/z 306 (11), 18 a mass lower than starting compound 8 together
with 13C NMR spectrum of 11 clearly revealed that its structure does
not incorporate the furan moiety.
The formation of the phenanthrene structure 11 instead of
expected bicyclic 9 prompted us to synthesize the compounds 12 and
13 (Scheme 4) as model compounds of 4,5-dialkyl substituted styr-
ylfurans that were not considered in our previous research. They re-
semble the compounds 7 and 8 where the methano-bridged junction
on furan moiety has been replaced by two methyl substituents.
The startingcompounds12 and 13 were synthesized followingthe
procedure described for styryl derivatives 7 and 8 (see Experimental)
Fig. 3. Aromatic region of the 1H NMR spectra: (a) bicyclic 3; (b) bicyclic 6a; (c) bicyclic 11 (CDCl3, 300 MHz).

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I. Kikas et al. / Tetrahedron 66 (2010) 9405e9414
Fig. 4. Aliphatic region of the 1H NMR spectra: (a) bicyclic 3; (b) bicyclic 6a; (c) bicyclic 11 (CDCl3, 300 MHz).
Scheme 4.

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9409
and submitted to irradiation under conditions for electrocyclization
and intramolecular cycloaddition, respectively. On irradiation of
10ꢀ3 M benzene solution of cis- and trans-12b, in the presence of io-
dine at 300 nm, a mixture of two naphthofuran derivatives 14a and
14b wasobtained in22%isolatedyield. Theirratio(1:2.5, respectively)
was established from the 1H NMR spectrum of the photomixture. The
presence of demethylated photoproduct 14a was confirmed on irra-
diation of 12a and formation of 14a in 56% of isolated yield. These
experiments demonstratethatstyryl derivativesofdimethylfurans 12
reacted in a same way as described for 7a and 7b. The irradiation of o-
vinylstyryl furan derivative 13 under anaerobic conditions afforded
benzobicyclo[3.2.1]octadiene derivative 15 in 33% of isolated yield,
besides traces of phenanthrene derivative 16. These results were
consistent to photochemistry of our o-vinylstyryl furan system
studied previously.2,6,7,9,10
If we compare the normalized UV curves of styryl bicyclic furan
derivative 8 and styryl furan derivative 13 (Fig. 5), we see the simi-
larity in absorption maxima and habitual pattern for geometrical
isomers with bathochromic shift of their absorption maxima for
trans-isomers. Irradiation experiments of 8 and 13 isomers followed
by UV spectroscopy showed that in both cases, depending on irra-
diation wavelength (300 or 350 nm), cisetrans or transecis isomer-
ization competes with the intramolecular cycloaddition reactions.
No exact conclusion could be made about various reactivity of these
two compounds with the same chromophore, o-vinylstyryl-furan,
responsible for photochemical reaction.
The formation of main photoproduct benzobicyclo[3.2.1]octa-
diene 15 is explained (Scheme 5) fromthe singlet state of 13 via a 1,4-
biradical followed by the preferred cyclohexene ring closure to 17
and photochemically allowed suprafacial 1,3-H shift. The byproduct
2,3-dimethylphenanthrene (16) can be explained by initial photo-
induced [4þ2] cycloaddition reaction of cis-13 to the epoxy de-
rivative 18, which loses water during the work-up procedure and
aromatizes to the final photoproduct 16. It is not surprising that only
traces of phenanthrene 16 have been found. The phenanthrene de-
rivative 16 could be formed only from cis configuration of 13 in its
particular conformation and this is the less favourable process.
The formation of the main bicyclo-phenanthrenephotoproduct11
is explained (Scheme 6) by the same mechanism as described for
phenanthrene 16. After excitation and initial photoinduced 1,4-bir-
adical formation the epoxy derivative 19 is formed, which loses water
during the work-up procedure and aromatizes to the final photo-
product 11. Formation of phenanthrene derivative 11 by thermal
intramolecular DielseAlder reaction of the vinyl group and the furan
moiety of the cis-8 is ruled out. Namely, no products were obtained in
a tube that was kept in the dark during irradiation experiments.
The initial intramolecular [2þ2]-photocycloaddition leading to
double bicyclic structures 9 is apparently a less favourable process.
The initial [4þ2]-photocycloaddition leading to 11 is a dominant
process. This unique behaviour of the o-vinylstyryl furan derivative
in the last case is ascribed to conformational changes (Scheme 7).
We assume that due to the pep intramolecular interaction the cis-8
is forced to reside in conformation A from which the fast ring clo-
sure to the epoxy derivative 19 is afforded. In case of dimethylfuran
derivative 13 no additional intramolecular forces are operating and
the ring closure from other most populated conformations of either
trans or cis configuration is possible leading to bicyclic structure 15.
In an effort to prepare the double bicyclic photoproducts 9 we
applied the new strategy: irradiation of 2,5-bis(o-vinylstyryl)furan
20 (Scheme 8). The starting compound 20 was prepared via formyl
derivative 21 and subsequent Wittig reaction with diphosphonium
salt and formaldehyde (see Experimental). Irradiation of the mix-
ture of isomers afforded only photoisomerization to trans,trans-20
and on continuing irradiation polymerization. No double bicyclo
photoproducts 9 were formed.
3. Conclusion
In summary, we have demonstrated that the naphthofuran-
benzobicyclo derivative 6 can be efficiently synthesized by photo-
electrocyclization of styryl benzobicyclo-furan derivative 7 and
fused phenanthrene derivative 11 by photocycloaddition reaction
of o-vinylstyryl derivative 8. Both types of annelated bicyclo[3.2.1]
Fig. 5. Normalized UV curves of cis-8, trans-8, cis-13 and trans-13 in 96% EtOH.
Scheme 5.

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I. Kikas et al. / Tetrahedron 66 (2010) 9405e9414
Scheme 6.
Fig. 6. Space filling model of benzobicyclo-phenanthrene 11.
reference. The assignment of the signals is based on 2D-CH corre-
lation and 2D-HeH-COSY experiments. UV spectra were measured
on a Varian Cary 50 UV/vis Spectrophotometer. Mass spectra were
obtained on a Varian Saturn 2200 equipped with FactorFour Cap-
illary Column VF-5ms. Melting points were obtained using an
Scheme 7.
Scheme 8.
octadiene derivatives, 6 (Fig. 1) and 11 (Fig. 6), are interesting for
their rigid methano-bridged junction of two aromatic units.
Original Kofler Mikroheitztisch apparatus (Reichert, Wien) and are
uncorrected. All the novel compounds were identified and proved
by GCeMS system. The GCeMS analysis was performed on a Varian
CP-3800 Gas Chromatograph-Varian Saturn 2200 equipped with
FactorFour Capillary Column VF-5ms, 30 mꢁ0.25 mm ID; GC op-
erating conditions for all experiments: column temperature pro-
grammed from 110 ꢂC to 300 ꢂC (6 min isothermal) at a rate of
33 ꢂC minꢀ1; carrier gas: helium; flow rate: 1 mL minꢀ1; injector
4. Experimental
4.1. General
The 1H and 13C NMR spectra were recorded on a Bruker AV-600
Spectrometer at 300 or 600 and at 75 or 150 MHz, respectively. All
NMR spectra were measured in CDCl3 using tetramethylsilane as
temperature: 300 ꢂC; volume injected: 5
recorded on PerkineElmer Spectrum One. Elemental analyses were
mL. IR spectra were

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I. Kikas et al. / Tetrahedron 66 (2010) 9405e9414
9411
carried out on PerkineElmer, Series II, CHNS Analyzer 2400. High-
resolution mass spectra (HRMS) were obtained on a matrix-assis-
ted laser desorption/ionizationetime-of-flight MALDI-TOF/TOF
mass spectrometer (4800 Plus MALDI-TOF/TOF analyzer, Applied
Biosystems Inc., Foster City, CA, USA) equipped with Nd:YAG laser
operating at 355 nm with firing rate 200 Hz in the positive ion re-
flector mode. 1600 shots per spectrum was taken with mass range
100e1000 Da, focus mass 500 Da and delay time 100 ns. Nicotin-
amide and azithromycin were used for external mass calibration in
positive ion mode. Each spectrum was internally calibrated, pro-
viding measured mass accuracy within 5 ppm of theoretical mass.
All preparative irradiation experiments were carried out in 10ꢀ3 M
solutions in a Quartz tube or in Pyrex vessels and in a Rayonet re-
actor equipped with RPR 3000 A and RPR 3500 A lamps. Silica gel
(Merck 0.063e0.2 mm) and aluminium oxide 90 (Merck
0.063e0.2 mm) were used for chromatographic purifications. Thin-
layer chromatography (TLC) was performed on Merck precoated
silica gel 60 F254 and on Merck Al2O3 neutral 1.5 mm 60 F254 plates.
Solvents were purified by distillation.
petroleum ether and petroleum ether/diethyl ether (0e5%) mixtures
as eluent. The product 7a was isolated in 96% (0.11 g) yield (cis/
trans¼1:7, according to 1H NMR), and the product 7b in 78% (0.10 g)
yield (cis/trans¼1:4, according to 1H NMR).
Compound cis-7a: Rf 0.71 (petroleum ether/diethyl ether 10:1);
colourless oil; UV (EtOH) lmax (3
/dm3 molꢀ1 cmꢀ1): 333 (9825) nm;
IR (evaporated film from diethyl ether) nmax/cmꢀ1: 2916, 2846,1737,
1457, 1258, 949, 750; 1H NMR (CDCl3, 600 MHz) dH 7.44 (dd, J¼7.8,
0.9 Hz, 2H, H-ar), 7.32e7.28 (m, 3H, H-ar), 7.25e7.22 (m, 1H, H-ar),
7.09e7.02 (m, 3H, H-ar), 6.27 (d, J¼12.7 Hz, 1H, H-et), 6.20 (d,
J¼12.7 Hz, 1H, H-et), 6.14 (s, 1H, H-f), 3.72 (d, JAE¼4.3 Hz, 1H, H-A),
3.58 (dt, JBE,BC¼5.0, JBD¼1.3 Hz, 1H, H-B), 3.09 (dd, JCD¼16.7,
JBC¼5.0 Hz, 1H, H-C), 2.58 (dd, JCD¼16.7, JBD¼1.3 Hz, 1H, H-D), 2.40
(ddd, JEF¼10.5, JBE¼5.0, JAE¼4.3 Hz, 1H, H-E), 2.02 (d, JEF¼10.5 Hz,
1H, H-F); 13C NMR (CDCl3,75 MHz) dC 129.1 (d), 128.8 (d), 128.6 (d),
128.3 (d), 128.0 (d), 126.5 (d), 126.2 (d), 125.6 (d), 123.8 (d), 120.6
(d), 118.2 (d), 108.6 (d), 42.8 (t), 40.2 (d), 39.2 (d), 30.9 (t), singlets
are not seen due to small quantities; MS m/z (EI) 298 (Mþ, 100%).
Compound trans-7a: Rf 0.80 (petroleum ether/diethyl ether
ꢂ
ꢂ
Furan-2-carboxaldehyde was obtained from
a
commercial
10:1); colourless solid; mp 157 ꢂC; UV (EtOH) lmax
(3/
source (Aldrich). The corresponding aryltriphenylphosphonium
dm3 molꢀ1 cmꢀ1): 337 (14,366), 350 (sh, 13,395) nm; IR (evapo-
rated film from diethyl ether) nmax/cmꢀ1: 2901, 2822, 1730, 1457,
1258, 948, 750; 1H NMR (CDCl3, 600 MHz) dH 7.38 (dd, J¼7.6, 1.0 Hz,
2H, H-ar), 7.32 (d, J¼7.4 Hz, 1H, H-ar), 7.29 (t, J¼7.6 Hz, 2H, H-ar),
7.18 (dt, J¼7.6, 1.0 Hz, 1H, H-ar), 7.13 (d, J¼7.4 Hz, 1H, H-ar), 7.08 (dt,
J¼7.4, 1.3 Hz, 1H, H-ar), 7.06 (dt, J¼7.4, 1.3 Hz, 1H, H-ar), 6.84 (d,
J¼16.2 Hz, 1H, H-et), 6.74 (d, J¼16.2 Hz, 1H, H-et), 6.22 (s, 1H, H-f),
3.81 (d, JAE¼4.3 Hz, 1H, H-A), 3.63 (dt, JBE,BC¼5.1, JBD¼1.2 Hz, 1H, H-
B), 3.19 (dd, JCD¼16.8, JBC¼5.1 Hz, 1H, H-C), 2.67 (dd, JCD¼16.8,
JBD¼1.2 Hz, 1H, H-D), 2.44 (ddd, JEF¼10.4, JBE¼5.1, JAE¼4.3 Hz, 1H, H-
E), 2.07 (d, JEF¼10.4 Hz, 1H, H-F); 13C NMR (CDCl3, 75 Hz) dC 151.6
(s),151.2 (s),147.3 (s), 144.8 (s), 137.4 (s), 128.6 (2ꢁd), 127.2 (d),127.0
(s), 126.6 (d), 126.3 (d), 126.1 (2ꢁd), 125.1 (d), 123.9 (d), 120.6 (d),
116.7 (d), 107.8 (d), 42.9 (t), 40.2 (d), 39.3 (d), 31.1 (t); MS m/z (EI)
298 (Mþ, 100%), 255 (10). Anal. Calcd (for the mixture of geo-
metrical isomers of 7a) for C22H18O: C, 88.56; H, 6.08. Found: C,
88.45; H 5.88.
salts (o-tolyl- and benzyltriphenylphosphonium bromides) and
a,a
0-o-xylyl(ditriphenylphosphonium)bromide were synthesized
from the corresponding bromides and triphenylphosphine. Com-
pounds 1 and 3 were prepared in our laboratory and published
before.10
4.1.1. Preparation
of
5-oxatetracyclo[6.6.1.02,6.09,14]pentadeca-2
(6),3,9,11,13-pentaene-4-carbaldehyde (10). To the compound
3
(0.29 g, 1.5 mmol) in dry N,N-dimethylformamide (1 mL, 0.013 mol)
ate12 ꢂC phosphorus oxychloride (0.25 g, 1.6 mmol) was added and
stirred for 15 min. The reaction mixture was allowed gradually to
warm up to room temperature, stirred for 1 day, worked up with
10% NaOH (2 mL) solution and the product extracted with diethyl
ether (60 mL). The diethyl ether extracts were washed with water
and then dried with MgSO4. After column chromatography on silica
gel using petroleum ether/diethyl ether (0e5%) as eluent the
product 10 was isolated in 88% (0.30 g) yield.
Compound cis-7b: Rf 0.64 (petroleum ether/diethyl ether
10:0.5); colourless oil; UV (EtOH) lmax
(3
/dm3 molꢀ1 cmꢀ1): 305
4.1.2. 5-Oxatetracyclo[6.6.1.02,6.09,14]pentadeca-2(6),3,9,11,13-pen-
taene-4-carbaldehyde (10). Rf 0.23 (petroleum ether/diethyl
ether 20:1); yellow solid; mp 135 ꢂC; UV (EtOH) lmax
(4534) nm; IR (evaporated film from diethyl ether) nmax/cmꢀ1
:
3013, 2924, 2852, 1598, 1460, 956, 749; 1H NMR (CDCl3, 300 MHz)
dH 7.34 (d. J¼6.9 Hz, 1H, H-ar), 7.30e7.01 (m, 7H, H-ar), 6.32 (d,
J¼12.5 Hz, 1H, H-et), 6.29 (d, 1H, J¼12.5 Hz, H-et), 5.79 (s, 1H, H-f),
3.65 (d, 1H, JAE¼4.2 Hz, H-A), 3.56 (dt, 1H, JBE,BC¼5.0 , JBD¼1.3 Hz, H-
B), 3.06 (dd, 1H, JCD¼16.8 , JBC¼5.0 Hz, H-C), 2.54 (dd, 1H, JCD¼16.8 ,
JBD¼1.3 Hz, H-D), 2.32e2.40 (ddd, 1H, JEF¼10.4 , JBE¼5.0 Hz,
(3
/dm3 molꢀ1 cmꢀ1): 308 (16,794) nm; IR (KBr) nmax/cmꢀ1: 1666
(C]O), 1504 (C]C); 1H NMR (CDCl3, 300 MHz) dH 9.41 (s, 1H, CHO),
7.32 (dd, J¼7.2 , J¼1.4 Hz, 1H, H-ar), 7.16e7.08 (m, 4H, 3H-ar, H-f),
3.91 (d, JAE¼4.4 Hz, 1H, H-A), 3.66 (dt, JBC,BE¼4.9 Hz, JBD¼0.5 Hz, 1H,
H-B), 3.20 (dd, JCD¼17.8 Hz, JBC¼4.9 Hz, 1H, H-C), 2.72 (dd,
JCD¼17.8 Hz, JBD¼0.5 Hz, 1H, H-D), 2.48 (ddd, JEF¼10.7 Hz,
JBE¼4.9 Hz, JAE¼4.4 Hz, 1H, H-E), 2.4 (d, JEF¼10.7 Hz, 1H, H-F); 13C
NMR (CDCl3, 75 Hz) dC 176.6 (d), 156.0 (s), 151.3 (s), 150.6 (s), 144.1
(s), 128.5 (s), 126.9 (d), 126.9 (d), 124.1 (d), 121.0 (2ꢁd), 42.5 (t), 39.6
(d), 39.1 (d), 31.4 (t); MS m/z (EI) 224 (Mþ, 100%), 167 (23), 115 (10).
Anal. Calcd for C15H12O2: C, 80.34; H, 5.39. Found: C, 80.41; H, 5.42.
JAE¼4.2 Hz, H-E), 2.22 (s, 3H, CH3), 1.98 (d, 1H, JEF¼10.4 Hz, H-F); 13
C
NMR (CDCl3, 150 Hz) dC 151.1 (s), 144.3 (s), 129.4 (d), 128.2 (d), 126.7
(d), 126.0 (s), 125.9 (d), 125.6 (d), 125.0 (d), 124.6 (d), 123.6 (d), 120.1
(d), 118.7 (d), 107.1 (d), 42.3 (t), 39.7 (d), 38.7 (d), 30.4 (t), 19.3 (q),
singlets are not seen due to small quantities; MS m/z (EI) 312 (Mþ,
100%), 269 (10), 115 (5).
Compound trans-7b: Rf 0.71 (petroleum ether/diethyl ether
10:0.5); colourless solid; mp 165 ꢂC; UV (EtOH) lmax
(3/
4.1.3. Preparation of 4-(2-phenylethenyl)-5-oxatetracyclo[6.6.1.02,6.09,14
]
dm3 molꢀ1 cmꢀ1): 338 (13,869) nm; IR (evaporated film from
diethyl ether) nmax/cmꢀ1: 3016, 2943, 1597, 1460, 954, 750; 1H NMR
(CDCl3, 300 MHz) dH 7.46 (d, J¼6.9 Hz, 1H, H-ar), 7.33 (dd, J¼6.1,
2.0 Hz, 1H, H-ar), 7.20e7.01 (m, 7H, H-ar), 7.05 (d, J¼16.0 Hz, 1H, H-
et), 6.65 (d, J¼16.0 Hz, 1H, H-et), 6.22 (s, 1H, H-f), 3.81 (d,
JAE¼4.26 Hz,1H, H-A), 3.64 (dt, JBE,BC¼5.0 , JBD¼1.2 Hz,1H, H-B), 3.20
(dd, JCD¼16.9 , JBC¼5.0 Hz, 1H, H-C), 2.68 (dd, JCD¼16.9 , JBD¼1.2 Hz,
1H, H-D), 2.40e2.48 (ddd, JEF¼10.4 , JBE¼5.0 , JAE¼4.26 Hz, 1H, H-E),
2.37 (s, 3H, CH3), 2.08 (d, JFE¼10.4 Hz, 1H, H-F); 13C NMR (CDCl3,
150 Hz) dC 151.1 (s), 151.0 (s), 146.7 (s), 144.3 (s), 135.8 (s), 135.1 (s),
129.9 (d), 126.6 (d), 126.4 (s), 126.0 (d), 125.8 (d), 125.6 (d), 124.2 (d),
123.4 (d),122.3 (d),120.1 (d),117.3 (d),107.2 (d), 42.3 (t), 39.7 (d), 38.8
pentadeca-2(6),3,9,11,13-pentaene (7a) and 4-[2-(2-methylphenyl)
ethenyl]-5-oxatetracyclo-[6.6.1.02,6.09,14]pentadeca-2(6),3,9,11,13-pen-
taene (7b). To the stirred solutions of the formyl derivative 10 (0.1 g,
0.4 mmol) and the corresponding aryltriphenylphosphonium salts
(0.5 mmol) in abs ethanol (30 mL) a solution of sodium ethoxide
(0.01 g, 0.5 mmol in 5 mL abs ethanol) was added dropwise. Stirring
was continued for 2 h at rt. After removal of the solvent, water (15 mL)
was added to the residue, extracted with benzene (45 mL) and the
benzene extracts dried with MgSO4. The crude reaction mixture was
purified and the mixtures of cis- and trans-isomers of the products 7a
and 7b were separated by column chromatography on silica gel using

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I. Kikas et al. / Tetrahedron 66 (2010) 9405e9414
9412
(d), 30.6 (t), 19.5 (q); MS m/z (EI) 312 (Mþ, 100%), 269 (10), 115 (5).
Anal. Calcd (for the mixture of geometrical isomers of 7b) for
C23H20O: C, 88.43; H, 6.45. Found: C, 88.59; H 6.29.
with water and benzene. The benzene extract was dried and con-
centrated. The crude reaction mixtures were purified and products
were isolated in 66% (1.10 g) yield for compound 8 (cis/trans¼1:5,
according to 1H NMR) and 69% (0.77 g) yield for 13 (cis/trans¼1:3,
according to 1H NMR). The mixtures of cis- and trans-isomers were
separated by TLC or column chromatography on aluminium oxide
using petroleum ether as eluent.
4.1.4. Irradiation experiments. Preparation of 13-oxahexacyclo
[14.6.1.02,14.03,12.04,9.017,22]-tricosa-2(14),3(12),4,6,8,10,17,19,21-non-
aene (6a) and 8-methyl-13-oxahexacyclo-[14.6.1.02,14.03,12.04,9.017,22
]
tricosa-2(14),3(12),4,6,8,10,17,19,21-nonaene (6b). To a mixture of
cis- and trans-isomers of 7a or 7b in benzene (7a: 3.4ꢁ10ꢀ3 M; 7b:
4.7ꢁ10ꢀ3 M) a small quantity (5 mg) of iodine was added. A solu-
tion was irradiated at 300 nm in a Rayonet reactor in a Quartz tube.
Irradiation time varied depending on the starting compound (for
compound 7a it was 15 h and for 7b, 10 h). After irradiation of
compounds 7a or 7b the solvent was removed in vacuo and the oily
residue chromatographed on silica gel column using petroleum
ether as eluent. While the irradiation of 7a resulted with only one
photoproduct 6a (in 53% yield, 0.01 g), the irradiation of derivative
7b resulted in a formation of two photoproducts 6a and 6b in the
ratio of 1:3 (0.01 g, 49% of isolated yield was found). In the last case,
the main photoproduct 6b was isolated from the photomixture by
thin-layer chromatography using petroleum ether as eluent.
Compound 6a: Rf 0.17 (petroleum ether/diethyl ether 10:1); col-
Compound cis-8: Rf 0.66 (petroleum ether/diethyl ether 10:1);
yellow oil; UV (EtOH) lmax (3
/dm3 molꢀ1 cmꢀ1): 307 (8916) nm; IR
(evaporated film from diethyl ether) nmax/cmꢀ1: 3020, 2950, 1593,
1468, 1003, 957, 752; 1H NMR (CDCl3, 300 MHz) dH 7.57 (d, J¼7.7 Hz,
1H, H-ar), 7.32 (dd, J¼7.7, 1.2 Hz, 1H, H-ar), 7.28 (dt, J¼7.6, 1.2 Hz, 1H,
H-ar), 7.27 (d, J¼7.3 Hz,1H, H-ar), 7.22 (dt, J¼7.6,1.2 Hz,1H, H-ar), 7.05
(dt, J¼4.7,1.2 Hz,1H, H-ar), 7.07e7.00 (m, 2H, H-ar), 6.84(dd, J1,3¼17.5,
J2,3¼11.0 Hz, 1H, H-3), 6.35 (ABq, 2H, H-et), 5.79 (s, 1H, H-f), 5.64 (dd,
J1,3¼17.5, J1,2¼1.0 Hz,1H, H-1), 5.18 (dd, J2,3¼11.0, J1,2¼1.0 Hz, 1H, H-2),
3.64 (d, JAE¼4.3 Hz,1H, H-A), 3.55(dt, JBC,BE¼5.2 , JBD¼1.2 Hz,1H, H-B),
3.05 (dd, JCD¼16.8 , JBC¼5.2 Hz, 1H, H-C), 2.53 (d, JCD¼16.8 Hz, 1H, H-
D), 2.53 (ddd, JAE¼4.3 , JBE¼5.2 , JEF¼10.1 Hz, 1H, H-E), 1.97 (d,
JEF¼10.3 Hz,1H, H-F); 13C NMR (CDCl3, 75 MHz) dC 151.9 (s),150.4 (s),
146.7 (s), 145.1 (s), 136.9 (s), 136.2 (s), 135.3 (d), 129.7 (d), 128.9 (s),
127.8 (d), 127.8 (d), 126.8 (d), 126.5 (d), 125.6 (d), 124.8 (d), 124.1 (d),
121.0 (d), 120.2 (d), 115.4 (t), 108.5 (d), 43.2 (t), 40.5 (d), 39.5 (d), 31.1
(t); MS m/z (EI) 324 (Mþ, 100%), 209 (15), 115 (9).
ourless oil; UV (EtOH) lmax
(5606), 331 (5338) nm; IR (evaporated film from diethyl ether) nmax
(3
/dm3 molꢀ1 cmꢀ1): 305 (5581), 316
/
cmꢀ1: 3062, 2930, 1769, 1678, 1467, 1349, 1272, 1118, 798, 752; 1H
NMR (CDCl3, 600 MHz) dH 8.61 (d, J¼8.2 Hz, 1H, H-ar), 7.92 (d,
J¼8.2 Hz,1H, H-ar), 7.63 (dt, J¼7.5,1.3 Hz,1H, H-ar), 7.57 (d, J¼8.9 Hz,
1H, H-ar), 7.50 (d, J¼8.9 Hz,1H, H-ar), 7.48 (dt, J¼7.5,1.3 Hz,1H, H-ar),
7.38 (d, J¼7.3 Hz,1H, H-ar), 7.29 (d, J¼7.3 Hz,1H, H-ar), 7.09 (dt, J¼7.5,
1.1 Hz, 1H, H-ar), 7.02 (dt, J¼7.5, 1.1 Hz, 1H, H-ar), 4.76 (d, JAE¼4.5 Hz,
1H, H-A), 3.76 (dt, JBC,BE¼5.0 , JBD¼1.3 Hz,1H, H-B), 3.41 (dd, JCD¼16.7,
JBC¼5.0 Hz, 1H, H-C), 2.85 (dd, JCD¼16.7, JBD¼1.3 Hz, 1H, H-D), 2.65
(ddd, JEF¼10.4, JBE¼5.0, JAE¼4.5 Hz, 1H, H-E), 2.29 (d, JEF¼10.4 Hz, 1H,
H-F); 13C NMR (CDCl3, 75 Hz) dC 151.5 (s), 151.3 (s),149.4 (s),144.6 (s),
130.6 (s), 129.0 (d), 128.2 (s), 126.6 (d), 126.4 (d), 125.9 (d), 124.0 (d),
123.9 (d), 123.6 (d), 123.1 (d), 122.0 (s), 120.8 (d), 120.4 (s), 112.4 (d),
42.9 (t), 39.8 (d), 39.6 (d), 31.5 (t); MS m/z (EI) 296 (Mþ, 100%). Anal.
Calcd for C22H16O: C, 89.16; H, 5.44. Found: C, 89.45; H 5.29.
Compound trans-8: Rf 0.74 (petroleum ether/diethyl ether 10:1);
yellow oil; UV (EtOH) lmax (3
/dm3 molꢀ1 cmꢀ1): 332 (13,689) nm;
IR (evaporated film from diethyl ether) nmax/cmꢀ1: 3060, 2952,
1624, 1468, 1003, 957, 752; 1H NMR (CDCl3, 300 MHz) dH 7.44e7.41
(m, 2H, H-ar), 7.32 (d, J¼7.3 Hz, 1H, H-ar), 7.23e7.18 (m, 2H, H-ar),
7.12 (d, J¼16.0 Hz, 1H, H-et), 7.12 (d, J¼7.3 Hz, 1H, H-ar), 7.10e7.06
(m, 1H, H-ar), 7.05 (dd, J1,3¼17.4, J2,3¼11.0 Hz, 1H, H-3), 6.63 (d,
J¼16.0 Hz, 1H, H-et), 6.22 (s, 1H, H-f), 5.60 (dd, J1,3¼17.4, J1,2¼1.3 Hz,
1H, H-1), 5.31 (dd, J2,3¼11.0, J1,2¼1.3 Hz, 1H, H-2), 3.81 (d,
JAE¼4.3 Hz, 1H, H-A), 3.63 (dt, JBC,BE¼5.1 , JBD¼1.3 Hz, 1H, H-B), 3.19
(dd, JCD¼16.9 , JBC¼5.1 Hz, 1H, H-C), 2.68 (d, JCD¼16.9 Hz, 1H, H-D),
2.43 (ddd, JAE¼4.3 , JBE¼5.1 , JEF¼10.2 Hz, 1H, H-E), 2.07 (d,
JEF¼10.2 Hz, 1H, H-F); 13C NMR (CDCl3, 75 MHz) dC 151.9 (s), 151.7
(s), 147.7 (s), 145.1 (s), 136.6 (s), 135.9 (s), 135.4 (d), 128.1 (d), 127.6
(d), 127.3 (s), 126.9 (2ꢁd), 126.6 (d), 126.0 (d), 124.2 (d), 123.0 (d),
121.0 (d), 119.2 (d), 116.6 (t),108.2 (d), 43.2 (t), 40.6 (d), 39.7 (d), 31.5
(t); MS m/z (EI) 324 (Mþ, 100%), 209 (15), 115 (9); HRMS (TOF ESþ)
m/z calculated (for the mixture of geometrical isomers of 8) for
C24H20O 324.1519; found 324.1506.
Compound 6b: Rf 0.15 (petroleum ether); colourless oil; UV
(EtOH) lmax (3
/dm3 molꢀ1 cmꢀ1): 307(3058), 320 (3017), 334 (3153)
nm; IR (evaporated film from diethyl ether) nmax/cmꢀ1: 3062, 2930,
1769, 1678, 1467, 1349, 1272, 1118, 798, 752; 1H NMR (CDCl3,
300 MHz) dH 8.53 (d, J¼8.2 Hz,1H, H-ar), 7.77 (d, J¼9.2 Hz,1H, H-ar),
7.59e7.52 (m, 2H, H-ar), 7.42e7.30 (m, 3H, H-ar), 7.11 (dt, J¼7.5,
1.2 Hz,1H, H-ar), 7.03 (dt, J¼7.5,1.2 Hz,1H, H-ar) 4.79 (d, JAE¼4.5 Hz,
1H, H-A), 3.77 (dt, JBC,BE¼5.0, JBD¼1.1 Hz,1H, H-B), 3.43 (dd, JCD¼16.9,
JBC¼5.0 Hz,1H, H-C), 2.87 (dd, JCD¼16.9, JBD¼1.1 Hz,1H, H-D), 2.76 (s,
3H, CH3), 2.66 (ddd, JEF¼10.5, JBE¼5.0, JAE¼4.5 Hz, 1H, H-E), 2.31 (d,
JEF¼10.5 Hz,1H, H-F); 13C NMR (CDCl3, 75 Hz) dC 126.6 (d),126.4 (d),
125.6 (d), 125.0 (d), 124.0 (d), 121.5 (d), 120.8 (d), 119.6 (d), 111.9 (d),
42.9(t), 39.8(d), 39.6 (d), 31.5(t), 20.2 (q), singlets arenotseen dueto
small quantities;MS m/z(EI) 310(Mþ,100%). Anal. Calcd for C23H18O:
C, 89.00; H, 5.85. Found: C, 88.85; H 5.58.
Compound cis-13: Rf 0.38 (petroleum ether); colourless oil; UV
(EtOH) lmax (3
/dm3 molꢀ1 cmꢀ1): 298 (11,584) nm; IR (evaporated
filmfromdiethylether)nmax/cmꢀ1:3066, 2920,1759,1616,1365,1126,
922, 760; 1H NMR (CDCl3, 600 MHz) dH 7.57 (dd, J¼7.6, 1.2 Hz, 1H, H-
ar), 7.34 (dd, J¼7.6, 1.2 Hz, 1H, H-ar), 7.27 (dt, J¼7.6, 1.2 Hz, 1H, H-ar),
7.22 (dt, J¼7.6, 1.2 Hz, 1H, H-ar), 6.90 (dd, J1,3¼17.5, J2,3¼11.1 Hz, 1H,
H-3), 6.40 (ABq, J¼12.0 Hz, 2H, H-et), 5.69 (s, 1H, H-f), 5.67 (dd,
J1,3¼17.5, J1,2¼1.2 Hz,1H, H-1), 5.22 (dd, J2,3¼11.1, J1,2¼1.2 Hz,1H, H-2),
2.10 (s, 3H, CH3), 1.79 (s, 3H, CH3); 13C NMR (CDCl3, 75 MHz) dC 149.4
(s),147.1 (s),136.8 (s),136.0 (s),135.2 (d),129.4 (d),127.6 (d),127.5 (d),
125.3 (d), 124.8 (d), 120.0 (d), 116.0 (s), 115.1 (t), 113.0 (d), 11.4 (q), 9.9
(q); MS m/z (EI) 224 (Mþ, 100%), 181 (4).
4.1.5. Preparation of cis- and trans-isomers of 4-[2-(2-Vinylphenyl)
ethenyl]-5-oxatetracyclo-[6.6.1.02,6.09,14]pentadeca-2(6),3,9,11,13-
pentaene (8) and 2,3-dimethyl-5-[2-(2-vinylphenyl)ethenyl]furan
Compound trans-13: Rf 0.32 (petroleum ether); yellow oil; UV
(EtOH) lmax (3
/dm3 molꢀ1 cmꢀ1): 332 (19,301) nm; IR (evaporated
(13). To a stirred solution of
a,a
0-o-xylyl(ditriphenylphosphonium)
film from diethyl ether) nmax/cmꢀ1: 3066, 2973, 1759, 1616, 1365,
1126, 922, 760; 1H NMR (CDCl3, 600 MHz) dH 7.49 (dd, J¼7.6, 1.2 Hz,
1H, H-ar), 7.45 (dd, J¼7.6, 1.2 Hz, 1H, H-ar), 7.19 (d, J¼16.0 Hz, 1H, H-
et), 7.27e7.19 (m, 2H, H-ar), 7.12 (dd, J1,3¼17.4, J2,3¼11.0 Hz,1H, H-3),
6.67 (d, J¼16.0 Hz, 1H, H-et), 6.14 (s, 1H, H-f), 5.63 (dd, J1,3¼17.4,
J1,2¼1.5 Hz,1H, H-1), 5.35 (dd, J2,3¼11.0, J1,2¼1.5 Hz,1H, H-2), 2.26 (s,
3H, CH3), 1.94 (s, 3H, CH3); 13C NMR 150.7 (s), 148.0 (s), 136.4 (s),
135.7 (s), 135.2 (d), 127.9 (d), 127.3 (d), 126.7 (d), 125.8 (d), 122.7 (d),
119.0 (d), 116.4 (s), 116.3 (t), 112.7 (d), 11.7 (q), 10.0 (q); MS m/z (EI)
bromide (3.94 g, 5.00 mmol), and the corresponding aldehydes (10:
5.50 mmol (1.20 g) and 4,5-dimethyl-furan-2-carbaldehyde:
5.50 mmol (0.68 g)) in abs ethanol (100 mL) a solution of sodium
ethoxide (0.63 g, 2.75 mmol in 10 mL ethanol) was added dropwise.
Under a stream of nitrogen gaseous formaldehyde (obtained by the
decomposition of an excess of paraformaldehyde) was introduced
and an additional quantity of sodium ethoxide (2.75 mmol) was
added. After removal of the solvent, the residue was worked up

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I. Kikas et al. / Tetrahedron 66 (2010) 9405e9414
9413
224 (Mþ, 100%), 109 (8); HRMS (TOF ESþ) m/z calculated (for the
mixture of geometrical isomers of 13) for C16H16O 224.1207; found
224.1199.
using petroleum ether as eluent. The product 12b was isolated in
71% (1.20 g) yield (65% (0.78 g) trans and 35% (0.42 g) cis, according
to 1H NMR), and the product 12a in 80% (1,28 g) yield (cis/
trans¼1:2, according to 1H NMR).
4.1.6. Irradiation experiment. Preparation of 13,14-dihydro-8H-8,13-
methanobenzo[5,6]cyclohepta[1,2-b]phenanthrene (11). A mixture
of cis- and trans-isomers of 8 in benzene (4.2ꢁ10ꢀ3 M) was purged
with argon for 20 min and irradiated at 350 nm in a Rayonet reactor
in a Quartz tube for 56 h. Solvent was removed in vacuum and the
oily residue chromatographed on a silica gel column using petro-
leum ether/diethyl ether (9%). The isolated product was phenan-
threne 11 in 33% (0.02 g) yield.
Compound cis-12b: Rf 0.53 (petroleum ether); colourless oil; UV
(EtOH) lmax (3
/dm3 molꢀ1 cmꢀ1): 306 (13,235) nm; IR (evaporated
film from diethyl ether) nmax/cmꢀ1: 2919, 2850,1734,1462,1054; 1H
NMR (CDCl3, 600 MHz) dH 7.35 (dd, J¼8.2, 1.1 Hz, 1H, H-ar),
7.22e7.17 (m, 2H, H-ar), 7.15 (dt, J¼7.4, 1.2 Hz, 1H, H-ar), 6.36 (ABq,
J¼12.5 Hz, 2H, H-et), 5.69 (s, 1H, H-f), 2.25 (s, 3H, CH3), 2.11 (s, 3H,
CH3), 1.80 (s, 3H, CH3); 13C NMR (CDCl3, 150 MHz) dC 149.5 (s), 146.9
(s), 137.6 (s), 136.1 (s), 130.0 (d), 128.8 (d), 127.4 (d), 125.6 (d), 125.5
(d),119.3 (d),116.0 (s), 112.5 (d),19.9 (q),11.4 (q), 9.8 (q); MS m/z (EI)
212 (Mþ, 100%), 169 (15).
Compound 11: Rf 0.20 (petroleum ether); colourless oil; UV
(EtOH) lmax (3
/dm3 molꢀ1 cmꢀ1) 258 (14,702) nm; IR (evaporated
film from diethyl ether) nmax/cmꢀ1: 2918, 2849, 1734, 1460, 1377,
1014, 807, 751; 1H NMR (CDCl3, 600 MHz) dH 8.52 (d, J¼8.2 Hz,1H, H-
ar), 8.27 (s, 1H, H-ar), 7.81 (dd, J¼8.2, 1.4 Hz, 1H, H-ar) 7.65 (d,
J¼9.0 Hz,1H, H-ar), 7.62 (d, J¼9.0 Hz,1H, H-ar), 7.61 (s,1H, H-ar), 7.55
(dt, J¼6.9, 1.4 Hz, 1H, H-ar), 7.50 (dt, J¼6.9, 1.4 Hz, 1H, H-ar), 7.33 (d,
J¼7.3 Hz,1H, H-ar), 7.21 (d, J¼7.3 Hz,1H, H-ar), 7.08 (dt, J¼7.3,1.1 Hz,
1H, H-ar) 7.04 (dt, J¼7.3, 1.1 Hz, 1H, H-ar), 4.15 (d, JAE¼4.2 Hz, 1H, H-
A), 3.62 (dt, JBE,BC¼5.1, JBD¼1.0 Hz, 1H, H-B), 3.54 (dd, JCD¼16.8,
JBC¼5.1 Hz, 1H, H-C), 3.08 (dd, JDC¼16.8, JDB¼1.0 Hz, 1H, H-D), 2.67
(ddd, JEF¼10.5, JBE¼5.1, JAE¼4.2 Hz,1H, H-E), 2.26 (d, JEF¼10.5 Hz,1H,
H-F); 13C NMR (CDCl3,150 MHz) dC 150.1 (s),145.6 (s),142.3 (s),133.1
(s),131.9 (s),130.4 (s),130.1 (s),129.5 (s),128.8 (d),127.1 (d),127.0 (d),
126.9 (d), 126.6 (d), 126.5 (d), 126.4 (d), 124.5 (2ꢁd), 123.6 (d), 122.6
(d),122.1 (d), 47.4 (d), 41.5 (t), 40.8 (d), 35.2 (t); HRMS (TOF ESþ) m/z
calculated for C24H18 306.1414; found 306.1401.
Compound trans-12b: Rf 0.32 (petroleum ether); yellow oil; UV
(EtOH) lmax (3
/dm3 molꢀ1 cmꢀ1): 319 (19,832) nm; IR (evaporated
film from diethyl ether) nmax/cmꢀ1: 2940, 2900, 1750, 1462, 1098;
1H NMR (CDCl3, 600 MHz) dH 7.51 (d, J¼7.6 Hz, 1H, H-ar), 7.13 (d,
J¼16.2 Hz, 1H, H-et), 7.19e7.12 (m, 3H, H-ar), 6.70 (d, J¼16.2 Hz, 1H,
H-et), 6.14 (s, 1H, H-f), 2.42 (s, 3H, CH3), 2.26 (s, 3H, CH3), 1.94 (s, 3H,
CH3); 13C NMR (CDCl3, 150 MHz) dC 150.8 (s), 147.8 (s), 136.5 (s),
135.8 (s), 130.5 (d), 127.2 (d), 126.2 (d), 124.8 (d), 122.8 (d), 117.9 (d),
116.4 (s), 112.6 (d), 20.1 (q), 11.7 (q), 10.0 (q); MS m/z (EI): 212 (Mþ,
100), 169 (15); HRMS (TOF ESþ) m/z calculated (for the mixture of
geometrical isomers of 12b) for C15H16O 212.1207; found 212.1211.
Compound cis-12a: Rf 0.35 (petroleum ether); colourless oil; UV
(EtOH) lmax (3
/dm3 molꢀ1 cmꢀ1): 228 (9191), 315 (12,885) nm; IR
(evaporated film from diethyl ether) nmax/cmꢀ1: 3027, 2925, 1679,
1610,1450,1364,1248,1120, 700; 1H NMR (CDCl3, 600 MHz) dH 7.48
(d, J¼7.6 Hz, 2H, H-ar), 7.31 (t, J¼7.6 Hz, 2H, H-ar), 7.23 (t, J¼7.3 Hz,
1H, H-ar), 6.33 (d, J¼12.6 Hz, 1H, H-et), 6.25 (d, J¼12.6 Hz, 1H, H-et),
6.05 (s, 1H, H-f), 2.15 (s, 3H, CH3), 1.86 (s, 3H, CH3); 13C NMR (CDCl3,
150 MHz) dC 149.4 (s), 147.2 (s), 137.9 (s), 128.8 (2ꢁd), 128.1 (2ꢁd),
127.2 (d), 126.1 (d), 118.3 (d), 116.0 (s), 113.6 (d), 11.5 (q), 9.9 (q); MS
m/z (EI) 196 (Mþ, 100%), 155 (17).
4.1.7. Irradiation experiment. Preparation of 2,3-dimethylfuro[3,2-b]-
6,7-benzobicyclo[3.2.1]octa-2,6-diene (15). A mixture of cis- and
trans-isomers of 13 in petroleum ether (2.6ꢁ10ꢀ3 M) was purged
with argon for 20 min and irradiated at 300 nm in a Rayonet reactor
in a Quartz tube for 16 h. Solvent was removed in vacuum and the
oily residue chromatographed on a aluminium oxide column using
petroleum ether/diethyl ether (5%). The isolated product was
benzobicyclic derivative 15 in 53% (0.06 g) yield.
Compound trans-12a: Rf 0.30 (petroleum ether); white solid;
mp 45 ꢂC; UV (EtOH) lmax /dm3 molꢀ1 cmꢀ1): 235 (8029), 331
(3
(28,306), 344 (sh, 22,331) nm; IR (evaporated film from diethyl
ether) nmax/cmꢀ1: 3060, 2978, 1704, 1610, 1450, 1364, 1248, 1166,
758; 1H NMR (CDCl3, 600 MHz) dH 7.43 (d, J¼7.6 Hz, 2H, H-ar), 7.31
(t, J¼7.6 Hz, 2H, H-ar), 7.20 (t, J¼7.5 Hz, 1H, H-ar), 6.91 (d, J¼16.3 Hz,
1H, H-et), 6.78 (d, J¼16.3 Hz, 1H, H-et), 6.14 (s, 1H, H-f), 2.25 (s, 3H,
CH3), 1.94 (s, 3H, CH3); 13C NMR (CDCl3, 150 MHz) dC 150.6 (s), 147.9
(s), 137.6 (s), 128.8 (2ꢁd), 127.2 (d), 126.6 (2ꢁd), 125.2 (d), 116.9 (d),
116.4 (s), 112.6 (d), 11.7 (q), 10.0 (q); MS m/z (EI) 196 (Mþ, 100%), 155
(12); HRMS (TOF ESþ) m/z calculated (for the mixture of geo-
metrical isomers of 12a) for C14H14O 198.1050; found 198.1045.
Compound 15: Rf 0.20 (petroleum ether); colourless oil; UV
(EtOH) lmax
(3
/dm3 molꢀ1 cmꢀ1): 251 (4467), 268 (1585), 284
(1349) nm; IR (evaporated film from diethyl ether) nmax/cmꢀ1
:
3062, 2932, 2868, 1756, 1720, 1454, 1151, 1114, 757; 1H NMR (CDCl3,
600 MHz) dH 7.28 (d, J¼6.4 Hz, 1H, H-ar), 7.09e7.01 (m, 3H, H-ar),
3.73 (d, JAE¼4.5, 1H, H-A), 3.56 (t, JBC,BE¼5.0 Hz, 1H, H-B), 3.07 (dd,
JCD¼16.2 Hz; JBC¼5.0 Hz, 1H, H-C), 2.52 (d, JCD¼16.2 Hz, 1H, H-D),
2.40 (ddd, JEF¼10.2, JBE¼5.0, JAE¼4.5 Hz, 1H, H-E), 2.07 (d, J¼0.6 Hz,
3H, CH3), 2.01 (d, JEF¼10.2 Hz, 1H, H-F), 1.93 (d, J¼0.6 Hz, 3H, CH3);
13C NMR (CDCl3, 150 MHz) dC 152.3 (s), 45.1 (s), 145.1 (s), 143.4 (s),
126.5 (d), 126.1 (d), 124.0 (d), 120.3 (d), 43.1 (t), 40.6 (d), 38.0 (d),
30.8 (t), 11.5 (q), 8.1 (q); MS m/z (EI) 224 (Mþ, 100%). Anal. Calcd for
C16H16O: C, 85.68; H, 7.19. Found: C, 85.45; H 7.41.
4.1.9. Irradiation experiments. Preparation of 1,2,6-trimethyl-naphtho
[2,1-b]furan (14b) and 1,2-dimethyl-naphtho[2,1-b]furan (14a). To
a mixture of cis- and trans-isomers of 12b or 12a in petroleum ether
(12b: 5.2ꢁ10ꢀ3 M; 12a: 5.3ꢁ10ꢀ3 M) a small quantity (5 mg) of io-
dine was added. A solution was irradiated at 300 nm in a Rayonet
reactor in a Quartz tube. Irradiation time varied depending on the
starting compound (for compound 12b it was 35 h and for 12a 16 h).
After irradiation the solvent was removed in vacuo and the oily
residue chromatographed on aluminium oxide column using pe-
troleum ether as eluent. While the irradiation of 12a resulted with
only one photoproduct 14a (in 56% (0.03 g) yield), the irradiation of
derivative 14b resulted in a formation of two photoproducts 14a and
14b in the ratio of 1:2.5 (22% (0.02 g) of isolated yield was found).
Compound 14b: Rf 0.65 (petroleum ether); colourless oil; IR
(evaporated film from diethyl ether) nmax/cmꢀ1: 3055, 2920, 2849,
1650, 1598, 1397, 990, 800, 750; 1H NMR (CDCl3, 600 MHz) dH 8.28
(d, J¼8.3 Hz, 1H, H-ar), 7.81 (d, J¼9.2 Hz, 1H, H-ar), 7.59 (d, J¼9.2 Hz,
1H, H-ar), 7.44 (dd, J¼8.3; 7.0 Hz, 1H, H-ar), 7.30 (d, J¼7.0 Hz, 1H, H-
4.1.8. Preparation of 2,3-dimethyl-5-(2-o-tolylvinyl)furan (12b) and
2,3-dimethyl-5-styryl furan (12a). To the stirred solutions of 4,5-
dimethylfuran-2-carboxaldehyde (1 g, 8.05 mmol) and the corre-
sponding aryltriphenylphosphonium salts (8.05 mmol) in abs eth-
anol (60 mL) a solution of sodium ethoxide (0.20 g, 8.84 mmol in
15 mL abs ethanol) was added dropwise. Stirring was continued for
24 h at rt. After removal of the solvent, water (20 mL) was added to
the residue, extracted with benzene (60 mL) and the benzene ex-
tracts dried with MgSO4. The crude reaction mixture of 12b was
purified by column chromatography on silica gel using petroleum
ether as eluent and the mixture of cis- and trans-isomers were
separated by TLC on aluminium oxide using petroleum ether as
eluent. The mixture of cis- and trans-isomers of the product 12a
were separated by column chromatography on aluminium oxide

ꢀ
I. Kikas et al. / Tetrahedron 66 (2010) 9405e9414
9414
ar), 2.74 (s, 3H, CH3), 2.55 (s, 3H, CH3), 2.47 (s, 3H, CH3); 13C NMR
(CDCl3, 150 MHz) dC 151.4 (s), 150.1 (s), 135.3 (s), 129.7 (s), 129.0 (s),
125.6 (d), 125.0 (d), 121.6 (d), 120.1 (d), 111.7 (d), 20.6 (q), 14.3 (q),
11.7 (q), one singlet is not seen; MS m/z (EI): 210 (Mþ, 100%).
Compound 14a: Rf 0.30 (petroleum ether); colourless oil; UV
introduced and an additional quantity of sodium ethoxide
(0.3518 mmol) was added. After removal of the solvent, the resi-
due was worked up with water (10 mL) and benzene (35 mL). The
benzene extract was dried and concentrated. The crude reaction
mixture was purified and the mixture of two isomers of product
was isolated by column chromatography on silica gel using pe-
troleum ether as eluent. After the photochemical isomerization of
the photomixtures of 20 the trans,trans-isomers of 20 was isolated
as the main isomer. A mixture of isomers of 20 in benzene
(e3.4ꢁ10ꢀ3 M) was purged with argon for 20 min and irradiated at
350 nm in a Rayonet reactor in a Pyrex tube. After 20 min the
reaction mixture of 20 contained pure trans,trans-20. The solvent
was removed in vacuum and the oily residue chromatographed on
silica gel using petroleum ether to isolate pure trans,trans-20 in
78% (0.08 g) yield.
(EtOH) lmax (3
/dm3 molꢀ1 cmꢀ1): 220 (27,691), 250 (19,555), 301
(6745), 515 (6042), 329 (5841) nm; IR (evaporated film from diethyl
ether) nmax/cmꢀ1: 3055, 2917, 2849, 1621, 1579, 1397, 1272, 993,
800, 743; 1H NMR (CDCl3, 600 MHz) dH 8.36 (d, J¼8.4 Hz, 1H, H-ar),
7.91 (d, J¼8.4 Hz, 1H, H-ar), 7.61 (d, J¼8.7 Hz, 1H, H-ar), 7.54 (d,
J¼8.7 Hz, 1H, H-ar), 7.52 (dt, J¼8.4, 1.2 Hz, 1H, H-ar), 7.42 (dt, J¼8.4,
1.2 Hz, 1H, H-ar), 2.53 (s, 3H, CH3), 2.45 (s, 3H, CH3); 13C NMR
(CDCl3, 150 MHz) dC 151.4 (s), 150.0 (s), 130.8 (s), 129.0 (d), 128.9 (s),
125.9 (d), 124.1 (d), 123.9 (d), 123.4 (s), 123.1 (d), 112.2 (d), 111.8 (s),
11.8 (q), 11.5 (q); MS m/z (EI): 196 (Mþ, 100%); HRMS (TOF ESþ) m/z
calculated for C14H12O 196.0894; found 196.0899.
Compound trans,trans-20: Rf 0.67 (petroleum ether/diethyl
ether 10:1); yellow solid; mp 79e81 ꢂC; UV (EtOH) lmax
4.1.10. Preparation of 5-[2-(2-vinylphenyl)ethenyl]-furan-2-carbox-
aldehyde (21). Compound 21 was prepared by Vilsmeier for-
mylation. The reaction was carried out from mixture of cis- and
(3
/dm3 molꢀ1 cmꢀ1) 385 (24,060) nm; IR (evaporated film from
diethyl ether) nmax/cmꢀ1: 3049, 2912, 2846, 1621, 1591, 1470, 955,
765; 1H NMR (CDCl3, 600 MHz) dH 7.56e7.53 (m, 4H, H-ar),
7.50e7.47 (m, 4H, H-ar), 7.41 (d, J¼16.1 Hz, 2H, H-et), 7.15 (dd,
J1,3¼17.4, J2,3¼11.0 Hz, 2H, H-3), 6.79 (d, J¼16.1 Hz, 2H, H-et), 6.41 (s,
2H, H-f), 5.67 (dd, J1,3¼17.4, J1,2¼1.4 Hz, 2H, H-1), 5.40 (dd, J2,3¼11.0,
J1,2¼1.4 Hz, 2H, H-2); 13C NMR (150 MHz, CDCl3) dC 153.7 (2ꢁs),
136.3 (2ꢁs), 135.5 (2ꢁs), 135.3 (2ꢁd), 128.2 (2ꢁd), 128.0 (2ꢁd),
127.1 (2ꢁd), 126.2 (2ꢁd), 125.2 (2ꢁd), 118.7 (2ꢁd), 117.0 (2ꢁt), 111.6
(2ꢁd); MS m/z (%, fragment): 324 (Mþ, 100%); HRMS (TOF ESþ) m/z
calculated for C24H20O 324.1406; found 324.1411.
trans-isomers of
b-(2-furyl)-o-divinylbenzene (1) (1.37 g,
7.01 mmol) dissolved in dimethylformamide (5.4 mL, 0.07 mol).
After being stirred ate10 ꢂC for 10, phosphorus oxychloride (1.18 g,
7.71 mmol) was added and the reaction mixture was allowed
gradually to warm up to room temperature and stirred for 28 h. The
reaction mixture was decomposed by the continuous addition
(with cooling) of 10% sodium hydroxide solution (9 mL) and the
product was worked up with ether. The ether extracts were washed
with water and then dried with MgSO4. After column chromatog-
raphy on silica gel using petroleum ether/diethyl ether (0e10%) as
eluent the product 21 was isolated in 89% (1.4 g) yield.
Acknowledgements
Compound cis-21: Rf 0.23 (petroleum ether/diethyl ether 10:1);
This work was supported by grants from the Ministry of Science,
Education and Sports of the Republic of Croatia (grant no. 125-
0982933-2926 and 098-0982929-2917).
red oil; UV (EtOH) lmax (3
/dm3 molꢀ1 cmꢀ1): 326 (20,035) nm; IR
(evaporated film from CHCl3) nmax/cmꢀ1: 1675 (C]O), 1501 (C]C);
1H NMR (CDCl3, 600 MHz) dH 9.50 (s,1H, CHO), 7.62 (d, J¼7.9 Hz,1H,
H-ar) 7.37e7.34 (m, 1H, H-ar), 7.30e7.27 (m, 1H, H-ar), 7.04 (d,
J3f,4f¼3.8 Hz, 1H, H-4f), 6.93 (d, J¼12.2 Hz, 1H, H-et) 6.85 (dd,
J1,3¼17.5, J2,3¼11.0 Hz,1H, H-3), 6.64 (d, J¼12.2 Hz,1H, H-et), 5.96 (d,
J3f,4f¼3.8 Hz, 1H, H-3f), 5.71 (dd, J1,3¼17.5, J1,2¼1.0 Hz, 1H, H-1), 5.27
(dd, J2,3¼11.0, J1,2¼1.0 Hz, 1H, H-2); 13C NMR (CDCl3, 75 MHz) dC
177.4 (d), 157.4 (s), 151.2 (s), 136.0 (s), 135.3 (s), 134.5 (d), 133.9 (d),
128.9 (d), 128.6 (2ꢁd), 128.1 (d), 125.8 (d), 119.6 (d), 116.3 (t), 111.9
(d); MS m/z (EI): 224 (Mþ, 100%), 195 (35), 166 (20).
Supplementary data
Supplementary data associated with this article can be found in
the online version at doi:10.1016/j.tet.2010.09.093.
References and notes
Compound trans-21: Rf 0.10 (petroleum ether/diethyl ether
10:1); red solid; mp 48e51 ꢂC; UV (EtOH) lmax /dm3 molꢀ1 cmꢀ1):
(3
1. Hoffmann, N. Chem. Rev. 2008, 108, 1052.
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354 (13,800) nm; IR (evaporated film from CHCl3) nmax/cmꢀ1: 1671
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7.67 (d, J¼16.0 Hz, 1H, H-et), 7.54 (dd, J¼6.7, 2.1 Hz, 1H, H-ar), 7.49
(dd, J¼6.7, 2.1 Hz, 1H, H-ar), 7.34e7.27 (m, 2H, H-ar), 7.26 (d,
J3f,4f¼3.7 Hz, 1H, H-4f), 7.11 (dd, J1,3¼17.4, J2,3¼11.1 Hz, 1H, H-3), 6.84
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2); 13C NMR (CDCl3, 75 MHz) dC 177.4 (d), 159.0 (s), 152.2 (s), 137.6
(s), 134.9 (d), 134.2 (s), 131.2 (d), 129.2 (2ꢁd), 128.3 (d), 127.3 (d),
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