Synthesis and photochemical transformations of new butadiene chromophores: The influence of the nature and position of chlorine substituent on the photoinduced behaviour

Article abstract of DOI:10.1016/j.molstruc.2013.07.052

The photochemical behaviour of mono- and dichloro-substituted butadiene derivatives was studied at low concentrations. These compounds display diverse photochemical behaviour. The α-chloro derivatives photocyclize to give six-membered ring photoproducts. p-Chloro-substituted butadienes undergo intramolecular [2 + 2] cycloaddition followed by formation of benzobicyclic structures. The steric hindrance of chlorine(s) in α-position(s) cause a greater deviation from planarity, relative to p-substitution, and shift conformer equilibria and affects the reaction pathways and yields.

Full text of DOI:10.1016/j.molstruc.2013.07.052

Journal of Molecular Structure 1051 (2013) 1–14
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis and photochemical transformations of new butadiene
chromophores: The influence of the nature and position of chlorine
substituent on the photoinduced behaviour
a
a
a
b
c
ˇ
´
ˇ
Dragana Vuk , Dalia Potroško , Marija Šindler-Kulyk , Zeljko Marinic , Krešimir Molcanov ,
c
a,
⇑
´
´
´
Biserka Kojic-Prodic , Irena Škoric
a
´
Department of Organic Chemistry, Faculty of Chemical Engineering and Technology, University of Zagreb, Marulicev trg 19, 10000 Zagreb, Croatia
Center for NMR, Rudjer Boškovi´c Institute, Bijenicka cesta 54, 10000 Zagreb, Croatia
Department of Physical Chemistry, Rudjer Boškovi´c Institute, Bijenicka cesta 54, 10000 Zagreb, Croatia
b
c
ˇ
ˇ
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
ꢀ
Initial mono- and dichloro-
substituted butadienes display
diverse photobehaviour.
Cl
R'
Cl
ꢀ
ꢀ
a-Chloro derivatives react in the
R
sense of electrocyclization reaction.
p-Chloro-substituted butadienes
undergo intramolecular
h
ν
Cl
Cl
R'
Cl
Cl
R
photocycloaddition.
ꢀ
Competitive effects of chlorine
substituents on the photoinduced
behaviour.
hν
Cl
R
R'
R, R' = H, Cl
Cl
Cl
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 June 2013
Received in revised form 12 July 2013
Accepted 22 July 2013
Available online 2 August 2013
The photochemical behaviour of mono- and dichloro-substituted butadiene derivatives was studied at
low concentrations. These compounds display diverse photochemical behaviour. The -chloro derivatives
photocyclize to give six-membered ring photoproducts. p-Chloro-substituted butadienes undergo intra-
a
molecular [2 + 2] cycloaddition followed by formation of benzobicyclic structures. The steric hindrance of
chlorine(s) in
conformer equilibria and affects the reaction pathways and yields.
Ó 2013 Elsevier B.V. All rights reserved.
a-position(s) cause a greater deviation from planarity, relative to p-substitution, and shift
Keywords:
Butadiene
Chlorine
Photochemistry
Reaction mechanism
Spectroscopy
1. Introduction
octadienes as unsaturated structural analogues of the bicy-
clo[3.2.1]octane skeleton which is found in numerous biologically
important active natural products [9–12]. By insertion of an addi-
tional double bond into the molecule of o-vinylstilbene, we ob-
tained the extended conjugated system of o-vinyl-1,4-diphenyl-
1,3-butadiene 1 (Fig. 1) which might allow the formation of a
new polycyclic structure with an double bond functionality for fur-
ther transformation. The photochemistry of conjugated butadiene
Previous publications [1–8] on the photochemistry of different
heteroaryl substituted hexatrienes showed interesting intramolec-
ular cycloaddition reactions and the formation of bicyclo[3.2.1]
⇑
Corresponding author. Tel.: +385 1 4597241; fax: +385 1 4597250.
E-mail address: iskoric@fkit.hr (I. Škoric´).
0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2013.07.052

2
D. Vuk et al. / Journal of Molecular Structure 1051 (2013) 1–14
CH3
CH3
CH3
1
2
3
4
CH3
endo-
5
endo-
6
7
8
Fig. 1. Structures of the known butadiene derivatives (1–4) and their photoproducts (5–8).
R'
R'
R'
1-(o-vinylphenyl)-4-phenyl-1,3-butadiene (1) undergoes intramo-
lecular photocycloaddition at 350 nm and only the endo-
phenyl-benzobicyclo[3.2.1]octadiene isomer (endo-5) was isolated
in very good yield (90%) due to the stereoselectivity of the photo-
R
R
R
reaction. The photoproduct endo-5 underwent further di-p-meth-
ane rearrangement at 300 nm leading to a tricyclic structure
(endo-6). The related substituted methyl derivative, 2-methyl-1-
(o-vinylphenyl)-4-phenylbutadiene butadiene (2), on the other
hand, rearranges to dihydronaphthalene derivative 7 upon phot-
oirradiation. The effect of the methyl substituents is even more
dramatic for dibutadienes 3 and 4. The parent unsubstituted com-
pound 3 undergoes stereoselective photoinduced intramolecular
cycloaddition giving benzobicyclo[3.2.1]octadiene 8, whereas the
9/10: R = Cl, R' = H; 11/12: R = H, R' = Cl
Fig. 2. Structures of the new butadiene derivatives (9–12).
derivatives 1–4 (Fig. 1), molecules that combine the properties of
both butadiene and hexatriene systems, has been examined for
the first time by our group [13,14]. The unsubstituted compound
Cl
1)
OHC
2) CH2O
NaOEt/EtOH
Cl
9
Cl
Cl
2
OHC
NaOEt/EtOH
Cl
CH2P+Ph3Br-
CH2P+Ph3Br-
10
Cl
1)
Cl
OHC
CH O
2)
2
NaOEt/EtOH
11
Cl
Cl
Cl
2
OHC
NaOEt/EtOH
12
Scheme 1. Structures of the new butadiene derivatives (9–12).

D. Vuk et al. / Journal of Molecular Structure 1051 (2013) 1–14
3
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Scheme 2. Possible conformations of trans-isomer of compound 9.
1,0
1,0
0,8
0,5
0,3
0,0
trans,trans-10
trans,trans-12
cis-9
trans-9
cis-11
0,8
trans-11
A
A
0,5
0,3
0,0
250
300
350
λ / nm
400
250
300
350
400
λ / nm
Fig. 4. Absorption spectra of the isomers of compounds 10 and 12 in n-hexane.
Fig. 3. Absorption spectra of the isomers of compounds 9 and 11 in n-hexane.
dimethylated derivative shows only geometrical isomerization due
to the steric effect of the substituents. Methyl groups on the
butadiene backbones reduce the extent of conjugation, causing a
blue-shift of the characteristic absorption band. Furthermore, the
fluorescence efficiency is dramatically decreased, as a consequence
of nonplanarity and reduced rigidity of the molecules due to the
crowding by the methyl and phenyl groups. Thus, four molecules
with very similar structures showed dramatically different photo-
induced behaviour and emphasize that changes of the nature and
position of the substituents are essential in understanding the pho-
tochemistry of these types of compounds.
(a)
(b)
20000
10000
9000
8000
7000
6000
15000
ε 10000
5000
ε
5000
4000
3000
2000
1000
0
0
250
300
350
400
250
300
350
400
λ / nm
λ / nm
Fig. 5. Spectral change during the irradiation of cis-9 in n-hexane (a) after 0, 1, 2, 4, 8, 16, 32, 64, 128, 256 and 512 s and trans-9 in n-hexane (b) after 0, 1, 2, 4, 8, 16, 32, 64 s
(kir = 350 nm, ‘ = 1 cm).

4
D. Vuk et al. / Journal of Molecular Structure 1051 (2013) 1–14
(a)
(b)
0.5
0.4
0.3
0.2
0.1
0.0
0.6
0.4
A
A
0.2
0.0
250
300
350
400
250
300
350
400
nm
λ /
λ /nm
(c)
0.2
A
0.0
250
300
350
400
λ /nm
Fig. 6. Spectral change during the irradiation of cis,cis-10 in n-hexane (a), cis,trans-10 in n-hexane (b) and trans,trans-10 in n-hexane (c) after 0, 1, 2, 4, 8, 16, 32, 64, 128, 256,
512 and 1024 s (kir = 350 nm, ‘ = 1 cm).
(a)
(b)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0.6
0.4
0.2
0.0
A
A
250
300
350
400
250
300
350
400
λ / nm
λ / nm
Fig. 7. Spectral change during the irradiation of cis-11 in n-hexane (a) after 0, 1, 2, 4, 8, 16, 32, 64 and 128 s, and trans-11 in n-hexane (b) after 0, 1, 2, 4, 8, 16, 32, 64 s
(kir ¼ 350 nm, ‘ = 1 cm).
As a part of our increasing interest in the photochemistry of
conjugated butadiene systems we extended our research to new
chloro derivatives 9–12 (Fig. 2). New mono- and dichloro butadi-
enes 9–12 were synthesized by Wittig reactions. Compounds 9–
12 undergo photochemical reactions to give new polycyclic struc-
tures. We predicted that electronic and steric effects of one or two
chlorine atoms as substituents at different locations in the mole-
cule would provide new, complex polycyclic structures based on
the known photochemistry of chloro substituted stilbene deriva-
tives [15–20].
2. Results and discussion
2.1. Synthesis
The starting materials, chloro substituted butadiene deriva-
tives (9–12) were prepared by Wittig reactions from the corre-
sponding diphosphonium salt and cinnamaldehydes (Scheme 1)
[13,14,21,22]. The products were obtained in good yields
(51–78%) as mixtures of two (compounds 9 and 11) or three
geometric isomers (compounds 10 and 12). The syntheses were

D. Vuk et al. / Journal of Molecular Structure 1051 (2013) 1–14
5
In these new systems with extended conjugation, the influence
of chlorine atom at the double bond or at the benzene ring was
examined to see whether intramolecular [2 + 2] photocycloaddi-
tion was followed by formation of the benzobicyclic structures
and/or photoelectrocyclization led to photoproducts possessing
six-membered rings. The steric hindrance of the chlorine in 9
(Scheme 2) and 10 should cause larger deviations from planarity
[20] than in 11 and 12, thereby shifting the equilibrium between
conformers and altering the reaction pathways and yields.
Although the conformers of each isomer studied in this work
may display deviating photoinduced behaviour, similar to some
2-vinylbiphenyls [23], 1,2-dinaphthylethenes [24] and 1-naph-
thyl-2-phenylethenes [25], deeper investigation of the effects of
the conformational diversity within the steric influence of the
starting geometric isomers on the reaction pathway was not the
aim of this work.
The geometric isomers of 9–12 can be easily identified from
their 1H NMR spectra by the characteristic vicinal coupling con-
stants of the cis- and trans-ethylenic protons. According to 1H
NMR spectra of the crude reaction mixtures the ratio of cis- and
trans-isomers of 9 was ꢁ1:3 and of 11 was ꢁ1:1, whereas the ratio
of cis,cis-, cis,trans- and trans,trans-isomers of 10 was ꢁ1:6:2. The
isomers of 9–12 were separated combining column and prepara-
tory thin-layer chromatography on silica gel using petroleum ether
as the eluent, completely analysed and identified spectroscopically.
0.25
0.20
0.15
0.10
0.05
0.00
A
250
300
350
400
λ / nm
Fig. 8. Spectral change during the irradiation of trans,trans-12 in n-hexane after 0,
1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024 and 2048 s (kir = 350 nm, ‘ = 1 cm).
performed using the corresponding (Z) or (E) stereoisomers so the
second double bond (relative to the ortho substituted central ben-
zene ring) in the starting compounds 9–12 retains the (E)
configuration.
Hence, the number of the geometric isomers was reduced and
the reaction mixtures contain cis- and trans-isomers of 9 and 11,
and cis,cis-, cis,trans- and trans,trans-isomers of 10 and 12 (only
the stereochemistry of the first double bond connected to the ortho
substituted central benzene ring is fixed).
2.2. UV absorption spectra
The UV spectra (Figs. 3 and 4) of separated isomers of 9–12,
clearly show the substituent and configurational influence on
Cl
Cl
Cl
[1,5-H] shift
DDQ
13 (7%)
Cl
13'
hν
350 nm
Cl
Cl
hν
350 nm
9
Cl
Cl
Cl
exo
-14 (2%)
endo -14 (1%)
15 (traces)
Scheme 3. Proposed mechanism for the photochemistry of the o-vinylbutadiene 9.
Cl
Cl
Cl
Cl
hν, 350 nm
[1,5-H] shift
Cl
Cl
10
16 (11%)
Scheme 4. Proposed mechanism for the formation of photoproduct 16.

6
D. Vuk et al. / Journal of Molecular Structure 1051 (2013) 1–14
Cl
Cl
Cl
trans
-11
h
ν
h
ν
350 nm
17'
Cl
17''
Cl
Cl
endo-17 (77%)
cis-11
Scheme 5. Proposed mechanism for the photochemistry of p-chloro-substituted derivative 11.
Cl
Cl
Cl
hν
Cl
Cl
18'
Cl
Cl
Cl
hν
350 nm
Cl
Cl
trans-12
hν
Cl
Cl
Cl
Cl
[4+2] cycloaddition
endo,trans-18(50%)
endo,cis-18(10%)
Cl
Cl
19'
endo-19(10%)
Scheme 6. Proposed mechanism for the formation of photoproducts 18 and 19.
absorption characteristics. As expected, the trans-9 and trans-11
isomers show a bathochromic shift and an increase in molar
absorption coefficients relative to the cis-isomers due to increased
molecule planarity of the trans configuration and resultant im-
by the photolysis, and that the electronic systems of the aromatic
rings were isolated.
In numerous cases, as the initial changes of the absorption spec-
tra indicate (Figs. 6a,b and 7a,b), photoisomerization is one of the
primary process, which is either followed or accompanied by a
competitive photochemical reaction [26,27]. It is difficult to dis-
cuss about the composition of the photostationary mixture be-
cause of unsymmetrical structure of the starting compounds 9–
12 and possibility of existence and interconversion of the configu-
rational isomers.
proved delocalisation of
p-electrons (Fig. 3). In the related mole-
cules 9/11 or 10/12, with the same configuration but different
locations of chlorine atom(s) substitution, compounds 11 and 12
show a bathochromic shift in comparison to 9 and 10, due to better
delocalisation of p-electrons in the absense of the chlorine on the
butadiene unit(s) (Figs. 3 and 4).
The separated isomers of 9–12 were irradiated and the reaction
course followed by UV spectroscopy (Figs. 5–8). For all compounds,
the longest-wavelength absorption band gradually disappeared
upon irradiation.
These spectral changes generally indicate that the conjugation
between the phenyl groups via the butadiene link was interrupted
2.3. Photochemistry
The preparative irradiation experiments of 9–12 were per-
formed in petroleum ether solutions under anaerobic conditions
at 350 nm and at low concentrations, ꢁ10ꢂ3 M. Depending on

D. Vuk et al. / Journal of Molecular Structure 1051 (2013) 1–14
7
HX
HA/B
H
HA
B Cl
HX
HA/B
13
PPM
4.4
4.0
3.6
3.2
2.8
2.4
HB
Cl
HA
HB
HA
HD
HC
HB
HC
HD
exo-14
PPM
4.4
4.0
3.6
3.2
2.8
2.4
HB
HA
HA
Cl
HB
HD
HC
HB
HC
HD
endo -14
PPM
PPM
4.4
4.0
4.0
3.6
3.2
2.8
2.8
2.4
Cl
Cl
HA
HB
HA/B
HA/B
16
4.4
3.6
3.2
2.4
Fig. 9. Aliphatic region of the 1H NMR spectra: (a) 13; (b) exo-14; (c) endo-14; and (d) 16 (CDCl3, 300 MHz).
the structure of the starting compound, different types of
photoproducts were isolated and identified. The formation of the
photoproducts was generally accompanied by the formation of
polymeric products which were not investigated.
on the double bond precluding the allyl system resonance in the
intermediate.
In an effort to study the influence of extended conjugation in
our systems to the course of the photoreaction, we introduced a
second styryl substituent at the b-position of the vinyl group,
and synthesized the new dichloro-dibutadiene derivative 10.
Photolyses of these isomers display different characteristics at
the initial period of irradiation, depending on the configuration
of the starting isomer. These conformational predictions were con-
firmed upon product analysis. Only one conformer of the trans,-
trans-isomer is favoured and the unique final product 16 was
formed in 11% yield (Scheme 4). The remaining product mass
was tarry material. The proposed mechanism involves a six-mem-
bered ring-closure followed by sigmatropic 1,5H-shift to give the
stable photoproduct 16 (Scheme 4). In comparison with the corre-
sponding monosubstituted derivative 9, the photoreaction is more
selective giving only one photoproduct.
Preparative irradiation of p-chloro-phenylbutadiene derivative
11 at 350 nm, results in the formation of bicyclo[3.2.1]octadiene
structure endo-17, in a very good 77% yield (Scheme 5). The stere-
oselective formation of endo-benzobicyclic structure could be ex-
plained by initial intramolecular cycloaddition and formation of
resonance-stabilized intermediate 170 followed by 1,6-ring closure
(Scheme 5), as seen previously in the photochemical reactions of
b-heteroaryl substituted o-divinylbenzenes [2,4,6,8] and butadie-
nylstilbenes [13,14]. It might be assumed that even if the 1,4-ring
closure [2,26] to benzobicyclo[2.1.1]hexene derivative 1700 is
operating the formed derivative 1700 could thermally reverse to
On preparative irradiation of 2-chloro-1-(o-vinylphenyl)-4-
phenylbutadiene derivative (9) at 350 nm, cyclohexadiene deriva-
tive 13 was isolated as the main photoproduct (7%). This product
results from the primary electrocyclic ring closure process charac-
teristic for 1,3,5-hexatriene (Scheme 3) [28,29]. The proposed reac-
tion mechanism for transformation of the o-butadienylstyrene 9
involves a six-membered ring-closure followed by sigmatropic
1,5H-shift to give the stable photoproduct 13. The reaction is not
selective and several minor products (Scheme 3) exo-14 (2%),
endo-14 (1%) and 15 (in traces) were also formed during the irradi-
ation of 9 (Scheme 3). The photoproducts 13, exo-14 and endo-14
were separated by column chromatography on silica gel and the
structures deduced unequivocally from spectral studies and from
characteristic NMR data after the dehydrogenation reaction with
DDQ to fully aromatized structure 130 [30].
Product 15 was seen only in enriched chromatographic frac-
tions and was identified according to the very well resolved six-
proton-pattern in the 1H NMR spectrum and by the characteristic
couplings for this type of rigid bicyclo[3.2.1]octadienes [13,14]. It
might be assumed that the 1,4-ring closure to benzobicy-
clo[2.1.1]hexene derivative 14 could thermally revert to 9 and sub-
sequently give the more stable product 15, but that did not
happen. The less stable benzobicyclo[3.1.0]hexene structure
formed due to the electronic and steric influence of the chlorine

8
D. Vuk et al. / Journal of Molecular Structure 1051 (2013) 1–14
HA
HB
HB
HA
Cl
endo -17
PPM
6.0
5.6
5.2
4.8
4.4
4.0
3.6
3.2
2.8
2.4
2.0
Cl
HA
HA
HB
HB
endo,cis-18
Cl
PPM
6.0
5.6
5.2
4.8
4.4
4.0
3.6
3.2
2.8
2.4
2.0
Cl
HA
HA
HB
HB
Cl
18
-
endo,trans
PPM 6.4
6.0
5.6
5.2
4.8
4.4
4.0
3.6
3.2
2.8
2.4
2.0
Cl
Cl
19
endo-
PPM
6.0
5.6
5.2
4.8
4.4
4.0
3.6
3.2
2.8
2.4
2.0
Fig. 10. Part of the 1H NMR spectra: (a) bicyclic endo-17; (b) bicyclic endo,cis-18; (c) bicyclic endo,trans-18, and (d) tricyclic endo-19; (CDCl3, 300 MHz).
intermediate 170 and subsequently give the more stable product
endo-17. The ring closure predominantly gives endo-isomer. The
stereoselectivity of the reaction of o-butadienylstyrene 11 and
preferable ring closure to endo-isomer can be ascribed to the sta-
bilization of the transition state in endo-orientation by the strong
one of the styryl bonds giving the polycyclic compound 19
(Scheme 6).
The isolated photoproducts 13–19 were completely character-
ized by spectroscopic methods (see Section 4). The 1H NMR spec-
trum of 13 shows the characteristic ABX pattern between 3.2 and
4.8 ppm (Fig. 9a). The 1H NMR spectrum of isolated photoproduct
16 shows two doublets between 3.7 and 4.3 ppm with geminal
coupling constants (Fig. 9d) in the aliphatic region and the singlet
for HX proton is deshielded to 5.9 ppm (see Section 4). The aliphatic
regions of the 13C NMR spectra of 13 and 16 are very similar with
two signals assigned to one CH and one CH2 group.
attractive intramolecular
phenyl groups [31–33].
p–p interactions of the benzo-p-chloro-
Contrary to the
a-dichloro-substituted dibutadiene derivative
10, introduction in compound 11 of the second p-chlorostyryl
substituent at the b-position of the vinyl group, gaining new p-di-
chloro-dibutadiene derivative 12 resulted in different photochem-
ical behaviour (Scheme 6). On irradiation of the mixture of isomers
of 12, under the same conditions as for the starting material 10,
photoisomerization to trans,trans-12 is the primary process fol-
lowed by two competing processes, photocycloaddition to 18
(through the initial five-membered-ring-closure via 180, followed
by intramolecular trapping of the formed biradical) or by electro-
cyclic six-membered-ring-closure to 19 via 190. During the column
chromatography in the first fractions endo- and exo-18 photoprod-
ucts were isolated and followed by benzotricyclic compound endo-
19 in the last fractions. High-molecular-weight products remained
on the column. The dihydronaphthalene intermediate 190, formed
The very well resolved seven-proton-pattern in the 1H NMR
spectrum of the photoproduct endo-17 between 2.3 and 6.4 ppm
unmistakably point to the benzobicyclo[3.2.1]octadiene structure
(Fig. 10). The multiplets in the lower field between 5.2 and
6.4 ppm are assigned to the A and B alkenyl protons. One of the
aromatic protons of the benzo-moiety is shifted to higher field
due to the anisotropic effect of the other aromatic ring, endo-
substituted (see Section 4) and indicating the same structure. Sim-
ilar spectra is obtained in the case of the main photoproducts endo-
18 which differ only in the configuration of the styryl double bond
attached to the methano-bridge. The benzotricyclic structure endo-
19 has a completely different pattern in 1H NMR spectrum. All six
by 6p electrocyclization process, is intramolecularly trapped by

D. Vuk et al. / Journal of Molecular Structure 1051 (2013) 1–14
9
Fig. 11. ORTEP-3 [34] drawing of a molecule of trans,trans-12. Displacement ellipsoids are drawn for the probability of 30% and hydrogen atoms are shown as spheres of
arbitrary radii.
Fig. 12. Crystal packing of trans,trans-12 viewed in the direction [010].
protons appear between 1.6 and 3.6 ppm with the corresponding
multiplicity (see Section 4, Fig. 10). MS spectra data was used to
determine the presence of one or two chlorine atoms in the mole-
cule (see Fig. 11).
Concerning the mechanistic considerations, the formation of
the six-membered ring in 13 (Scheme 3) is more plausible, given
the steric hindrance of the chloro substituent,[23] in contrast with
unsubstituted derivative 1 providing the benzobicyclic structure
endo-5 as the only photoproduct (Fig. 1). The initial intramolecular
photocycloaddition from the other conformer, leading to the bicy-
clic structures 14 and 15, is a less favourable process than the ini-
2.4. X-ray study
The structure of the trans,trans-isomer of starting compound 12
was finally confirmed by X-ray analysis. The observed solid-state
conformation corresponds with the conformation required for
the formation of the main photoproduct 18 with a benzobicy-
clo[3.2.1]octadiene skeleton. The molecular symmetry of trans,-
trans-12 is Cs, with crystallographic mirror plane passing through
the central phenyl ring (i.e. midpoints of C13–C13i and C11–C11i
bonds). The only intermolecular interaction in the crystals are
rather long C6–H6ꢃ ꢃ ꢃCl1 bonds (Fig. 12; d(C–H) = 0.93 Å;
d(Hꢃ ꢃ ꢃCl) = 3.04 Å; d(Cꢃ ꢃ ꢃCl) = 3.823(8) Å; (C–H–Cl) = 142°; symme-
try operator i) 1/2 ꢂ x, ꢂy, ꢂ1/2 + z), which link the molecules into
layers parallel to the plane (101). There are only dispersion inter-
actions between the layers.
tial 6p electrocyclization leading to 13. We assume that due to the
changes induced by the steric effect of the chlorine in the excited
state of the 9, delocalization through the non-planar part of the
molecule, which contains the chloro substituent, is generally not
favourable. The similar effect can be assumed in the case of a-di-
chloro-substituted butadiene 10. Mono- or di-p-chloro-substituted
butadienes 11 and 12 gave intramolecular photoadducts as the
main structures in the photoreaction in the absence of the steric
hindrance of the chlorine (as in the case of 9 and 10). The shift of
the conformer equilibrium affects the reaction pathway and final
yields. Of the a-chloro substituted compounds examined, 10 was
the most selective but with relatively low yield for the single elec-
trocyclization product. For the p-chloro substituted derivatives, 11

10
D. Vuk et al. / Journal of Molecular Structure 1051 (2013) 1–14
Table 1
benzobyciclo[2.1.1]hexene
products
14
and
benzobyci-
Crystallographic, data collection and structure refinement details.
clo[3.2.1]octadiene product 15 are less favourable. The photoreac-
tion mechanism of molecule 9 includes electrocyclic ring closures
and hydrogen shift, which selectively leads only to dihydronaph-
thalene derivative 13. On the other hand, the irradiation of o-
butadienylstyrene 11 preferentially leads to an intramolecular
cycloaddition where the major photoproduct is benzobyci-
clo[3.2.1]octadiene derivative endo-17. In dichloro-substituted
conjugated compounds 10 and 12, the position of the chlorine
atoms directs the dominant photoreaction pathway based on the
conformation of the trans,trans-isomers of 10 or 12. Four molecules
of similar structures showed dramatically different photoinduced
behaviour and demonstrate how changes in the position of the
chlorine substituent direct the photochemistry of these related
compounds. Chlorine atoms can affect on mono- and dibutadiene
unit through mesomeric and inductive effects. Understanding the
dominant effects of chlorine substituents in photochemical reac-
tions of related new butadiene derivatives and explanation of reac-
tion mechanisms in obtaining photoproducts, makes the synthesis
of these systems suitable for routing photoreaction towards vari-
ous interesting structures for further transformations and func-
tionalization using simple approach with light as reagent.
Compound
trans,trans-12
C26H20Cl2
Empirical formula
Formula wt. (g molꢂ1
)
201.66
0.12 ꢄ 0.10 ꢄ 0.09
P m n 21
36.487(2)
4.0092(2)
6.8891(3)
90
90
90
4
1007.76(9)
1.329
2.943
4.85–75.66
293(2)
1.54179 (Cu K
Xcalibur Nova
ꢂ42 < h < 45
ꢂ5 < k < 3
ꢂ8 < l < 5
2436
Crystal dimensions (mm)
Space group
a (Å)
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
Z
V (Å3)
Dcalc (g cmꢂ3
)
l
(mmꢂ1
)
H
range (°)
T (K)
Radiation wavelength
Diffractometer type
Range of h, k, l
a)
Reflections collected
Independent reflections
Observed reflections (I P 2
Absorption correction
Rint
1504
1458
Multi-scan
0.0319
r
)
4. Experimental section
R (F)
0.0741
0.2110
Rw (F2)
4.1. General information
Goodness of fit
H atom treatment
No. of parameters
No. of restraints
0.967
Constrained
128
The 1H spectra were recorded on a spectrometer at 600 MHz.
The 13C NMR spectra were registered at 150 MHz, respectively.
All NMR spectra were measured in CDCl3 using tetramethylsilane
as reference. The assignment of the signals is based on 2D-CH cor-
relation and 2D-HH-COSY experiments. UV spectra were measured
on a UV/VIS Cary 50 spectrophotometer. IR spectra were recorded
on a FTIR–ATR (film). Irradiation experiments were preformed in a
quartz vessel in petroleum ether solution in a photochemical reac-
tor equipped with 3000 Å lamps. All irradiation experiments were
carried out in deaerated solutions by bubbling a stream of argon
prior to irradiation. Melting points were obtained using apparatus
equipped with microscope and are uncorrected. HRMS analysis
were carried out on a mass spectrometer (MALDI TOF/TOF ana-
lyzer), equipped with Nd:YAG laser operating at 355 nm with firing
rate 200 Hz in the positive (H+) or negative (Hꢂ) ion reflector
mode. Silica gel (0.063–0.2 mm) was used for chromatographic
purifications. Thin-layer chromatography (TLC) was performed sil-
ica gel 60 F254 plates. Solvents were purified by distillation.
1
D
q
max, Dqmin (eÅꢂ3
)
0.352; ꢂ0.320
gave one stereoisomer of benzobicyclo[3.2.1]octadiene skeleton, in
very good yield. The electronic effect of the chlorine substituent(s)
greatly influenced the product yields. Methyl and chloro substitu-
ents have similar steric requirements but very different electronic
effects. In comparison with the methyl analogues 2 (Fig. 1) the
overall yield for the analogous electrocyclization products is lower
than from 9. The chlorine atoms reduce the resonance of the inter-
mediate more than a methyl group in the same position, directing
rather the formation of bicyclo[2.1.1]hexene as the minor cycload-
duct 14, instead the bicyclo[3.2.1]octadiene skeleton 15. The a-di-
chloro derivative 10 selectively gives the electrocyclization
product 16 (Scheme 4) whereas the corresponding dimethyl deriv-
ative 4 (Fig. 1) shows only geometrical isomerization due to the
bulky methyl substituents. The unsubstituted butadienylstyrene
1 gave the intramolecular photocycloaddition product in 90% yield
the corresponding p-chloro substituent in 11 gave the same type of
the product 17 but in lower yield. The photoreaction of p-dichloro
substituted compound 12, was less selective than the unsubstitut-
ed analogue 3. The same methodology applied earlier at 300 nm
(instead 350 nm) to the chloro-vinylstilbenes [3–7], gave com-
pletely different photoproducts. The reaction mechanism at
300 nm was explained by primary cleavage of the C–Cl bond or
HCl elimination from the molecule and the obtained unsubstituted
compounds reacted by known mechanism without the influence of
chlorine substituent.
a-Chloro-(Z)-cinnamaldehyde and p-chloro-(E)-cinnamalde-
hyde were obtained from a commercial source, b,b-o-xylyl(ditri-
phenylphosphonium) dibromide was prepared from o-
xylyldibromide and triphenylphosphine in dimethylformamide.
4.2. General method for the synthesis of 9 and 11
Starting compounds 9 and 11 were prepared by Wittig reaction
from o-xylylenebis(triphenylphosphonium bromide) and the
corresponding aldehydes,
a-chloro-(Z)-cinnamaldehyde and p-
chloro-(E)-cinnamaldehyde. To a stirred solution of the triphenyl-
phosphonium salt (0.010 mol) and the corresponding aldehyde
(0.011 mol) in absolute ethanol (200 mL), a solution of sodium eth-
oxide (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 formaldehyde (ob-
tained 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 drop-
wise. The reaction was completed within 3–4 h (usually was left to
3. Conclusions
The initial compounds 9–12 display diverse photochemical
behaviour. In dilute solution, besides unidentified degradation
and high-molecular-weight products, photoreaction of o-butadie-
nylstyrene 9 leads to the major product 13 generated by electrocy-
clic ring closure while the intramolecular cycloaddition into

D. Vuk et al. / Journal of Molecular Structure 1051 (2013) 1–14
11
stand overnight). After removal of the solvent, the residue was
worked up with water and toluene. The toluene extracts were
dried (anhydrous MgSO4) and concentrated. The crude reaction
mixture was purified and the isomers of products 9 (51%) and 11
(78%) were separated by repeated column chromatography on sil-
ica gel using petroleum ether as the eluent. The first fractions
yielded cis- and the last fractions trans-isomers.
(0.253 g, 0.011 mol in 15 mL of absolute ethanol) was added drop-
wise. The reaction was completed within 3–4 h (usually was left to
stand overnight). After removal of the solvent, the residue was
worked up with water and toluene. The toluene extracts were
dried (anhydrous MgSO4) and concentrated. The crude reaction
mixture was purified and the isomers of products 10 (55%) and
12 (50%) were separated by repeated column chromatography on
silica gel using petroleum ether as the eluent. The first fractions
yielded cis,cis-, cis,trans- and the last fractions trans,trans-isomers.
Cl
Cl
Cl
Cl
9
11
Cl
cis-9: 13%; Rf 0.35 (petroleum ether); colourless oil; UV (96%
EtOH) kmax (log
) 227 (4.38); 1H NMR (CDCl3, 600 MHz) d 7.51
Cl
e
12
10
(dd, J = 7.7; 1.5 Hz; 1H), 7.45 (d, J = 7.7 Hz, 2H), 7.32–7.26 (m,
4H), 7.24–7.22 (m, 4H), 7.19 (dt, J = 7.7; 1.5 Hz, 1H), 6.92 (dd,
J = 17.5; 10.9 Hz, 1H), 6.68 (d, J = 12.0 Hz, 1H), 6.48 (s, 1H), 6.32
(dd, J = 12.0; 0.9 Hz, 1H), 5.68 (dd, J = 17.5; 1.2 Hz, 1H), 5.31 (dd,
J = 10.9; 1.2 Hz, 1H); 13C NMR (CDCl3, 150 MHz) d 132.6 (s), 134.6
(s), 134.5 (d), 134.3 (s), 130.3 (d), 130.1 (d), 129.0 (d), 128.8 (d),
128.7 (d), 127.6 (2d), 127.4 (2d), 127.2 (d), 126.9 (d), 125.0 (d),
115.3 (t) (too small quantities for detection of all singlets); IR mmax
3056, 1601, 1453, 698.
cis,cis-10: 6%; Rf 0.79 (petroleum ether/dichloromethane = 7:3);
colourless crystals; mp 65–66 °C; UV (96% EtOH) kmax (loge) 251
(4.36); 1H NMR (CDCl3, 600 MHz) d 7.44–7.40 (m, 6H), 7.27–7.24
(m, 4H), 7.23–7.13 (m, 2H), 7.18–7.15 (m, 2H), 6.61 (d,
J = 12.0 Hz, 2H), 6.52 (s, 2H), 6.29 (dd, J = 12.0 Hz, 2H); 13C NMR
(CDCl3, 150 MHz) d 134.9 (s), 134.2 (s), 130.0 (d), 129.9 (d), 128.8
(d), 128.7 (2d), 128.6 (d), 127.7 (s), 127.6 (2d), 127.5 (d), 126.8
(d); IR mmax 3022, 1619, 1491, 1081, 688.
trans-9: 38%; Rf 0.32 (petroleum ether); colourless crystals; mp
cis,trans-10: 37%; Rf 0.76 (petroleum ether/dichlorometh-
ane = 7:3); colourless oil; UV (96% EtOH) kmax (loge) 319 (4.43);
46 °C; UV (96% EtOH) kmax (loge
) 319 (4.49); 1H NMR (CDCl3,
300 MHz) d 7.74 (d, J = 7.6 Hz, 2H), 7.53–7.46 (m, 2H), 7.43–7.35
(m, 3H), 7.09 (dd, J = 17.4; 10.9 Hz, 1H), 6.83 (d, J = 15.2 Hz, 1H),
6.78 (s, 1H), 5.66 (dd, J = 17.4; 1.3 Hz, 1H), 5.39 (dd, J = 10.9;
1.3 Hz, 1H); 13C NMR (C6H6, 150 MHz) d 136.6 (s), 134.7 (s), 134.3
(d), 134.3 (s). 129.8 (d), 129.3 (d), 129.1 (d), 129.0 (d), 128.9 (s),
128.0 (d), 127.9 (d), 127.8 (2d), 127.6 (2d), 126.3 (d), 126.0 (d),
116.1 (t); IR mmax 3058, 1694, 1491, 754; HRMS for C18H15Cl:
Mcþalcd: 266.0857; Mfþound 266.0848 (for a mixture of isomers of 9).
cis-11: 45%; Rf 0.69 (petroleum ether/dichloromethane = 9:1);
1H NMR (CDCl3, 600 MHz) d 7.72 (d, J = 7.3 Hz, 2H), 7.54 (d,
J = 7.5 Hz, 1H), 7.46 (d, J = 7.3 Hz, 2H), 7.39–7.33 (m, 3H), 7.31–
7.19 (m, 7H), 6.87 (d, J = 15.1 Hz, 1H), 6.75 (s, 1H), 6.73 (d,
J = 12.1 Hz, 2H), 6.51 (s, 1H), 6.39 (dd, J = 12.1; 0.6 Hz, 1H); 13C
NMR (CDCl3, 75 MHz) d 135.1 (s), 134.89 (s), 134.84 (s), 131.68
(s), 131.62 (s), 131.4 (s), 131.1 (d), 130.5 (d), 130.0 (d), 129.9 (d),
129.77 (2d), 129.71 (2d), 129.4 (d), 129.3 (2d), 128.8 (d), 128.3
(2d), 128.2 (d), 128.1 (2d), 128.0 (d), 127.8 (d), 127.7 (d), 125.8 (d).
trans,trans-10: 12%; Rf 0.73 (petroleum ether/dichlorometh-
colourless oil; UV (96% EtOH) kmax (loge) 317 (4.43), 237 (4.33);
ane = 7:3); colourless oil; UV (96% EtOH) kmax (loge) 306 (4.00);
1H NMR (CDCl3, 600 MHz) d 7.56 (dd, J = 8.0; 2.3 Hz, 1H), 7.30–
7.28 (m, 3H), 7.26–7.23 (m, 4H), 6.97 (dd, J = 15.4; 11.0 Hz, 1H),
6.90 (dd, J = 17.5; 11.1 Hz, 1H), 6.64 (d, J = 11.2 Hz, 1H), 6.61 (d,
J = 15.4 Hz, 1H), 6.47 (t, J = 11.2 Hz, 1H), 5.69 (d, J = 17.5 Hz, 1H);
5.29 (d, J = 11.1 Hz, 1H); 13C NMR (CDCl3, 150 MHz) d 136.5 (s),
135.8 (2s), 135.6 (s), 135.1 (d), 133.0 (d), 130.9 (d), 130.2 (d),
129.9 (d), 128.7 (2d), 127.7 (2d), 127.6 (d), 127.4 (d), 126.1 (d),
125.8 (d), 115.7 (t); IR mmax 3025, 1489, 1091, 771.
1H NMR (CDCl3, 600 MHz) d 7.75 (d, J = 7.5 Hz, 4H), 7.53–7.51 (m,
2H), 7.44 (d, J = 15.3 Hz, 2H), 7.38 (t, J = 7.5 Hz, 2H), 7.31–7.27
(m, 4H), 6.84 (d, J = 15.3 Hz, 2H), 6.79 (s, 2H); 13C NMR (CDCl3,
150 MHz) d 134.9 (s), 134.5 (s), 130.8 (s), 130.1 (d),129.2 (2d),
129.1 (d), 129.0 (d), 127.8 (2d), 127.7 (d), 127.6 (d), 126.5 (d); IR
mmax 3021, 1445, 1143, 950, 690; HRMS (ꢂH+) for C26H20Cl2:
Mþcalcd: 401.0869; Mþfound 401.0888 (for a mixture of isomers of 10).
trans,trans-12: 50%; Rf 0.88 (petroleum ether/dichlorometh-
trans-11: 33%; Rf 0.66 (petroleum ether/dichlorometh-
ane = 1:1); yellow crystals; mp 262 °C; UV (96% EtOH) kmax (loge)
ane = 9:1); colourless crystals; mp 110–113 °C; UV (96% EtOH)
355 (4.17), 319 (4.27); 1H NMR (CDCl3, 600 MHz) d 7.52 (d,
J = 9.1 Hz, 1H), 7.38 (d, J = 8.5 Hz, 2H), 7.31 (d, J = 8.5 Hz, 2H),
7.28–7.24 (m, 1H), 7.03 (d, J = 15.3 Hz, 1H), 6.98 (dd, J = 15.5;
10.5 Hz, 1H), 6.84 (dd, J = 15.3; 10.5 Hz, 1H), 6.64 (d, J = 15.5 Hz,
1H); 13C NMR (CDCl3, 150 MHz) d 135.3 (s), 135.0 (s), 132.7 (s),
131.2 (d), 130.8 (d), 130.3 (d), 129.5 (d), 128.4 (2d), 127.3 (d),
127.0 (2d), 125.8 (d); IR mmax 3040, 1742, 1488, 1089, 974; HRMS
kmax (loge
) 340 (4.57), 329 (4.56, sh), 265 (4.53); 1H NMR (CDCl3,
600 MHz) d 7.51 (dd, J = 7.3; 1.7 Hz, 1H), 7.45 (dd, J = 7.3; 1.7 Hz,
1H), 7.36 (d, J = 8.5 Hz, 2H), 7.29 (d, J = 8.5 Hz, 2H), 7.27–7.23 (m,
2H), 7.06 (dd, J = 17.3; 11.0 Hz, 1H), 6.98 (d, J = 15.3 Hz, 1H), 6.95
(dd, J = 15.4; 10.5, 1H), 6.82 (dd, J = 15.4; 10.5 Hz, 1H), 6.61 (d,
J = 15.4 Hz, 1H), 5.63 (dd, J = 17.3; 1.2 Hz, 1H), 5.36 (dd, J = 11.0;
1.2 Hz, 1H); 13C NMR (CDCl3, 150 MHz) d 135.9 (s), 135.4 (s),
134.7 (s), 134.4 (d), 132.7 (s), 131.0 (d), 130.5 (d), 130.4 (d),
129.6 (d), 128.3 (2d) 127.3 (d), 127.2 (d), 127.0 (2d), 126.3 (d),
125.4 (d), 116.1 (t); IR mmax 2923, 1739, 1489, 1092, 986; HRMS
(+H+) for C26H20Cl2: Mþ
403.1015; Mþfound 403.1019 (for a mix-
calcd:
ture of isomers of 12).
for C18H15Cl: Mþ
266.0857; Mþfound 266.0867 (for a mixture of
4.4. Irradiation experiments of 9 and 11
calcd:
isomers of 11).
4.3. General method for the synthesis of 10 and 12
To stirred solution of the triphenylphosphonium salt
A mixture of cis- and trans-isomers of 9 or 11 in petroleum ether
(3.7 ꢄ 10ꢂ3 M) was purged with argon for 20 min and irradiated at
350 nm in a Rayonet reactor (12 lamps) in a Quartz vessel for 16 h.
After irradiation the solvent was removed in vacuo and the oily
residue chromatographed on a silica gel column using petroleum
ether as the eluent. The photoproducts 13–15 obtained from 9 or
a
(0.005 mol) and the corresponding aldehyde (0.011 mol) in
absolute ethanol (100 mL) the solution of sodium ethoxide

12
D. Vuk et al. / Journal of Molecular Structure 1051 (2013) 1–14
the photoproduct 17 obtained from 11 were isolated from the en-
riched first chromatographic fractions followed by a mixture of
several unidentified products (<2%). High-molecular-weight prod-
ucts remained on the column.
endo-17: 77%; Rf 0.66 (petroleum ether/dichloromethane = 9:1);
colourless oil; UV (96% EtOH) kmax (log ) 276 (3.19), 268 (3.22),
224 (4.20, sh); 1H NMR (CDCl3, 600 MHz) d 7.14 (d, J = 8.4 Hz, 2H,
e
Har2), 7.12 (d, J = 7.3 Hz, 1H), 7.03 (td, J = 7.4; 1.0 Hz, 1H), 6.84
Cl
HA
HB
H
B Cl
HA
HA
Cl
HB
HX
HB
HC
HB
HC
HD
HD
13
exo-14
endo-14
13: 7%; Rf 0.32 (petroleum ether); colourless crystals; mp 60–
62 °C; UV (96% EtOH) kmax (log ) 325 (3.32), 317 (3.34), 311
(td, J = 7.4; 1.0 Hz, 1H), 6.65 (d, J = 8.3 Hz, 2H, Har1), 6.40–6.35 (m,
1H, HA), 6.23 (d, J = 7.3 Hz, 1H, Har), 5.25 (ddd, J = 9.6; 4.0; 1.9 Hz,
1H, HB), 3.96–3.92 (m, 1H), 3.34 (t, J = 9.4; 4.7 Hz, 1H), 3.29 (dd,
J = 6.1; 4.7 Hz, 1H), 2.54–2.50 (m, 1H, HF), 2.37 (d, J = 10.0 Hz, 1H,
HG); 13C NMR (CDCl3, 150 MHz) d 140.6 (s), 137.3 (s), 132.9 (s),
130.9 (s), 134.7 (d), 129.2 (2d), 127.3 (d), 125.7 (d), 125.6 (d),
125.4 (2d), 124.7 (d), 119.7 (d), 48.0 (d), 45.3 (d), 43.7 (t), 39.9;
e
(3.35), 292 (3.40), 281 (3.46), 270 (3.43), 229 (4.33); 1H NMR
(CDCl3, 600 MHz) d 7.89 (d, J = 8.2 Hz, 1H), 7.79 (d, J = 8.2 Hz, 1H),
7.75 (d, J = 8.2 Hz, 1H), 7.52–7.42 (m, 3H), 7.34–7.19 (m, 6H),
4.80–4.77 (dd, J = 5.1; 2.0 Hz, HX, 1H), 3.96–3.91 (dd, J = 13.6;
5.1 Hz, HA/HB, 1H), 3.28–3.24 (dd, J = 13.6; 2.0 Hz, HA/HB, 1H,);
13C NMR (CDCl3, 150 MHz) d 144.6 (s), 142.9 (s), 141.2 (s), 133.4
(s), 129.6 (d), 128.4 (2d), 128.1 (d), 127.0 (2d), 126.5 (d), 126.4
(d), 125.1 (d), 122.2 (d), 121.3 (d), 46.6 (d), 38.2 (t); IR mmax 2922,
IR mmax 2950, 1490, 1090, 752; HRMS (ꢂH+) for C18H15Cl: Mþ
calcd:
265.0789; Mþfound 265.0786.
1656, 1453, 1028, 814; HRMS for C18H15Cl: Mþ
266.0857;
4.5. Irradiation experiments of 10 and 12
calcd:
Mþfound 266.0870.
exo-14: 2%; Rf 0.28 (petroleum ether); colourless oil; UV (96%
EtOH) kmax (log ) 317 (3.64), 281 (3.71, sh), 273 (6700, sh), 249
A mixture of cis,cis-, cis,trans- and trans,trans-isomers of 10 or
12 in petroleum ether (2.2 ꢄ 10ꢂ3 M) was purged with argon for
20 min and irradiated at 350 nm in a Rayonet reactor (10: 12
lamps; 12: 16 lamps) in a Quartz vessel for 16 h (10) or 65 h
(12). After irradiation the solvent was removed in vacuo and the
oily residue chromatographed on a silica gel column using petro-
leum ether/dichloromethane (4:1) as the eluent. The photoprod-
ucts 16 (from 10), endo,cis-18, endo,trans-18 and endo-19 (from
12) were isolated from the enriched first chromatographic frac-
tions followed by a mixture of several unidentified products
(<2%). High-molecular-weight products remained on the column.
e
(17,476), 229 (23,231); 1H NMR (CDCl3, 600 MHz) d 7.50–7.46
(m, 2H), 7.35–7.28 (m, 4H), 7.20–7.24 (m, 2H), 7.01–6.98 (m,
2H), 3.72–3.68 (m, 1H, HC), 3.46 (d, JAD = 7.6 Hz, 1H, HA), 3.34 (d,
JBC = 2.4 Hz, 2H, HB), 2.45 (dd, JCD = JAD = 7.6 Hz, 1H, HD); IR mmax
2923, 1645,þ 1492, 1070, 754; HRMS for C18H15Cl: Mcþalcd:
266.0857; Mfound 266.0851.
endo-14: 1%; Rf 0.24 (petroleum ether); colourless crystals; mp
60 °C; UV (96% EtOH) kmax (loge) 317 (3.43), 281 (3.56), 273 (3.61),
247 (4.07), 232 (4.05); 1H NMR (CDCl3, 600 MHz) d 7.27–7.24 (m,
2H), 7.17–7.12 (m, 4H), 7.05–7.00 (m, 4H), 3.85 (t, JAB = 2.4 Hz,
1H, HA), 3.41 (t, JAB = 2.4 Hz, 2H, HB), 2.72–2.69 (m, 1H, HC), 2.34
(d, JCD = 6.1 Hz, 1H, HD); 13C NMR (CDCl3, 150 MHz) d 149.5 (s),
138.3 (s), 135.4 (s), 133.4 (s), 131.1 (d), 127.8 (d), 127.8 (d),
127.5 (2d), 127.1 (2d), 124.5 (d), 124.0 (2d), 119.9 (d), 59.4 (t),
Cl
HA
HB
HX
50.4 (d); IR þmmax 2924, 1490, 753; HRMS for C18H15Cl: Mþ
calcd:
266.0857; Mfound 266.0857.
Cl
HG
HF
16
HE
HA
16: 11%; Rf 0.71 (petroleum ether/dichloromethane = 4:1); col-
ourless oil; UV (96% EtOH) kmax (log ) 227 (4.52), 272 (3.90, sh),
HB
e
HD
Har
283 (3.80), 294 (3.71); 1H NMR (CDCl3, 600 MHz) d 8.29 (d,
J = 8.0 Hz, 1H), 7.88 (d, J = 8.0 Hz, 1H), 7.77 (d, J = 8.0 Hz, 1H),
7.59–7.54 (m, 2H), 7.52 (t, J = 7.6 Hz, 2H), 7.36 (d, J = 8.0 Hz, 2H),
7.28 (t, J = 7.6 Hz, 1H), 7.13 (d, J = 7.6 Hz, 2H), 7.07 (t, J = 7.1 Hz,
2H), 6.64 (s, 1H), 6.61 (s, 1H), 6.28 (s, 1H), 5.97 (s, 1H, HX), 4.21
(d, J = 15.4 Hz, 1H, HA/B), 3.72 (d, J = 15.4 Hz, 1H, HA/B); 13C NMR
(CDCl3, 150 MHz) d 144.8 (s), 142.2 (s), 137.3 (s), 137.1 (s), 133.2
HC
Har1
Har2
Cl
endo-17

D. Vuk et al. / Journal of Molecular Structure 1051 (2013) 1–14
13
(s), 132.8 (s), 132.1 (d), 131.3 (s), 131.1 (d), 129.9 (d), 128.6 (d),
128.5 (d), 128.2 (2d), 128.1 (d), 127.5 (d), 127.4 (2d), 127.0 (2d),
126.5 (d), 125.6 (2d), 123.5 (d), 60.1 (d), 33.6 (t); IR mmax 3056,
135.9 (s), 132.6 (s), 132.5 (s), 131.5 (s), 130.5 (d), 129.1 (d), 128.9
(2d), 128.4 (2d), 127.7 (2d), 127.2 (2d), 126.5 (d), 126.3 (d), 125.2
(d), 124.8 (d), 48.2 (d), 44.1 (d), 44.0 (d), 21.8 (d), 21.1 (d), 18.0
(d); IR mmax 2920, 1640, 1488, 1091, 751; HRMS (ꢂH+) for
1637, 1492, 1026, 700; HRMS for C26H18Cl2: Mþ
400.0780;
calcd:
Mþfound 400.0797.
C
26H20Cl2: Mþ
401.0869; Mþfound 401.0851.
calcd:
Cl
Cl
Cl
HF
HF
HE
HE
HF
HA
HA
HB
HC
HG
HE
HA
HB
HD
HD
HC
HC
HB
Cl
Cl
Cl
18
endo-19
18
-
endo,trans
-
endo,cis
endo,cis-18: 10%; Rf 0.87 (petroleum ether/dichlorometh-
ane = 1:1); colourless oil; 1H NMR (CDCl3, 600 MHz) d 7.37 (d,
J = 8.5 Hz, 1H), 7.27 (d, J = 8.5 Hz, 1H), 7.24–7.28 (m, 1H), 7.14 (d,
J = 8.4 Hz, 2H), 7.08 (td, J = 7.4; 0.9 Hz, 1H), 6.88 (td, J = 7.4;
0.9 Hz, 1H), 6.65 (d, J = 8.4 Hz, 2H), 6.61–6.67 (m, 1H), 6.42–6.46
(m, 1H), 6.28 (d, J = 11.8 Hz, 1H), 6.24 (d, J = 7.4 Hz, 1H), 5.44 (dd,
J = 11.8; 9.8 Hz, 1H), 5.29–5.31 (m, 1H), 3.95–3.98 (m, 1H), 3.70
(d, J = 9.8 Hz, 1H), 3.20 (d, J = 5.9 Hz, 2H); 13C NMR (CDCl3,
150 MHz) d 150.0 (s), 139.6 (s), 139.3 (s), 135.5 (s), 134.7 (d),
134.5 (d), 132.1 (s), 131.6 (s), 129.5 (d), 129.5 (d), 129.3 (2d),
128.0 (d), 127.8 (d), 127.4 (2d), 127.4 (d), 126.7 (d), 126.2 (d),
125.9 (d), 125.1 (d), 120.9 (d), 54.1 (d), 53.7 (d), 46.2 (d), 45.8
(d); IR mmax 3022, 1670, 1490, 1092, 1014, 735; HRMS for
Single crystal measurement was performed on an Oxford Dif-
fraction Xcalibur Nova R (microfocus Cu tube) at room temperature
[293(2) K]. Program package CrysAlis PRO [35] was used for data
reduction. The structure was solved using SHELXS9736 and refined
with SHELXL97 [36]. The model was refined using the full-matrix
least squares refinement; all non-hydrogen atoms were refined
anisotropically. Hydrogen atoms bound to C atoms were modelled
as riding entities using the AFIX command. Molecular geometry
calculations were performed by PLATON [37], and molecular
graphics were prepared using ORTEP-3 [34], and CCDC-Mercury
[38]. Crystallographic and refinement data for the structures re-
ported in this paper are shown in Table 1.
Supplementary crystallographic data for this paper can be ob-
tained free of charge via www.ccdc.cam.ac.uk/conts/retriev-
ing.html (or from the Cambridge Crystallographic Data Centre,
12, Union Road, Cambridge CB2 1EZ, UK; fax:+44 1223 336033;
or deposit@ccdc.cam.ac.uk). CCDC-928402 contains the supple-
mentary crystallographic data for this paper.
C
26H20Cl2: Mþ
402.0937; Mþfound 402.0921.
calcd:
endo,trans-18: 50%; Rf 0.87 (petroleum ether/dichlorometh-
ane = 1:1); colourless crystals; mp 151 °C; UV (96% EtOH) kmax
(log
262 (4.35), 291 (3.42), 302 (3.14); 1H NMR (CDCl3,
e
)
600 MHz) d 7.10–7.20 (m, 7H), 7.07 (td, J = 7.4; 0.8 Hz, 1H), 6.87
(td, J = 7.4; 0.8 Hz, 1H), 6.65 (d, J = 8.3 Hz, 2H), 6.44 (d,
J = 15.9 Hz, 1H), 6.42–6.46 (m, 1H, HA), 6.22 (d, J = 7.3 Hz, 1H),
5.31 (ddd, J = 9.4; 3.5; 1.7 Hz, 1H, HB), 4.00–4.03 (m, 1H), 3.39 (d,
J = 8.4 Hz, 1H), 3.25 (d, J = 4.7 Hz, 1H), 3.22 (d, J = 6.7 Hz, 1H); 13C
NMR (CDCl3, 150 MHz) d 149.9 (s), 139.8 (s), 139.0 (s), 135.4 (s),
134.7 (d), 132.3 (d), 132.2 (s), 131.6 (s), 129.3 (2d), 128.8 (d),
128.0 (2d), 127.4 (2d), 126.8 (2d), 126.6 (d), 126.6 (d), 126.2 (d),
125.7 (d), 125.1 (d), 120.8 (d), 58.4 (d), 53.8 (d), 46.1 (d), 45.9
(d); IR mmax 3024, 1648, 1490, 1091, 1014, 730; HRMS (ꢂH+) for
Acknowledgements
This work was supported by grants from the Ministry of Sci-
ence, Education and Sports of the Republic of Croatia (Grant Nos.
125-0982933-2926, 098-0982929-2917, and 098-1191344-2943).
References
C
26H20Cl2: Mþ
401.0869; Mþfound 401.0860.
ˇ
´
´
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